Zeiss aplanatic-achromatic condensor

[dtvmcdonald]

I have a personal Zeiss Axioscope microscope. It came with a 0.9 condensor so I bought a Zeiss 1.4 achromatic-aplanatic one
off ebay. It looks exactly like this one on ebay:
https://www.ebay.com/itm/Zeiss-Microsco ... :rk:8:pf:0

(all one line) but is not "POL".

It works sort of OK with my 1.3 Neofluar oil objective but isn't "quite right". First, it does not
focus with the "works" screwed all the way in it. Second, it really does show spherical
aberration with an oil objective and oil applied to both condensor and objective.
If I look at the objective back with an eyepiece removed,
with the iris that sets the size of the illuminator opening set to just illuminate the
field, at best condensor focus there is a ring with no light seen at the back of the objective.
I have to increase the size of the illumination iris to fill the objective back with light.

Are these things supposed to be good enough that that is not needed? Advice needed.
I suspect that the focus problem is tell me that the condensor I bought is
for a different scope stand.

My old 1940s microscope with an Abbe condensor does not show this effect
on its 1.25 oil objective.

I have an Axiovert 100 scope I bought new with a grant. It uses a Fluar 100x N.A. 1.3
objective, but uses laser epi-illimination so I could not look for this effect.

Doug McDonald

[MicroBob]

Hi Doug,
here is a price list that includes the top lens of the ebay condenser:
https://www.google.com/url?sa=t&rct=j&q ... gQa5qfRddl
Perhaps this helps to identify the parts (condenser and top lens) you have.

The different condensers provide the same beam to the slide, but the design ist diffenernt on the other side: Where is the field stop located and how big is the diameter. So what you see might be a signs of a mismatch.

Can you lift the condenser right below the slide?


Bob

[ImperatorRex]

Hi Doug,
the ebay link points to a condenser with serial number 46xxxx. Such numbers indicate use for the old Zeiss finite microscopes, the Zeiss "Standard" system. Maybe also it can be used on the earlier Zeiss Axioskope systems.
But note that Zeiss changed the condenser carriers for the Axioskope Microskopes after 1989, so condensers before 1989 only matches for the Condenser Carrier "Z" style and may not work on the Axios after that. Condenser working distance have changed from 38mm to 41mm (distance of the mounting level of condensor to top of the table)
The condensor front lense maybe the same still...not sure if you can just use this lense on your Axio condenser?

[75RR]

On my 160 tube finite system condenser the 46 52 68 top lens also screws down on to a 0.32 lens. The distance between the two is likely critical. Might be worth making sure yours is screwed on cleanly.

As mentioned, the distance between the top lens and the slide is also worth checking.

[92111]

bought a garbage-like condenser today,cost me 20 Dollar。does it support darkfeild for 100x objective?

[Hobbyst46]

I do not know this specific condenser. But provided that it is similar to other Zeiss turret condensers, there is a chance it has one darkfield position, which will be marked by "D". If so, it might provide darkfield with low magnification, medium NA objectives, like the 20X/0.4-0.5 or 40X/0.6-0.7, PROVIDED the condenser is oiled to the objective. 100X objectives are usually of NA 1.25-1.3. If the objective has no iris to decrease the NA, this condenser will probably not yield darkfield with the 100X objective.

[75RR]

That needs a careful and patient clean!

Zeiss pdf on cleaning microscopes: https://microscopy.duke.edu/sites/micro ... scsope.pdf

I think I can make out 46 52 72 as the catalogue number. If that is correct then it does not have a dedicated darkfield port.

http://www.science-info.net/docs/zeiss/ ... ystems.pdf

[dtvmcdonald]

"Condenser working distance have changed from 38mm to 41mm " and that explains one thing I noticed.
However, the two lenses together screw out enough to make up that 3mm ... just insert a spacer,
which I have already done. Thanks for that piece of real info! The condensor does
fit correctly in the holder. A slight out-of-focus-ness of the condensor iris is harmless.

However, last night I had a thought which proved correct: the iris determining the
field is optically about its physical distance from the condensor. Pehaps the condensor expects
collimated light. Inserting an approximately 3" focal length lens just below
the condensor mechanism does that. This improved the behavior a lot. Experimentation
with different lenses will be needed.

[MicroBob]

With your additional lens you give your condenser "reading glasses" This was common practice with some Zeiss West models.
The distance between top lens and lower lens of the condenser will be important for the optical properties of the condenser. Is there a way to mount the whole condenser higher?

[photomicro]

I have a personal Zeiss Axioscope microscope. It came with a 0.9 condensor so I bought a Zeiss 1.4 achromatic-aplanatic one
off ebay. It looks exactly like this one on ebay:
https://www.ebay.com/itm/Zeiss-Microsco ... :rk:8:pf:0

(all one line) but is not "POL".

It works sort of OK with my 1.3 Neofluar oil objective but isn't "quite right". First, it does not
focus with the "works" screwed all the way in it. Second, it really does show spherical
aberration with an oil objective and oil applied to both condensor and objective.
If I look at the objective back with an eyepiece removed,
with the iris that sets the size of the illuminator opening set to just illuminate the
field, at best condensor focus there is a ring with no light seen at the back of the objective.
I have to increase the size of the illumination iris to fill the objective back with light.

Are these things supposed to be good enough that that is not needed? Advice needed.
I suspect that the focus problem is tell me that the condensor I bought is
for a different scope stand.

My old 1940s microscope with an Abbe condensor does not show this effect
on its 1.25 oil objective.

I have an Axiovert 100 scope I bought new with a grant. It uses a Fluar 100x N.A. 1.3
objective, but uses laser epi-illimination so I could not look for this effect.

Doug McDonald

Have you got the correct supplementary lens underneath the condenser? There should be two swing out holders, the upper one takes colour filters, the lower one the supplementary lens. There were several types.

[dtvmcdonald]

Nope, no supplementary lens. I tried a few and find that any achromat from 50 to about 75 mm
will work fine optically. Mounting will be a problem unless I use the 50 and
a swingout. I was using old scratched lenses to test, hand-held. I ordered up some new ones.
When they come I will worry about mounts. I probably will permanently mount one
with machined fittings in the 1.4 condenser ... I will use it only for oil.

I'll add a question here rather than a proper new topic. The microscope's grease is getting a bit old.
Is it possible to fix this without taking it apart and risking damage? I have an
instruction manual for my Axiovert (this is a same-age Axioskop) but it says
nothing about maintanence.

[Hobbyst46]

Nope, no supplementary lens. I tried a few and find that any achromat from 50 to about 75 mm
will work fine optically. Mounting will be a problem unless I use the 50 and
a swingout. I was using old scratched lenses to test, hand-held. I ordered up some new ones.
When they come I will worry about mounts. I probably will permanently mount one
with machined fittings in the 1.4 condenser ... I will use it only for oil.

On the old Zeiss Standard models, the separate lens in the condenser carrier (call it "external lens"), I mean the one that sits below the swing in/out filter holder, is only useful for low magnification, low NA objectives, that are typically used dry. For brightfield mode, I swing the external lens in, to fill the FOV with light for the 6.3X/0.16 or 10X/0.30 objective, whereas with the higher NA objectives, the external lens can be in or out - no difference. For darkfield mode, the external lens is swung out - not used.

[dtvmcdonald]

I received a nice new expensive (Thor Labs) 75 mm FL 25.0 mm dia achromat.

This turns out to fit inside the condenser I bought. The back of it needs to
be about 0.1 inch in front of the back (bottom) mounting surface of the condensor
for best focus. I've got it stuck in with tape (is a tight fit) and will glue it in
with specks of removeable glue (Elmer's or hot glue). The position depends on
the microscope, not the condensor, since it essentially collimates.

The condenser now nicely illuminates the oil objective.