MicrobeHunter.com Microscopy Forum

It seems that not all the 'fun' UV is absorbed by the glass in the front of darkfield condensers.
I started off with jamming a UV torch into the bottom of an Amscope dry darkfield condenser: This condenser doesn't self-fluoresce at all so the result was a true darkfield :
(pond water sample) Here with a bit of oblique white top-light : (The three things in the harbour above the blue fibre, that have a bit of a visible internal structure, are rotifers )


Another: Unfortunately the torch produces quite a small spot when close and maybe 70%-80% of its output hits an opaque stop at the back of the dry condenser and so really the torch needed to be tilted somewhat, which was fiddly.

The patch on the back of a Watson (oil) paraboloid is smaller and a small Beck RMS-threaded oil condenser was easier still. Both of these condensers 'glow' internally so the effect isn't darkfield but more 'lilac field' Using a torch might not be the best way forward, however the output of its UV LED's seemed to be enough to get through the glass.

[Using a whole torch was possible on a tilting stand, but using the head alone on other stands might work ...or just pointing a UV torch at the slide from the side of course ]

Very nice images !
Looks like you have practiced the very old modality of trans-illumination fluorescence microscopy. Which was popular before the advent of the much more safe and light-efficient epi-illumination fluorescence microscopy. The advantage of your setup over the ancient ones is the intense "cold" beam, vs the heating halogen or incandescent beam of the past.
I hope that you do not LOOK into the eyepieces - because the images indicate that direct UV reaches the eyepieces.

Use yellow ski goggles. very neat idea.....the illumination, not the goggles.

I hope that you do not LOOK into the eyepieces - because the images indicate that direct UV reaches the eyepieces.

Hobbyst46 ...thank you so much for spotting this
(A piece of white cotton placed over the eyepiece tube gave a startling blue replica of the sample I was looking at ! ) I will find myself something safer to do.

apochronaut...no ski goggles to hand, sadly, but a genuine Tiffen haze filter seemed promising (unlike cheapo skylight filters) again, sadly, this is not actually mine.

I imagine that there must be filter glass made for this task; any idea what sort of thing should I be searching for?

Update; I came across a piece of Wratten No.85 gelatin filter (a sort of light orange) it appears able to block nearly all the UV light from the torch itself (nothing appeared to fluoresce in a darkened room) !

Nice images and interesting experiment!

< sorry, double-post >

Intended for use with Dental ‘resin-curing’ lamps, there are plenty of things like this available at modest prices:
https://www.ebay.co.uk/itm/234470376574

Forgive me for being a spoil-sport, but

it appears able to block nearly all the UV light from the torch itself

seems a risky basis on which to work.

MichaelG.

MichaelG. wrote: ↑

Thu Jan 12, 2023 7:54 am

Intended for use with Dental ‘resin-curing’ lamps, there are plenty of things like this available at modest prices:
https://www.ebay.co.uk/itm/234470376574

Forgive me for being a spoil-sport, but

it appears able to block nearly all the UV light from the torch itself

seems a risky basis on which to work.

MichaelG.

I believe that dentists do not look directly into a UV light source, rather they illuminate into the the patient's mouth to cure the resin, so their exposure is short-term and weak.
I tried to find the transmission of the Kodak gelatin filter but failed. Yet, I believe that it does transmit some UV.
In epi-illumination fluorescence microscopy, the viewer microscopist is protected by the combination of dichroic mirror in series with an emission filter. So the total transmission (multiplication of the two transmissions) is negligible. Especially when those components are interference devices such that they really block almost all UV.
In the trans-illumination setup, the only protection is a single filter. Perhaps I am overly cautious.
IMHO, the lack of visible fluorescence when using the filter is an indication but not evidence of safety, because excitation is stronger than any fluorescence by orders of magnitude.

Chas wrote: ↑

Wed Jan 11, 2023 1:17 pm

I hope that you do not LOOK into the eyepieces - because the images indicate that direct UV reaches the eyepieces.

Hobbyst46 ...thank you so much for spotting this
(A piece of white cotton placed over the eyepiece tube gave a startling blue replica of the sample I was looking at ! ) I will find myself something safer to do.

apochronaut...no ski goggles to hand, sadly, but a genuine Tiffen haze filter seemed promising (unlike cheapo skylight filters) again, sadly, this is not actually mine.

I imagine that there must be filter glass made for this task; any idea what sort of thing should I be searching for?

Update; I came across a piece of Wratten No.85 gelatin filter (a sort of light orange) it appears able to block nearly all the UV light from the torch itself (nothing appeared to fluoresce in a darkened room) !

An ordinary UV block dslr/photographic filter should do the job. Else maybe safety specs if you have long eye relief oculars.

Louise

Certainly if using UV with the intention of image capture the Idea of burning the image onto the retina is avoidable.
Just stick to using the camera, it's replaceable.

Hobbyst46 wrote: ↑

Thu Jan 12, 2023 8:46 am

I believe that dentists do not look directly into a UV light source, rather they illuminate into the the patient's mouth to cure the resin, so their exposure is short-term and weak.

Absolutely correct … the shielding filters that I referenced are only intended to protect against accidental reflections.
[ similar to the shields which we discussed in a ‘microplastics’ thread a while ago. ]

The point that I was trying to make with my spoil-sport comment was that
“it appears able” and “UltraViolet” are, by definition, NOT terms which sit well together.

I should perhaps have been more blunt.

MichaelG.

“it appears able” and “UltraViolet” are, by definition, NOT terms which sit well together.

Absolutely right
The filter is about making it safer.
There appear to be 'not so expensive' longpass filters (not so different in cost to a good photographic haze filter) and seemingly at about the right size to make an eyepiece cap.

https://www.edmundoptics.co.uk/f/colore ... ers/39673/

I am guessing that the ND5 specification applies to the to left hand side of the graph.

I did come across a Wratten 85 curve but as the Y axis was linear (like the one above ) it was hard to make much of it. There are tables for it, but they end at the 400nm mark and the torch is notionaly a 365nm one.

I guess that the UV level in ordinary daylight might make a good benchmark.