What's the easiest and most affordable way for obtaining UV reflectance images?

ProfHankD wrote:

petrochemist wrote:

Not surprisingly focus afterwards was way off.

This is actually my #1 issue with full-spectrum conversions. Generally, if you remove a 1mm thick piece of glass typically with index around 1.5, you've basically pushed the sensor about 0.5mm closer to the flange. MFT uses a 4mm cover glass, so we're talking about a potential shift of 2mm!

Could you explain it to me please?

What I have learned from the internet is that the filter stack increases the focal distance by about 1/3rd of its thickness. Leaving the sensor at its position would mean to lose the ability to focus to infinite.

My question: Must the sensor without the filter stack be moved nearer to the lens mount, or further away in order to be able to focus to infinite für visible light?

For DSLRs, that's well out of the adjustment range for aligning the focus sensor (or screen). Fortunately, most lenses just loose a bit of close focus with a shift like that. However, I own some lenses (ultrawide/fisheye) where the entire focus range is a fraction of a mm. So, the take-away message is that you might want to make a custom adapter that compensates for the missing cover glass. That's easy if you 3D-print adapters, it can be a bit harder to change a commercial adapter's length that much, but it is do-able.

I'll also note that focus plane for NIR or NUV is often pretty far off from visible, so that alone might make you want a customized adapter if you're shooting only with one of those bands.