Unable to get focus on field diaphragm by moving condenser

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MichaelBrock
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Unable to get focus on field diaphragm by moving condenser

#1 Post by MichaelBrock » Mon Sep 25, 2017 2:08 am

The subject pretty much sums it up. I'm still learning my way around my AO 20 microscope. I recently picked up a 1084 condenser and switched out my 1248 single-annulus phase condenser (with 1242 top lens). With the 1248 I had no problem getting the edge of the field diaphragm into focus by raising/lowering the condenser. However, with the 1084, despite the overall image quality appearing better, I am unable to get even a mediocre view of the diaphragm and certainly no where close to having it in focus. Nothing more than a fuzzy outline. Any clue as to what the issue might be? I'm certain to make certain that the auxiliary lens is out of the way.


Michael

apatientspider
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Re: Unable to get focus on field diaphragm by moving condenser

#2 Post by apatientspider » Mon Sep 25, 2017 9:24 pm

Hello:

I own neither a series 10 nor a series 20 scope, but I do own a cat. #1084 condenser. I purchased it some time ago to use on my old black beauty series 15 microscope. It fit the yoke of my model, but I experienced the same problem you are having. I couldn't get a sharp focus of the field iris (I use a separate lamp and a mirror.)

After some experimentation and a perusal of AO's manuals and catalogs I found out what the problem was. The 1084 condenser has a very short focal length, which means that the field iris needs to be positioned directly under it, within two or three inches or so, and that the illuminant source needs to be close or have a collector lens system that makes it appear close. It is designed for use with certain illuminators - such as the 1036-A - used on some of the series 10 microscopes, which have the field iris directly beneath and close to the front aperture of the 1084. The 1084 will fit the condenser yokes of various series of AO/Spencer microscopes, but it won't work with any but a particular model of series 10.

Looking at pictures of the series 20 in the AO catalog, it appears to have the field iris located back a ways from the light well - even though the lever for it is in front at the base of the microscope. Also, all the various model combinations of the 20 appear to list only the #1088 abbe condenser for use with them.

Here's an easy way to test: Take a piece of card stock - such as an index card - and punch a 1/4 to 1/2 inch diameter hole in it. Place it over the light well of your series 20 microscope, directly under the 1084 condenser. Now try to focus the hole in the card stock in the object plane of your microscope. If it focuses nice and sharp, then you've found the problem - you need a different condenser that was intended for your model scope - such as the 1088.

It may be that the lamp collector lens assembly can be adjusted to allow use of the 1084, but I rather doubt it. Failing that - possibly you could find some sort of corrective or "spectacle" lens to place over the light well, under the substage condenser.

I can well understand the desire to be able to use the 1084 condenser, because it is aspheric and a better condenser than just a simple abbe. American Optical also made a series of various condenser elements ranging from a simple abbe, to a wide angle, to a highly corrected achromatic, and they all fit the same mount. The mount itself will fit the substage yokes of various series/models of their microscopes, but doesn't necessarily always work with a particular model - either because it doesn't rise high enough under the stage or because it may not work with the built-in illuminator optical system. All I can tell you there is to try and see - or talk to someone who has.

Jim

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mrsonchus
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Re: Unable to get focus on field diaphragm by moving condenser

#3 Post by mrsonchus » Mon Sep 25, 2017 10:28 pm

Yes, this (as described by Jim) sounds like the same scenario met with Leitz 'scopes that take the 'series 600' condenser -

Leitz models such as the Orhoplan, SM-LUX etc will all physically take the 'base' 600 condenser, but have varying distances between the illumination bulb, collecting lens, field-iris leaves, FOV diameter (extra-wide for Orthoplan) and bottom of focused condenser. These different configurations are handled by a series of supplemental lenses that push into the base of the 600 series condenser to match it with each particular 'scope.
For example the Orthoplan takes a 'K4' lens, the SM-LUX takes a 'K1' lens etc..

Perhaps there are similar possibilities with your condenser?

John B.
John B

MichaelBrock
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Re: Unable to get focus on field diaphragm by moving condenser

#4 Post by MichaelBrock » Tue Sep 26, 2017 11:45 am

That is almost certainly the issue and makes perfect sense. I had actually salvaged the 1084 from an AO 10 that I bought for the accessories it came with. I put the condenser back on the 10 and had no issues focusing it. In my naivety I pictured myself switching parts back and forth between the 10 and 20 at will. Apparently not going to be that simple. :lol:

Edited to add: The wealth of knowledge in these forums never fails to amaze me. Thank you both for your excellent responses.

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Re: Unable to get focus on field diaphragm by moving condenser

#5 Post by apochronaut » Wed Sep 27, 2017 2:24 pm

Dead on , Jim. I can add a little history, and some observations and speculations about condenser evolution at AO.

The AO 10 did not have Köhler illumination. Nor did it specifically have critical illumination. It had a possible 4 types of illumination, from mirror( with which Köhler was possible), two modest 110v. illuminators, one including a built in aspheric condenser lens, and a short, modified Köhler system powered from a 6v. transformer. Later, they added a halogen illuminator, powered from an in situ transformer but it's characteristics were the same as the earlier tungsten version, with the remote transformer. The original # 1088 abbe condenser worked well with all of them and with the AO 20, when it arrived around 10 years later, which does have Köhler illumination, something necessary for some applications it had a better design for intrinsically, phase and DIC. It was the basic general purpose condenser and similar ones are found on millions of microscopes. Having one of those on a microscope, is like having pneumatic tires on a car.
The illumination system on the 10 was not suitable for DIC but you could use phase, once it's short focus, modified Köhler system was lengthened , with the addition of a special achromatic doublet lens installed in the base of the phase condenser. With that you get perfect even illumination for a phase system, the equal of that on the 20.

The cat.# 1084 abbe aspheric condenser came out in , probably 1974, or over 10 years after the series 10 was originally introduced. It has a very short w.d. and does improve the imaging on a series 10, when used with some of the later generation of plan objectives, and the 2 apochromats that came along with them. It wasn't really possible to make one that could accommodate both of the 10 and 20 systems and have as fine a w.d. Far fewer series 20 were sold , mostly for phase( which included a dry achromat condenser), high resolution DF or even DIC( which included a 1.3 N.A. achromat). It is possible and likely that AO intended to later make an abbe aspheric for the 20 too, in order to better illuminate the better planachros, and the two apos they had recently designed but the 20 was introduced much later than the 10...as much as 10 years later, and by the time the cat. # 1084 condenser was in production, they were probably already planning the series 120, 100 watt stand, for which an abbe aspheric was engineered, and aside from the .90 achromat, was the only condenser available, for that stand. They completely abandoned plain abbe condensers, for their professional line of stands, after the series 20, because they were basically, by then becoming obsolete for a professional microscope.

I do use the 1084 abbe aspheric on a 20 and even without dead on Köhler, it provides some advantages over the 1088 abbe. Mostly, though, I use a .90 achromat, dry condenser, screwed into a # 1240 phase body, for BF on the 20. The only objectives that can be fitted to that microscope that might demand more than that condenser can provide would be the 5, 100x planachros # 1023( the original planachro), 1029, 1129,1311 and the iris equipped 1014. For these, an oiled # 1084 works pretty good, maybe a nudge better than the 1201 .90 achromat. Really only, the 1029, 1311 and 1014( when used wide open for BF) are that demanding , though.
Until the end of production of the series 4, AO made the two 1.3 N.A.( cat. # C 235) and 1.4 N.A. ( cat.# C 236) achromatic aplanatic condensers, for use with the 1.3 and 1.4 N.A. apochromats they made until the infinity era. Both of those will thread into the series 20 condenser bodies, and being originally designed to be used with a remote illuminator set for Köhler, work really well to provide superb illumination for the more elite objectives, AO produced during the later 70's and 80's.

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Re: Unable to get focus on field diaphragm by moving condenser

#6 Post by apatientspider » Wed Sep 27, 2017 9:17 pm

Thank-you, thank-you, thank-you for that post, Phil! It certainly clears up some puzzles and confirms a few suppositions of my own. Why couldn't American Optical have explicitly included all this information in one spot, in one of its manuals or catalogs over the years? Would have been extremely helpful!

I take it then that the 1084 condenser can be used with the AO 20 with acceptable brightfield results most of the time, even though it can't focus the field iris sharply in the object plane? That would agree with my own experience. Using it on an old AO/Spencer #15 I still get better views with it (though it is out of focus) than I do with the ordinary abbe that came with that model. In support of that, I know I have read somewhere (probably several somewheres) that it is acceptable in casual work to de-focus a substage condenser a bit - for lower power magnifications anyway.


Until the end of production of the series 4, AO made the two 1.3 N.A.( cat. # C 235) and 1.4 N.A. ( cat.# C 236) achromatic aplanatic condensers, for use with the 1.3 and 1.4 N.A. apochromats they made until the infinity era. Both of those will thread into the series 20 condenser bodies, and being originally designed to be used with a remote illuminator set for Köhler, work really well to provide superb illumination for the more elite objectives, AO produced during the later 70's and 80's.

Didn't they also offer an ordinary abbe and a 1.4 wide angle (aplanatic but not achromatic) condenser in that series of condensers - all made to fit the same mount? I know they made the former, because I have one, but I'm sure I've seen at least one wide angle version on ebay in the past (was not inexpensive.)

Speaking of N.A.1.4 wide angle or aplanat condensers: I own one that was part of the catalog series offered for their black scopes prior to 1950 - such as the various research models, but also some of their ordinary lab scopes.

In addition to that one, a few years ago I serendipitously came across a very old one of a slightly smaller diameter and with external threads on it for a ridiculously low price. I didn't need it, but I snapped it up anyway, because Spencer's and American Optical's more highly corrected condensers are scarce on ebay. It isn't designed to fit any of the dovetail mounted bodies of the thirties and forties era, but I found that by wrapping a thin layer of cardboard or other shim around the threaded portion it will sit snugly in those mounts and also in the much later mounts that you mentioned.

Subsequently I discovered that it was intended for use with the more expensive instruments offered by Spencer Lens Co. in their 1917 catalog: https://catalog.hathitrust.org/Record/008593215 These were scopes with their old-style, two-part substage that swung down and off to both sides. Odd thing is that this wide angle condenser was offered as standard on their best microscopes rather than a fully aplanatic, achromatic one.

Jim

edited to post the proper link for the 1917 Spencer catalog: https://catalog.hathitrust.org/Record/012305435
The previous link in the text above is for the 1914 catalog.

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Re: Unable to get focus on field diaphragm by moving condenser

#7 Post by apochronaut » Thu Sep 28, 2017 12:48 am

All correct in my experience, Jim. I have occasionally seen those wide angle 1.4 condensers on ebay and they usually are priced pretty high.

Those old sleeve mount ones that you mention, were pretty common as you say in the better microscopes made after w.w.1. The principal of an auxiliary lens, I first see in catalogues on the 1.3 and 1.4 achromats used on the Spencer 5, in the early 30's, so using a wide angle condenser was the way they could fill the field with scanning objectives, prior to that.

A Spencer # 4 I have, from 1920 , has one of those 1.4 sleeve mount wide angle condensers that swing out, you speak of. It's a very lovely little stand. Small, more in the European style for the day but the base and arm are cast brass, so it weighs over 14lb. I think it was considered a small research stand, at the time, and is binocular, when many established microscopists still viewed a binocular view with scepticism. The big research stands, the # 5 ( older design) and the # 15 were monocular.

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Re: Unable to get focus on field diaphragm by moving condenser

#8 Post by Brad_ » Fri Sep 29, 2017 1:38 pm

Condensers are classed into two broad catagories: infinity
corrected and those corrected to around ten or fifteen inches.

See: http://www.microscopy-uk.org.uk/index.h ... uk/primer/

Read section 7 "Illumination"

The AO 20 requires an infinity corrected condenser.

Read the manual. Pay attention to the phase contrast
instructions. Notice the illustrated instructions for modifying
the AO 10's turret condenser. Let us know how it works out.

Have fun.

Brad

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