Re: Amount of shear needed for DIC imaging (and provided by Zeiss objectives)

Posted by Barbara Foster on
URL: http://confocal-microscopy-list.275.s1.nabble.com/Amount-of-shear-needed-for-DIC-imaging-and-provided-by-Zeiss-objectives-tp590130p590131.html

Search the CONFOCAL archive at http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal Hi, Shalin

The shear is actually defined by the prisms in the system and it tied to the NA.

Set up DIC then remove the eyepiece and peer down the tube into the back focal plane of the objective.  If everything is set correctly, you should see a white background with a dark fringe in down the middle.  This is an interference fringe, derived from the shear between what can be thought of the real image and the reference image. That shear is created by the prism.  The reason that you don't see a ghost image in conventional DIC (which you WOULD see in other, related techniques, such as Jamin-Lebedeff), is that the shear is smaller than the resolving power of the objective.  Hence the name "differential" (small).

For the DIC background to be even, the fringe pretty much needs to fill most of the back focal plane, so the prism is engineered to fit the NA. 

Since your 40x dry is lower in NA than your oil objective, I would go ahead try the prism. You may have to adjust the compensator a bit further, but it is worth the try.  If one of the Zeiss specialists is "lurking," perhaps they can give you a more definitive answer.

I wrote a comprehensive "lay" article on DIC in American Lab, April 1988 that you might find helpful.  We've tried scanning it but have had problems. I am on the road through 10Sept but can try again after that, if you are interested.  There is also a detailed description in "Optimizing Light Microscopy," and I suspect that there will be dynamic Java tutorials on both the Olympus micro site and the Nikon uUniversity. 

By the way, because of all the mis-interpretation that comes from features in the field that respond to polarized light, I modified my instructions for DIC set up some years ago. The "Foster Method" :
1. Establish Koehler and observe any native color
2. Cross polars and observe any features that are bright against the dark background.  They will respond to the polarizing part of the system rather than the DIC beam shearing part.
3. Insert the DIC prisms (usually in the nosepiece and the MATCHING prism in the condenser)
4. Tune the compensator to soft dove gray background (the article explains why this is the most sensitive position).

Hope this is helpful.  Good hunting!
Barbara Foster, President

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At 09:08 PM 8/26/2007, you wrote:

Search the CONFOCAL archive at http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal Dear List,

What does the shear required by DIC depend on? Magnification or NA? To me it appears that only magnification should matter as DIC measures the phase gradient in direction of shear between two points in space. Any good reference that quantitatively relates magnification/NA to the shear required?

I wish to do time-lapse of live cells in DIC. I have a 40x 0.75 NA and 40x 1.3 NA oil objectives from Zeiss. For the 0.75 NA objective we do not have DIC prism but for 1.3NA we have (as per Zeiss nomencleture DIC III). During time-lapse I see lot of focal drift with oil objective but with air objective focus is relatively stable. Is it alright to use 1.3 NA objective's prism with 0.75 NA objective?

I have taken some images with such configuration and I think the match is not perfect - because when changing the bias retardation by moving prism I do not see transition from positive gradient to zero contrast to negative gradient.

Thanks for all inputs

Best regards
Shalin

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