Most microscopy pictures I saw by a DSLR camera are ...let's say.... below expectation. But pictures with a small sensor (5 MPX) are quite OK. Some very expensive dedicated camera (16.25MP for more than $11000) are stunning. How comes that DSLRs are so bad at the job, even with a quality sensor up to 60 MP? I may have a clue, and a solution that needs some testings.
First thing first, aren't you amazed that the tube you need to use a DSLR on your favorite microscope is so long, so bulky? When you see videos from our guest, Oliver -all hail to him
![Wink ;)](./images/smilies/icon_e_wink.gif)
There are two main factors creating these deformations, IMHO... The lengthy tube, even manufactured with care, cannot ensure the top lenses are exactly on the optical axis. Any small misalignment, even with a very small angle creates the purple-yellow fringes. I got this effect on my microscope, and slightly tilting the tube worsen the fringes. If you try to shorten the tube, to minimize the misalignment effect, you need to set the microscope objective above its nominal working distance, creating a severe pincushion deformation.
I find a solution to these problems on my Optika IM-3 (inverted microscope) using a SONY Alpha 7 R4 (61 MP) to get sharp and crisp images even at the border. The trick I use is quite simple: a 2x tele-extender! The image formed by the objective is 22mm, but to frame it properly in a full frame sensor you need 44mm... hence the 2x extender "trick". The distance between the "trinocular port" and the extender is only 15mm when the microscope objective is at its nominal working distance. I mean I set the image on focus looking through the eyepieces, lock the focus knob and then put the camera with the extender above the video tube until getting a sharp image. Distance is around 15mm in my configuration.
If you are interested to test this you need a quality 2x extender for a full frame size sensor, and 1.4x extender for an APS-C size sensor. Using a 2x extender on APS-C should work, but you will get a somewhat enlarged image. If it works... because I have only tested this on an inverted microscope with infinity objective. It may be different for upright microscope with 160mm objectives or other optical configurations. So if you try this, please let me know the results you have.