IR digital camera mod keeps autofocus intact

There are many, many instructions available about converting digital cameras and webcams into IR capable cameras. However, if you simply remove the IR filter which is often a thick piece of optical glass you will lose the auto-focus capability as the glass alters the focal length. This Instructable lets you keep the auto-focus because your not removing the glass, only removing the IR coating.

I had read about how the filter - essentially a thick piece of glass, should be replaced to maintain the autofocus ability. Finding a replacement piece of glass the correct thickness isn't easy and dealing with optical companies is difficult and expensive for such a small piece of glass. I had thought of using microscope slides, the glass from photographic glass slide mounts or even an old filter (glass or optical acrylic). This involves cutting and layering the glass to the correct thickness.

This is too much work for something that may not be successful anyway. So this is what I did instead.....

Step 1 Open up your camera

Open up your camera and find the IR filter which will probably be a thick piece of glass this is also known as a 'hot mirror' since it reflects IR radiation whilst allowing visible light through. Hot mirrors are often laminates which presumably have slightly different refractive indices, re-using it will maintain exact focus.

I modified a FujiFilm MX2700. Looking at the reflected surface on one side of the glass showed that it appeared to have a yellowy reflective coating which was optically transparent when viewed straight-on. The other side looked like a normal optical coating. So why not just remove the IR reflective coating and place the glass back into the camera with a thin piece of dark filter to cut visible light and allow IR through?

Note that this is for the MX2700, your camera may have a different arrangement. The important thing is to find and remove the IR blocking coating once you've resigned yourself to modifying the camera and otherwise having to throw away the glass filter anyway.

Comments

[ozdigicams]

Hi, Great idea! You may want to use the Manual White Balance of the camera to remobve the colour cast. Just do a manual white baalnce on a white piece of paper, or even the green grass/foliage. Regards, ozdigicams

[Whatnot]

If the lens is glass would some cotton with aceton not work perfectly fine to remove the coating without needing abrasives? It dissolves a lot of materials/plastics after all. Just an idea.

[Oreyeon]

Hello, I was wondering. Anyone done this with a Canon Powershot G1? I'm soon to receive one in the mail and want to convert it to a complete IR camera. The mod now is to remove the IR Cut filter and replace it with a piece of clear glass in similar dimensions, or glue appropriately cut microscope slides together and drop them in. However, if the coating on the existing IR Cut filter glass can be removed, it would save alot of headache. I'd be interested in knowing if anyone knows. :)

[dharmabum]

Can't speak for other models, but my Nikon uses an IR absorbing glass layer in the glass hot-mirror 'sandwich' that blocks the infrared spectrum... removing the coating sadly has no effect on IR transmission for mine.

[gomiboy]

I followed these (had modded my Sony DSC-P71 by removing the IR filter earlier), but this didn't work for me. I used a different product (petroleum based, but silica abrasive) which very slightly scratched the glass, but even after the IR coating was apparently removed (no reddish film left) the glass still blocks IR. Tested by blocking my TV remote with it - no IR signal gets through. Any thoughts?

[uhf]

Hello, both sides of the glass filter are possibly coated. On my MX2700 one side was a normal optical coating and the other was the IR coating. Different manufacturers probably go about it in different ways. Make sure the coating is completely removed, it is quite tough. The glass shouldn't really scratch unless your using some kind of industrial abrasive cream (which shouldn't be the case if it's just a car paint renovator). Perhaps it's the coating that's scratched? In which case more work is needed. It took me about 15 minutes of rubbing on a flat piece of acrylic to remove the coating and there weren't any significant scratches afterwards. You can test the filter by putting it in front of the camera lens and doing the IR remote control test.

[trebuchet03]

many, if not most, webcameras have a way to manually set the base focus... I never had any problems with focus when I used a logitech messenger cam...