Will a different filter be required for 365nm flashlight?

[Doug A]

I have a full spectrum camera, ioriginal Kyoei 35mm clone with his ZWB1 2mm and BG39 2.3mm filters. Looking at a chart for the ZWB1, it appears to have almost 0% transmission at 365nm. Is a different filter required for the lens? Perhaps I don't need the ZWB1 at all since a filter is fitted to the flashlight?

 

Thanks,

Doug A

[Andy Perrin]

Ok, if you are trying to do UV reflectance photos (not fluorescence), then you need a filter on the camera only. Filter on the flashlight can't hurt but is unnecessary.

 

Putting the filter on the flashlight only will only work if the only source of light is the flashlight. You would probably have IR/visible contamination from other sources of light in the room.

 

If you want to do UV induced visible fluorescence (UVIVF), you need a UV/IR cut filter and you also need to filter the visible light out of the flashlight with ZWB or Hoya.

[Cadmium]

My opinion is that UV torches/flashlights are really only good for one or two things,

1) UVIVF

2) UV focusing

 

When shooting reflected UV torch LED's have such narrow band illumination that the photo will be void of most false color UV and look fairly monochrome.

If monochrome is what you like, then that is fine, but I like the more colorful UV, and you need a broader range illumination.

 

It is also my opinion and I think the general rule of thumb that the best filter to use for a UV torch is something that cuts below 400nm, being that the whole point of filtering the torch is to remove

any visual range leak above 400nm. So I use U-340 rather than U-360.

Some use U-360 because it has a slightly higher % transmission at 365nm, but it can also transmit some above 400nm.

Again, this is for UVIVF not for reflected UV illumination.

[dabateman]

I am confused by your question.

Zwb1 doesn't have 0% transmission at 365nm.

Zwb1 is like Ug11 and U340 glass. Its quite a broad UV transmission glass, with small bump into IR. It has very low visible light transmission, if thats what you meant.

 

[Andy Perrin]

dabateman, people who are new to UV sometimes don’t realize that the linear transmission charts are useless, so when it says “0 percent” they take it literally. (Said with a broad wink in Doug’s direction also. :-) )

[Doug A]

I am confused by your question.

Zwb1 doesn't have 0% transmission at 365nm.

Zwb1 is like Ug11 and U340 glass. Its quite a broad UV transmission glass, with small bump into IR. It has very low visible light transmission, if thats what you meant.

 

I did misinterpret JWC's chart. Thanks for clearing it up.

dabateman, people who are new to UV sometimes don’t realize that the linear transmission charts are useless, so when it says “0 percent” they take it literally. (Said with a broad wink in Doug’s direction also. :-) )

 

Besides thinking 0% meant no light, I read the chart incorrectly. Thought the divisions were 350 and 400nm. But the correct value is 450.

 

I probably shouldn't read charts on a small tablet, at lunch. Filters do remind me of high-end loudspeaker crossover design. Fascinating.

 

Thanks for the help,

barondla

[Andy Perrin]

Yeah, you really need either a logarithmic y-axis or a diabatic one (that's the log/linear combination that the Schott software produces) to be able to correctly interpret transmission. Our cameras work on a log scale (just like the loudspeaker situation, in fact) so what looks like 0% on a linear scale is really just "too small to see on a linear plot, but not too small for your camera to see with its logarithmic response."