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Natural Science Forum / Physics / Optics / March 2007Green Filter
I have a microscope which came with a blue and a green filter. I use the blue to create a white background. I can find anyone that knows what you would use the green filter for. Any help? Hello, the green filter is for illumination for phase-contrast according to Zernike. As the human eye has its maximum sensibility in the green part of the optical spectrum, chromatic errors of the achromatic objectives are minimised ba the green filter. Kind regards Rainer Teubner sathered@wvi.com schrieb: > I have a microscope which came with a blue and a green filter. I use the blue to > create a white background. I can find anyone that knows what you would use the > green filter for. Any help? > Hello, > [quoted text clipped - 13 lines] >> use the >> green filter for. Any help? The green filter is used for B&W (film) photography, especially when using achromatic objectives. Black and white photographic film has a different sensitivity for the colour spectrum than the human eye (and no 'correction in the brain'). The chromatic aberrations of an objective will be more visible in an B&W photo, than what appears when we look through the oculars. A green filter is used to reduce the effects of chromatic aberration. PS: I'm not sure of the differences in practice between using Pan-chromatic or Ortho-chromatic B&W film, the latter is not sensitive to red light.  SignatureTrond Kvitvik (M.Sc Botany) Fin-00170 Helsinki Address & Tel: "http://home.no.net/tkvitvik/images/address.gif" Hi, you are not creating "white light" with a blue filter! As lenses are something like round prisms, light containing all wavelength from red to blue would be split up each time light is reflected or bent, resulting in chromatical aberrations. So it makes sense to take one part only, the red or green or blue section. As resolution is depending on the wavelength, is makes sense to take short wavelength light: blue That's what the blue filter is for! On Mar 28, 7:37 am, sathe...@wvi.com wrote: > I have a microscope which came with a blue and a green filter. I use the blue to > create a white background. I can find anyone that knows what you would use the > green filter for. Any help? yours, Heinrich >Hi, >you are not creating "white light" with a blue filter! [quoted text clipped - 14 lines] >yours, >Heinrich The "white background" is the topic. It is a color temperature issue. There are blue filters that are indeed blue. I suspect the one you have is a daylight correction filter. This converts the 2900K halogen to 5500K daylight for daylight color film. Of course it isn't exact since much depends on the intensity of the halogen light source. But assuming it is around 2900K, then the conversion is good. The green filter has several uses but I think the main one is for high contrast with b/w film. It can also be used with monochrome CCD cameras. gg Kiss French. Drink California. gary at gaugler dot com >>Hi, >>you are not creating "white light" with a blue filter! [quoted text clipped - 35 lines] > > gary at gaugler dot com Gary, One point is that there are soooo many "blue" and "green" filters. Now mostly green filters are used for things like phase contrast or for making a better looking specimen by restricting the range wave lengths of incoming light to the objective. If you restrict the wavelengths you get an apochromatic effect with achromat objectives as long as the specimen is naturally black and white like chromosomes. Now with interference filters its real easy to get exactly the blue or green the customer wants. When I started my company I thought I'd always keep a blue filter in my tool box and when a customer needed one I'd throw the new one on the microscope, thus ends the discussion. Jeez was I ever wrong. Either it was to blue or not blue enough, to thick or not thick enough. I hope I finally threw it out of my speeding car! There are a bunch of filters to try if you want to fool around with the instrument, blues, greens and (my fave) didymium. Thanks, Kevin Cunningham SMS What type of green filter is it? If it is a color contrast filter, you can use it to enhance contrast for certain specimen. You most like use then a B&W image sensor. If it is an interference filter, you can use it for phase contrast illumination to improve the phase contrast effect. Cheers, Gregor PS: The following is from one of my old web pages: Color Contrast Filters These filters are chosen to be complementary in color to whatever color in the object is to appear dark on B&W film. For instance, take a red R(25A) filter if you want the blue sky to appear black. Mostly, these filters are based on selective absorption and transmission. The glass filters from HOYA type red R(25A), green G(X0), orange 85B, and yellow Y(K2) are examples. Didymium Filters These are special filters to improve the reproduction of certain biological stains (such as Eosin). It is a recommended filter to be used when looking at histology sections with H&E stain. The filters SCHOTT BG-20 and HOYA V-10 are examples. Color Correction Filters These filters are used to change the color temperature of of the light source illuminating an object. The glass filters from HOYA type 80A and 80B are examples. Polarizing Filters These filters have a preferred vibrational direction and hence transmit preferentially light whose plane of polarization is parallel to a particular axis of these filters. The filters from HOYA type PL and PL-CIR are examples. Blocking Filters These filters block frequencies above or below a certain frequency. Examples are UV and IR blocking filters. IR blocking filters are also known as heat filters. The filter SCHOTT KG1 is an example. Interference Filters Instead of selective absorption and transmission, these filters function by selective reflection and transmission. The have the advantage of providing a narrow bandwidth and usually avoid the built-up of heat. Green interference filters are an example, which are used for phase contrast microscopy. Neutral Density or Grey Filters These filters are used to decrease the intensity of light but keep the color temperature unchanged. The glass filters from HOYA type NDx2, NDx4, and NDx8 are examples. >I have a microscope which came with a blue and a green filter. I use the >blue to > create a white background. I can find anyone that knows what you would use > the > green filter for. Any help? |
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