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Why do I get a white halo?

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Why do I get a white halo?

January 28, 2012
20:34

Gekko

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January 16, 2012

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I frequently get a wide, white halo around my images (e.g., 2nd image in http://www.microbehunter.com/f…..orticella/). Does anyone know why or how do I avoid it? As far as I can tell, the microscope is adjusted properly (field diaphragm, condenser, etc.) Thank you for any suggestions.

January 28, 2012
20:56

Oliver

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September 19, 2010

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Hi,

Diffraction patterns maybe? The halo appears also in other parts of the image, this one is an enlargement of the dark dots towards the top of your image. A light halo can also be seen here.

By closing the condenser diaphragm, the halo should become stronger. Phase contrast optics produce an even stronger halo. Check this post here:

http://www.microbehunter.com/2…..-contrast/

Oliver.

http://www.microbehunter.com – Oliver Kim Science may set limits to knowledge, but should not set limits to imagination. (Bertrand Russell)

January 28, 2012
22:04

Gekko

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January 16, 2012

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Many thanks Oliver for the quick reply, which makes perfect sense. I'll try to see if when I open up the aperture up I can reduce the halo. I try not to reduce the aperture beyond what gives a clear image (usually 70% to 60%, occasionally down to 50% by eye) but I will experiment with its effect on the halo. Thank you so much for taking the time and trouble to actually blowing up my image and examining it at the pixel level!

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