Cushion & spherical optical aberation with DSLR on µscop

[yminter]

Here is my problem:

I have a Leica DMLM µscope which is currently equipped with an old Leica 780X852pixels digital camera.

I tried to adapt a Canon 550D on it using a commercial optical adapter that is to be screwed to tha C-mount adapter of the µscope and which offers the right adapter for the 550D.

The problem is that the result is not exactly as I thought it would be:

Here is what I get using the old camera:



Here is what I get using the adapter & DSLR:



(Both images were shot without moving the sample, just by replacing the camera by the DSLR + adapter & refocusing).

The provider of the adapter tells me that it must be due to the magnification factor of the Leica 0.63X C-mount adapter that is not high enough and that the outer part of the optics of the µscope is responsible for the aberrations. He tells me that a 1X mechanical adapter (hence certainly lens-less) would correct the problem.

The explanation looks a bit strange to me since I can see the same part of the sample through the oculars, without any aberration... The only difference in this case is that I don't look through the Leica 0.63X C-mount adapter.

The point that I find strange is that parts of the image that look crisp on the camera have beginnings of aberrations with the adapter & DSLR, thought the optical path is exactly identical up to the C-mount adapter...

Does anyone have already seen something like this or an idea of what kind of problem could cause it?

[enricosavazzi]

I cannot comment on the specific equipment, but here is what I can say - and ask.

[rjlittlefield]

[yminter]

Hi Enrico, thank you for this reply; I'll try to give you a little more details below.

[yminter]

[Pau]

Some complemantary comments:

- You want the camera parfocal with the eyepieces, if your dSLR setup do not accomplish this it will be much less convenient to work. And as Rik said you're pushing the objectives far from its desing point.

- The amount of aberrations shown is IMO too high to be due just to the above problem, in special with low power objectives that are usually fairly tolerant to changes of the "tube lengh"

- Most if not all infinite corrected modern microscopes have the tube lens inside the trinocular head in the common optical path for eyepieces and photoport. If the Leica infinite objectives do need any kind of secondary correction it will be done in the tube lens, so this isn't likely the problem.

- With a APS-C dSLR the total relay magnification for an eyepiece FN of 18-20mm is about 1.5X-1.6X. If your scope is a largefield one the 1X adapter sugested by the retailer may be adequate to fill the sensor. Your Leica 0.63X C-mount adapter would not provide good coverage for your Canon. If it does, likely you're placing the camera sensor at a much different position of the relay lens than expected. This may be the cause of your parfacality and aberration issues. So perhaps he is right.
You can test it removing the 0.63X adapter and holding the camera with a tripod or repro support over the trinocular tube in a position that was parfocal, if it is posible.

- If you can post pictures of the microscope with both cameras and of the dSLR adapter it may be useful to understand the problem.
_________________
Pau

[Charles Krebs]

[rjlittlefield]

[yminter]

Here is a detail of the C-mount adapter; I had made a mistake between this one and the one of our binocular : this one is a 0.5X and not a 0.63X!
I don't understand the end of this marking (the ^= 16 ) if you know what this means ...


And another one of the whole setup.

I tried to place the adapter and DSLR directly over the tube => it works without image aberration but there is a large focus offset : to get it parfocal with the oculars it needs to be around 10cm over the upper end of the tube.

=> It looks like it's clearly the 0.5X C-mount adapter that creates the problem.

I tried the same with the binocular but did not succeed in getting an image but since the trinocular head has a tilt capability, it's rather difficult to place it in a stable manner.

[Charles Krebs]

Are there any optics in, or markings on the "black tube" adapter attached to the camera?

In any event, as I mentioned earlier, the 0.5X C mount adapter doesn't belong there when using a camera with an APS-C sized sensor. That adapter is made for cameras that use a 1/2" sensor (6.4x4.8mm, diagonal of 8mm).

[yminter]