10/11/2008

DOs and DON'Ts in IR

1. Consider the conditions of the filters

You need to select the correct thread-size glass or gelatin filter holder and mount the filter normally (if your DSLR has a lens threaded for filters), and since the case most DSLR cameras don't have those kind of lenses, you'll have to make special adjustments to mount the filter. Gelatin filters can be cut to size with scissors and taped in place. 

To increase the classic infrared effect filters are placed in front of the lens or inside the camera. These filters are designed to reduce the total of blue and green light reaching the film, or block all visible light to trace only infrared light. Visible light arrays from 400 nanometers (violet) to 700 nanometers (red).

2. Lens preference

 For ease of focus, use wide angle lens to increase your "depth of field", but you may try other different lenses for experiments. The easiest thing to prefer the right lens is by choosing the lens which are marked with a mark (usually colored in red), to show how to correct them for IR in focusing. At most conditions, it usually best to stop down the lens aperture by (minimum) two stops from wide open. This will increase your chance in getting the better quality of the image and has the advantage since the DOP is raised.

3. Calculating exposure

Calculating exposure is somewhat easy. The problem with most camera and hand held light meters are that they are neither calibrated nor filtered for infrared light. Different meters also differ in their sensitivity to infrared light. So, here are little simple rules of thumb which should allow you to get some useful results. These rules are based on the "sunny 16" rule.

For normal film, the sunny 16 rule simply states: In bright sunshine with an aperture of f16 use a shutter speed of 1/ISO.

So at f16 using a normal 100 ISO film in bright sunshine you should use a shutter speed of 1/100.

With film each maker provides some guess ISO values for you to try. You usually have to guess and bracket, since only experience will enlighten you what works well when. In other words, your light meter reads light, not IR. Even if you find an ISO value that works well one day the ratio of IR to visible light is always changing so any ISO value won't work consistently.

With digital just keep trying different values till it looks right on the screen. Easy.

4. Storing

For non-digital DSLR, it is best to store your IR film from places that keep the film refrigerated or frozen, especially if you do not think to use the film right away. If you want to use it you have to take out the film from the storage (fridge/other containers) up to room temperature before you load it to the camera. This will avoid condensation forming on the film. In general, Infrared films are pretty much needs to be treat in the samecondition as other types of films. Keep it cool.

5. Focusing

The accurate point of focus will depend on which filter you use as this order which wavelengths are most important in your image. Most people move towards or to the red infra-red mark on most lenses. If your lens is missing this mark then push it to a slightly closer focus. The rule of thumb is to move the lens forwards 1/4 of one percent of the focal length of the lens if you do not have an infrared focusing mark.

Note: don’t stop down too far! Diffraction is twice as bad with long IR waves as it is with visible light! Stopping down to minimum aperture is a bad choice. Infrared Ektachrome focuses normally. Given the fact that Ektachrome IR records from yellow/orange till the IR area, this is no surprise; it is a compromise between focus of the visible and of the IR.

6. Flash Guns and Bulbs

Electronic flash guns and flash bulbs discharge plenty of infrared light together with visible light. This means that you can use fill-in flash and flash alone for shooting in infrared. You will need to calibrate your flash for the infrared film of alternative through test exposures.

The use of flash allows a fascinating possibility - you can use a filter over the flash to reduce or eliminate the visible light output and take infrared photos in the dark without any apparent light. This means that you can take photos without out disturbing your subject or alerting them to the fact that a photo has been taken. If there is no ambient light then an infrared filter over the flash gun is all that is required. If there is ambient light then a filter will also be required over the lens as most infrared film is sensitive to some visible light.

7. Post-photograph

Process as soon as possible. This is good advice for any film but especially for IR film which seems to be more prone to fogging. There are many professional photo graphics labs which will process infrared film.

8. Printing

Choose your basic printing exposure to bring out the uniqueness you were using. As with any black and white print you can also tone or tint the picture to increase its mood or highlight a particular element.

The printing process lends itself particularly well to printing infrared negatives. Grainy blacks and wonderful detailed midtones together with subtle tones in the highlights. Colors depend to a great level upon choice of paper as certain papers produce their own characteristic colors without the use of toners. 

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