Question about window on the underside of Olympus trinocular head

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jmc
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Question about window on the underside of Olympus trinocular head

Post by jmc »

A bit of advice needed please. I have an Olympus BHB which I am gradually converting into a UV microscope to allow me to image down to about 280nm. Most glass becomes opaque down there, so I'm changing the internal optics of the microscope for fused silica ones.

In the trinocular head, there is a window on the underside of the head, and I was wondering whether this is just a window (a physical barrier to help keep dust out of the head) or whether it served a more important function? If it's just a window, I can do without it. If the thickness etc is crucial then I'll need to replace it with fused silica.

Here's a picture of it. Any advice welcome please.
20200910_164234 v small.jpg
Jonathan Crowther

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

Post by Duke »

I have very similar trinocular head, it was installed on Leica Monozoom 7, and has marks "Bausch & Lomb" on the rear side, however, on the dovetail it says "Olympus Japan" and part number identical to Olympus CH-2 trinocular head. Looks like it was special order, made by Olympus for Leica US/Bausch&Lomb. It seemed to me this "window" is actually a long focus negative achromatic lens. But may be not.
I'll take a look on monday.
“Thoroughly conscious ignorance is the prelude to every real advance in science.” - JCM

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

Post by Scarodactyl »

I would be very interested to see how that head hooks up to a monozoom 7. I've seen references to it but no documentation is available online.

carlh6902
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Re: Question about window on the underside of Olympus trinocular head

Post by carlh6902 »

I think, at a minimum, the removal of that glass (assuming it is optically neutral) will upset the resulting tube length.

Carl

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

Post by jmc »

Thanks Duke, any information is welcome, so I look forward to seeing your results.

Carl, yes that is a concern. What I'm trying to get a feel for is how much of an impact it will have. I have a horrible feeling the only answer will be to remove it and see.....
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enricosavazzi
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Re: Question about window on the underside of Olympus trinocular head

Post by enricosavazzi »

In a worst-case scenario, the window may have been computed as part of the optical system w.r.t. axial chromatic aberration, and removing it may increase said aberration.

I have seen several examples of optical windows in Olympus infinite microscopes where a thick optical window has a thin cladding (1 mm thick or so) of a different kind of glass cemented on one optical surface. The different refraction index and thickness of the two materials is likely computed to compensate for axial chromatic aberration (not just the axial chromatic aberration of the window itself, but also of the rest of the optical system). A thick window or prism made from a single glass material does introduce axial chromatic aberration even if light rays are perpendicular to its entrance and exit faces.

I do not see any other likely explanations for the need to build a two-layer sandwich structure of two flat glass plates. It seems unlikely to me that this cladding is meant to protect from atmospheric exposure, because then the cladding should be present on both entrance and exit faces. The common types of glass used in the VIS range are also pretty insensitive to corrosion by air or humidity, unlike special types of glass like those used for UV-pass filters.

A flat glass plate also introduces spherical aberration if some of the light rays are not perpendicular to its surfaces. In a well-designed system, this aberration is then corrected somewhere else in the system. In a 160 mm finite tube space, the non-normal rays are probably sufficiently close to normal that spherical aberration introduced by a thin flat window is quite small, and removing the window probably has no significant effects w.r.t. this type of aberration.
--ES

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

Post by jmc »

Interesting, thanks Enrico. I'll have to see if I can get it out of one of my spare binocular heads and try and take a better look at it then. Hopefully with mine being a 160mm finite tube setup, it will have a minimal effect.
Jonathan Crowther

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

Post by Duke »

Here's some photos of my trinocular. The inner element is thick cemented glass doublet with 2 flat surfaces.
I've focused the image with the 4x/0.13 CFN Plan. Then, I removed the dovetail with optical element by unscrewing 3 screws at the bottom. Placed head back on the microscope to see the difference.
To my surprise, there was no apparent focal shift, I've adjusted fine focus using the eyepiece tubes. Image focal plane moved about 1 mm down. However, there is a visible difference in magnification of about ~1.1x with the element installed. The field illumination as well as general image quality is visibly better with the element in place.
Attachments
Olympus trinocular
Olympus trinocular
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Duke
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Re: Question about window on the underside of Olympus trinocular head

Post by Duke »

Scarodactyl wrote:
Fri Sep 11, 2020 7:56 am
I would be very interested to see how that head hooks up to a monozoom 7. I've seen references to it but no documentation is available online.
The head piece adapter for Monozoom-7 is pretty underwhelmingly simplistic. Its optical path made of meniscus negative singlet and an image erecting roof prism (exactly the same prism can be found in telescope erecting eyepiece). Adapter with 3 centring screws accepting finite heads with dovetails from 37 to 49 mm. Tube length from flange is standard for finite heads, about 120mm (zeiss, lomo, olympus, nikon... but not leitz or pzo).
Attachments
Monozoom 7
Monozoom 7
“Thoroughly conscious ignorance is the prelude to every real advance in science.” - JCM

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

Post by Scarodactyl »

Thanks! That might be something I can assemble myself. I just got a (hopefully) working monozoom to replace the roached one on my good stand and I'd love to put soem eyepieces on it. It's not something I really need per se but I've been really curious about it for a long time, and I'm a sucker for a nice macroscope.

I have a tiny monocular head off a bhm which does not have this window. It also seems to place the eyepiece a lot lower than a binocular olympus head. Haven't checked if it is parfocal with the binocular head.

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

Post by jmc »

Thanks Duke, so it looks like I can expect some image degradation then if I remove it.

Scarodactyl - is the monocular tube you have like this - https://www.ebay.co.uk/itm/Olympus-Vert ... 4067291859 ? If so I have one in a box of parts waiting for me to collect the next time I am in the US. I was wondering whether that had a lens in or not.
Jonathan Crowther

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

Post by Alan Wood »

Jonathan

The Olympus vertical monocular tube (BH2-PT) is just a tube - there is no glass in it.

The inclined monocular tube (CH-MO45) has the same sort of window as the binocular and trinocular heads.

They are both parfocal with the binocular and trinocular heads.

Alan Wood

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

Post by Scarodactyl »

The one I have is inclined and certainly looks much like a CH-MO45, though without a "CH-MO45" label:
Image
Image
Image
Image
Image
There is glass visible through the bottom, but opening it up it is just the first surface of the prism, and there is no other element in the light path.
That said, this head may have been modified in some way. It came as part of a very odd industrial DIY setup.

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

Post by jmc »

Scarodactyl, Alan, thanks for the information. Good to know the monocular tube has no glass in it, so I have at least one option which doesn't need the glass.
Jonathan Crowther

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

Post by René »

FWIIW, there has been a discussion on a german forum concerning an Olympus SWF trinotube that showed an uneven field in DIC, not due to the DIC unit. It was concluded that there must be a depolarizer installed in the head that has been removed. So you might want to check also the effect in polarized light.

Best wishes, René

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