Glistering on image center from camera adapter

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Naphthalene
Posts: 124
Joined: Sun Mar 29, 2015 7:34 am
Location: Moscow, Russia

Glistering on image center from camera adapter

#1 Post by Naphthalene » Sat Jan 30, 2021 4:39 pm

Hello!
I have recently purchased a used Olympus OM-D EM-5 camera and attempted to use it with my microscope. I got an inexpensive 2X DSLR camera adapter from e-bay for mounting this camera on the eyepiece tube and c-mount phototube. Much to my regret this adapter causes glistering/flare/fleck (sorry I don't know the proper word for this artifact) in the center of my images no matter if I mount the camera on the eyepiece or phototube.
Image

When I attempted to use a dual c-mount (male/female thread) adapter with 2x magnification and the glare was even brighter.
Image
Changing the field and condenser aperture settings do not solve this problem

This is not observed when I replace this adapter with a simple lens-free micro 4/3-c-mount adapter or when I use other cameras.
Image

Could you provide me some clues what is the root of this problem?

Scarodactyl
Posts: 2760
Joined: Sat Mar 03, 2018 9:09 pm

Re: Glistering on image center from camera adapter

#2 Post by Scarodactyl » Sat Jan 30, 2021 7:56 pm

Easy to tell--remove your camera and look down the tube with the lights on. You'll see where the flare is coming from. It's even possible it's an accessible sirface you could flock.

MicroBob
Posts: 3154
Joined: Sun Dec 25, 2016 9:11 am
Location: Northern Germany

Re: Glistering on image center from camera adapter

#3 Post by MicroBob » Sat Jan 30, 2021 9:38 pm

So you have two different adapters for you new camera and get the hot spot with only with the one with 2x lens? This might be an incompatibility of the flat sensor and the inner lens surface of the adapter. Flat glass surfaces in direction of the sensor can sometimes have this effect. I had this problem with a 1970s Tamron macro camera lens. I was also astonished to get this problem with my Pentax Q when mounted on my Zeiss Phomi 1. The same microscope and adapter, but different camera and camera lens and no hot spot. Same camera setup on other microscopes - no hot spot.

Bob

mootoom
Posts: 4
Joined: Sat Mar 27, 2021 8:12 pm

Re: Glistering on image center from camera adapter

#4 Post by mootoom » Sat Mar 27, 2021 11:43 pm

A T2 ring with adapter without optic that slot directly into trinocular/eyepiece have a very high chance of introducing optical artifact. An eyepiece is design such as way that lenses are place in the right distance to project the light before the reflection occur.

https://en.wikipedia.org/wiki/Eyepiece#Eyepiece_designs

I have a T2 ring to 23mm adapter that allow me to slot directly into trinocular tube/eyepiece tube, it show a grey halo ring on the image.

Then I get a T2 ring to 1.25inch (31.75mm) adapter that fit he 23mm eyepiece, the ring is gone. However, there is a catch : Longer eyepiece will protrude into your camera. I put a plumbing sealing ring (you can use band) on every eyepiece to prevent protrusion.

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