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Forum: Pentax K-01 08-06-2017, 06:37 PM  
Full spectrum converted K-01, bought new lens, IR filters not working
Posted By Bob 256
Replies: 9
Views: 2,655
Some lenses just don't work well in infrared. It might be the anti-reflection coatings which are designed for visible light, and actually become reflective at IR wavelengths, but in any case, internal reflections similar to those you are having are common with some lenses and IR. I've heard round-about that the 18-55mm DA performs satisfactorily and the shorter focal length would allow you to work closer to the paintings though that lens might not be the best in terms of image quality (can't speak to that). It should be available for a reasonable cost in the DA L version (around $60US on ebay).

Are you trying to do infrared fluorescence capture or just take an IR shot of the painting? For either, an IR source would be best. You can make your own using a string of IR LEDs. These are available in two different wavelengths 850 and 940 nm. It's probably easier to buy an assembly already put together like this one:

48-LED Infrared Illuminator Board for 60mm- Shell CCTV Security Camera 816412 2017 ? $1.63

You might have to work with it to get even illumination (possibly use several just like regular lights), but if you extinguish your visible lighting, you wouldn't need a camera filter - just the IR light source. The liveview image on the K-01 will show what you are getting. Use a little caution with these and don't look into them when they're on. You can't see the light but it can cause eye damage when you look into an intense source like these LEDs. No problem with the reflected light off a subject.

Tungsten lighting has infrared in it but not in abundance so that could be another reason you're not getting an image. Raw sunlight is pretty good though you may want to limit your painting's exposure to it because of the UV content which will fade the painting. Of course, you would use an IR lens filter if you use sunlight and sunlight isn't the best choice if you're going for IR florescence.

Although the K-01 autofocus should work in infrared, it's no guarantee, so use manual focus, zoom in with the liveview image (using the adjustment dial) and tweek your lens for the best focus. That might sharpen up the image significantly.

Know this was an old post but you might still be hanging on or there may be others with similar interest down the road so thought I'd post.
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