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PostPosted: Mon Jul 29, 2019 2:37 pm 
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Has anyone tried this method? If so, what does the author mean when he says "Imagine a small opaque (black) disk attached in the middle of the objective lens..." (near top of second page)? Does the dot need to be in the middle of the objective lens or could it be at the top/readily accessible part of the objective?

http://www.staff.science.uu.nl/~hooft10 ... ntrast.pdf

Heather


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PostPosted: Mon Jul 29, 2019 3:36 pm 
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Sauerkraut wrote:
Has anyone tried this method? If so, what does the author mean when he says "Imagine a small opaque (black) disk attached in the middle of the objective lens..." (near top of second page)? Does the dot need to be in the middle of the objective lens or could it be at the top/readily accessible part of the objective?

http://www.staff.science.uu.nl/~hooft10 ... ntrast.pdf

Heather

First; Thanks for the interesting link, Heather

I'm almost certain that the author simply means the disk to be concentric with the objective lens, and that he is contemplating a fairly simple objective, not a complex multi-element design.

MichaelG.

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PostPosted: Mon Jul 29, 2019 6:01 pm 
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Thank you for the clarification. I'll give this method a try.


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PostPosted: Mon Jul 29, 2019 6:13 pm 
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Hi Heather,

Thanks for the link!... It looks doable...

The Best
BillT


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PostPosted: Mon Jul 29, 2019 6:15 pm 
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An interesting idea from a Physics Nobel Prize Laurate. Thanks for the link, Sauerkraut.
My understanding is that the dot or disk is to be placed on the rear glass surface of the objective.
On the other hand, I wonder how easy it is do actually make and attach that disk. Would have been nice to see a real-world example. My new unbranded 4X0.1 plan objective looks a good candidate... ;)

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PostPosted: Mon Jul 29, 2019 8:02 pm 
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Hobbyst46,

For my first attempt I'm going to try placing dots of various sizes on plastic discs, made from salvaged plastic packaging. There would likely be some distortion from the plastic but it could be enough to prove concept without putting dots directly on the objective lens.


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PostPosted: Tue Jul 30, 2019 2:53 pm 
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So far small dots have achieved no noticeable changes and larger dots have given very nice dark field. It's possible the dot needs to be directly on the lens or very close.


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PostPosted: Tue Jul 30, 2019 4:01 pm 
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Sauerkraut wrote:
So far small dots have achieved no noticeable changes and larger dots have given very nice dark field. It's possible the dot needs to be directly on the lens or very close.

That appears to be what the author illustrated ... Although, of course, it's only a diagram not a scale drawing.

MichaelG.

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