Desmid image: DIC background correction

[gekko]

Cosmarium image under DIC (I have posted a brightfield image of the same desmid here: viewtopic.php?f=6&t=2364 ).
The view through the eyepiece shows a neutral grey background, yet the image captured by the camera on my system (Nikon Optiphot microscope & Olympus E-P1 camera body) shows a distinct cyan background. I don't really know why this is. The first image is the image as captured by the camera, and in the 2nd image I've desaturated the background, which is what I saw through the eyepieces. If anyone has an idea why the cyan background, I would be very happy to learn. My current suspicion is that it may have to do with the polarizers, but this is only an uninformed guess. I will try next time to use a different polarizer (though the analyzer cannot be easily changed). Thank you for looking and for any clues.

[billbillt]

Very fine DIC images...
Billt

[gekko]

Many thanks, BillT, for your kind comment.

[Raul]

Very nice images gekko, tell me did you use this technique for DIC (http://www.microscopy-uk.org.uk/mag/ind ... iydic.html) a filter, or do you have accesss to the real thing?

[75RR]

Perhaps you could remove the camera and look through the projection eyepiece, it might help to isolate the problem.

[JimT]

That is a nice image of the cosmarium. I have no idea why the cyan background. As you said, maybe the polarizer.

[gekko]

Raul and JimT, many thanks for your comments.
75RR, many thanks for your good suggestion. I'll try removing the camera and projecting the image on a piece of white paper to see what I get.

[zzffnn]

gekko,
Have you tried using custom white balance or kevin temperature option of your camera? You can adjust DIC first with a subject, then move to a blank part of your slide and tell camera "use this as white or grey".

[gekko]

Thank you zzffnn for your suggestion. Yes I have, and I do get a neutral background but the colors don't look the same. Which method is better I don't know, Because I don't know why the camera sees blue whereas my eyes see grey. What I do now is set custom white balance in bright field and leave it there for DF, DIC, POL, and phase, my (il)logical argument being that, cameras apart, people don't adjust the light color temperature with filters, etc. when changing the contrast or illumination method.
But I'll try your suggestion again. And I will also try 75RR's suggestion of looking at the light that the camera sees. The third thing to try is a different polarizing filter. The reason for the latter is that some filters, when crossed, pass some light in the short end of the visible spectrum (dark purplish blue). Without disassembly, I cannot take out the analyzer, but even if I could, I cannot replace it.
Thanks again.

[zzffnn]

My apologies. Now I remember that you mentioned it before in another thread. I did hesitate a bit, before I mentioned custom white balance, as it is obvious for an experienced photographer/microscopist like you.

Did your polarizer/analyzer combo come from a microscope manufacturer such as Nikon? If so, they should fully extinct when crossed. Camera polarizers may not.

If you want to change your polarizer:
I heard, from photomacrography. net, that many members there like TechSpec polarizering film as polarizer and dedicated microscope glass analyzer (not the other way around and they have done experiments). You want to sandwich the film between glasses before putting it over a hot light source though.

[gekko]

Thanks again, zzffnn. No apologies are called for. I am very likely to overlook things (even things I know), so your reminder was certainly in order.
The polarizers are "native" to my Optiphot and the analyzer is "built-in" and replacing it (other than with an identical spare part) requires "surgery" which I am loath to undertake, especially when I don't really know the reason for the cyan background I get. It is not a major problem, but I am curious why this happens.
By the way, I just checked by crossing the microscope polarizer with a camera polarizer and I get complete extinction.
Thanks again for your interest and suggestions.

[zzffnn]

^ In that case, you probably don't need to replace the polarizer, unless yours has been burned severely. A replacement may not provide better quality (dedicated microscope polarizers/analyzers are said to be the best for your application).

Did you replace your Nikon polarizer with a camera polarizer and shoot a DIC photo to judge its quality? I am just curious. In some cases, human eyes are not as sensitive ad camera sensors. And amount of light may matter too (seemingly full extinction at low light may not be so at strong light)?

[gekko]

Did you replace your Nikon polarizer with a camera polarizer and shoot a DIC photo to judge its quality? I am just curious. In some cases, human eyes are not as sensitive ad camera sensors. And amount of light may matter too (seemingly full extinction at low light may not be so at strong light)?

I'll do that next time I use the microscope. Thanks for the suggestion.

[gekko]

Very nice images gekko, tell me did you use this technique for DIC (http://www.microscopy-uk.org.uk/mag/ind ... iydic.html) a filter, or do you have accesss to the real thing?

Many thanks for your comment. No, I did not use the method in the link you provided, but thank you for the interesting link. My microscope has "real" DIC,