Two diopter-adjustable eyepiece mounts on one head -- why?

[hans]

One of my Reichert 410 heads has the eyepiece mounting tubes with diopter adjustment on both sides. (All the other ones have one side adjustable, the other fixed.) Is there any reason to do that (seems redundant) or chance it came from the factory that way? Or just a sign of some other hack before me mixing and matching parts?

[hans]

Just noticed the head with two adjustable eyepiece mounts also has the telan lens mounted 1-2 mm further out of the head (toward the objective) than the rest of the heads. The telan lens looks to be thoroughly cemented in place -- unlikely the original factory position could be changed without obvious signs of tampering.

[apochronaut]

All of those that I have seen are trinocular. Is this the case with yours?

[MicroBob]

I don't know this specific microscope, but it is typical to have two adjustable eyepiece sockets in binocular tubes where the tube length changes with the interpupillary distance. You first set the ipd, then read the set value, then transfer it to the eyepiece sockets. A Siedentopf bino tube design doesn't need this step. My new old B&L Dynazoom needs it but does the adjustment on it's own.

Bob

[75RR]

I don't know this specific microscope, but it is typical to have two adjustable eyepiece sockets in binocular tubes where the tube length changes with the interpupillary distance. You first set the ipd, then read the set value, then transfer it to the eyepiece sockets. A Siedentopf bino tube design doesn't need this step. My new old B&L Dynazoom needs it but does the adjustment on it's own.

Bob

Agree. That is the procedure on the Zeiss Jentsch
.

[hans]

All of those that I have seen are trinocular. Is this the case with yours?

The one trinocular head I have only has one side adjustable, but of course, no guarantee that is the original configuration. The one with both sides adjustable is binocular.

A Siedentopf bino tube design doesn't need this step.

The heads are all Siedentopf. I did not know the design had a name -- thanks for pointing that out.

[hans]

Ah, looking at the heads again now, there is a bit of information I left out, not realizing it was relevant, that probably explains the difference -- the head with both sides adjustable and telan lens positioned differently came with the 410 I bought with a teaching bridge, so the "extra" adjustment would be necessary to set the overall focus of the auxiliary head relative to the main head. (As far as I can see there is no focusing control on the teaching bridge itself.) The different position of the telan lens is still a mystery though.

I guess I got lucky buying the teaching 410 complete with the correct auxiliary head. It had not occurred to me it might require a special head and I wasn't paying attention to that when I bought it.

[Scarodactyl]

Both sides have to be adjustable to ensure parfocality is possible for (almost) everyone's eyes, regardless of the type of head. One being fixed is just them saving money at the expense of the user. This matters less on non-zoom systems where small adjustments between mags aren't such a big deal.

[apochronaut]

It was an option . It improves the focusability of the system. Once the objective is focused , when turning to another, which although ostensibly parfocal might not be dead on parfocal, all it takes is a quick tweak of both eyepieces.
It is specially important with two viewers who might have widely differing focus points.

[hans]

Both sides have to be adjustable to ensure parfocality is possible for (almost) everyone's eyes...

Once the objective is focused , when turning to another, which although ostensibly parfocal might not be dead on parfocal, all it takes is a quick tweak of both eyepieces.

Thanks, the issue with parfocality is what I was originally missing thinking the second eyepiece adjustment would be redundant. To make sure I am understanding: To focus for a specific viewer (ignoring difference between eyes) you could move either the objective or the eyepieces. The distance the objective needs to move depends on the magnification and since all the objectives move together there is the problem with parfocality. Moving both eyepieces together has the advantage that the distance depends only on the person's vision so the same adjustment works for all objectives?

[Scarodactyl]

Exactly.

[hans]

Makes sense also then, as apochronaut was implying, the dual-adjustable head is useful on its own as an option, and was probably included standard with the teaching bridge since in that case it is necessary if you want relative focus adjustment between the two heads. But not specific to the teaching bridge, as I was thinking it might be.

[apochronaut]

Also where multiple users might be stepping up to a microscope , in a school or lab for instance , especially where a photo might be in the making. It removes the necessity of tweaking the fine focus, since the oculars can be adjusted to suit any number of inquisitive pairs of eyeballs.

[wabutter]

The two adjustable eye tubes are for use on dual and multi view microscope systems so the secondary users can adjust each eye for acuity differences from the main user.

[hans]

Thanks for all the info. The 2 mm difference in axial position (shifted toward the objective, away from the eyepieces) of the telan lens in the head with two adjustable eye tubes is still a mystery to me, any thoughts? I measured more carefully, probably +/-0.1 mm or so, and the position is very consistent among the other heads with single adjustable eye tube. I am wondering because I have an excess of heads with a few bad parts among them (one cloudy splitter, spotty damage to the AR coating at the base of one eye tube, etc.) and was considering doing some part swapping/consolidation. The shift of the telan lens relative to the eyepieces is obviously going to shift the overall focus range a bit but could there be any more subtle issues that would make part swapping a bad idea?