Jenaval Kontrasttubus - Photo Output Magnification

[a.katanski]

Hello fellow microscopists,

Unfortunately I don't speak German, so please excuse me. I'm new to the forum but microscopes fascinate me since I was a kid.

Recently I got a Jenaval Kontrasttubus microscope with a few objectives and some accessories. While I'm searching for the missing parts I cleaned and oiled everything and started testing the image quality. I have the GF-Pw 10x (25) eyepieces set in the binocular and I put the camera (Canon 600D) on the photo output above with just a focusing helicoid. The image is parfocal in the eyepieces and in the camera. This is great. The thing that I don't understand is why I get the same view/magnification in the eyepieces and in the camera since I don't use a projecting eyepiece of any kind in the photo light path? As I said just a hollow helicoid.

I will be grateful if anybody has an explanation about this. It doesn't make sense for additional 10x magnification to be added in the photo light path by default.

Thank you in advance,
Andrey

[Peter V.]

Hello Andrey,

I have no Jenaval contrast but  "normal" Jenavals, Jenavert and Jenameds. It is correct that you get nearly the same field of view on the camera chip and in the eyepieces by using an empty extension tube without any optical components. An additional lens in the camera lightpath is n o t necessary, a 1,6 x lens (as usually offered to connect a DSLR to the microscope) is only useful if you have a full frame camera. Using an APSC-camera, an adaptor without any lens (in Germany called "stovepipe") is better - and much cheaper! 

Regards
Peter

[a.katanski]

Hi Peter,

Thank you for this information! I didn't know nor didn't expect that.

This is my first "infinity" microscope and the first microscope with "trinocular" head. So far with my finite system microscopes I have used only "stovepipe" between the body and the camera and used objectives that do not need compensating. I sort of expected to get the same results here - only the magnification of the objective itself.

So I guess there is some element in the photo light path that is adding that magnification? Though I didn't see any in the sliding prisms area. I suspect it must be there. I would appreciate if anyone who knows the optical diagram, share some thoughts on this. What I want to achieve is the magnification of the objective itself. I will test the objectives on a 250 mm camera lens as a tube lens to see the results too.

Thank you once again,
Andrey

[JB]

Hi Andrey,

You put your camera sensor (Canon APS-C) in the plane of the intermediate image. The sensor has a diagonale of about 27 mm, so you have approx. the same image size on your sensor as you see through the eyepieces (25 mm, as in GF-Pw 10x (25)).

When you observe the image through the binoculars, the eyepieces first magnify the intermediate image ten-fold (10x), then your eyes reduce the image again to fit onto your retina (a few mm in diameter).

So the eyepieces are only necessary because you use your eyes for observation. When you use a camera sensor, you can observe the intermediate image directly. (And as Peter said, the intermediate image of the Jenaval is fully corrected for lateral colour, so eyepieces are not necessary for correction of the image either.)

Regards,

Jon