Carl Zeiss Large Toolmakers microscope

[William SParticipant @williams]

Okay, I seem to have acquired the above bits of kit, the 2 to the left I'll cover in another post.

Now the Zeiss has come out of the naval base down in Gosport, last calibrated in 2002. The chap I brought it from had 2, the one that followed me home is mostly complete;

Namely it has 90% of the attachments, however you could say its missing the most vital part, the main lighting unit that hangs off the back of the machine;

I have most of the information/dimensions to reproduce the item, the previous owner has gone as far as he is willing to go to ascertain the information which I am much obliged for him to have taken the time to help me out, from his complete machine.

Its main job is to hold the bulb so really its just tube, however it has a lense in one end which has kinda scuppered me! what follows is all the information I have on the lighting assembly;

Continued on next post;

[William SParticipant @williams]

Information and documentation about this bit of kit

[Michael GilliganParticipant @michaelgilligan61133]

It doesn’t provide a simple answer to your problem, William … but you might find this thread of general interest:

**LINK**

http://www.photomacrography.net/forum/viewtopic.php?t=10332

MichaelG.

[William SParticipant @williams]

So I hope that all makes sense, what I really want to know is about the lens, am I right in thinking its a "condenser" lens, what is the exact purpose of said lens?, is it really necessary? (I'm guessing it is!) I only ask this as with a light source it the microscope seems works as it should even with the projection screen.

As one can hopefully see the dimensions are given so how does one go about finding what lens I require?

That should be enough for now but I will be back to ask more (stupid) questions that I am sure the clever folks of this site will hopefully answer!

Many thanks and I look forward to hearing your responses

William

[Clive SteerParticipant @clivesteer55943]

This William

The condenser lens converts the light from a point source such as an incandescent filament into a parallel light beam and the type of glass it is made from also blocks the Infrared wavelengths( heat) from the light . This arrangement is more commonly found on 35mm slide projectors.

Although one might want to restore to original condition using a Tungsten Halogen light bulb I found that a high intensity LED downlighter lamp works well on my Projectina projection microscope. They are more compact, use less power and therefore generate less heat.

CS

[Clive HartlandParticipant @clivehartland94829]

Leica are now the title holders of Leitz, make contact with the microscopy dept. in Milton keynes

[Michael GilliganParticipant @michaelgilligan61133]

Posted by William S on 17/07/2022 20:24:17

As one can hopefully see the dimensions are given so how does one go about finding what lens I require?

…

.

If it’s a single element, then it will almost certainly be aspheric

… and it will almost certainly have been Pyrex or similar

It ain't easy to ‘reverse engineer’ the original design !!

MichaelG.

[Andy_GParticipant @andy_g]

Posted by William S on 17/07/2022 20:24:17:

…what I really want to know is about the lens, am I right in thinking its a "condenser" lens, what is the exact purpose of said lens?, is it really necessary? (I'm guessing it is!) I only ask this as with a light source it the microscope seems works as it should even with the projection screen.

 

Yes, it looks like a condenser lens. Its function is as per Clive Steer's post above.

Everything will "work" without it, but there will be a lot of stray and scattered light that will reduce contrast, make edges indistinct and probably create other artifacts. (The fins on the inside of the tube are there to try and reduce stray light, so it was clearly a design consideration.)

This sort of application is very common, and I suspect that the lens will be a generic one, rather than something designed specifically for the microscope.

The key parameters are the outside diameter and effective focal length (EFL).

The condenser will probably be aspheric, which makes it difficult to establish the EFL without having the lens in hand. You will be able to get a good idea of EFL by measuring the axial distance from the lamp filament, at ~mid travel on the slider, to the plane of the back of the lens. This will be the back focal length (BFL). EFL will be somewhere between the front edge of the lens (BFL + 1.5mm from your sketch above) and the very front of the lens (BFL + 1.5mm +9mm from your sketch above) – more likely nearer the +1.5mm dimension (especially if the lens is spherical, rather than aspheric).

The good news is that the lamp is on a slider, so it is possible to accomodate some error / differences in EFL here.

With your lens diameter & EFL estimate, you can try and find a suitable replacement, for example from Edmund Optics:

Condenser lenses

If/when you find something that is likely to be suitable, you may be able to find a more convenient source for it.

I doubt that the material is anything special (the application is visible light only, and the power / heat levels are modest).

ETA: Anti reflection coating would be nice to have, but I doubt that it is critical here.

Good luck!

Edited By Andy_G on 18/07/2022 09:41:49

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