Fitting an AO (American Optical) Substage with a Leitz Heine Condenser

by Steve Neeley (USA)

"It is the only part of the optical system that the user can employ in more than one way; the objective and eyepiece are brought into focus and stay there, but the illumination system is capable of considerable modification during observation" 1

I am grateful to own two scopes - the AO (American Optical) Series 10 and the AO Series 2. Both are fine instruments. But being anxious to explore COL, and not having dry, high power Dark Field capability, I found myself envious, to be honest, of Leitz microscope owners. For them the Heine condenser furnishes both continuously variable COL and dry Dark Field. Historically, AO never offered a similar condenser (going immediately to a standard Zernike phase condensers when phase came on the scene). Leitz also produced a fine dry Dark Field condenser - the D80 - in addition to the immersion lens, while AO produced only the latter. The Heine, the D80, and many other fine Leitz dovetail condensers, some of which have no counterpart in the AO offerings, appear regularly on eBay . . . So why not just use the Leitz condensers on the AO?

The problem: AO standardized on a fork mount2 prior to the 1930’s, which offers no compatibility to the Leitz dovetail

Faced with this dilemma, I approached Gordon Couger a knowledgeable microscopist (and tinkerer), who gave encouragement to the feasibility of the idea of producing an adapter for the AO substage that would accept a Leitz dovetail. So with some patience and sheer luck, I was able to obtain a both a Heine and a D80 from eBay for a ‘reasonable’ cost.

Mark Simmons, of Perspective Images LLC, kindly agreed to design and produce the adapter despite the frustrating trial and error aspects of such an effort.

The solution: Mark found that rather than trying to adapt the fork-mount to the dove-tail, a better solution was to replace the fork mount itself (which is secured to rack-and-pinion system with only two screws) with a custom dovetail mount modified to fit the AO substage’s vertical and horizontal ‘space’. By ‘space’ I mean the practicalities of being able to mount the condenser, bring it into ‘focus’, centered, underneath the slide, using the AO substage’s rack-and-pinion and illumination system, and without interfering and colliding with the AO’s stage’s understructure - Leitz and AO scopes differ decidedly in these aspects.

Mark’s replacement mount is shown below next to the original AO fork mount and also mounted on the AO Series 10 condenser mount in place of the original.

The riser is needed to bring the Heine to the same height as a mounted AO condenser on the AO substage rack-and-pinion system. Notice how the brass dovetail mount, and riser, had to be cut away to allow the dovetail Leitz condensers to be centered within the AO illumination train.  A small setscrew, which drives a brass plug, allows the dovetail condenser to be snugly secured (without marring the brass dovetail) after which the condenser’s centering screws can be used to adjust final alignment.

Swapping the fork mount for the dovetail and back again, while not a quick-change operation (screws have to be dealt with) can be done in a few  minutes. I’m looking forward to trying other Leitz dovetail condensers in this mount in the future.

Then again, Oblique beckons . . . AO made a fine oblique condenser in the 30’s which is seen rarely today, but LOMO makes one of similar capability . . . Hmm . . . I wonder if you could adapt the LOMO condenser to the AO substage? This may be a future project!?

"The bibliography of the subject expands exponentially as new generations of workers develop and re-discover what is already known, but often forgotten, and novel needs bring forth new practices and relegate to limbo considerations formerly essential" 3

Comments to the author, Steve Neeley, are welcome.

1. W. G. Hartley, B.Sc., Hon. F.R.M.S. “The Light Microscope: Its Use and Development”, Senecio Publishing Company, Oxford, p. 205.

2. Note: A great advantage to AO users in that the standard fork mount stayed standard from the ‘30s pretty much through the early ‘70s (AO s Series 10 & 20 era) providing 40+ years of condenser compatibility between various AO scopes.

3. W. G. Hartley, B.Sc., Hon. F.R.M.S. “The Light Microscope: Its Use and Development”, Senecio Publishing Company, Oxford, p. 349.

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