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Oblique illumination question

 
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germpore



Joined: 02 Nov 2011
Posts: 3

PostPosted: Wed May 09, 2018 5:54 pm    Post subject: Oblique illumination question Reply with quote

I have a few questions about the underlying mechanism of oblique illumination, which I don't entirely understand. I know that when one blocks one side of the light path and has the remaining light transmit through the specimen off axis, the position of the zero order of light is shifted off-center, and more orders of light are captured on one side of the zero order than the other.

If I'm not mistaken, the orders on one side of the zero order are referred to as "sidebands" and those that are captured without the corresponding order on the other side are "single sidebands". (Correct me if I'm wrong in my understanding of terminology here.)

The part I don't understand - apparently the interaction of single sidebands with the zero order will undergo optical interference that is visible as relief differences in the final front focal plane image. What I'm not clear about is why optical interference takes place when you have single sidebands but not when you have both sidebands of an order present, as you do in bright-field.

I'm also unclear as to why the path-length differences manifest as differences in relief of the image rather than the amplitude differences seen in phase-contrast microscopy.

Also, because of the uneven capture of orders of light, resolution on the side of the specimen facing the direction of incident light is better than on the opposite side of the image, correct?
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