Eyepieces different brightness

[aztk]

Hello, I've got an Optech binocular microscope and noticed that the right eyepiece is quite less bright than the left (the one with diopter correction).
The prisms seem fine, but the distance between the prism and the right eyepiece is bigger (longer tube).

Is the different brightness normal?
I don't remember noticing this on other microscopes.
It is very dim on x400 and I suppose will be virtually unusable under greater magnification.

[MicroBob]

Hi,
it is not unusual that the two optical ways are somewhat different in colour or brightness as the light pathes are different. A severe difference is not usual and might be the result of a delaminated prism. The air layer between the components leads to reflection losses.

Bob

[apochronaut]

If the microscope is a used one, sometimes they can spend some time sitting with one eyepiece out, allowing some dust to settle in on one of the upper prism surfaces or optical window.

[PeteM]

I've also seen differences in some heads if/when polarizers are inserted in the path.

[aztk]

Hi, thanks for the answers. I suppose a delaminated prism must be the problem, although visually couldn't find anything.

[MicroBob]

You can try tro relaminate them:
- Let a couple of drops of xylene soak into the gap
- Apply a 1:1 canadabalsam-xylene mix
- heat to 60°C
- Reapply mix if necessary to keep the gap filled

There is always the risk to do more harm than good - your decision

[Wes]

Did you try switching the eyepieces? In other words is the problem at the eyepiece or the binocular head?

I had similar experience (albeit not a huge difference in brightness) and found out it was the result of light polarization due to the reflection inside the binocular head. Place a polarizer in the optical path and slowly rotate it to 180°, you may notice a point where the brightness is equal and then it inverts so that once the brighter eyepiece gives a dimmer image.

BR
Wes