Piracetam crystals

Images made through a microscope. All subject types.

Moderators: rjlittlefield, ChrisR, Chris S., Pau

rjlittlefield
Site Admin
Posts: 23693
Joined: Tue Aug 01, 2006 8:34 am
Location: Richland, Washington State, USA
Contact:

Post by rjlittlefield »

bromodomain wrote:Thanks for the explanation! If I use light of a certain wavelength am I going to see light intensity differences instead of colour differences?
That is certainly what I'd expect. Haven't done the experiment though.

--Rik

Ecki
Posts: 775
Joined: Wed Aug 13, 2008 2:04 am
Location: Cape Town, South Africa
Contact:

Post by Ecki »

The explanation for the usage of the neutral grey filters is correct - they control the light intensity without changing the color temperature.

Here we go demystifying the green filter, too ...

Achromatic objectives are corrected for green. With a green filter they produce an image without any chromatic aberration - the same an Apochromat with the identical NA would produce. Using a green filter was standard practice and every microscope came with it.

In phase contrast a green filter will give you the best image, too. Although the phase object is not absorbing light (thus being invisible in bright field) , it is retarding the lightwave by 1/4 of the wavelength. Through the phase ring in the objective the phase shift between retarded and not retarded light is increased to 1/2 of the wavelength to enable the interference that gives us the phase contrast image. To calculate the phase ring of the objective green light was used as the reference wavelength. Therefore, phase contrast works best with a green filter.

Combining these allowed even achromatic phase contrast objectives to produce an high contrast image without any chromatic aberration.

Green was chosen because the eye is most receptive to green.

Cactusdave
Posts: 1631
Joined: Tue Jun 09, 2009 12:40 pm
Location: Bromley, Kent, UK

Post by Cactusdave »

Thanks for that nice explanation of the use of the green interference filter Ecki. It is one of those pieces of microscope 'lore' that I was taught, but alas these days has gone into 'off line storage' :wink: .
Leitz Ortholux 1, Zeiss standard, Nikon Diaphot inverted, Canon photographic gear

bromodomain
Posts: 156
Joined: Sun Jan 02, 2011 11:50 am

Post by bromodomain »

Ecki wrote: Achromatic objectives are corrected for green. With a green filter they produce an image without any chromatic aberration - the same an Apochromat with the identical NA would produce. Using a green filter was standard practice and every microscope came with it.
Excellent, thank you very much! So the green filter turns a simple achromatic objective into something rather like a plan-achromat? If I use it for photomicrography how do I render the images in their original (ie non-green) colour?

EDIT: doh! I was thinking of spherical aberration. Yes I see what you mean now, I was looking for correction of spherical aberration, my bad. I think I'll get used to the green filter. Normally I'd never go without a regular blue glass filter. Which one would you use?
Last edited by bromodomain on Fri Jul 08, 2011 1:23 pm, edited 1 time in total.

Ecki
Posts: 775
Joined: Wed Aug 13, 2008 2:04 am
Location: Cape Town, South Africa
Contact:

Post by Ecki »

Achromatic objectives are corrected for green. With a green filter they produce an image without any chromatic aberration - the same an Apochromat with the identical NA would produce.


Of course this only works because the non corrected colors are suppressed. You will have a monochrome image. Restoring the color information for microphotografy is impossible.

bromodomain
Posts: 156
Joined: Sun Jan 02, 2011 11:50 am

Post by bromodomain »

So its good for black&white photomicrography?

Post Reply Previous topicNext topic