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Possible to "disable" IR filter by chemicals?
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hap2001:
Hi.
I'm going to do "IR convert" on my cameras, but finding a suitable replacement glass is tricky and expensive.
Is the actual filtering happen on the surface by a coating, or inside the glass itself?
If it's only on the surface, can I use some kind of chemical to dissolve them? What chemical should I use?
Thanks.
switchabl:
Yes, it is almost certainly a multi-layer dielectric coating. It might be possible to remove it chemically but the first problem is that you don't even know the materials (SiO2, TiO2, Al2O3, MgF2, ...?). And some of the stuff that could work is pretty nasty and will attack the glass substrate as well. If you really have to, polishing it off should work, it won't be more than a couple of microns.

Most optics/glass suppliers will do custom sized windows (with a suitable AR coating). If you can't afford that, you could try buying a larger sheet in a standard size and cut that yourself.

You will probably get more helpful replies if you ask on a photo/astronomy forum, like Cloudy Nights.
Someone:
Alternate opinion: IR (long cut) filters in cameras are predominantly not dichroic/interference filters, although some are. Even those that aren’t thin film filters they usually have some anti reflective coating, and may include LPF.

Unpopular opinion: Your lenses won’t be focused far outside their visible wavelengths anyway. Replacing an IR filter with an AR coated plain glass is nice in theory, but makes very little difference to just leaving it open.
switchabl:
I think I was extrapolating mainly from the discrete (lab-grade) long cut filters I've seen, so you may very well be right. There is a relatively easy way to check for your camera without taking it apart: shine an infrared source on the sensor and check the reflection. A dielectric filter should be highly reflective in the IR.

If you want to retain full VIS performance (autofocus on DSLRs and image quality with wide-angle lenses) I think you really need to keep the optical path length intact. Otherwise, leaving the window off might indeed be an option.

EDIT: I found a Canon service manual (http://cholla.mmto.org/photography/gear/repair/eos_40d_service_manual.pdf) that indeed mentions an "Infrared-absorption glass" in the sensor assembly.
Stray Electron:
   I looked into converting my old Olympus E-2 to IR use and I found that most people simply removed the filter and left it out. AFIK it's only a filter and not a lens.

   YMMV.
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