Daniel,
The additional information was helpful. Your adapter has a 2.5X magnification (at least it is marked as such). How this is accomplished we don't know (and it has no manufacturers markings). You can get a 2.5X "projection" magnification several ways. It's possible to do it by "raising" a conventional viewing eyepiece some millimeters higher than it's normal position (sometimes this can cause other optical "problems" to creep in). It can be done or by altering the “eye lens” spacing of a viewing eyepiece . But it is best done by designing a projection type eyepiece for that specific purpose (such as the NFK's that I use with my Olympus). My suspicion is that yours is a 2.5X projection design, but does not provide any additional chromatic correction. So instead of doing the final color "correcting" (as would be provided by a corrective Leitz Periplan viewing eyepiece) it simply magnifies the intermediate image 2.5X (which makes the existing CA more noticeable). It is also entirely possible that it is adding some of its own CA to the final image as well.
CA in these older objectives varies. (And it should be emphasized that this is not really a "defect"... the manufacturers designed them with the intent that the eyepieces would "complete" the image, and thus be considered an integral part of the overall optical system). With some objectives, the CA (and possibly field curvature), is strong and really does need to be corrected. With others it is there, but some viewers may not find it too objectionable.
"Direct projection", as you have done by holding the camera body close to the trinocular head, is an interesting option with the smaller frame sized ("APS" and 4/3) DSLR's. (It obviously does no correction for CA, but it would avoid additional CA form a poorly matched relay optic.) It is not always easy or possible to do. Often the camera body (even with all trinocular tube adapters removed) can't be positioned close enough to the objective so that the image is in focus in the camera at the same time as it is in focus with the viewing eyepieces. You
could focus the microscope for the camera, but then you are altering the designed optical tube length, which is really not a good idea with higher power, higher NA objectives. Also, many trinocular heads have physical internal dimensions that will not permit exposures to the full frame (mechanical vignetting…dark circular edges). But you have already found out that you are not satisfied with the CA characteristics in direct projection since you did try them on bellows.
So if you are not satisfied with the CA correction you are now getting, there are a couple things you could try.
The first (and perhaps others here can offer advice since I am not very familiar with Leitz products) would be to see what Leitz offered to be used in the trinocular head with this series objectives when a 35mm camera was used. This would be the best option, but finding (and probably paying for) this might not be easy.
Second would be to try a corrective Leitz Periplan objective slightly elevated in the trinocular tube. This could provide some needed chromatic correction, but as I said earlier, seems to introduce some problems as well. The overall result might be better than you get now, never know unless you try it.
The third approach would be to go to an “afocal method”. Put a proper corrective Leitz Periplan “high eyepoint” eyepiece in the trinocular tube, and adjust things so that it is in focus (with your eye) at the same time as the viewing eyepieces. Then attach a lens to your camera and position it above the eyepiece. This can work surprisingly well. The difficult part is finding a proper lens. Zoom lenses are too deep, and the aperture is too far back into the lens. The lens needs to be relatively “thin” so that so that it can be positioned close enough to the eyepiece that entrance pupil of the lens coincides with the “eyepoint” of the eyepiece. Ideally you would want a focal length of about 40mm for an “APS” sized sensor and about 63mm for a 24x36mm sensor. The lens should be focused at “infinity”. Remember that there are many “adapters” that allow other makers lenses to be attached to Canon bodies and still allow “infinity focus”, so there are more choices than just Canon lenses. (There are some older “pancake” style lenses certain manufacturers made in the 40-45mm range that might be very good for this use when adapted to the EOS body.)
Some other links that you might find interesting:
http://www.photomacrography.net/forum/v ... hp?p=48278
(check the Ted Clarke links given in this post as well)
http://www.microscopy-uk.org.uk/mag/img ... oscope.pdf
And one last point... even good achromats will show some chromatic "issues" when examined closely. They are, after all, achromats. (And the digital camera seems to be much less forgiving of CA than the human eye) There's a reason that manufacturers charge 10 to 20 times as much money for an Apo or Superachromat. See:
http://www.dantestella.com/zeiss/achromat.html
But if you are seeing very significantly more CA in your pictures than you see through the eyepieces than you can probably do better. The camera/microscope link can be a tricky one!
