I have a painting where one can see underwriting under the painting. I purchased a used Olympus E-510 and a 950nm IR filter, but I cannot figure out how to use it. Do I have the correct filter?
I thought I would be able to see the underwriting. Can someone give me detailed steps? Do I need to buy Hundesten lights or infrared light? What ISO do I need to set the camera? What shutter speed? Do I perform the shooting in normal lighting or with no lighting?
If the E-510 you purchased is not modified for IR work, it may not be the appropriate tool. Digital cameras these days come with UV/IR blockers over their sensors to keep colors true (UV/IR sensitivity can throw off greens and purples on sensors). This blocker greatly reduces the IR sensitivity of the sensor. It doesn't completely reduce it, but it does lower it to a high enough degree that infrared capture with an IR pass filter on the lens is typically done at very long shutter speeds even in bright sunlight (say, 30s to a minute).
You may want to look into getting the camera converted (or returning it and purchasing one that's already converted. Conversion involves removing the IR/UV blocking filter over the sensor and replacing it with an IR filter or clear glass that allows all spectrums through. (See the lifepixel website). Whether you use a converted camera or not will have an impact on which settings you can use, ISO or otherwise.
To use an IR filter, you usually screw it onto the front of your lens. The filter should be the same size or larger than the filter thread on the lens (if it's larger, you use a step-up ring to make everything fit). The filter size of the lens should be written on it, with the diameter symbol (e.g., ∅58mm).
From reading an Introduction to Infrared Reflectology article, it also sounds as if you probably need to be in a dark room, and using only IR lamps on the painting.
Optical filters block some frequencies (colors) of light and allow other frequencies to pass. The IR filter allows infrared light to pass while blocking all other colors. Visually, the IR filter looks opaque. When we image a vista or object that is illumined with visible light (sunlight or artificial) it is likely that some percentage of infrared is also illuminating the subject. If we want to record this scene as seen by IR radiation we mount an IR filter. Its job will be to exclude all but the IR rays.
You can image your artwork illuminated only by IR without a filter. You place the object in an area that can be made pitch black (dark room). If the camera used can record IR radiation, you illuminate it with an IR light source.
Set the object to be imaged in its place and compose and focus in normal room light. Factorial: We focus our camera via visible light. The IR focus is different. You will need to manually offset the focus. Say the object is 4 feet from the camera, try 3 feet and shoot. Examine the resulting image and reset the focused distance a smidge. By trial and error you can obtain focus.
You can test your camera to see if it will image in the IR region. Many TV remote controls operate using IR radiation. In total darkness, activate the TV remote while looking at it via the camera’s viewfinder. Likely you see the IR bursts off the TV remote. Try and photograph them. Note the camera’s IR filter is integral to the cover glass over the image sensor. You might figure out how to remove it! For your purposes, maybe removal is unnecessary.
Now to light the object with IR radiation: IR is also heat radiation. I have seen IR done with a flatiron used as the light source. You can mount your IR filter and try to image the IR from your TV remote. You can purchase an IR heater and/or R40 or R20 IR flood bulbs. These are the reflector heaters with glowing coil. The R40 and R20 are common reflector flood lamps from the hardware store. The IR versions are " people heaters" used in bathroom ceiling light fixtures. Good luck! You are now in the realm of experimentation.
