Ray,
I understand your position. All it takes is about 20 minutes on Ebay to realize the huge amount of microscope "hardware" out there. I'll throw out a few thoughts based on your "details".
You want a microscope with a trinocular head. This gives you the third "port" for your camera. If you anticipate working with subjects that move, then I strongly recommend a trinocular head that will allow you to view through the eyepieces and photograph simultaneously. This it done by "splitting" the light so that most goes to the camera, but some is still directed to the eyepieces... about an 80/20 split is common. Some trinocular heads direct 100% to either the trinocular tube or the eyepieces. As a result, you cannot see the subject when taking pictures with these.
Choosing between a stereo and a "research" style compound mono is an important decision. (To make this discussion easier I'll use "stereo" to refer to microscopes where you get a slightly different view with each eye and as a result you see a "3D" image. I'll uses "compound" to refer to a microscope where both eyes sees the same image). Stereo's are great for modest level observation, but (IMO) not as good as a compound microscope for photography above 8x. This is primarily because of the NA (numerical aperture) available. Most stereos have a NA in the 0.08 to 0.10 range. With these, the photographs begin to suffer diffraction losses when used to photograph above about 6X-8X
on sensor! (Some of the new, very high-end stereo microscopes will boost the NA to 0.20 to 0.30, but the prices on these are astronomical
). Photography up to 6X on sensor (and somewhat higher) is fairly easy to do with bellows or "stacked lenses". And the image quality will likely be better. You see many great examples on this site. So while I think a modest stereo is really necessary for finding, sorting, and preparing subject material, a compound microscope offers much greater photographic possibilities.
When you look at "compound" microscopes there will be two basic types of optical systems encountered. One is "
finite". With these there is a specific designed "tube length" (extension) that is the distance between the shoulder of the objective and the image it forms. The aperture of the microscope eyepiece is positioned at this distance, and magnifies this image so that it can be viewed by the eye. The second type, "
infinity", is not dependent on a specific "tube length", but utilizes an additional lens between the objective and the eyepiece. Just about all current models from the "Big Four" (Nikon, Olympus, Leica, Zeiss) are "infinity" designs. These are more suitable for inserting all sorts of additional components used for some sophisticated methods such as fluorescence and DIC (differential interference contrast). While "infinity" systems go back quite a few years, the big switch-over occurred in the 70's and 80's.
It is important to understand the following. Most microscope objectives were/are designed so that not all chromatic and field flatness corrections were made in the objective themselves. The manufacturers knew that the objective had to be used with either an eyepiece (finite system) or both a tube lens and an eyepiece (infinity systems). As a result final optical corrections were/are made, by design, in the eyepiece (for finite) and in the tube lens (for infinity). What this means is that the image that reaches the eyepiece in a finite system is (in most cases.... one big exception) not fully corrected. The image that reaches the eyepiece in an infinity system is as corrected as it is going to be... this having been accomplished either in the more modern objective or with the internal tube lens). This becomes an important consideration when figuring out how to "optically" connect the camera to the microscope (more on this below).
Infinity type objectives should not be used on finite microscopes, and finite objectives should not be used on infinity scopes.
The objectives from infinity systems are not interchangeable between manufacturers. You are pretty much "wedded" to a specific manufacturers offerings when you use an infinity scope.
The objectives from finite systems are more interchangeable between manufacturers (with some important caveats).
but I do want quality in design, construction and optics. I'm fairly flexible on the price, but I don't know whether say up to $1500 is achievable.
A big decision you will need to make is "new" or "used". A new microscope (with the specs you want) from one of the four "name" manufacturers will be expensive. A new microscope from a Chinese (or Indian) manufacturer will be readily available in your price range.
Many argue for looking for used "Big Four" microscopes. The feeling is that these older scopes are of higher quality mechanical construction. And if you use their more "modern" objectives (1970's and more recent) the optical quality will be better.
Others understandably don't want to be bothered by potential problems with used gear.
Both are valid approaches. My thinking is that I want the best optics I can afford, and would be willing to put up with a solid workable stand. (Sort of like in the days of film, using a camera manufacturers best lenses on one of their more modest camera bodies). Personally I started off with a Meiji ML2000, which is a smaller Japanese manufacturer with good mechanics. This is a "160mm tube length" microscope. I tried to get the best Olympus 160mm tube length objectives I could. (These are great! The Meiji 160tl objectives were just "good"). Eventually I wound up with an Olympus BHS stand. This gave me DIC lighting, and higher quality mechanics, but other than that the images were no better.
A key consideration is the optical "connection" between the microscope and camera. Normally with 35mm and larger formats (where the image was projected directly onto the film... no lens on camera body) you placed a photo-eyepiece (projection type) in the trinocular tube. The "magnification" of this photo-eyepiece was based on the size of the film format. Typically a 2.5X was used with 35mm format (24x36mm). This would appropriate for use with a "full frame" DSLR that has a sensor of the same dimensions. A problem is that with the older microscopes 35mm was about the smallest format used for photography. As a result, corrective photo-eyepieces with magnifications less than 2.5x are rare. The camera you have said you will be using has a 4/3" sensor. The size of this sensor (17.3 x 13 mm, with a diagonal of 21.6mm) would work "best" with a photo-eyepiece in the 1.25 to 1.5 range. But this sensor size could also be used in a "direct projection" mode. This is when no projection "photo-eyepiece" is used and the image goes directly from the objective to the sensor.
There was one manufacturer that made "finite" objectives that were color corrected in the objective. This was the Nikon CF series, which was introduced in the mid-70's.
Because of the sensor size you are using I'll suggest a few approaches that could work.
Look for a used Nikon Labophot or Labophot 2 with a trinocular head. (The only trinocular head I would not recommend that was made for these microscopes is the "Model F". This one does not split the light between eyepieces and trinocular tube). Look for Nikon CF objectives. There is a good chance a used Labophot will have some of these mounted already. I've put a Nikon CF brochure on my site. You might want to look it over.
http://krebsmicro.com/Nikon_CF.pdf
The lowest power CF photo-eyepiece (that would provide a large enough image at your sensor) I am aware of is 2.5X. This would be "doable" although it would provide a significant crop of the view through 10X viewing eyepieces. An interesting possibility with your camera (if you are comfortable with some DIY work
) is a direct-projection arrangement. This is not really feasible with most DLR's because of the flange-to-sensor distance, but with the 20mm flange-to-sensor distance of micro 4/3 it should be possible.
A second approach would be a used Olympus 160mm tube length stand. A model CH2 (lower price, more basic model) or a BHA or BH2 are good options. Look for Olympus LB series objective. S Plan Achromats or S Plan Apo's ($). Olympus made a 1.67 NFK photoeyepiece that could be used with your camera. (But it is hard to find, and sells for about 4X the price of the much more common 2.5X)
There are other approaches as well... but I've got to go for now!
Think this stuff over and get back with more questions.
Charlie
