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RWR · #31 (**permalink**) 01-20-2012, 01:08 PM

Quote:

Originally Posted by Ruptor

I think common sense dictates the answer for me as well as g2b2's explanation. Light travels in straight lines so if the condenser cross slot exactly matched the objective cross no light would be seen up the tube in a perfect world. Therefore making the slot smaller would definitely block all the light. When a sample is put in the light path of perfectly matched crosses then it would refract and bend the light so some would pass the objective cross and be seen in the eyepiece. It seems logical then that the condenser cross slots should be, if anything, slightly larger so light is guaranteed of getting past the cross especially since it would be impossible to match the crosses exactly.

I think there is a misunderstanding here: the phase plate (phase ring, or, in your case, "phase cross") does not block direct light waves**; it shifts their phase (hence "phase contrast"). You might want to read about this (Wikipedia, or Olympus or Nikon Microscopy sites). Light skirting the "phase cross" will reduce the effectiveness of the technique, just as misalignment of the phase stop in the condenser would.
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** It does absorb part of the light, but that is not germane to the phase contrast method.

Ruptor · #32 (**permalink**) 01-24-2012, 11:30 PM

I have made a narrower cross than I had and I get the characteristic beige background with the fine lines around features but I don't have anything to compare my image against. As I wind the focus up and down the feature lines change with the contours so I guess the system is working.

One area had some refracted colours but I guess it depends upon what one has as a sample. If someone could suggest a standard sample to look at that with a x40 phase contrast set up where I could compare the images it would be appreciated.

MitchM · #33 (**permalink**) 01-24-2012, 11:53 PM

Most flies, mosquitos, houseflies, butterflies and moths have wing scales. They seem to be one of the things that everyone shoots, so there should be plenty around of 40x. I even have some if that's what your looking for.

Ruptor · #34 (**permalink**) 01-25-2012, 01:06 AM

Hi Mitch
I want to get an idea of how good or bad my Cross Phase Contrast system is but when I compare it to images here
Illumination in Microscopy. Phase Contrast Illumination.
and here
http://www.microscopeforums.com/f13/...ject-1265.html
Things start getting blurry.
Mine has the same background as the second image but I don't have thick dark lines and very little refracted colour bits. My image looks nothing like the first example in fact it looks more like the bright field picture on the left of the page. Ideally I would like to see an image from a cross phase contrast system to make a direct comparison really but nobody admits to having one of them scopes and I haven't found anything on the Net.

MitchM · #35 (**permalink**) 01-25-2012, 01:16 AM

Ah, OK. I am using a regular, although older, phase condenser and PH lenses. I believe the scales and even diatoms are great subjects though. They are flat, relatively thin, and the lines in both are more or less a known distance apart, which will tell you if the lens is resolving detail good.

Ruptor · #36 (**permalink**) 01-25-2012, 01:41 AM

Oh no not the Diatom again. I grabbed some pond water and saw all sorts of bugs but I ain't seen a Diatom yet. Are you sure these are not a joke you microscope experts play on new enthusiasts? When I used the purple laser pointer light source I saw some things that came up red and long but they were very small on x40 I could hardly seen them so where do I find some big ones?

MitchM · #37 (**permalink**) 01-25-2012, 02:09 AM

You mean you have not seen a diatom yet? Well, they are very real and beautiful and all sizes or shapes. With a 40x objective and 10x eyepieces, they can still be quite small in the frame and I have seen some that almost fill the frame, but that was a very rare diatom. Some move and some don't, some move slow and some are fast enough that it's hard to keep them in the frame. You'll know it though, when you see one. They are in almost all water too, so you may have already seen some.

Ruptor · #38 (**permalink**) 01-25-2012, 02:15 AM

Ok thanks I will have a snoop around tomorrow.

RWR · #39 (**permalink**) 01-25-2012, 07:40 PM

Another possibility might be to prepare a slide of cheek cells:

Cheek Cells | APPLIE'S PLACE

but don't stain the cells, then compare what you get under your microscope with both bright field (when the phase condenser annulus is completely out of alignment with objective phase ring) and phase contrast in the following Olympus Microscopy Resource Center tutorial (in the "Choose A Sample" drop-down menu select "Cheek Cells"), focus on the cells, then experiment with the effects of the phase annulus alignment.

Olympus Microscopy Resource Center | Phase Contrast Microscopy - Java Tutorial
.

Ruptor · #40 (**permalink**) 01-25-2012, 10:53 PM

Thanks RWR it is a good easy source of cells. From todays tests with pond bugs I am not too impressed with the cross version of phase contrast compared to my bright field set up because it gave less detail and information about the bugs only drawing lines around features. It might come in to its own at high magnifications though where the bright field runs out of steam because it will still give the lines around detail.

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C.Baker Phase Contrast Cross Objective use

C.Baker Phase Contrast Cross Objective use