Very bad image quality when using polarizers on a microscope, why?
Posted: Fri Apr 02, 2021 5:36 am
Hi,
I
started a thread at Photomacrography.net but I will do it also here, as it is more microscopy oriented
I realised I am getting very bad image quality when using polarizers, I have one on top of the source light and another one (Analyzer) between the microscope body and trinocular head (firstcut from 3D cinema glasses but I just receivednew filters ), the effect is not so evident at high magnification I guess due to higher effective f number but at low magnification with high NA lenses quality is pretty bad, fuzzy sometimes like double image. As you move focus the out of focus areas become very weird.
I was leaving the analyzer inside all the time as I thought without the polarizer on the source light was not doing anything; I was clearly wrong.
What is causing this? the filter being too far away from the camera? the prisms in the trinocular head? Is it the type of filter? Placing the filter close to the camera seems to solve the problem but I do not know if may cause some loss of contrast maybe from sensor reflections..
This is why some low magnification stacks were looking kind of weird, closing condenser iris fixed it somehow..
100% 400x400px central crops, with (right) and without the filter (left); no filter on the source light. Nikon CF Fluor 10/0.50, subject is a piece of printed paper with no cover glass, still shows the difference.
Ok, it is clear to me that second polarizer (analyser?)placement has a big effect on the image quality; this time both polarizers in use.
Again 100% crops with Nikon CF Fluor 10/0.50; the first picture (left) is with analyzer 2cm away from camera sensor, second one (right) with it just bellow trinocular head. I feel so stupid...
One more with (right) and without the analyser (left), apart from 1EV light loss it does not seem to affect resolution that much
The only bad thing ( quite bad) is now I only see the effects on the camera, not on the eyepieces but the camera part is more important to me. I found a provisional solution though, did buy two 34mm filters (I am using one bellow the camera) and two 27mm; the 27mm filters fit perfect in the olympus eyepieces, I can use those when using polarizers, just have to rotate them to have same effect as in the camera
Still not sure if the issue is solve, maybe filter not being 100% flat is causing the problem, sometimes I see that weird effect sometimes I do not.
And a couple more tests, with and without filter (analyzer) close to the camera with fluor 10 and CFN 40 PlanAchro; condenser focused and iris wide open
There is some quality loss but this is a 10$ filter, I have been told a good analyser is 500$; I can live with it anyway. Weird enough with the CFN 40 seems to be a little bit less purple fringing with the filter on
I
started a thread at Photomacrography.net but I will do it also here, as it is more microscopy oriented
I realised I am getting very bad image quality when using polarizers, I have one on top of the source light and another one (Analyzer) between the microscope body and trinocular head (firstcut from 3D cinema glasses but I just receivednew filters ), the effect is not so evident at high magnification I guess due to higher effective f number but at low magnification with high NA lenses quality is pretty bad, fuzzy sometimes like double image. As you move focus the out of focus areas become very weird.
I was leaving the analyzer inside all the time as I thought without the polarizer on the source light was not doing anything; I was clearly wrong.
What is causing this? the filter being too far away from the camera? the prisms in the trinocular head? Is it the type of filter? Placing the filter close to the camera seems to solve the problem but I do not know if may cause some loss of contrast maybe from sensor reflections..
This is why some low magnification stacks were looking kind of weird, closing condenser iris fixed it somehow..
100% 400x400px central crops, with (right) and without the filter (left); no filter on the source light. Nikon CF Fluor 10/0.50, subject is a piece of printed paper with no cover glass, still shows the difference.
Ok, it is clear to me that second polarizer (analyser?)placement has a big effect on the image quality; this time both polarizers in use.
Again 100% crops with Nikon CF Fluor 10/0.50; the first picture (left) is with analyzer 2cm away from camera sensor, second one (right) with it just bellow trinocular head. I feel so stupid...
One more with (right) and without the analyser (left), apart from 1EV light loss it does not seem to affect resolution that much
The only bad thing ( quite bad) is now I only see the effects on the camera, not on the eyepieces but the camera part is more important to me. I found a provisional solution though, did buy two 34mm filters (I am using one bellow the camera) and two 27mm; the 27mm filters fit perfect in the olympus eyepieces, I can use those when using polarizers, just have to rotate them to have same effect as in the camera
Still not sure if the issue is solve, maybe filter not being 100% flat is causing the problem, sometimes I see that weird effect sometimes I do not.
And a couple more tests, with and without filter (analyzer) close to the camera with fluor 10 and CFN 40 PlanAchro; condenser focused and iris wide open
There is some quality loss but this is a 10$ filter, I have been told a good analyser is 500$; I can live with it anyway. Weird enough with the CFN 40 seems to be a little bit less purple fringing with the filter on