An AO Spencer  Objectives Reference

Using the various available manuals and catalogs it is possible to construct a reference of Cat #'s (Catalog Numbers) and Objectives that may be useful in finding objectives for your AO Spencer microscope.   

The rules for objectives:

Eyepieces, on the other hand, are quite forgiving can be used interchangeably on 160mm TL and Infinity corrected scopes with good results.*  

*Note: The 'purist' in me wants to note that the very best, optimum results will be obtained by using the eyepieces specifically  made for each objective set (e.g.  a Cat# 146 10x eyepiece on a 160mm TL Series 2 scope, a Cat# 176 10X eyepiece on an infinitely corrected Series 10 scope, etc.) -- but the 'practical side' of me says it really, truly doesn't make a heck of a lot of difference -- use what you have.  But if you are wondering what the differences might be between different brands of eyepieces, Mervhob of Yahoo's Microscope Group has furnished the useful information below (also see Mikrofibel page 55) :

You can see that B&L (Bausch & Lomb) eyepiece are very close to the same specifications as AO eyepieces.  It is quite common to find B&L eyepieces on AO scopes and, probably, vice-versa.  Amazingly, you'll often find B&L objectives on AO scopes, without an shims, even though their parfocal distance is 35.6mm vs. the 34mm distance for AO Objectives.

OK, Here is a list of the AO and Spencer Objectives 'known' to me from either experience, or from the AO Spencer Literature (i.e. a catalog or a manual).  (Note: You can select the whole list, top to bottom, and past it into Excel to create a spreadsheet that can be sorted on any column if you'd like)

Sources:

 Note: A 'C' at the beginning of the Cat#, at least in the Series 15 and 35 era (1930's and 40's), meant 'C'oated.  For example, you could order either a Cat# 115 uncoated 43x objective, or a Cat# C115 coated (Americote) objective.  A 'K' at the beginning of a Cat# designated a 'special order' item.

*In the only case I know of, AO, strangely, reused a Catalog number.  In 1969, the Cat# 1029 was clearly a 50x (without a iris diaphragm).  Then sometime later AO brought out a Cat# 1029 100x Oil ( I've seen three examples of these -- they were 'new style' objectives so I would guess the 1029 was maybe produced in 1975 or 1976?)

**Unsure if this whole number is the Cat#.  Only have seen on example of this objective, but this is what was on it:

Stan Ayers -- "I just bought a phase-contrast microscope. It seems to be from the '50's. The objectives and condenser turret are familiar, except for one. There's a 50x reflecting objective, marked 922968. I have never seen one of these, and was wondering what they are for, or why they were specified."

Needham's 'Practical Use of the Microscope' p.137: "A recent computation is that of the American Optical Company.  The reflecting objective is 50x with an N.A. of 0.56.  The quartz optics made by this Company for the objective are a 10x Huygens eyepiece and an Abbe substage condenser."  Read the full account here.

***The catalog says N.A. 0.80, but I've seen, on ebay, an example that clearly says 0.85 

FAQ Question:  Can I use other manufacturer's 160mm T.L. objectives with my 160mm T.L. AO Objectives?

Answer:  Sure . . . for almost 100 years, people have been happily exchanging 160mm objectives  But, there could be a few 'gotchas'.  First, color and flatness correction sometimes occur in an intermediate lens (e.g. some B&L designs) or, more commonly, in the eyepiece.  But you have a good chance of being successful without any loss of resolution and contrast.

Also, remember the parfocal distance challenge.  Sometimes, if the difference isn't too great, you can use shims between objective and nosepiece to defeat this challenge (e.g. see www.cynmar.com's affordable parfocal rings).  

A very useful table of parfocal distances is found in Mikrofibel page 55 -- 1st column = Manufacturer, 2nd column = tubelength, and the 3rd column = parfocal distance in mm -- which is what you need to know.  Can't read German?  Me neither, but 'mining' this document we can produce a table of good candidates as below:

FAQ Question:  Can I use other manufacturer's infinity corrected objectives with my infinity corrected AO Objectives?

Answer:  Not like you can 160mm objectives -- in theory, many advise against it.  But when did that ever stop you? :-)  After a rousing discussion on Yahoo's Microscope group about this (see this message for instance), and reading various references, I have concluded (with not much authority I might add :-)  ) that it may work, or it may not work, depending on which objectives and which scopes you use them on.  A very good reference, and read, is: 

http://www.microscopyu.com/articles/optics/cfintro.html

that addresses the history and issues well.  

Basically, bottom line, even an infinity system is designed with a tube-length in mind for the upper part of its optical train, which varies by manufacturer, and the design 'mismatch' can cause trouble when mixing various makes of infinity corrected objectives.  (Note:  A interesting overview of objective correction can be found here.  The issue comes down to the question: "How can a single objective cost $4000?",  with the answer:  "Because there's a lot to correct for in attaining the ultimate resolution.")

But theory is one thing, practice is another.  In practice, people have found that it is often possible to swap infinity corrected objectives without appreciable, or at least, noticeable, loss of resolution and contrast.   Remember though you will still face the parfocal distance challenge mentioned above.

FAQ Question:  Can I use Leitz 170mm T.L. lenses on my 160mm T.L. AO Scope? 

Answer:  Sure.  The Parfocal distance problem will be there (i.e. many Leitz lenses are 45mm parfocal, some are 37mm parfocal, etc.****), but it will work.  The definitive document on this is Leitz-160mm-Memo.pdf  at Gordon's site -- a very interesting read.

* Note: Determining the parfocal distance of an AO objective is not as easy as it sounds -- well accurately at least.  I have two LOMO 160mm T.L. objectives which are very clearly stated by the manufacturer to be 33mm parfocal.  Using the 1 micron graduated fine focus on the Series 4 scope, I found these LOMO objectives to be within 0.065mm parfocal to each other.  I then used them to compare against same power AO 160mm T.L objectives (which are within 0.040 mm parfocal to each other) and found the AO's parfocal distance to be almost exactly 1.0mm longer than the two LOMOs (0.925 mm in one case,  1.030 mm in the other).  So using the two Russian objectives as a standard (well, it was the best I had), I compute the AO Objective's parfocal distance to be 34mm.

**Note:  I compared an AO 97x Oil objective to a B&L 97x Oil objective -- both gave excellent images (by the way, the 97x AO was exactly parfocal with the 10x AO objective noted in the LOMO comparison above).  The B&L parfocal distance was exactly 1.67mm longer than the AO's distance.  Thus 34 + 1.67 = a 35.67mm parfocal distance for B&L objectives.  One message on the Yahoo's Microscope forum says that B&L objectives are 35.5mm parfocal, but that is 0.17mm too short per my measurements.

***Note:  Quoting from Needham (1958 -- The Practical Use of the Microscope, p. 153):  "American Optical Company (Spencer) has designed objectives in which the central beam is not changed while the diffracted light is both retarded and reduced in intensity.  This modification has been named by them, B minus contrast.  American Optical manufactures a very complete series of phase-contrast objectives for bright, dark, and B minus contrast, each with three degrees of contrast of low, medium, and high . . . The consensus of opinion of several of the foremost independent workers with the phase-contrast microscope is that the Zernike, 1/4 (lambda) retardation, negative (bright) contrast or positive (dark) contrast is preferred for the great majority of objects with very little contrast.  Also they object to the fact that too many variations in phase-contrast objectives complicate and confuse the beginner in this field, and that such modifications are not generally necessary, and that they add greatly to the cost."

****Note:  Leitz objectives are a tough one to unravel.  Older Leitz objectives (before 1960?) seem to be all 37mm parfocal.  But when Leitz brought out PL (plan) and NPL (neo plan) objectives, they designed them  with the longer 45mm parfocal design.  But, unfortunately, it turns out to be no that simple.  Note Mike Andre's comment to a question about availability of 170mm T.L 37mm Phaco or PV objectives -- Yahoo Microcope forum message #33059:

"Re: Looking for a Leitz Phaco or PV objectives -- 170mm T.L. , non-plan

Hello all,

Looking at my copy of the Leitz manual "Image-forming and Illuminating Systems of the Microscope"***** it states on page 49: Phaco phase contrast objective for the Zernike condenser are 170/0.17/45mm (with the exception of the Fl Oel 70 - 170/0.17/37mm)

Page 50 lists the Phaco NPL Phase Contrast Planachromats for the Zernike condenser at 170/0.17/45mm, but page 51 lists PV Phase contrast objectives for the Heine condenser at 170/0.17/37mm (with three exceptions for 170/0.17/38.5mm!)

I have sets of the achromat phacos as well as the NPL Phacos, all or which are 45mm (none for sale, I'm afraid!)

Hope this helps.

All the best, Mike"

***** Don Grybeck kindly has contributed this wonderful document, which was subsequently scanned, and you can download it here:  "Image-forming and Illuminating of the Microscope -- objectives, eyepieces, and condensers" (23.4 MB zipped file)   

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