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

ProfHankD wrote:

petrochemist wrote:

UV imaging is neither easy or cheap.

You said it all there... but....

I'll just mention that decoding multispectral information can be cheaper and easier than you'd think. If you look at the spectral profiles for typical RGB Bayer filters, they're really not narrow-bandpass filters, yet we get decent RGB extracted from captures with them. Basically, as long as the filters being used have different levels of response to the bands you care about, being able to extract the bands is primarily a matter of calibration and a bit of math.

For example, if you have a filter that does almost nothing beyond blocking UV, relatively simple differencing with an unfiltered view can give a decent UV image. For NIR, even the spectral response differences of Bayer RGB can allow extraction of a noisy NIR channel. However, I don't think the Bayer RGB colors differ much in NUV. There are cheap gel filters that differ significantly in NUV response -- see the samplers from Rosco ; each (designed for theatrical lighting) filter comes with a response curve going from 360-740nm in 20nm steps.

BTW, you'll want to do the band extraction math on a linear representation of the pixel values, which generally means raws -- the log encoding used in JPEGs makes add/subtract behave more like multiply/divide, which is not what you want.

I know it can be cheaper than I described, The OP want cheap & easy, so I thought suggesting a self modified compact & combining filters which might be the cheapest way wouldn't fit.

Your post does suggest I'd could get much better results from my poor mans UV set up if I learnt to process RAW better. Differencing is not something I'd ever considered I can see several potential applications for it in IR photography (where i already have a wide range of cut offs) I'm not a fan of extensive processing so even with that I'll probably never try it. I don't think any of my gel sample books have the wide range of long pass filters you mention - I'll have to keep my eyes open for other types...

Most of my experience with UV is in organic spectroscopy where I can clearly see how much UV is blocked by glass. The glass cells used for visual light have walls about 1mm thick, 2 of these walls effectively blocks all light below about 320nm, while UV quartz cells of the same dimension go right down to about 190nm about the point where air itself becomes opaque to UV..

I've played around with the works spectrometer for some of my photographic gear & have found a few of my lenses actually block all UV (blocking everything below 410nm) more effective than some UV filters. Without careful research the RAW files you try processing could have no significant UV data even in the 'unfiltered' shot.