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Assumption: If I have some cheap/used/partially-broken-but-picture-taking DSLM, and want to use it as an experimental full spectrum camera, the only downsides to cleanly removing the filter stack and substituting it with nothing would be a changed registration distance and a more difficult sensor cleaning process. The changed registration distance will not matter if adapted manual focus lenses are used, since one can use short build adapters, helicoids, bellows, extension tubes etc to accomodate that.

What problems or risks am I overlooking?

  • cleanly removing the filter stack and substituting it with nothing would be a changed registration distance: not necessarily, and if it does (focus on the filter instead of the sensor) then by removing the filter you increase it, and it will be quite hard to shorten it again with the standard lenses for that camera. – xenoid Apr 4 at 14:52
  • While there is no absolute need for them, plain glass filter replacements are almost always the simplest and easiest way to compensate for removing the filter stack. – Michael C Apr 4 at 19:21
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Removing glass from the light pathway would result in the loss of infinity focus unless you can decrease the distance between the lens and sensor "past" infinity. Helicoids, bellows, extension tubes will not be helpful because they increase the distance between the sensor and lens.

I suppose what you mean by "short build" adapter is that it is shorter than usual? Such an adapter would work, but I do not know of any commercially available ones. You would have to grind down an existing adapter or build one from scratch. I'm currently working on converting a lens to EF by replacing the mount with a lens reversal ring. Grinding it down to the correct thickness is much more difficult than it is to type. It would be far easier to just replace the glass in the filter stack during camera conversion.

Some compact cameras inherently focus past infinity, and removing the hot mirror filter would not affect infinity focus. However, the only way to know whether a particular camera will work is to try it.

You could also just use lenses that you already know focus significantly past infinity or that can be adjusted for infinity focus. Adjusting the focus on lenses would be easier than building adapters. It's usually just a matter of locating and loosening a set screw. The best candidates would be third-party lenses that were made for different camera mounts. First-party lenses are likely to not have enough room for adjustment.

  • Short-register M42 adapters for various mirrorless systems exist - quite common for NEX (though I am not planning to convert a NEX here, rather a Nikon 1 which might require more patience to find an adapter for) - amazon.com/Fotasy-Mount-Adapter-Focusing-Helicoid/dp/B06Y5HDLNN for example. Can be turned into almost whatever register you need with extension plumbing ... – rackandboneman Apr 4 at 19:48
  • I think of those as M42 helicoid adapters (to attach the M42-M42 helicoids). I've seen them for most mirrorless mounts. The problem is they're suitable only for M42 lenses. You're still better off replacing the glass filter. – xiota Apr 4 at 19:53
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    I heavily dabble in adapting folder and rangefinder lenses, so I tend to have that kind of plumbing around anyway - and an uncoated triplet might actually be more useful for full spectrum than modern SLR lenses... – rackandboneman Apr 4 at 20:40
  • Sounds like you're all set then. – xiota Apr 4 at 20:59

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