Filters for ultraviolet fluorescence and sunny day photography

[Avalon]

So I want to do not just UV reflectography but as well UV fluorescence photography of paintings and other materials. Standart UV filters and camera built in hot mirrors do not block completely UV. So good quality ultraviolet block filter must cut spectrum in violet region already. Schneider B+W 415 were used effectively for this purpose but pigment based UV filters have problem of internal fluorescence while interference filters do not have this problem and and absorb better UV:

https://www.research...ference_Filters

Suggested B+W 415 UV, B+W 486 UV IR cut and Baader UVIR rejection filters where shown to produce superior image quality when compared to classic UV block filters. I’m curious are there more UV filters like these, maybe newer and better?

I imagine better UV filter would also benefit not only in UV fluorescence photography but also ir normal spectrum photography especially during sunny midday time period when UV spectrum amount is highest.

[Andy Perrin]

Baader, I think, is the standard still. They do revise their filters now and then. Baader does not attenuate the red very much, but the camera is more sensitive to red than blue, leading to images that are very reddish and need to be carefully adjusted in post processing.

 

Interference filters have their own issues, however. For one thing, they have a strong angular dependence that will give color variations if the lens is wide angle.

[Cadmium]

If you are concerned about Schott GG400/420/430 filters fluorescing, the B+W 415 is Schott GG400 glass.

I think GG400 and B+W 415 are exactly the same, and they will both fluoresce exactly the same.

Those will only fluoresce in some situations. I use the GG420 or GG435 most of the time for UVIVF and they work fine for me.

I would not recommend GG400/B+W 415 for UVIVF, because they will transmit some UV, I would use 420 or 435 instead.

You could also try to find Schott KV-418, (no longer made) hard to find, and expensive ($200-$300 ? 52mm):

https://www.itos.de/...lter/kv-filter/

 

Or just use a Wratten 2E gel filter.

https://en.wikipedia.../Wratten_number

[ulf]

So I want to do not just UV reflectography but as well UV fluorescence photography of paintings and other materials.

This is what I assumed when I said that ZWB1 was a better alternative than ZWB2 for filtering the UV-LED's light.

The ZWB2 has less attenuation at the beginning of the VIS range.

Even if the emission tail of a proper UV-LED into VIS is not strong even this low levels of light will indeed contaminate a fluorescence image if the fluorescence is weak.

 

B+W 415 = GG400

B+W 420 = GG420

Both are ionic absorsion filters.

 

B+W 486 has cutoff wavelengths (-50%) at ca 385nm and 675nm

Baader UV/IR-cut has cutoff wavelengths (-50%) at ca 420nm and 680nm.

 

A combination of UV-LEDs filtered with ZWB2 and a B+W 486 on the camera lens will give you much contamination of LED-light, confusing light from materials fluorescing.

 

For UV fluorescence photography you could use an unmodified camera instead. The internal filters are often efficient filtering out both UV and IR.

My Canon EOS 60D had these internal filters, before the modification: http://www.ultraviol...dpost__p__17625

[Cadmium]

Indeed, the whole reason we would filter the light is to limit it to 400nm and below.

UG11/U-340 type will cut below 400nm, which is what you want.

UG1/U-360 is more borderline, and can contain some visual violet especially depending on thickness, which undermines the whole point in filtering the light,

so don't use UG1/U-360/ZWB-2 'type' filter glass for filter the light.

[Avalon]

I guess B+W 420 is best bet.

 

I'm not sure yet what transmission spectrum of Sony A3000 hot mirror. I seen somewhere list of many unmodified camera's and their UV tranmission differs as hell. Too bad I forgot where I seen this list.

Maybe I don't even need to buy UV pass hot mirror or on opposite side UV block filter. My guess that under UV light image blueness is good enough way to test this?

[Cadmium]

If you need it, but I can't seem to find a B+W 420 filter, seems to be unavailable everywhere I looked...?

The B+W 420 is the same as the Schott GG420, those are available.

You were worried about fluorescing however... B+W and GG are no different in that respect.

If you are using a stock camera then you may not need any filter on your lens, and you may see very little difference between an unfiltered UVIVF shot and a filtered shot.

The Wratten gel filters are readily available, new/used.

Don't think about it, try it out with no filter first.

If you are using an MTE 301/303 or a Convoy S2+ Nichia 365nm torch, and a stock camera, then try it all out first with no torch or lens filters,

'Blueness' is from unfiltered UV light (no filter on the torch/light), but it can be minimal, especially when using Nichia 365nm LED's.

[ulf]

With a properly filtered light source, (not ZWB2), it is unlikely that you will need a GG420-filter.

[Avalon]

I was wrong about B+W 420. Done research on it and found that it does also produce orange fluorescence: https://chsopensourc...et-photography/

 

Got point about ZWB2.

[Avalon]

Here is the list I think I was talking about listing spectral transmissions of unmodified camera's. Some have so good UV transmission that they could be used for UV photography. Couldn't find Sony A3000 although I see there is are NEX series camera's which are similar to it and they have good UV suppression. But to know for sure I have to do tests. Here is list: https://kolarivision.com/articles/internal-cut-filter-transmission/