Photo outside the visible range

26.08.2004

26.08.2004


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A bit of theory


The boundaries of the visible (eye) is considered to be the range of ultraviolet UV (380 nm) and infrared IR (760 nm). All of that is behind them, the eye can not distinguish. Retin-A, in fact, sensitive and shorter region of the spectrum. But the lens and vitreous body to protect it from the relatively "hard" radiation. However, the retina can perceive the "leftovers" in the form of ultraviolet fluorescent bluish glow of the lens (re-emission in the longer wavelength region of the spectrum). In the IR range, we do not see, because otherwise would be blinded himself by his own heat.

Outside the visible area of the spectrum of the radiation does not end there. And the mechanisms and principles of optics continue to operate (there are both lenses and mirrors). Radars see in the invisible zone of radio range (even longer wavelengths than IR), and the mirror-dish radio waves everywhere spoil the architectural views. Sources of light shining in the infrared and ultraviolet ranges. And in the mountains and the sea without UV filter can not do, or what is invisible eye can significantly damage the pictures (by the sea and in the mountains there is no haze which absorbs ultraviolet light). Scattered light smoke gives the impression of deep space, but if you need clarity of black and white film and distant objects — put the camera orange filter.

UV conventionally area extends up to 1 nm, and IR and 1 mm. Atmosphere (ozone, steam, dust) absorbs and dissipates plot range 10-300 nm, and cuts off the window and a longer wavelength, so pictures (without additional light sources, and special lenses) can be used practically only the near UV region — 300-400 nm.

The main limitation still photographs. Sensitized photosensitive materials are sensitive in the range of 350-450 nm, so at the dawn of photography is nothing but "blue" color and UV imprint was not. But in the darkroom printing, you can use the red and green filters and control the process of developing visually. To shoot in the IR need special photographs. Typically, infrared film requires special conditions of storage and use, and the camera body does not have to be "transparent" for the beams shining on the infrared film.

To illustrate the various aspects of the visible and "invisible" photos, consider the following flash movie. It is a graphical representation (conventionally, but close to the actual values): the spectrum visible to the eye colors, the spectra of light sources, the spectral sensitivity of the eye and photographic emulsions, the spectral characteristics of the filters and glass. By default, only the visible spectrum. In order to understand what can be rented for a photographic emulsion at a specific light source and a specific filter to "turn on" (check) the items you want. At the intersection of the left that portion of the spectrum, which will be filmed or see.

 

Note the following important points for taking pictures:

1), the spectral composition of light when the sun is at its zenith and allows you to take in the IR and in the UV range and is the only powerful and versatile light source, the light of the sun above the horizon is almost completely devoid of the UV component;

2) Tungsten is well suited for infrared photography;

3) comprises a flash light both IR and UV radiation;

4) the maximum sensitivity of the eye under normal illumination is about 555 nm and about 510 nm dusk (Purkinje effect);

5) almost all photographs are suitable for UV photography, and for the IR only infrahromaticheskie;

6) optical glass with the thickness of "cuts" more ultraviolet radiation, for shooting better to use old lenses or special date;

7) filter matrix digital camera cuts substantial portion of IR and UV radiation;

8) the degree of transmittance of optical filters and glass depends on the thickness, the filters, opaque to visible light can pass both IR and UV.

Practice


To take a picture in the "invisible" rays will use digital cameras. Known test "sensitivity" to the IR range — to remove the remote control (IR source is directed at the camera, the button is pressed on the remote control) to determine whether the camera is suitable for IR photography. If your photos or display a compact camera clearly visible glow IR source control — perfect. In a filter matrix usually substantially the cutting infrared and ultraviolet radiation, so to remove in this range require long exposure and filters more effectively cut off visible light (using ebonite and thin plates). The following is a table of common IR filters of different manufacturers, which identifies the boundaries of a complete cut-off and 50% transmission of IR radiation.

Filter Kodak

B + W

Hoya

Heliopan

and here


0%

50%

A 88 WRATTEN








5715 (RG715)


720


750


WRATTEN 87








5780


740


795


WRATTEN 87 C


093





5830


790


850


WRATTEN 87 B





RM90


5850


820


930


A 87 WRATTEN


094


RM100


5100


880


1050


For photography filters used in domestic UFS 6 (4 mm), X 1 and X 3 more contrast (2.5 mm), camera Canon EOS 300D and the Canon PowerShot G2, mounting kit Cokin. Set relatively thick filters in standard holders for Cokin filters proved impossible, so the filter simply fastened with rubber bands to the ring Cokin. If, however, you will be able to attach to the holder Cokin filter in a standard way, well, close all gaps with foil, or at slow shutter speeds remains of visible light glare of the matrix stronger IR.




Ring and Cokin filters.




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Filters for Canon 300D

Filters for Canon G2

When taking photos in the IR and UV range, there are two "difficulties" in which the operational features of "numbers" are very useful. These challenges — determining exposure and simplify back focus. Since "by eye" is not any different in the case of "invisible" light will set up, we have to do a few takes and on a picture on the display is to introduce the necessary adjustments. Determine the exposure is easier than the correct focus. After all, the focus for the "green" visible light and IR or UV is not the same (so good modern lenses those invisible to the eye but visible rays are trying to wrap completely cut off, so they do not reduce visibility on the print sharpness and contrast). We have to set the distance to the eye and stop down the lens. Compact digital cameras such as Canon G2, having a small matrix and the greater relative depth of field at the same aperture, it is more convenient for the first method (focus on eyes). But when exposed to 10 seconds, and the sensitivity of 400 picture they get very noisy. With the SLR camera will have to do more takes, try different focus distance, but the picture will be clearer.

->


On a good lens usually has a special mark (red line "R") for IR photography. This is certainly a plus, but the universal line for different IR filters and films not, as it does not exist, and for UV. Therefore, a trial in general only.




Photos


Sunny Day





Canon EOS 300D, ISO 100, f / 9,0, 1/200 with.

->


X
1, Canon EOS 300D, ISO 800, f/11, 0, 15
with.









X 1, Canon EOS 300D, ISO 800, f/11, 0, 15, the processing of Photoshop.

Cloudy Day


->


Canon EOS 300D, ISO 200, f / 4,0, 1/1250 with.









Canon EOS 300D, ISO 200, f / 4,0, 1/1250 sec, processing in Photoshop — conversion to a monochrome image.




->


UFS 6, Canon EOS 300D, ISO 400, f / 8,0, 30. The UV and IR.



UFS 6, Canon EOS 300D, ISO 400, f / 8,0, 30, the processing in Photoshop — conversion to a monochrome image.


->


X
1, Canon EOS 300D, ISO 400, f / 8,0, 90
with.









X 1, Canon EOS 300D, ISO 400, f / 8,0, 90, the processing in Photoshop — conversion to a monochrome image.




Note the greens, reflections on the water and the walls of houses, as well as to the "depth of field" on the B & W versions images taken with different filters without them.

Sources:




·                   
DS Gurlev. Reference photos (Lighting and materials). (Kiev, "Equipment").

·                   
R. Heiman. Filters. (Publishing House "MIR").

References:




·                   
WJ's Photo Homepage (www.a1.nl/phomepag/markerink/irfilter.htm)



·                   
Sony DSC-V1 (overview on iXBT.com)


·                   
Sony Cybershot DSC-F828 (overview on iXBT.com)


·                   
Anatomy of a digital camera pictures (article in iXBT.com)

Planned to continue: IR and UV with artificial light sources.

 

Sergey Shcherbakov


(Sherbakovs@ixbt.com)

Posted by — August 20, 2004

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