Testing 3 lenses as tube lenses for microscope objectives

[ForenSeil]

Hi
I bought an used el cheapo microscope (26€) with RMS- objective and standart eye pieces (around 1") mount and modified it to RMS/M27 and M42 camera mount. Some "planachromat" objectives came with it - but they were all crap, showing heavy CAs, curved focues field and so on anway. So I needed a good microscope lens.
I found that Nikon and Olympus microscope lenses are good and bought a modern Nikon 10x 0.30 NA infinity microscope lens.
These good modern microscope lenses are not projecting a picture directly like their older counterparts - they are "corrected for infinty".
http://www.microscopyu.com/tutorials/java/components/infinitymicroscope/index.html

So they need another "normal" lens around 200mm which is focused to infinity to produce a picture.
Good native 200 so called "tube lenses" for microscopes cost around 200€ and above. And I didn't wan't to spend so much money for an experiment so I decided to try alternatives.

The competitors are the Schneider Kreuznach G-Claron 150 f/9 (APO), Rodenstock Rodagon 150mm f/5.6 and Tokina RMC 200mm F3.5. All are very cheap used.


Here are some pics of the setup:






And here's the direct comparision:
Here some test shots around 10:1 magnification:

Rodagon 150 f5.6


G-Claron 150 f9


Tokina 200 f3.5


Tokina 200 F3.5 (2)


Rodagon 150 f5.6 (2) von Chloressigsäureethylester auf Flickr


G-Claron 150 f9 (2)

And here a pic of the coin with exatly 1:1 magnification for comparision:


Which is the best one to your eyes?
Tokina has best colors and lowest vignetting but is less sharp than Rodagon and Claron.
Rodagon has better overall colors than the G-Claron but the G-Claron has best CA control at highlights and the highest acutance to my eyes.

[s58y]

They look about the same to me.

I seem to recall old discussions over at photomacrography.net, where the most important thing about the tube lens was entrance or exit pupil location/size, etc. and its effect on vignetting at the corners. I don't recall the details.

The effective aperture of a 10x objective at its rated magnification is something like f/15 to f/20 (depending on N.A. and all that), so as long as the lens can produce an image at the sensor at f/15 that is as good the best lenses out there, it's good enough to be a tube lens. With the 150mm lenses, I guess you'd be working at 7.5x with an effective f/11-f/15 aperture, so your lens needs to work as well at these f ratios.

Is the lower vignetting from the 200mm Tokina because it gives 10x and a narrower field than the other two 150mm lenses?

Maybe some expert over at photography.net will come along with a better answer, but I don't see any responses over there yet.

[poilu]

[visualopsins]

Now I'm confused...

I thought this RMS-M42 adapter (Click here to see on Ebay) is for use only with infinity corrected RMS objectives.

[kds315*]

ehemm, I would look up "infinity objectives" and "tube lens" - google is your friend

[ForenSeil]

I think I will keep the G-Claron as it's the cheaper (it did cost around 22€) than the Rodagon and also a little easier to adapt to my microscope.

Bye the way I'm a litte astonished as the speed of the tube lens it didn't interfere with the effective apertures... all produced the about same effective speed.