A Cooke, Troughton & Simms

[Mraster2]

Hello,
I have been given a very old microscope to play with and am looking for advice/suggestions how I should use &/or refurbish it.
I dont know what is in the disk assembly, it looks to be a plain hole and assorted (dimming?) filters.

I though to remove the complex substage gubbins to leave only the condenser/iris bit and start from there with a simple LED, but I can not yet see how to get it all off ! There is a forest of sticky-out bits (sorry for that technical term) but I dont know which ones fix it in place.

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[BramHuntingNematodes]

Aww c'mon, it's not that old! I think loosening the two screws on the sides of the fork will let the entire complex come off from where it should be easier to see how it is joined. I have had great luck with an external lamp that points at the mirror in my horseshoe scope. You will need to fit it with a collector lens and possibly a iris-- or buy a stand-alone unit from that period designed to do the same.

[apochronaut]

Actually, that is a real gem. It is an old CTS phase microscope. You might recognize the name Cooke in there. That's Cooke as in Cooke lenses. The "Cooke Look"The cine lens branch of the company still make the most prized motion picture camera lenses, for Panavision cameras, Imax and I think they did the U2 spy camera lenses too. Nikita Kruschev did not prize those. CTS microscopes morphed into Cooke-Baker and later became Vickers. They were one of the first to ptoduce an interference microscope, in the esrly 50's. AO produced a version of the Cooke-Baker interference microscope based initially on the series 35, then later on the 4.
You also have a camera adapter.

Presumably the objectives are marked phase. In use the phase diaphragm and the objective matched to it based on magnification are combined.. Cleaning that up will result in a very useful scope.

[Mraster2]

Aww c'mon, it's not that old! I think loosening the two screws on the sides of the fork

! maybe just me feeling old then !

which two screws and what fork

I used a flat panel LED + diffuser propped up in front of the mirror, I have some other 3W star that I can try later.
Below is more info on the wheel looking through an info hole.

That's Cooke as in Cooke lenses. make the most prized motion picture camera lenses
Nikita Khrushchev did not prize those.
Cleaning that up will result in a very useful scope.

Very interesting, thank you for that, I thought I recognized Cooke from my (main) astronomical interests,
I remember Khrushchev as well

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[Mraster2]

You also have a camera adapter.

It took me some time to figure out what it was! At first an inspection revealed nothing through it, till I found that the side arm (eyepiece tube ? presumably) was just very stiff but could be slid out of the way.

[MichaelG.]

Here’s that patent, to get you started:
https://worldwide.espacenet.com/patent/ ... A?q=467926

Click the vertical column of three dots, at upper right, to find the pdf dowload link

MichaelG.

[Mraster2]

Here’s that patent, to get you started:

thank you but totally above my pay-grade, sorry.

[BramHuntingNematodes]

The fork is a two-tined fork actually connected to the rest of the stand-- its screws are the largish, silver flat-heads.

[Mraster2]

The fork is a two-tined fork actually connected to the rest of the stand-- its screws are the largish, silver flat-heads.

Thank you @Bram, well done, I see where you are, it turned out to be a sliding fit as-is,
and now I see what is going on with the disk, has three clear apertures and the rest (as you all will have known long before me ! ) have various sizes of annular openings. So those will be the phase things that @apo is saying.

The next puzzle is how to clean the mirror. Will it be SiO overcoated or is it silvered/aluminized and vulnerable ?

[apochronaut]

You will be able to find some BF objectives in achromat, fluorite and apochromat around. The apochromat will need compens eyepieces. I have a set of 8X compens, if you ever need. Hopefully, the phase are still good. If you need one or more replacements, you must use the original type of objectives due to considerations involving the size and location of the diaphragm and annuli. Other phase objectives won't likely work or not work well.

[75RR]

That is a beautiful looking microscope. It will take expert care to bring it up to scratch.

May I suggest it is better off in the hands of an 'afficionado' (read professional collector)

[BramHuntingNematodes]

I had thought that it might be best to set it aside for later cleaning wisdom, and instead substitute with an LED of some sort. (which I think is your earlier suggestion to point up through the horseshoe) But it does not want to come out.

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No no, the plano mirror is good, real good. You just have to point the light at it!

[BramHuntingNematodes]

Oh yeah and as far as cleaning goes, yeah read up on it but don't fret too much scopes of that era are quite tanklike. Some warm water with a tiny bit of dish soap or dilute alcohol would be a good start. Also, I can testify that the optics from a quality maker from an old scope back at least the 30s can look surprisingly, astonishingly good. If you don't mind being non-plan there might be no need to get newer.

[Mraster2]

Thanks Bram, noted on the cleaning

[Mraster2]

If you don't mind being non-plan there might be no need to get newer.

Yes, deffo happy with achro in my present state of understanding,

Would anyone like to educate me on what those numbers and the red symbol appearing in the little window mean, in my post #4

[BramHuntingNematodes]

Would anyone like to educate me on what those numbers and the red symbol appearing in the little window mean, in my post #4

I should think that ideally they would correspond with the power of the phase objective you are using. The annuli are sized specifically for each objective. I believe that there have been attempts to use a single-size stop, but this system was left behind as suboptimal even before turret condensers became de rigeur.

The zero should be the BF or "no annulus" setting. The red may be a darkfield stop.

[BramHuntingNematodes]

Sometimes you can get phase objectives to match up with your annuli entirely by coincidence. For instance, I have a Tiyoda turret condenser whose 40x annulus more or less works with a Wild 20x Phase objective. However, this is still suboptimal as it may require cranking the condenser up or down, slightly out of its ideal position. Additional, the phase rings in the objective are made to be ever so slightly larger than the ring of light produced by the annular stop when looking through the eyetube to ensure that all of the light not deflected off the subject passes through the phase ring. Randomly matched phase objectives and annuli may not have this relationship. Tht being said, I was able to get a pretty good phase image out of the Wild/ Tiyoda pairing, but if you have the objectives that went with this condenser then treasure them.

[apochronaut]

If you don't mind being non-plan there might be no need to get newer.3

Yes, deffo happy with achro in my present state of understanding, I just want to see things and experiment, dont need perfection, , yet, , that can come later

Would anyone like to educate me on what those numbers and the red symbol appearing in the little window mean, in my post #4

There is a little diagonal icon in one of the windows. I have never seen a symbol like that before but it looks like it could indicate an oblique setting. The red symbol might be a pol filter. DF is possible as Bram pointed out. There would be a large occluder in that case; likely larger than the 95X phase . Usually, you can get at least 10X D.F. by using the 95X or 43X phase diaphragm with the 10X objective. If the 10X and 43X pair well, you can usually get 20X DF with the 95 or 100, whichever one has.

[Mraster2]

Fascinating, yes the 0 corresponds to the larger of the three clears, I'll document the others later, the 95 confused me, never heard of one of those.

At first glance, two of the objectives have a dull patina (of age?) and two are silvery, which made me think that they were a mixed bunch, (not easy to photo by flash at night, will try tomorrow,,, )
however, all four are marked Cooke ! ! and thus :-

10x 16mm NA 0.28 PH
40x 4mm NA 0.65 PH
45x 3.75mm Flourite NA 0.95 Oil PH
1.8mm NA 1.3 Oil PH (this last has no x on it)

It's all way above my paygrade, but very interesting !!

[Sabatini]

I love it when this kind of topic comes in.

the restorations and image of these instruments are fascinating.

Thank you

[apochronaut]

Fascinating, yes the 0 corresponds to the larger of the three clears, I'll document the others later, the 95 confused me, never heard of one of those.

At first glance, two of the objectives have a dull patina (of age?) and two are silvery, which made me think that they were a mixed bunch, (not easy to photo by flash at night, will try tomorrow,,, )
however, all four are marked Cooke ! ! and thus :-

10x 16mm NA 0.28 PH
40x 4mm NA 0.65 PH
45x 3.75mm Flourite NA 0.95 Oil PH
1.8mm NA 1.3 Oil PH (this last has no x on it)

It's all way above my paygrade, but very interesting !!

Very few phase objectives are made specifically for phase alone. They start life as conventional BF objectives to which phase plates are added. These can be made from various materials, even soot. Early plates were made by etching but very shortly thereafter metallic and dielectric films were vacuum evaporated to create the absorptive layers..
It is interesting that your scope has a fluorite objective. That would have been very unique for it's day. and it most likely is a very good objective.
It was only in the 1950's that the practice of putting the focal length on an objective began to wane. 95 to 100X were common magnifications for a standard 1.8mm oil immersion lens.

[Mraster2]

45x 3.75mm Flourite NA 0.95 Oil PH

It is interesting that your scope has a fluorite objective. That would have been very unique for it's day. and it most likely is a very good objective.

Lots more to investigate if/when I get up to speed !

I wonder what particular advantage was desired when the fluorite was added,
and I have not seen oil mentioned on less than 100x before.
I think I need to do some googling.

[apochronaut]

45x 3.75mm Flourite NA 0.95 Oil PH

It is interesting that your scope has a fluorite objective. That would have been very unique for it's day. and it most likely is a very good objective.

Lots more to investigate if/when I get up to speed !

I wonder what particular advantage was desired when the fluorite was added,
and I have not seen oil mentioned on less than 100x before.
I think I need to do some googling.

Optical grade natural fluorspar allows lens designers to produce low dispersion lenses, which can be used to increase the N.A. and colour correction of the objective.
Fluorites are just sharper and render a cleaner image: freer of primarily chromatic abberation , than an achromat.
Oil or any other immersion medium have two uses. One is to allow the designer to increase the NA. of the objective above that limited by air, which is 1 . Since N.A. , and the higher the better, is very closely associated with resolution , this allows a higher resolution objective to be made.
This might not seem to make sense , when the N.A. of the objective is still less than 1, as in the case of your .95 Fluorite. Well firstly, it is easier to make a high N.A. immersion objective than a dry objective. Oil , which becomes homogenous with glass, to a large degree controls the working distance of the system due to it's plasticity, whereas an air/glass interface requires a correcting mechanism because the working distance will vary with the cover glass thickness. Second, immersion and in particular oil immersion is desirable in a lower magnification objective, when one of it's primary design goals is as a partner objective to a higher magnification objective. Often the microscopist needs to go to a lower magnification from the high magnification high resolution objective, which has been historically an oil immersion objective in most cases. This is a total p.i.t.a. , if the lower mag. is dry. Having a harmonious immersion medium power objective makes microscopy a breeze, sometimes. It is particularly usefull in fields such as bacteriology or with blood smears.

[Mraster2]

There is a little diagonal icon in one of the windows. I have never seen a symbol like that before but it looks like it could indicate an oblique setting. The red symbol might be a pol filter.

On closer inspection : The 0 is the large clear aperture and there are two un-filled filter-holders (for want of a better name?) of smaller diameter, on each side of it, both missing their threaded retaining rings. One is associated with the red symbol and has markings in the surrounding paintwork. Maybe from sticky tape ?? maybe holding experimental filters etc. The other with the unknown mark shows no tampering/use; and the rest are the varying diameter annuli.
So the red may be a previous owner mark.
Not all the filter holders are the same size though and one is not even on the same index/radial line spacing as the others, someting more to investigate later.

Thanks for the great fluorite explanation, I am understanding !
If only I had a time machine to go back and ask him what field he was into !

[Sabatini]

Apo rules!

[Mraster2]

Cant see anything about apo on my Cooke things ! How would I know ?

The good news is that they are RMS threaded, so I am able to use 2 cheap achros off ebay (more to come) to experiment with on the massive beast (it has a beautiful focus action and stage mechanism) and put the Cookes to one side while awaiting better experience/knowledge of phase stuff

[MichaelG.]

This, from 1998 mentions a Cooke 45x fluorite:

http://www.microscopy-uk.org.uk/mag/ind ... 8/cts.html

The 45x fluorite objective was specifically intended for medical workers and described by 'CTS' (ref. 7, p. 105) as 'the ideal lens for examining blood films for differential counts and stained sputum for tubercle bacilli. It has a large field, long working distance, brilliant detail owing to its high numerical aperture, and great depth of focus.'

MichaelG.

[Mraster2]

This, from 1998 mentions a Cooke 45x fluorite:

http://www.microscopy-uk.org.uk/mag/ind ... 8/cts.html

The 45x fluorite objective was specifically intended for medical workers and described by 'CTS' (ref. 7, p. 105) as 'the ideal lens for examining blood films for differential counts and stained sputum for tubercle bacilli. It has a large field, long working distance, brilliant detail owing to its high numerical aperture, and great depth of focus.'

MichaelG.

Ohhh Nice find, thank you !

EDIT later
PS Gosh ! I am impressed
and I found (ref. 7, p.) on Amazon , , , "Currently Unavailable", grrrr
dont you just hate that.

[MichaelG.]

Try this: http://www.science-info.net/docs/CTSmod ... e1940s.pdf

MichaelG.

[Mraster2]

Try this: http://www.science-info.net/docs/CTSmod ... e1940s.pdf

Another excellent find, thank you.

And including price lists from the time, fascinating.
Temporary one in April 45 and a 'proper' one in 48, that tells a story as well.
Eyewatering.