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Old February 19th, 2006, 01:38 PM   #1
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A different approach to get a shallow DOF

I'm working on a static adapter for Nikon lenses and waiting for parts I've ordered from Optosigma.

This sunday morning I was playing with my set of macro lenses (+1 +2 +3 and +10) to discover what I allready know : macro lenses are positive diopter lenses that incraese the DOF to allow focusing also on very close subjects (but not only on the close ones).

It's exactly the opposite of what we are looking for. Yes, I know that we use them to zoom and focusing correctly on the GG, but...
mmhh... opposite... positive... negative... +1,-1...+2, -2...+3,-3...+10,-10...

I start wondering : if photographers uses positive diopter lenses to encrease the DOF, does the negative diopter ones reduce it ?

Here some exemple of negative diopter lenses

http://www.optosigma.com/Miva/mercha...OS&SCREEN=SRCH

Sorry for my poor English but I hope it's clear what I mean.
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Old February 19th, 2006, 01:51 PM   #2
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i could be wrong but i dont believe the macro will effect your DOF because its just used to magnify the projected image off the gg
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Old February 19th, 2006, 02:31 PM   #3
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I could be wrong too, but this means that if you use a negative diopter lens (that work in the opposite way) you will have a smaller image, so you have to zoom inside it and more you zoom less DOF you have.
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Old February 19th, 2006, 02:45 PM   #4
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DOF using macros in front of camera lens

Marco, I'm not 100% sure I get your point perfectly...but let's try: using a macro in front of your lens will indeed give shallower DOF but make focusing beyond a maximum distance (decreasing proportionally with the macro's positive diopter value) impossible. This is why such an add on lens is called a macro.
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Old February 24th, 2006, 02:14 PM   #5
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Quote:
Originally Posted by Marco Polimeni
I could be wrong too, but this means that if you use a negative diopter lens (that work in the opposite way) you will have a smaller image, so you have to zoom inside it and more you zoom less DOF you have.

but you're zooming in on a projected image.. the projected image wont change.. (DOF wont change) the only outcome i can see is a degraded image because it is smaller and requires more zoom.
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Old February 24th, 2006, 07:34 PM   #6
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I believe he's asking if using a negative diopter filter will eliminate the need for a gg screen by simply changing the DoF. I don't know the answer, but that's what I read.
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Old February 24th, 2006, 07:35 PM   #7
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Quote:
Originally Posted by Andrew Todd
but you're zooming in on a projected image.. the projected image wont change.. (DOF wont change) the only outcome i can see is a degraded image because it is smaller and requires more zoom.
Ardew, I'm not talking about an srl lens adapter with a gg but just about a an optical device like divergent lens that reduce the DOF and works like a macro lens but in the opposite way and that is much more easy to screw on the standard camcorder lens.
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Old February 24th, 2006, 07:42 PM   #8
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i see...sorry about my confusion...
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Old February 25th, 2006, 09:58 AM   #9
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It'll only work when you have the subject right up to the front of the lens - at silly distances that you wouldn't really find practicable in real-life situations.
I've tried it and it isn't the Holy Grail of shallow DOF - that is still a function of larger CCDs only I'm afraid.

Robin
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Old February 25th, 2006, 10:05 AM   #10
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Originally Posted by Robin Davies-Rollinson
It'll only work when you have the subject right up to the front of the lens - at silly distances that you wouldn't really find practicable in real-life situations.
I've tried it and it isn't the Holy Grail of shallow DOF - that is still a function of larger CCDs only I'm afraid.

Robin
Robin, do you mean you've done a test with a -10 lens ? (and for "-" I mean "minus" or negative lens, not a positive +10 macro lens).
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