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Fiducial lines on a Zeiss Microscope Eyepiece

Question: Why are there two ? ...

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Michael Gilligan19/09/2019 18:16:42
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I have already posed this question on a microscopy forum; with only one answer to date ... which both the author and I find unconvincing.

Therefore, I throw it open to this diverse community:

Here is a 'crop' from p74 of a Zeiss booklet:

8x_kpl.jpg

For anyone interested; the whole document is at: **LINK**

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

____

I have a couple of the 8x Kpl eyepieces, as illustrated on the left, and described on the third line of Table 29

The scale is obviously for dioptric adjustment, but why are there two fiducial lines, and how would one use them ?

Zeiss appears to be totally silent on the matter ... so can any 'Reverse Engineers' devise the instructions for use [please] ?

MichaelG.

Clive Foster19/09/2019 18:54:59
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If I recall correctly we had some optical equipment in the lab with similarly marked eyepieces arranged so that optical components could be inserted beneath the eyepiece mount. Presumably graticules or similar. I'd always understood that the two lines were provided to correct the calibration when the extra component was fitted. Presumably makes some sort of sense with binocular system with a graticule on one side.

Never used the kit they originally came off, not sure we still had it, as the tubes and eyepieces had been robbed for other purposes. Probably some sort of bespoke, lab built, test gear. Not something I'd built.

Clive

Michael Gilligan19/09/2019 20:42:56
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Posted by Clive Foster on 19/09/2019 18:54:59:

If I recall correctly we had some optical equipment in the lab with similarly marked eyepieces arranged so that optical components could be inserted beneath the eyepiece mount. Presumably graticules or similar. I'd always understood that the two lines were provided to correct the calibration when the extra component was fitted. Presumably makes some sort of sense with binocular system with a graticule on one side.

Never used the kit they originally came off, not sure we still had it, as the tubes and eyepieces had been robbed for other purposes. Probably some sort of bespoke, lab built, test gear. Not something I'd built.

Clive

.

Thanks, Clive ... That was actually the hypothesis that my microscopical friend offered: Unfortunately we cannot reconcile it with the fact that the W version [illustrated to the right] only has one line.

MichaelG.

Clive Foster19/09/2019 21:30:54
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Full inscription on the one on the right is Kpl-W.

First two lines of the data table says the plain 8x and 12.5x eyepieces are compensating ones. Presumably the left hand one in the picture.

Third entry is separated by a heavy line and simply says 8x Kpl eyepiece with no mention of being compensating. Also focal length, eye relief and field of view is slightly different to the compensating 8x.

Suggests they are different designs. First two are compensating where one line is used when a graticule or whatever is fitted and the other when used as an ordinary eyepiece. The Kpl-W version being an ordinary style where you either need to adjust the position in the tube if a graticule is fitted or have a plain glass in the clear view tube to compensate.

But microscopes have never been my thing except for casual use and as sources of optics for other duties.

Clive

Michael Gilligan19/09/2019 22:03:28
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Posted by Clive Foster on 19/09/2019 21:30:54:

Full inscription on the one on the right is Kpl-W.

First two lines of the data table says the plain 8x and 12.5x eyepieces are compensating ones. Presumably the left hand one in the picture.

Third entry is separated by a heavy line and simply says 8x Kpl eyepiece with no mention of being compensating. Also focal length, eye relief and field of view is slightly different to the compensating 8x.

[ ... ]

.

It's a bit more complicated than that, I'm afraid, Clive

You may find it interesting to look at the full document; but the gist of it is on p40

"As is the general practice today, the magnification of the eyepieces is indicated by a figure followed by " x ". Letters before the magnification mark the type of eyepiece. Since we manufacture only compensating eyepieces, such an identification would normally be superfluous. However, our eyepieces of higher power are so designed that they produce a flat field, which is not necessary for the low-power systems. The latter are therefore marked C (compensating eyepieces) to distinguish them from the former marked Kpl (compensating flat-field eyepieces)."

The two eyepieces illustrated are both marked Kpl and are therefore compensating and planar ... The one to the right has the suffix W for wide-field.

The table has several more lines, but Kpl 8x is the one in question, and is the one illustrated to the left.

zeiss_kpl.jpg

.

Apologies if I caused confusion by cropping the table short ... I was trying to maximise resolution of the relevant parts.

MichaelG.

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Edit: Here's the full page:

zeiss_p74.jpg

Edited By Michael Gilligan on 19/09/2019 22:14:20

Edited By Michael Gilligan on 19/09/2019 22:24:31

Diogenes20/09/2019 07:32:30
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Apologies if this turns out to be a stupid comment, I know very little about microscopy - but don't camera lenses employ an alternative fiducial line for focussing in the infra-red part of the spectrum?..

Diogenes20/09/2019 07:35:53
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..but of course you wouldn't see it through an eyepiece.blush

Clive Hartland20/09/2019 07:42:31
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Fiducial lines are usually on the focal plane and appear on the negative or print for measuerment purposes, I wonder if the lines in the eyepice appear when used with a camera?

Michael Gilligan20/09/2019 07:50:51
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Posted by Diogenes on 20/09/2019 07:32:30:

Apologies if this turns out to be a stupid comment, I know very little about microscopy - but don't camera lenses employ an alternative fiducial line for focussing in the infra-red part of the spectrum?..

.

Not stupid at all ... it may well be the right general line of thinking

[subject of course to your follow-up post]

What I can't understand though, is why I have found no explanation in any of the Zeiss literature that I have looked at.

MichaelG.

Michael Gilligan20/09/2019 07:54:09
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Posted by Clive Hartland on 20/09/2019 07:42:31:

Fiducial lines are usually on the focal plane and appear on the negative or print for measuerment purposes, I wonder if the lines in the eyepice appear when used with a camera?

.

Sorry, Clive ... another ambiguity rears its ugly head.

I'm referring to the two 'setting lines' on the barrel of the Kpl 8x

MichaelG.

Neil Wyatt20/09/2019 09:35:18
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I'm minded to not that some camera lenses have an extra fiducial line for specialist photography, but as this is an eyepiece that might be an infra-red herring.

I do agree that it must be intended to compensate for some predictable change in the optical train.

pgk pgk20/09/2019 10:13:48
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More thoughts for the mix

If considering IR light then also consider UV used for instance with flourescent antibody techniques. Also possibly the difference between collimated transillumination and surface illumination methods???

pgk

Clive Hartland20/09/2019 10:31:27
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There are many factors in Microscopy that are made for different usage, I have seen some where incident light use and reflected light so maybe a different focus there. My own use has been with reflected light looking at PCB's and the resolution is critical for dry joints in multi layer boards.

Sadly I no longer have contact with Leica since I left in 1999. I would think my contempries were no deceased.

It might I wonder if it to focus on meniscus plates where the focus changes through the meniscus?

 

Edited By Clive Hartland on 20/09/2019 10:32:36

Bill Davies 220/09/2019 11:20:04
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I had a camera bought in the 70s with an index line for UV. Outdoor UV photography was popular around that time, for the interesting effects it gave, so perhaps for that purpose. However, I don't recall the two index lines being very far apart, but that would depend on the fineness of the eyepiece's thread. In any case, this adjustment isn't for focussing purposes (that's the rack and pinion's job), so I've nothing to the discussion.

Ian Parkin20/09/2019 11:24:31
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Bill

surely IR ( infra Red)

Michael Gilligan20/09/2019 14:05:38
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Posted by Bill Davies 2 on 20/09/2019 11:20:04:

... I don't recall the two index lines being very far apart, but that would depend on the fineness of the eyepiece's thread. In any case, this adjustment isn't for focussing purposes (that's the rack and pinion's job) ...

.

Thanks for your thoughts, Bill ... But this adjustment is, in a sense, for 'focussing purposes'

The scale is for near-sighted/far-sighted correction of the eyepiece [essential if a 'micrometer disk' is fitted, and also useful in other situations]

MichaelG.

Bill Davies 220/09/2019 17:50:40
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Thanks, Michael, you're right. I understood that but expressed myself poorly. And I think Ian is right (and Neil's earlier comment) about IR. That and solarisation was popular at the time.

Bill

Michael Gilligan20/09/2019 18:45:40
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Posted by Bill Davies 2 on 20/09/2019 17:50:40:

Thanks, Michael, you're right. I understood that but expressed myself poorly. [ ... ]

.

No problem, Bill ... I'm grateful for all comments on this one; it's driving me nuts !

Incidentally: Whilst I doubt if the colour is significant; the right hand fiducial mark [as we view the picture] is Red.

MichaelG.

SillyOldDuffer20/09/2019 20:01:02
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Here's my guess. The eye-piece is designed to be used with a micrometer disc inserted or not - the disc isn't a fixture, and I see Zeiss offer a few different graticules.

The usual purpose of the focusing eye-piece is to adjust for right/left eye differences when using a stereo microscope. (One eye-piece is fixed and focussed with the ordinary rack, then the other eye-piece is adjusted independently to suit the other eye.) I suggest the first fiducial mark is for operator convenience - it allows the eye-piece to be quickly set to suit each individual who might be sharing the microscope or eye-piece.

Normally the focus is adjusted for best image. But when a micrometer disc is inserted the eye-piece should be adjusted to sharpen the graticule. I think one fiducial mark is for the plain eye-piece, the other represents the offset necessary to accommodate the micrometer disc. The advice on micrometer discs starting end of page 40 may support the idea: These figures are engraved on glass plates (micrometer disks) which are inserted in the diaphragm plane of the eyepieces. However, since they will not necessarily be seen sharply with normal eye-pieces, above all if the eye of the observer is not free from visual defects, eyepieces with a focusing eye lens are used for this purpose.

The eye-piece is provided with two fiducial marks so users can quickly set the eye-piece for either disc in or disc out viewing.

If anyone has a spare Zeiss microscope and accessories I'd be delighted to test the hypothesis. Distinct chance I'd fall in love and refuse to return it though!

Dave

Edited By SillyOldDuffer on 20/09/2019 20:01:53

Michael Gilligan20/09/2019 20:23:43
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I think the mystery is solved ... and the answer is what was first suggested.

The current version of Zeiss document 'Microscopy from the very beginning' describes the modern 'infinity' microscopes [which have superseded the 'finite tube length' models] ... but it includes the following brief statement:

[quote] The eyepieces are labelled with a diopter scale (  + 0 - ) and “foc”. If an integrated reticle is used, the red dot represents the zero mark because of the image shift which then occurs. [/quote]

One can only assume that the red line on the old eyepieces corresponds to the red dot on the new ones.

Thanks to everyone for their thoughts.

MichaelG.

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Ref. http://www.its.caltech.edu/~bi177/private/Microscopy%20from%20the%20very%20beginning.pdf

Edited to remove stupid smliey thing, and to thank Dave for his contribution

[ there was a meal-break involved between starting and completing this post ]

Edited By Michael Gilligan on 20/09/2019 20:29:53

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