Compare UV output filters for Conroy S2+ UV flashlight?

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Chris S.
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Compare UV output filters for Conroy S2+ UV flashlight?

Post by Chris S. »

Is anyone interested in a comparison between two brands of ultraviolet emission filters for the popular Conroy S2+ UV 365nm flashlight (aka "torch")? If so, please say so! And if there is interest, can anyone give advice on how to perform such a comparison?

I have a $24 USD Conroy S2+ UV flashlight (365nm), fitted with two ZWB2 20.5mm x 2mm ultraviolet band pass Filters that cost $1 USD each. On behalf of a forum member, I've just taken delivery of two much more expensive UV pass filters: Hoya 340nm ultraviolet band pass filters 20.2mm x 2mm filters for 365nm Convoy S2+ flashlight. These Hoya filters were much more expensive, costing $35 USD each. The vendors claim slightly different transmission spectra for each filter--see below.

Not sure if a comparison between these filters is useful. But if so, I can perhaps perform it before sending the Hoya filters on. If there is interest, can anyone advise on what to do? I've used my UV flashlight to look at subjects in the field, but have never done UV photography. In particular, while I understand that I've placed an "emission filter" on my UV flashlight, and that these more expensive Hoya filters may be a better or worse emission filter. I have no notion of what what "fluorescence filter" I'd need to make UV photographs with such a flashlight.

Here are the claimed transmission spectra for each flashlight emission filter:

ZWB2 20.5mm x 2mm ($1 USD) [red-orange line in graph]:
Image



Hoya 340nm 20.2mm x 2mm filters ($35 USD):
Image

Cheers,

--Chris S.

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Post by enricosavazzi »

I have a single ZWB2 on each of my Convoys (all four of them), as well as a Hoya 340 (I don't remember the thickness, but might be 2 mm) on an MTE UV 301 (also 365 nm, like the Convoy). There is, or used to be, an eBay source for the Hoya 340 in the right size for the MTE torch.

Nothing beats the low cost of the ZWB2, and they substantially reduce the VIS "tail" of the emission curve of the 365 nm LEDs. However, quite some of the VIS is still detectable. It stands to reason that doubling the filters further reduces the VIS, but I have not tried this.

The Hoya 340 cuts much more of the VIS leak compared to a single ZWB2, but also cuts some of the 365 nm peak emission and slightly "shifts" the peak to lower wavelengths (by selective absorption of longer wavelengths in the relatively broad LED emission, not any fancy excitation/conversion effects).

Whether this difference is important depends on how much VIS contamination your application can tolerate. Without filters, both types of torch emit quite a bit of VIS, enough to affect the imaging of UV-excited VIS fluorescence in the violet and blue, and enough to require a lens-mounted VIS-cut filter for UV imaging.
--ES

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Post by Pau »

I have the same Convoy torch and ZWB2 filters (I put only one in each torch) and some other UV excitation filters for microscope fluorescence.

Looking at the graphs the Hoya seems superior in two aspects: much less transmission in the far red and maybe it could cut better violet (starts about 400nm, but this is not exact...) , being the UV transmission very similar.

This may be important or not depending of your application. If your application is for fluorescence, your source is a UV LED like the Nichia on the Convoy that doesn't emit any red and you use an emission filter that cuts both UV and violet the usefulness will be the same. If your emission filter doesn't cut violet or if you don't use an emission filter the Hoya seems superior.
Here are the claimed transmission spectra for each flashlight emission filte
In your posted first graph it says "ZWB2 (UG1)" and in my tests this is not really true. I have a Schott UG1 and they are a similar filters but the Schott is better: a bit less violet and clearly less red transmission, although both are equally useful with the adequate emission filter.

Interference UV filters I use:
- Chroma AT350/50x , cleaner than both aforementioned black absorption filters but with lower UV transmission, although in most cases the Schott performs equally well.
- Chroma ET380x not so good for general excitation with the Nichia 365 but excellent with 385 LEDs
- Omega 330WB70 Very clean but it cuts too much excitation light

How to test them?
Well, the best test would be quantitative with a spectrophotometer. I don't have such equipment and I've only done visual "qualitative" tests.

A very good test place is the washing machine room: most detergents have strong whiteners that produce strong blueish white fluorescence, also most white tissues and plastics do it for the same reason. Of course I also have tested them at the microscope with a classic epifluorescence setup.
Wear adequate UV protective eyeglasses. Usually protection glasses are made of polycarbonate that is a very effective UV absorber, also most sunglasses are adequate (although of course they also absorb visible). In fact I use the Convoy torch to test sunglasses at the wash machine room. With the adequate eye protection you can also see the violet and far red transmission of the filters briefly looking at the torch (far red with the filter alone over a white light, of course)
...while I understand that I've placed an "emission filter" on my UV flashlight, and that these more expensive Hoya filters may be a better or worse emission filter. I have no notion of what what "fluorescence filter" I'd need to make UV photographs with such a flashlight.
In fact the filter at the torch is the excitation filter. The filter you put at the camera side to cut the excitation light is the emission filter

You need a filter that cuts all excitation light, beginning from 420 - 440nm and passing all visible, or only some colors, depending of your subject and goals.
Microscope EX filters are easy to find in 18mm and mostly 25mm sizes, adequate if you use microscope objectives and small diameter macro lenses. I've tested a pair of cheap "UV" camera filters and they are pretty bad, also the old Nikon L39 which is better but still lets to pass too much UV.
Pau

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