UV torchlight through Darkfield Condensers

Here you can discuss different microscopic techniques and illumination methods, such as Brightfield, Darkfield, Phase Contrast, DIC, Oblique illumination, etc.
Post Reply
Message
Author
Chas
Posts: 422
Joined: Tue Jan 19, 2021 3:11 pm

UV torchlight through Darkfield Condensers

#1 Post by Chas » Tue Jan 10, 2023 8:26 am

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:
Jaxman in dry darkfield 640.jpg
Jaxman in dry darkfield 640.jpg (32.28 KiB) Viewed 3676 times
This condenser doesn't self-fluoresce at all so the result was a true darkfield :
(pond water sample)
52 UV DF only.jpg
52 UV DF only.jpg (47 KiB) Viewed 3676 times
Here with a bit of oblique white top-light :
51 combined UV df and side lit.jpg
51 combined UV df and side lit.jpg (67.02 KiB) Viewed 3676 times
(The three things in the harbour above the blue fibre, that have a bit of a visible internal structure, are rotifers )


Another:
amscope dry df and uv torch water  2.jpg
amscope dry df and uv torch water 2.jpg (42.69 KiB) Viewed 3676 times
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'
018 shrunk only.jpg
018 shrunk only.jpg (61.94 KiB) Viewed 3676 times
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 :-) ]
Last edited by Chas on Wed Jan 11, 2023 10:14 pm, edited 1 time in total.

Hobbyst46
Posts: 4277
Joined: Mon Aug 21, 2017 9:02 pm

Re: UV torchlight through Darkfield Condensers

#2 Post by Hobbyst46 » Tue Jan 10, 2023 2:59 pm

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.

apochronaut
Posts: 6272
Joined: Fri May 15, 2015 12:15 am

Re: UV torchlight through Darkfield Condensers

#3 Post by apochronaut » Tue Jan 10, 2023 4:26 pm

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

Chas
Posts: 422
Joined: Tue Jan 19, 2021 3:11 pm

Re: UV torchlight through Darkfield Condensers

#4 Post by Chas » 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 ! :oops: ) 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) ! :-)
Last edited by Chas on Wed Jan 11, 2023 10:34 pm, edited 5 times in total.

Javier
Posts: 806
Joined: Tue May 09, 2017 11:19 am
Location: Buenos Aires, Argentina.

Re: UV torchlight through Darkfield Condensers

#5 Post by Javier » Wed Jan 11, 2023 1:45 pm

Nice images and interesting experiment!

MichaelG.
Posts: 3976
Joined: Mon Apr 10, 2017 8:24 am
Location: North Wales

Re: UV torchlight through Darkfield Condensers

#6 Post by MichaelG. » Thu Jan 12, 2023 7:50 am

< sorry, double-post >
Last edited by MichaelG. on Thu Jan 12, 2023 7:56 am, edited 1 time in total.
Too many 'projects'

MichaelG.
Posts: 3976
Joined: Mon Apr 10, 2017 8:24 am
Location: North Wales

Re: UV torchlight through Darkfield Condensers

#7 Post by MichaelG. » 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.
Too many 'projects'

Hobbyst46
Posts: 4277
Joined: Mon Aug 21, 2017 9:02 pm

Re: UV torchlight through Darkfield Condensers

#8 Post by Hobbyst46 » Thu Jan 12, 2023 8:46 am

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.

LouiseScot
Posts: 1167
Joined: Tue Jul 07, 2020 1:51 pm
Location: Scotland

Re: UV torchlight through Darkfield Condensers

#9 Post by LouiseScot » Thu Jan 12, 2023 10:01 pm

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 ! :oops: ) 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
A Nikon CF plan 20x; A Swift 380T; A DIY infinity corrected focus rail system with a 40x/0.65 Olympus Plan, a 10x/0.30 Amscope Plan Fluor, and a 20x/0.75 Nikon Plan Apo

Phill Brown
Posts: 603
Joined: Mon May 24, 2021 1:19 pm
Location: Devon UK.

Re: UV torchlight through Darkfield Condensers

#10 Post by Phill Brown » Fri Jan 13, 2023 12:03 am

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.

MichaelG.
Posts: 3976
Joined: Mon Apr 10, 2017 8:24 am
Location: North Wales

Re: UV torchlight through Darkfield Condensers

#11 Post by MichaelG. » Fri Jan 13, 2023 7:36 am

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.
Too many 'projects'

Chas
Posts: 422
Joined: Tue Jan 19, 2021 3:11 pm

Re: UV torchlight through Darkfield Condensers

#12 Post by Chas » Fri Jan 13, 2023 11:49 am

“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/

420 longpass.jpg
420 longpass.jpg (62.15 KiB) Viewed 3295 times
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.

Post Reply