DIY Fluorescence with Zeiss fluoro condenser - help needed

[viktor j nilsson]

Would be interesting to see transmission data for commercial UV protection screens, but I haven't found any.

I have an orange protection screen, which I believe is a Zeiss one. I'll run it through my spectrometer and see what it looks like.

That'd be great!

[jmc]

Would be interesting to see transmission data for commercial UV protection screens, but I haven't found any.

I have an orange protection screen, which I believe is a Zeiss one. I'll run it through my spectrometer and see what it looks like.

That'd be great!

No problem. I've found it. When I've done the measurement I'll post what I find on here along with a picture of it. As far as I can tell it is from a Zeiss Axioskop 2 fluorescence microscope, but I'm not a Zeiss expert so perhaps someone else can confirm that when I post the picture.

[jmc]

Here's the UV shield I have. Looking at pictures on line I think it's from a Zeiss Axioskop 2 fluorescence microscope - it came with a Zeiss mercury xenon lamp I got. The filter is 3mm thick and plastic.

Some transmission measurements, taken with an Ocean Optics FX spectrometer and deuterium halogen light source. First full range - 250nm to 800nm. Two graphs, one with just the deuterium lamp (mainly UV region), the other with both lamps (450nm onwards).

There is a gap between 420nm and 450nm in the graph above. These sort of long pass filters can produce some artefacts when measuring their spectra (looks like transmission in regions where there isn't any). I could probably correct that in time if needed, but for now it's simpler to leave out the region with the artefact rather than have it confuse the data.

Also a blown up graph of the important region from 250nm to 420nm.

There is effectively no leak with this one below 400nm unlike the one you measured Viktor. I've seen something similar to what you saw with a particular Orange camera lens filter - a sizeable transmission around 350nm. I think it was a Tiffen one but would need to check.

Personally, I'd not use a UV blocking filter which had any significant transmission below 400nm, but then I do not have LED lights - I have xenon and mercury xenon lamps.

[viktor j nilsson]

Many thanks for doing that. That is a very clean spectrum for sure. I think you've made it pretty clear that UV guards from reputable microscope companies aren't only regular orange acrylic with a higher price tag (as someone argued in one of the threads I linked to in that earlier thread).

If I end up using the cheap one I will definitely make sure to at least use double layers (and polycarbonate goggles).

[Lou Jost]

Of course you can test any material just by seeing if it blocks fluorescence of paper when inserted into the UV light path; I am not sure there is a need for anything more complicated. Is this not sufficient?

[Pau]

Of course you can test any material just by seeing if it blocks fluorescence of paper when inserted into the UV light path; I am not sure there is a need for anything more complicated. Is this not sufficient?

Lacking access to spectrophotometers this is basically what I do, white paper and textiles are highly fluorescent due to the whiteners employed, although I've find wash machine detergents and some plastics even more intense. This is why I often test my filters at the wash machine room. For the microscope I got a set fluorescence plastic slide samples distributed by Chroma, some of them are really bright. This is why I say qualitatively
That said I still think that if well performed spectrophotometry will be better.

[viktor j nilsson]

I will do that test as well. Since we now know that my orange acrylic allows some UV to pass, it'll be interesting to see if it passes that test or not.

[iconoclastica]

DIY photospectrometer.

For the general idea (qualitatively), google for "CD spectrometer".

[viktor j nilsson]

I just tested the orange acrylic with my Nichia Convoy S2+ UV flashlight on a piece of white printer paper. Here's some quick and dirty phone shots:

Left: fluorescence of paper without any filtering
Center: ditto with one layer of orange acrylic
Right: ditto with two layers of orange acrylic

Without any filtering, the Convoy S2+ produce extremely strong fluorescence.

With one layer of acrylic, there is a faint but clearly visible area of fluorescence in the centre.

With two layers of acrylic, the fluorescence is completely gone.

My conclusions:

1. The "laundry room method" works pretty well and is quite sensitive. Even without the spectrometer readings, I would have concluded that the orange acrylic let a non-negligible amount of UV through.

2. Two layers of cheap orange acrylic does a pretty decent job at cutting the UV radiation from the Nichia 365nm LED. I would feel pretty safe behind two such layers (and googles).

[Lou Jost]

Yes, it's easy and I think it is reliable. Highly fluorescent chemicals are purposely added to white paper to make it fluoresce, which makes it look more white. For that to work, the UV from the sun must be enough to excite visible amounts of fluorescence. So if the paper doesn't show fluorescence, the level of UV light must be lower than that of normal scattered daylight, hence not a problem for your eyes unless they are very dark-adapted with big pupils. In general I think is a good idea to leave some lights on when working with UV, though you may need to screen the subject and camera. It may be a bad idea to work in the dark.

https://en.wikipedia.org/wiki/Optical_brightener

[enricosavazzi]

This thread is already quite long, so I might be repeating some information already state above. However, here it goes:

Non-stained acrylic (=Plexiglas and other names in commercial nomenclature) transmits UV well into the UVB range. Many Acrylic formulations have UV-absorbing dyes mixed in, but not all. Non-stained acrylic is used for example in tanning beds, where high UV-transmission is desirable. That said, an Acrylic UV shield from a reputable manufacturer is probably safe to use, but you should test yourself any bulk sheeting that you intend to use for this purpose. My point is that acrylic material per se is not a reliable UV-cut filter. There are orange acrylic "UV shields" from China-based eBay sellers that transmit some UV wavelengths relatively well for example, while amber-stained acrylic seems to work better. Even some orange UV-protection goggles transmit more UV than amber ones from the same manufacturer (I do not recall at the moment whether this has been discussed on photomacrography.net or ultravioletphotography.com, but I am sure on at least one of these).

Non-stained polycarbonate (=Makrolon, Lexan etc.) is by itself an excellent UV-cut shield (with a very sharp transmission drop to virtually nothing around 400 nm). It does not block blue light, which may be of some concern (especially royal-blue power LEDs). If you use amber or orange stained polycarbonate, you will probably get as much protection as possible at reasonable cost. With this in mind, I would trust a polycarbonate shield better than an acrylic one.

While a shield blocks UV radiation from directly reaching your eyes, it does not protect your hands while operating the stage and focus controls (unless of the remote type). UV reaching your eyes after being reflected by microscope parts or surrounding objects may be a concern even with a shield.

Most of these matters have been discussed at length on ultravioletphotography.com. Check for example their UV safety guidelines.

[Lou Jost]

Speaking of exposing your hands, I now use a souped-up Convoy C8 with output stablization, which is miles above the old Convoy in terms of intensity. Sometimes I forget and my fingers get in the beam while I hold it. My fingers hurt for days afterwards.

[jmc]

Viktor, my apologies, I just realised I never responded to this. Yes with 2 layers you should be fine - you'll be down at around 1% transmission. But I'd still recommend wearing UV safety glasses whenever using the light.

[ModelZ]

The little windows in welder's helmets are polycarbonate. They protect the users eyes form sparks and UV. Just checked the latter (2-3 stacked) with the method described above - passed with flying colors. Been using them with orange camera filter on top to block the blues, too. Standard size is just right, about 6 x 11 cm. Available at hardware stores & dirt cheap.
-Karl

[ModelZ]

Forgot to say that these polycarb. bits are available at least in clear, smoked and very dark. I was referring to the first ones.