Question about window on the underside of Olympus trinocular head

Have questions about the equipment used for macro- or micro- photography? Post those questions in this forum.

Moderators: Pau, rjlittlefield, ChrisR, Chris S.

palaephatus
Posts: 11
Joined: Fri Feb 05, 2016 4:47 pm

Re: Question about window on the underside of Olympus trinocular head

Post by palaephatus »

If the lens seen works as a depolariser, it may already be made from quartz.

One way of depolarising light is to use the so-called Lyot depolariser. This is constructed by having two plates of a birefringent material placed with their axis rotated 45 degree to one another, one plate being double the thickness of the other. A typical material for this use is quartz.

More advanced constructions uses wedge-shaped plates, this is sometimes called the "advanced Lyot depolarized" or some such. These find application in spectrophotometry where polarisation introduced by mirrors and gratings can cause spurious readings.

If you have access to a spectrophotometer is may be worth to measure the transmission - at 280nm it is not all optical cement that will interfere. The polarisation properties can be easily determined by crossing two polarisers, minimising optical transmission, and then observing what happens when the Olympus optical element is introduced in between.
Last edited by palaephatus on Sun Sep 20, 2020 9:32 am, edited 2 times in total.

jmc
Posts: 112
Joined: Fri Apr 17, 2020 3:14 am

Re: Question about window on the underside of Olympus trinocular head

Post by jmc »

Thanks yes, if I can get the window out easily (or get everything else out the head so I can measure just the window) I can measure the transmission. I've got a fiber optic spectrometer and deuterium light source, and can measure transmission down to 250nm.
Jonathan Crowther

palaephatus
Posts: 11
Joined: Fri Feb 05, 2016 4:47 pm

Re: Question about window on the underside of Olympus trinocular head

Post by palaephatus »

On the excellent homepage of Alan Wood one can find the brochure for the microscope in question (http://www.alanwood.net/downloads/olymp ... ochure.pdf). On pages 4-5 are shown the optical construction. It would seem - from the thickness - that is not just a window to keep dust out. The pictures by Duke also shows a significant thickness of the optical element.

It is not obvious how the mechanical selection between vision or photoport works, or if the photoport is accessed without the light passing a prism. This is where having the instrument at hand is convenient.

jmc
Posts: 112
Joined: Fri Apr 17, 2020 3:14 am

Re: Question about window on the underside of Olympus trinocular head

Post by jmc »

A few weeks ago I had a microscope arrive with a broken trinocular head (the seller had shipped the microscope with the head still attached and not packed it very well, and trinocular part got pushed into the head). I took the head apart last night. These old Olympuses certainly were built well, but simple enough to dismantle.

The window at the based of the head looks to be a single piece - 20.9mm diameter and 9.9mm thick. There was a little bit of glue on the outside to help keep it in place, but other than that it was a push fit. It seems to just be a window - no magnification.
20200923_204843.jpg
The slider which selects between eyepieces only and eyepieces plus photoeyepiece is a lot more complex. As far as I can tell it is an asymmetric prism. When it is in the position for the photoeyepiece and the eyepieces, there is another prism on top of the main one, presumably to bring the top and bottom faces in to a parallel arrangement.
20200923_204945 small.jpg
20200923_205014 small.jpg
20200923_205047 small.jpg
With this setup there is no 'straight through' path to get the light to the photoeyepiece without it going through that beam splitter.

Not measured the transmission spectra through these parts yet - that's the next job.
Jonathan Crowther

jmc
Posts: 112
Joined: Fri Apr 17, 2020 3:14 am

Re: Question about window on the underside of Olympus trinocular head

Post by jmc »

Unfortunately neither the window nor the beamsplitter are ideal for my UV imaging work - they'll be ok for 365nm work, but certainly no good for UVB imaging. Transmission measured using an Ocean Optics FX spectrometer and deuterium halogen light source.
Bino head optics.jpg
Both show the characteristics of being glass rather than quartz, and block the short wavelength UV. The window should be easy enough to replace with quartz. The beamsplitter will be more complicated to do and I shall have to have a think about that one. One option is just to go with a vertical monocular tube - take the binocular head off, and put the monocular on - but I do like the idea of an integrated setup, where I can select either eyepieces of camera it with a beamsplitter.

Depending on the orientation of the 9.9mm window during the measurement, I got some transmission readings above 100%. I suspect this is due to the thickness of the window, rather than it being a lens. The beam from the collimator is still slightly diverging and I think such a big chunk of glass in the way is acting to bring that beam slightly together again before it is then being collected. I do have a different measurement setup to try - designed for measuring lens transmission - so will try it through that at some point to verify.
Jonathan Crowther

Scarodactyl
Posts: 585
Joined: Sat Apr 14, 2018 10:26 am

Re: Question about window on the underside of Olympus trinocular head

Post by Scarodactyl »

On the plus side lots of malers have made 42mm dovetail heads. You can probably find one with no window and a straight through path that will fit if you don't mind some inpurity.

Pau
Site Admin
Posts: 5317
Joined: Wed Jan 20, 2010 8:57 am
Location: Valencia, Spain

Re: Question about window on the underside of Olympus trinocular head

Post by Pau »

Jonathan,

As far as I understand you want to take pictures with UVB radiation, not of its induced fluorescence.
Because UVB is invisible and very dangerous the only use of binocular and its eyepieces I can imagine is for setting up the sample with visible light, am I right?
If no needed you will be better with an empty monocular tube
Pau

jmc
Posts: 112
Joined: Fri Apr 17, 2020 3:14 am

Re: Question about window on the underside of Olympus trinocular head

Post by jmc »

Scarodactyl - excuse my ignorance, but what's a 'maler' please? If I put 'maler microscope' into Google nothing really comes up.

Pau - yes the plan will be to do UVB transmission microscopy. Absolutely, UVB is incredibly dangerous, and the idea of looking at an unfiltered source containing lots of UVA and UVB would be madness. My thought with the head with the eyepieces, would be use something like a GG420 long pass filter in each eyepiece to cut out all UV to eliminate the risk of it getting to the eyepieces themselves. I'd then have UV protecting glasses and my own glasses (which have a UV blocking coating on them) for focusing the sample, before going ahead and taking the UV photos through the vertical tube. I'd also measure the UV throughput at the eyepiece to determine whether it is safe to view using my spectrometer. If I can get the UV level at the eyepieces down to below that my eyes would experience on a normal sunny day, then I'd be happy with that.

I cannot stress enough to anyone working with UV how dangerous it is, especially the shorter wavelengths. The risk of skin burns and eye damage is high unless precautions are taken.

Using a vertical monocular tube is certainly an option, and would be the simplest thing to do (and will be my fall back option). However I like the idea of being able to visually focus it like a normal microscope before taking the photo.
Jonathan Crowther

Scarodactyl
Posts: 585
Joined: Sat Apr 14, 2018 10:26 am

Re: Question about window on the underside of Olympus trinocular head

Post by Scarodactyl »

jmc wrote:
Thu Sep 24, 2020 8:43 am
Scarodactyl - excuse my ignorance, but what's a 'maler' please?
Phone typo for 'maker'.

jmc
Posts: 112
Joined: Fri Apr 17, 2020 3:14 am

Re: Question about window on the underside of Olympus trinocular head

Post by jmc »

Scarodactyl wrote:
Thu Sep 24, 2020 11:47 am
jmc wrote:
Thu Sep 24, 2020 8:43 am
Scarodactyl - excuse my ignorance, but what's a 'maler' please?
Phone typo for 'maker'.
Ok, cheers.
Jonathan Crowther

jmc
Posts: 112
Joined: Fri Apr 17, 2020 3:14 am

Re: Question about window on the underside of Olympus trinocular head

Post by jmc »

Little bit of an update on this one.

As shown above both the prism and the glass window block the short wavelength UV, which means that they will be no good when I am doing UVB imaging. I've taken the plunge and ordered a replacement circular window in UV fused silica.

This leaves the issue of the prism. This is more complicated, and having a replacement prism made in UV fused silica would be outside my budget. For this I am taking a different approach. The prism sits in a slider. In one position, all the light goes to the eyepieces. In the other position, the light is split between the eyepieces and the photoeyepiece which is vertically upwards.

The aim is to make a radical modification to the prism. The existing prism will be cut in half and the half which split the light between the eyepieces and photoeyepiece will be replaced by a simple block of UV fused silica. Now with the prism in the first position, the light goes to the eyepieces, while in the second position, it all goes to the photoeyepiece directly above. With live focus on the camera this is fine, and should increase the amount of light reaching the camera.

The UV fused silica block and window should be with me in December, so hopefully in the new year I'll have this up and running.

Safety is obviously a huge concern here, with the UV light source having a direct path to the eyepieces. Retaining the original glass part of prism for the light to the eyepieces will help there with blocking the UV. However I will also add in yellow long pass glass filters to the base of each of the 2 eyepieces. I sourced some 23mm diameter yellow filters from a camera supplier (these were used on camera lenses for black and white imaging), which have <0.05% transmission below 400nm. These were one thing that was cheap in this project, costing all of 5GBP for the 2. As the light source will have some visible as well as UV, it'll still allow me to focus with it, but with the UV being very effectively blocked. I will also be wearing my normal glasses (which have a UV blocking layer) and yellow safety UV glasses to be absolutely certain. When the final device has been constructed, I'll also be testing the spectral output at the eyepieces with my spectrometer to see how safe it is.

Sorry, this is quite a wordy update, hopefully more pictures to follow.
Jonathan Crowther

Post Reply Previous topicNext topic