Purpose of IR filters for lenses. Infrared filters for photography
Infrared photography is a very complex form of photography. During the lessons you need to be very attentive to the process of setting up equipment and filming. I have prepared a list for you that is convenient for checking your actions. I recommend printing it out and putting it in your bag along with your camera. We will consider all the items on the list later in the lesson.
Can your camera receive infrared rays?
Before you go out and buy a filter, test your camera for infrared detection. Some cameras can't do this. The easiest way to check this is to point the camera at the LED light on the remote control and press a few buttons on it. If you notice that the red light is flashing, then the camera is detecting infrared rays.
If the light from the LED is dim, then the camera is detecting infrared rays, but the exposure time will increase due to internal filter blocking them.
If you don't see the LED blinking, set a long exposure and take several pictures while pressing the buttons on the remote control pointed at the camera lens. The red light from the LED should be visible in the photographs. If it is not there, then your camera cannot receive infrared rays, and this lesson It won't help you.
Purchasing a filter
I have a few suggestions when choosing an infrared filter. These are screw-on filters like Hoya, and square filters from Cokin.
Screw-on filters are a very good tool for infrared photography. One, they are relatively expensive. I recommend purchasing filters from reputable brands for best results. For example, I have a Hoya R72 filter, which really impressed me with its results, even though it costs more than $100.
Square filters are quicker to put on and take off. At this moment, the risk of spoiling the photo with light rays is much higher than when working with screw-on filters. The average price for such a filter is $60.
If you are going to buy a large screw-on filter, also get an adapter ring so that this filter fits all other lenses. This will save you from having to buy a separate filter for each lens.
Wavelength and other options
The 720nm filter is considered the standard for infrared photography. I believe that it is worth starting with him. There are other options, for example, 900nm (RM90), but the prices for such filters are very high, they exceed $300. These filters are designed for professional infrared photographers with deep pockets.
There is another option if you don't want to use a filter. You can set your DSLR camera to always sense the infrared spectrum. To do this, you need to calibrate the camera and lens. This is a very expensive service, after which your camera will only shoot in infrared mode.
When and where to shoot?
One of the most popular genres of infrared photography is landscape photography. Due to the effects created when shooting, the foliage may appear white when rendered, making the photo very dark and haunting. You can experiment with trees, flowers and grass.
Ideal conditions for shooting are sunny days. During the rendering process (if color processing is incorrect), the sky will have a deep blue, and the leaves are white. But this does not mean that in bad weather you cannot achieve the desired result.
If you set a long exposure time for the IR filter, the results are almost the same as working with the Neutral Density (ND) filter. There will be a strong movement effect in the photographs.
Don't be afraid to experiment and don't limit yourself to simple situations and objects.
Lens problems
Some lenses can create anomalous effects when shooting infrared, namely hot pixels. When this happens, you may notice a light, discolored spot in the center of the image. It happens that stripes appear throughout the photo. They can be removed in post-processing, but this takes a lot of time and effort.
Does not currently exist full list lenses that work correctly and those that create discolored spots. The website dpanswers.com provides a rather large list of most lenses and their problems.
1. Setup
Camera setup is very important to get good infrared photography. Do not install the filter until you have adjusted the focus, exposure, and white balance.
To begin, mount your camera on a tripod. Hang your camera bag on a tripod hook to maximize the entire tripod and minimize movement.
The following tips will help you get a clean image:
- Shooting in RAW format. Shooting in RAW allows you to easily change the white balance in post-processing. Never shoot in JPEG format, otherwise you will get noise and other defects will be very noticeable.
- Turn off Long exposure noise reduction. Since a long exposure time is required for infrared photography, you need to turn off this parameter. There will be no noise during processing. This will also help you change the intensity of the noise in post-processing.
- Enable Exposure delay mode / Mirror Lock-Up. If you enable any of these modes, you will minimize vibration when releasing the shutter.
- Remote shutter release or timer. Using a remote control is not necessary, but can reduce the amount of vibration since you are not touching the camera while shooting. Alternatively, you can set the timer to 2 seconds.
2. White Balance
White balance is very good when shooting infrared. You can use the preset values or Pre-White Balance to get the normal balance in the current conditions. In any case, you will need to spend time on this during post-production.
There is nothing wrong with using preset settings. For example, the Incandescent setting is most suitable.
Go to the White Balance menu and select PRE. Then do the following:
- Click OK.
- Select Measure and press OK.
- Select Yes and overwrite the existing information.
- Make sure that the main part of the subject appears green in the viewfinder. You can point the camera at a patch of grass.
- Take a photo and wait for the camera to respond. “Data Acquired” or “Gd” should appear.
- If the camera shows the message “Unable to acquire” or “No Gd”, then check the exposure.
The result should be a photo with a strong red-orange-purple tint. We will fix it in post-processing.
3. Focusing and stabilization
Focusing can take a lot of time if there are no infrared markings on the lens. It's better to use a small aperture like f/20 to get good depth of field and minimize focusing problems.
If your lens has focus marks for IR shooting, adjust the focus according to the focal length. If there are no such marks, then focusing on the object will be difficult. The best thing you can do is set a small aperture to get a large depth of field. Thanks to this, the pictures will have good sharpness, but this does not mean that you can use a large aperture for a small depth of field. Without calibrating the lens for continuous infrared photography, it is impossible to achieve the desired focus with a large aperture.
First, focus on the subject using regular Auto Focus. Then switch to manual mode. If you have a camera with a rotating ring on the lens, then be careful not to move the ring.
Any stabilization system must be disabled. Using VR/IS/OS is not recommended due to the fact that the camera is mounted on a tripod and also because the lens will make unnecessary corrections which may result in blur.
4. Aperture
One of the important settings when shooting infrared is a small aperture. It gives greater depth of field and minimizes the focusing problems described above.
5. ISO
In most cases, it is better to use the lowest ISO sensitivity to minimize the amount of noise. Take into account the length of the exposure as well. I would recommend using ISO no more than 800 for shooting between 10 seconds and a minute. For exposures longer than 1 minute, use ISO 400 or lower.
Any values exceeding these limits increase the risk of getting large number noise and hot pixels during post-processing.
If you use ISO from 100 to 200, then the waiting time for IR exposure will be halved. An 8 minute exposure at ISO 100 will be reduced to 4 minutes at ISO 200. The amount of noise will increase slightly, but this will help you when time is very short.
6. Shutter speed.
Finally, let's talk about shutter speed. First you need to determine the exposure time. Have a stopwatch ready.
IR filters require a slow shutter speed. As with ND filters, you can calculate the amount of delay you need to compensate using the Exposure Calculator.
For example, if the visible light exposure is 1/30, ISO 100, f/11, and the best IR exposure is 1 second, then you should have a 5-stop light blocking filter.
7. Take a photo!
Now you can screw the IR filter to the lens. After this, do not change the settings or turn the focus ring. Press the shutter button and wait for the result!
In the second part of the lesson we will process IR images in Lightroom.
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Translated from the site photo.tutsplus.com, the author of the translation is indicated at the beginning of the lesson.
Infrared photography allows us to see a world that is inaccessible to our eyes.
At first, these photographs may seem lifeless, but if you look closely, you can see in them a different space and a different reality. The pictures obtained using infrared photography are very surreal: hot summer turns into cold winter, the sky and water become almost black.
All these are pictures from other, parallel worlds.
Pleasure boats on the canal
This is not winter, this is summer, here the trees and grass are green.
What needs to be done to capture this fabulous, invisible world? The first step is to determine whether your camera is suitable for infrared photography. Then equip yourself with specialized filters and a tripod. But there is also a folk method.
One of the specialists shared his experience and several works in the field of infrared photography:
“In order to get such pictures, I bought a used Canon 350D digital camera and “broke” it, replacing the hot mirror with regular glass. It was very scary to accidentally break the device completely. But the operation was successful, everything works, although I still had a couple of “extra” screws after assembly.”
Infrared radiation beyond the visible range was first discovered by the Englishman William Herschel back in 1800. At first, infrared photography was used by astronomers, used in aerial photography, as well as by the military and restorers when working with paintings by great painters.
Today, infrared photography is a great technique for those photographers who want to capture something unusual and make their creations stand out from the crowd.
Infrared photography began in the film era, when special films capable of recording infrared radiation appeared. But, since nowadays digital SLR cameras are much more popular than film ones and it has become quite difficult to get special film (besides, it should be noted that not every film SLR will allow you to shoot on IR film due to the presence of an infrared sensor inside the camera that will expose frames), in this photo tutorial we will only touch on aspects infrared
First, to understand the process of obtaining infrared images, you need to understand the theory. The radiation that forms the color image perceived by the human eye has a wavelength ranging from 0.38 microns ( purple) up to 0.74 µm (red). The peak sensitivity of the eye occurs, as is known, at green, having a wavelength of approximately 0.55 µm. The wave range with a length of less than 0.38 microns is called ultraviolet, and more than 0.74 microns (and up to 2000 microns) is called infrared. Sources of infrared radiation are all heated bodies.
Reflected solar IR radiation most often forms an image on the film or matrix of the camera. Since the most common application of infrared photography is in the landscape genre, it should be noted that grass, leaves and pine needles reflect IR radiation best, and therefore they appear white in the photographs. All bodies that absorb IR radiation appear dark in the photographs (water, earth, tree trunks and branches).
Now you can move on to the practical part.
Let's start with filters. To obtain an infrared image, it is necessary to use IR filters that cut off most or all of the visible radiation. In stores you can find, for example, +W 092 (transmits radiation from 0.65 microns and longer), B+W 093 (0.83 microns and longer), Hoya RM-72 (0.74 microns and longer), Tiffen 87 (0.78 µm and longer), Cokin P007 (0.72 µm and longer). All filters except the last one are regular threaded filters that screw onto the lens. Filters from the French company Cokin must be used with a proprietary mount, which consists of a ring with a thread for the lens and a filter holder. The peculiarity of this system is that for lenses with different thread diameters you only need to purchase the corresponding ring, while the filter and holder itself remain the same, which is much cheaper than purchasing the same threaded filters for each lens. In addition, a standard holder can accommodate up to three filters with different effects.
Since we are looking at IR photography exclusively with digital SLR cameras, it should be noted that different models cameras different ability to registration of infrared radiation. Camera matrices themselves perceive infrared radiation quite well, but manufacturers install a filter in front of the matrix (the so-called Hot Mirror Filter), which cuts off most of the infrared waves.
This is done to minimize the appearance of unwanted effects in pictures (for example, moire). The ability to use the camera for IR photography depends on how much IR radiation is filtered. For example, the Nikon D70 camera with the Cokin P007 filter can be shot handheld, but for the Canon EOS 350D and most other cameras due to long exposures You will always need a tripod. Some photographers interested in infrared photography resort to modifying the camera by removing the infrared filter.
Now let's touch on image processing in Photoshop. The resulting frames, depending on the white balance setting, will have a red or purple tonality. To obtain a classic black-and-white infrared image, you will need to desaturate the image, for example, using a gradient map, after adjusting the levels and contrast. There are also several ways to produce very impressive color infrared photographs. For example, you can use the Channel Mixer tool by first setting the red channel to Red - 0%, Blue - 100%, for the blue channel - Red - 100%, Blue - 0%, and then by slightly manipulating percentage of one color or another in the channels, select such values at which the picture will look most attractive.
The human eye is capable of perceiving rays in the wavelength range from 380 nm to 760 nm (violet to red). Anything that goes beyond these limits is without special equipment impossible to see.
Visible light is only a small part wide range waves Neighboring regions of the spectrum are ultraviolet and infrared rays. They can be captured in a photograph because they are refracted by the lens of the lens, and the image can be focused onto the camera's sensor. Infrared photography allows us to capture wavelengths in a range that is inaccessible to our eyes - from 700 to 1100 nm.
In conclusion, we note the main advantages of infrared photography: the absence of haze in the images and always a well-developed sky, the absence of debris, since it does not reflect IR rays, and, of course, the most important thing was what was said at the very beginning - the opportunity to see unusual, an unusual world in which, in addition to fairy-tale colors, all moving objects disappear or turn into “ghosts”.
Would you like to know what it would look like the world around us, if the human eye perceived light rays not only from the so-called “visible spectrum”, but also far beyond it?
One way to see the world as the human eye cannot see it is through infrared photography.
IR filter on the lens, a necessary element for infrared photography
Long ago, from a purely technical, applied field, infrared photography entered the world of artistic photography. By shooting in the infrared range, you can get incredibly beautiful, “cosmic” landscapes.
In general, this type of shooting and subsequent processing is the subject of a separate large article or even a series of articles. But today our goal is simply to get to know the basics.
So how do you get an infrared image? There are many options. Previously, special photographic film was used for this. Specialized digital technology uses special matrices.
But you can try to take an infrared photograph with a simple digital camera.
Infrared Photography Equipment
By and large, the optics of any camera transmit rays in the IR range. But the problem is that the matrices of modern cameras are equipped with special Hot-mirror filters. And these filters often cut off the IR spectrum almost completely.
There is an easy way to check how suitable your DSLR is for infrared photography. Take a regular remote control - for a TV, stereo system, etc. All of them work on the basis of IR rays.
Place your camera on a tripod and, in complete darkness, take as many pictures as you can at different shutter speeds and aperture values. At the same time, keep the remote control pointed at the lens and hold down any button.
If a bright dot appears on the frames taken, it means that your camera’s filter transmits IR rays sufficiently and you can move on. If not, then there are several options. Look for another camera or try to act further “at random”. It is curious that relatively inexpensive soap dishes, rather than sophisticated DSLRs, are often equipped with weak Hot Mirrors.
Experiment with shutter speed and aperture. To achieve your goal, you may need a very long shutter speed to allow the IR rays to penetrate the filter.
Some go to great lengths, tuning the insides of their digital SLRs for IR photography. If you decide to go this route, then for this purpose it is quite possible to inexpensively buy a “donor” from among used DSLRs. The essence of tuning is the mechanical removal of the Low Pass filter, onto which the Hot Mirror filter is usually mechanically sprayed.
There are many communities on the Internet, especially in English, where there are detailed instructions on disassembling and removing filters from different camera models.
Mechanical removal of the filter after disassembling the camera
The second integral part is the purchase of a filter for the lens. The most popular and proven models are Hoya R72 and Cokin 007. But given the expensive cost of IR filters (from $80-100), it makes sense to first test your camera with this filter, and not buy blindly in an online store.
True, there are guides for making an IF filter from improvised materials. But that's a separate conversation.
Landscapes look most interesting in the infrared range. This is due to the fact that, in essence, we record the ability of objects not to emit, but to absorb IR waves. For example, the sky absorbs them in huge quantities and will disappear into blackness in the picture; the greenery of the trees, on the contrary, reflects the rays and will look white in the picture, as if covered with frost on a frosty day.
Considering that when using IR filters, the amount of light falling on the matrix is extremely small, you will have to shoot at long exposures and therefore need a tripod.
Hoya R72 is one of the most popular infrared filters.
In addition, it is worth switching the camera to manual focusing mode, since autofocus can shamelessly lie due to the filter.
Then you should experiment with various parameters exposure, analyzing the results obtained.
After we have received the coveted shot, we should start post-processing. Since a rare shot taken in the infrared range will be a masterpiece without processing.
There are a great variety of processing methods. Let's look at one, the simplest one.
Infrared photography processing
Exists huge amount post-processing technician for infrared images. Let's take a brief look at one of the simplest ones.
When you leave the chamber you will get something like this.
Infrared photo coming out of the camera
If you were shooting in RAW, it makes sense to change the white balance to make the greens as close to pure white as possible.
Then, open the image in Photoshop and adjust the Levels. It is better to do this for each channel separately (Red, Green, Blue).
Approximate view of Levels for a raw image
Correction levels - move the sliders to the edges of the histogram
As a result, our photo will become more contrasty and acquire visual “depth”.
Photo after changing white balance and level correction
The next step is color inversion.
To do this, open Channel Mixer (Image – Adjustments – Channel Mixer.)
Select the red channel and for it we remove Red to 0, and raise Blue to 100
adjusting the Red channel
Then open the Blue channel and do the opposite for it. Red is 100% and Blue is 0%
Adjusting the blue channel
Then click Ok and enjoy the result. To achieve a better effect, you can also work with the color saturation tools – Adjustments – Hue/Saturation
Final IF shot
Examples of infrared photographs
Well, for inspiration, so that you have a desire to try shooting in this technique, here is a large gallery of infrared images.
I don’t know about you, but I’ve always wondered: what would the world look like if the RGB color channels in the human eye were sensitive to a different wavelength range? After rummaging around, I found infrared flashlights (850 and 940 nm), a set of IR filters (680-1050 nm), a black and white digital camera (no filters at all), 3 lenses (4mm, 6mm and 50mm) designed for photography in IR light. Well, let's try to see.
We have already written on the topic of IR photography with the removal of the IR filter on the hub - this time we will have more opportunities. Also, photographs with other wavelengths in RGB channels (most often capturing the IR region) can be seen in posts from Mars and about space in general.
These are flashlights with IR diodes: 2 left ones at 850nm, the right one at 940nm. The eye sees a faint glow at 840 nm, the right one only in complete darkness. For an IR camera they are dazzling. The eye seems to retain microscopic sensitivity to near-IR + the LED radiation comes with lower intensity and at shorter (=more visible) wavelengths. Naturally, you need to be careful with powerful IR LEDs - if you are lucky, you can unnoticed get a burn to the retina (as with IR lasers) - the only thing that saves you is that the eye cannot focus the radiation to a point.
Black and white 5 megapixel noname USB camera - on Aptina Mt9p031 sensor. I spent a long time shaking the Chinese about black and white cameras - and one seller finally found what I needed. There are no filters in the camera at all - you can see from 350nm to ~1050nm. 
Lenses: this one is 4mm, there are also 6 and 50mm. At 4 and 6mm - designed to work in the IR range - without this, for the IR range without refocusing, the pictures would be out of focus (an example will be below, with a conventional camera and IR radiation of 940 nm). It turned out that the C mount (and CS with a flange length different by 5mm) was inherited from 16mm movie cameras of the beginning of the century. Lenses are still actively produced - but for video surveillance systems, including by well-known companies like Tamron (a 4mm lens from them: 13FM04IR). 
Filters: I again found a set of IR filters from the Chinese from 680 to 1050 nm. However, the IR transmittance test gave unexpected results - these do not seem to be bandpass filters (as I imagined), but rather different "densities" of color - which changes the minimum wavelength of light transmitted. Filters after 850nm turned out to be very dense and require long shutter speeds. IR-Cut filter - on the contrary, transmits only visible light, we will need it when shooting money.
Visible light filters: 
IR filters: red and green channels - in the light of a 940 nm flashlight, blue - 850 nm. IR-Cut filter - reflects IR radiation, that's why it has such a cheerful color. 
Let's start shooting
Panorama during the day in IR: red channel - with a filter at 1050 nm, green - 850 nm, blue - 760 nm. We see that trees reflect the very near IR especially well. Colored clouds and colored spots on the ground were caused by the movement of the clouds between frames. Individual frames were combined (if there could be an accidental camera shift) and stitched into 1 color image in CCDStack2 - a program for processing astronomical photographs, where color images are often made from several frames with different filters.
Panorama at night: you can see the difference in color between different light sources: “energy efficient” - blue, visible only in the very near IR. Incandescent lamps are white and shine throughout the entire range. 
Bookshelf: Almost all ordinary objects are virtually colorless in IR. Either black or white. Only some paints have a pronounced “blue” (short-wave IR - 760 nm) tint. LCD screen of the game “Well, wait a minute!” - does not show anything in the IR range (although it works for reflection). 
Cell phone with an AMOLED screen: absolutely nothing is visible on it in IR, as well as the blue indicator LED on the stand. In the background, nothing is visible on the LCD screen either. The blue paint on the metro ticket is IR transparent - and the antenna for the RFID chip inside the ticket is visible. 
At 400 degrees, the soldering iron and hair dryer glow quite brightly: 
Stars
It is known that the sky is blue due to Rayleigh scattering - accordingly, in the IR range it has much lower brightness. Is it possible to see stars in the evening or even during the day against the sky?Photo of the first star in the evening with a regular camera:
IR camera without filter:
Another example of the first star against the background of the city: 
Money
The first thing that comes to mind to verify the authenticity of money is UV radiation. However, banknotes have a lot of special elements that appear in the IR range, including those visible to the eye. We have already written briefly about this on Habré - now let’s see for ourselves:1000 rubles with filters 760, 850 and 1050 nm: only certain elements are printed with ink that absorbs IR radiation: 
5000 rubles: 
5000 rubles without filters, but with lighting of different wavelengths:
red = 940nm, green - 850nm, blue - 625nm (=red light): 
However, the infrared money tricks don't end there. The banknotes have anti-Stokes marks - when illuminated with IR light of 940 nm, they glow in the visible range. Photography with a regular camera - as you can see, the IR light passes a little through the built-in IR-Cut filter - but because... The lens is not optimized for IR - the image does not come into focus. Infrared light appears light purple because Bayer RGB filters are IR transparent. 
Now, if we add an IR-Cut filter, we will only see luminous anti-Stokes marks. The element above “5000” glows the brightest, it is visible even in dim room lighting and backlighting with a 4W 940nm diode/flashlight. This element also contains a red phosphor - it glows for several seconds after irradiation with white light (or IR->green from the anti-Stokes phosphor of the same label).
The element just to the right of “5000” is a phosphor that glows green for some time after irradiation with white light (it does not require IR radiation). 
Resume
Money in the IR range turned out to be extremely tricky, and you can check it in the field not only with UV, but also with an IR 940nm flashlight. The results of shooting the sky in IR give rise to hope for amateur astrophotography without traveling far beyond the city limits.
Test: Alexander SLABUKHA, Sergey SHCHERBAKOV
Before us are two filters through which nothing is visible. More precisely, through one of them, which has a dark red, almost black color, it is still possible to see something. This is an infrared filter B+W Infrared Dark Red 092, manufactured by Schneider Optics, a subsidiary of the Schneider-Kreuznach concern.
Be this filter alone this material, most likely, would not have appeared. Cokin 007, Hoya R72, Heliopan RG715 - these filters, which have been on our market for a long time and have already been fully mastered by photographers, are practically analogues of the “ninety-second”. And in this regard, it is unlikely that any surprises should be expected from B+W 092.
But from the completely black B+W Infrared Black 093, and this is the second filter under consideration, surprises are quite possible. Their reason is in the spectral characteristics of this filter in relation to artistic photography, which are fundamentally different from the characteristics of B+W Infrared Dark Red 092.
The B+W Infrared Dark Red 092 filter blocks visible light up to a wavelength of 650 nm, transmits 50% at 700 nm. From 730 to 2000 nm, more than 90% of radiation is transmitted. Recommended for artistic photography on black and white infrared materials. Increasing exposure for various materials can be 20-40x.
The B+W Infrared Black 093 filter blocks visible light up to a wavelength of 800 nm, transmits 88% at 900 nm. Designed primarily for scientific photography. Rarely used in artistic photography due to the catastrophic drop in the photosensitivity of black-and-white infrared films general purpose.
To put it very briefly, the 093 filter transmits only infrared radiation, while in the 092 filter passband there is a certain proportion of the visible spectrum, which can be recorded, for example, by digital camera sensors.
Filters are available in round threaded frames with diameters from 30.5 mm to 77 mm. True, you won’t find such abundance in Moscow stores, and the range presented is usually limited to the most popular diameters, starting from 58 mm and above.
Filters with a diameter of 72 mm were received for testing. Frankly, we would like 77 mm to work with professional high-aperture zooms (remember that these lenses, as a rule, have just such a mounting thread for filters). However, a way out of the situation was found - a transitional reduction ring of 72/77 mm.
Whether or not there will be vignetting from the filter barrel depends on the design of the lens barrel and its focal length (more precisely, the angle of the field of view). The only lens where we observed vignetting was the Sigma 10-20/3.5-5.6 EX DC HSM extra-wide-angle zoom (for digital SLR cameras with an APS-C sensor). But even at focal lengths of 10-12 mm, only a slight cutting of the corners of the frame was observed, and starting from f=13 mm it completely disappeared.
Cameras
The fact that the tested filters are threaded, and large diameter, predetermined the choice of the type of test camera - a reflex camera with interchangeable lenses. And although we did shoot a video of infrared black-and-white photographic film, the main testing tool was a digital camera.
There is information on the Internet about the suitability of a particular digital camera for infrared photography. The matrix itself is sensitive, sometimes even quite significantly, to infrared radiation. But in front of the digital sensor there is a filter (internal IR cut filter), which blocks this radiation. And the spectral characteristics of the matrix and this filter determine how suitable a particular camera is for infrared photography. However, we somehow don’t believe in the absolute unsuitability of modern DSLRs...
We chose Nikon D50 and Canon EOS 350D as test cameras. It is believed that the first is well suited for infrared photography, and the second - not so much.
The main part of the shooting was done with Nikkor AF 24-120/3.5-5.6, Tokina AF 20-35/2.8 and Tokina AF 80-400/4.5-5.6 lenses on a Nikon D50 camera; EF-S 17-55/2.8 IS USM and EF 28-105/3.5-4.5 II USM - on Canon EOS 350D.
Focusing
Despite the fact that with the 092 filter installed, the image in the viewfinder is barely visible, the autofocus systems of both cameras turned out to be functional. In conditions of sufficient lighting, for example, during the day outdoors, the cameras focused quite clearly on the object (but it was difficult to see it in the viewfinder).
Does this mean that you can rely on camera automation? The answer will be this: depending on which camera, and even then not always. The fact is that in the infrared region of the spectrum the focal plane turns out to be slightly shifted, i.e. the lens draws a sharp image in a slightly different plane than for the visible part of the spectrum. And autofocus is configured to work specifically in the visible range.
There are, however, some nuances here. Thus, the Nikon D50 camera without and with the 092 filter installed focused strictly at the same distance. This means that shots taken with autofocus through this infrared filter will be out of focus.
With the Canon EOS 350D the picture is different. With the filter on, it autofocused at a slightly closer distance, and the pictures were quite sharp, so manual focus correction was not necessary. As practice has shown, when using the Canon EOS 350D, the correction scale for shooting in the infrared range is suitable for a strong filter 093, and for filter 092 the mark should be moved approximately twice as close to the usual focus mark in the visible range.
When we talk about focus correction, we mean the following. Sometimes on the lens frames, more precisely on the distance scale, there are one or more (in the case of a zoom lens) additional marks to the main one. Their purpose is to adjust the focus of the lens so that after installing an infrared filter, the image in the camera's focal plane remains sharp. Proceed as follows. First, without a filter, the subject is focused - automatically or manually. Then, having installed the filter and switched the camera’s autofocus to manual mode, they shift the lens meter scale so that the focusing distance opposite the main mark moves to “infrared”.
When working with filter 093 you have to do exactly this. And although cameras were sometimes able to focus through such a black filter, it is still worth recognizing that autofocus systems are not designed to work with it.
When performing this focus correction with filter 092, we obtained crystal-sharp infrared images every time on the Nikon D50 camera, and at a fully open aperture. Under exactly the same conditions, the image with filter 093 turned out a little soapy.
What to do if there are no infrared focusing marks on the lens (as a rule, these are budget, inexpensive lenses)? You need to try to independently determine in a practical way at least approximately the required movement and aperture the lens strongly. Aperture, however, will noticeably lengthen shutter speeds, and they are already long for infrared photography. If not - long-lasting.
Exposition
Shooting with infrared filters requires increasing the exposure, in practical terms - the shutter speed. For filter 092 this increase is significant, for 093 it is very significant.
Nikon D50 exposure metering works quite accurately through filter 092, while the increase in exposure is about 5-6 steps, which is very good. Let's call this exposure the base exposure for infrared photography. But even if the camera’s metering worked inaccurately with the filter or did not work at all (as with 093), it is not difficult to find the base exposure, at least from the histogram of the image - it should be “good”. By the way, having found a discrepancy between the basic and normal exposures (i.e. for shooting in the visible range of the spectrum) in EV steps, you can not use the camera’s exposure system, but measure it with an external exposure meter.
Exposure metering on the Canon EOS 350D also works through filter 092, but the pictures turn out dark (severe underexposure), and an additional 4-5 steps need to be added. In this case, the total increase in exposure to the base one is 10-11 steps.
Compared to 092, filter 093 will require increasing the exposure by another 4 stops. Thus, when shooting through it, you will have to increase the exposure: for Nikon D50 by 10 stops, for Canon EOS 350D - by 16 (!).
What are the 16 steps in practice? For example, on a sunny day at ISO 200, the shutter speed at f/5.6 can be 1/2000 s. An increase of 16 steps lengthens it to... 30 s! And in cloudy weather in poor lighting, minutes will count. So working at high ISO (at the same time shutter speeds will be shorter) is a necessary measure for a Canon camera, but this does not benefit the image. Long shutter speeds and high ISOs are exactly what make infrared shooting difficult on the Canon EOS 350D.
When shooting through the 092 filter, we would recommend not limiting yourself to the basic exposure, but taking an additional 2-3 frames, increasing the shutter speed by another stop each time. In this case, the picture on the camera’s LCD screen will look simply terrible, and the histogram will show severe overexposure, but it is still advisable to take these additional “defective” frames. We'll tell you why a little later.
Processing
Shooting with both filters results in highly colored images. For 092 the predominant shade is red-orange, for 093 it is red-violet. In any case, most of the outdoor shots with the Nikon camera were exactly like that. (The shade depends on the spectral composition of the lighting, the characteristics of the infrared filter, the characteristics of the internal cut filter and color filters on the sensor, as well as the color interpretation algorithm of the camera processor or computer program.) Therefore, strong white balance correction is inevitable, and it is better to do it in a RAW file. We used Adobe Camera Raw (ACR) and Pixmantec RawShooter 2006 (RS 2006) converters.
When converting the image to black and white, filter 093 turned out to be almost completely problem-free. It is enough to set the white balance with an eyedropper, and the image becomes monochrome gray (or almost so). Yes, it is sluggish, the contrast is greatly reduced, but this can be easily corrected directly in the converter or later in the editor. In short, filter 093 is an easy and fast conversion of an infrared image to black and white.
The same cannot be said about filter 092. In this case, the picture will never turn out pure black and white. The reason is that, in addition to the infrared filter, this filter also transmits part of the visible part of the spectrum, so the image in the picture is a combination of normal and infrared. So in the converter, despite the fact that the photo will look color, you need to create good foundation, so that later in the editor you can get a visually pleasing infrared effect. In a word, you will have to tinker.
How to distinguish a regular one black and white photo from infrared? First of all, in terms of the tone of the green vegetation - it becomes light gray and even almost white. That's right - greenery reflects infrared radiation well, so it should look light. This highlighting of it in a photograph is called the wood effect, but it has nothing to do with wood. (In fact, the effect is named after the famous experimental physicist who used ultraviolet and infrared photography in his research - Robert Wood).
As we noticed, some images were converted into black-and-white infrared images quite easily, while others were quite troublesome. In terms of the distribution of tones, the image differed from ordinary black and white, but it did not really resemble infrared either. It is clear that the infrared component of the image was somehow distributed across the RGB channels of the image. It is important to be able to find this information and extract it most effectively.
In the images taken with the Nikon D50, in most cases the infrared signal was in the blue channel of the image, sometimes in the green and very rarely in the red, or all three at the same time. (For other cameras, this relationship may remain the same, but may be different, so do your research on your model.)
In order not to stretch out the “weak” blue channel, we recommend doing several takes when shooting, increasing the exposure relative to the base one. An overexposure of 2-3 steps will be quite enough.
If there is such a stock source material The procedure for converting images taken through filter 092 is greatly simplified. You need to select a frame with the best blue channel and “pull” this channel, not paying attention to the others. This is general scheme, details may vary in each individual case.
And one more thing. Initially, a good fullness of the “infrared channel” (for example, blue) will require less conversion in the converter, and therefore there will also be less noise and artifacts in the final image. For example, we received absolutely clean, noise-free infrared images, although the original color frame looked more like an outright defect.
So the time spent shooting takes is completely justified.
Conclusion
Which of the considered infrared filters should you prefer? For photographers still loyal to film, it's unlikely to be B+W Infrared Black 093. It requires films that are highly sensitized to the infrared region.
But this same filter allows you to quickly (unless you take into account very long shutter speeds when shooting) and easily obtain digital black-and-white photographs.
The B+W Infrared Dark Red 092 filter can be considered universal, suitable for film and digital photography. And some of the hassle that may arise when processing frames taken with its help is more than offset by operational advantages - working camera automation and more short exposures when shooting.
F&V
If you close your eyes and bring your hand to your face, you can feel its warmth. When we open our eyes, we see the hand with our own eyes. Although both of these phenomena have been familiar to man for thousands of years, the fact that they are based general principle- radiation, we understood only relatively recently, practically simultaneously with the advent of photography.
The heat felt by the skin is the so-called. far infrared radiation (conventionally from micron to millimeter wavelengths), which is located beyond the visible part of the spectrum 400-700 nm. And right next to it is near-infrared (700-900 nm), which can now be used for photography without much difficulty.
In the history of infrared photography, there are two events and two people associated with them that definitely deserve mention. The first event proved that behind the visible there is invisible light, the second demonstrated the possibility of photography in this invisible range.
By sorting light into a spectrum using a prism, the English astronomer William Herschel discovered in his experiments (1800) that there is something beyond the visible range that can act on photosensitive materials in the ultraviolet region and heat thermometers in the infrared region.
Using sensitized emulsions and self-created filters, the famous American physicist Robert Wood took the first infrared photographs in 1910. Among them were landscape photographs demonstrating the whiteness of living greenery and the blackness of a clear daytime sky, which was unexpected for inexperienced viewers.
To photograph in the infrared range, it was necessary to invent sensitization and filters that cut off the visible component of light. The sensitizer substance works as an intermediary - it captures the energy of infrared radiation and then starts the process of illumination of silver salts that are sensitive in the short-wave region of the spectrum. Because At the same time, their sensitivity to visible radiation is preserved; it is impossible to separate the infrared image from the one visible to the eye, unless the latter is cut off with a filter. If this is not done, then the mixture of visible and infrared images will give landscape scenes a dull, low-contrast picture, in some ways close to a mixture of positive and its own negative.
Digital camera matrices, unlike traditional materials, have good photosensitivity to both visible light and near-infrared light. Because The brightness contrast of the infrared image does not coincide with the brightness contrast in the visible color channels; to correctly reproduce the image visible to the eye, the infrared component must be cut off with a special filter, which is usually installed directly on the matrix.
Another reason why it is necessary to cut off the infrared range in digital (and for general-purpose photographic films, which are not sensitive to it, such a problem simply does not exist) is dispersion - the dependence of the refractive index on the wavelength.
A longer wavelength is refracted less by photographic lenses than a shorter wavelength. To ensure clear photographs, optical systems made of glass are used. different varieties, which allows you to more or less reduce visible rays to one point. But such achromats and apochromats do not take into account infrared rays. As a result, either the visible image or the infrared image is unfocused, and the resulting image appears blurry and lacks contrast.
Infrared photography is quite accessible to the modern amateur photographer. To do this, you will need to solve two problems: find a photographic material (film or matrix) that is sensitive to infrared radiation and a filter that cuts off the visible image. In this case, such a pair must be correctly selected based on the following principle: the filter must cut off the visible and ultraviolet regions as much as possible and leave only the infrared - and at the same time intersect with the region in which the photosensitive material still has sufficient sensitivity.
The instructions for infrared films provide recommendations on which filters and under what processing conditions you can get a good result. Manufacturers of digital cameras (with the exception of highly specialized ones) do not write how to shoot in the infrared range with their help.
Light passing through the lens different lengths waves are refracted differently. As a result, only rays of a certain spectral range are precisely focused in the plane of the film or matrix. Focusing on the image visible in the viewfinder leads to the fact that infrared rays are not focused to a point, but form a spot in this plane. If the photographic material is insensitive to infrared radiation, this spot will not significantly affect the sharpness of the image.
With infrared photography, the opposite is true. We want to highlight the rather weak infrared signal against the background of the strong visible one. In this case, two conditions must be met: focus the infrared rays and not allow the visible rays to blur the image.
Focusing during infrared photography can be done either manually or using camera automation. Since visual focusing through an infrared filter is impossible, you have to manually focus, either using the sequential sampling method (for digital, even mirrored, this is a completely suitable technique), or using the shift indicator for shooting in the infrared range. This indicator is usually marked on the distance scales of most good lenses. (To get an idea of the specific numbers, let’s give an example. For Canon lens EF 28-105/3.5-4.5 II USM at focal length 28 mm focus for infrared rays coming from infinity is achieved by setting the distance scale to approximately 4 m.)
Correction scales for shooting in the infrared range, which are applied to lenses, are calculated for the case of using certain photosensitive materials and specific filters. Therefore, you cannot hope that they can be used for any infrared filter on any digital SLR.
Autofocus system SLR camera uses sensors with a certain spectral sensitivity. If their sensitivity range is extended into the infrared region, then these sensors will work behind the filter. But you shouldn’t rely on them too much either. For filter + matrix and filter + autofocus sensor systems, the maximum sensitivity, generally speaking, should not coincide at all.
So, the most reliable way to focus is by successive trials. If you constantly use a specific set of equipment for infrared photography, you will know its features and put your own marks on the lens scale, or if you are lucky, you will simply use autofocus.
The second condition - not to allow visible rays to blur the infrared image - is not difficult to satisfy by choosing the “right” filter. For strong filters this is done automatically. But for weak ones, through which the visible image passes, it is sometimes difficult to get a clear picture. When buying a filter, it is better to focus on “opaque”, i.e. completely cutting off the visible part of the spectrum.
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Infrared filters Schneider
Both Schneider filters were measured in our laboratory on a spectrometer. For comparison, the measurement results of the Heliopan RG715 IR filter are presented. As can be seen from the graphs of the spectral dependences of the transmittance (1), the results obtained are in good agreement
with the declared characteristics of the filters. The maximum transmission of 092 IR and RG715 is located in the visible region at a wavelength of 750 nm. The maximum transmission of 093 IR lies outside the laboratory spectrometer bandwidth (792 nm) in the near-IR region.
Graph (2) shows the spectral dependence of the transmittance of the thermal filter installed in front of the matrix to cut off IR radiation. The tested filter was removed from a 1/1.8-inch CCD from a compact camera. As can be seen, the intersection of the transmission regions of the tested filters and the protective thermal filter lies in a narrow wavelength band of 650-700 nm, and the transmittance in this band does not exceed the level of 0.1. Therefore, a significant increase in exposure is required to develop the tonal elaboration of the image. The wave nature of the transmittance at wavelengths of 450-600 nm is a sign that the filter is interference (in old literature you can find the term dichroic).
What is the spectral sensitivity of the digital sensor itself? We present the typical relative sensitivity of a 1/3-inch Sony CCD matrix made using EX view HAD CCD technology (manufacturer's data). The matrix is black and white without color mosaic filters in front of the photodiodes. Graph (3) shows that the spectral sensitivity extends to the near-IR region of the spectrum, up to 1000 nm. At the level of 50% of the maximum, the cutoff wavelength is 800 nm, and at the level of 20% - 910 nm.
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Schneider B+W Infrared Dark Red 092
Characteristics: transmittance 0% at 650 nm, 90% at 730 nm
Approximate price: 2900 rub. (D 72 mm)
Pros: High image sharpness
Cons: Troublesome obtaining an IR image
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