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Diopters for soft-focus background effect


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#1 Matt Irwin

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Posted 13 April 2007 - 12:41 PM

I have an HVX project coming up that requires soft to completely out of focus backgrounds on dialogue coverage. 35mm adapters are no-go due to budget constraints, as well as the 2-stop light loss through the relay.

The idea popped into my head to try diopters (like the schneider achromatics or similar), since they effectively shift inifinity closer to the lens and therefore should throw the background more out of focus than the stock lens normally would.

Has anyone ever tried this? Am I crazy?
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#2 Michael Nash

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Posted 15 April 2007 - 11:06 PM

Close focus diopters simply compress the entire focus range closer. You can buzz the background as long as you don't mind your sharp focus being only mere inches from the lens...
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#3 Phil Gerke

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Posted 23 April 2007 - 10:38 PM

Close focus diopters simply compress the entire focus range closer. You can buzz the background as long as you don't mind your sharp focus being only mere inches from the lens...


I have no experiance with diopters. Are there any drawbacks or does it simply make your minimum focus closer?

Thanks!
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#4 Michael Nash

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Posted 25 April 2007 - 04:10 PM

I have no experiance with diopters. Are there any drawbacks or does it simply make your minimum focus closer?


They are basically like magnifying glasses that attach to the front of your taking lens. Sometimes they're not as optically "pure" as a decicated macro lens, but much simpler (and often cheaper) to use. You might get chromatic distortion, lowered contrast and sharpness compared to your lens without the diopter, but since close-focus is usually only used for tight inserts it's usually not a problem. If you were doing an entire project that needed close focus (like a documentary on insects or something), then you might be better off using lenses that have better close-focus capability, instead of diopters.

Most ENG/HD zoom lenses and even prosumer cameras have a macro-focus element at the rear that defeats the need for separate close-focus diopters. It just so happens that the HVX200 doesn't have a macro.
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#5 Michael Nash

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Posted 25 April 2007 - 04:24 PM

I have no experiance with diopters. Are there any drawbacks or does it simply make your minimum focus closer?

Like I said they compress the entire focus range, not just the minimum focus. The focus marks on your lens are altered by the power of the diopter. In practice you just set focus by eye, since it's impractical to try to figure it mathematically.

They are basically like magnifying glasses that attach to the front of your taking lens. Sometimes they're not as optically "pure" as a decicated macro lens, but much simpler (and often cheaper) to use. You might get chromatic distortion, lowered contrast and sharpness compared to your lens without the diopter, but since close-focus is usually only used for tight inserts it's usually not a problem. If you were doing an entire project that needed close focus (like a documentary on insects or something), then you might be better off using lenses that have better close-focus capability, instead of diopters.

Most ENG/HD zoom lenses and even prosumer cameras have a macro-focus element at the rear that defeats the need for separate close-focus diopters. It just so happens that the HVX200 doesn't have a macro.
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#6 Chris Keth

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Posted 30 April 2007 - 02:44 PM

Like I said they compress the entire focus range, not just the minimum focus. The focus marks on your lens are altered by the power of the diopter. In practice you just set focus by eye, since it's impractical to try to figure it mathematically.


A nice rule is that the reciprocal of the diopter number is the maximum focus distance in meters, so a +3 diopter would focus from damn close out to 33cm.

For the OP: Unfortunately, tricking physics is isn't that easy. Depth of field is still linked to enlargement size and aperture. There's no getting around that so a given framing at a particular aperture will always have the same DoF, no matter what combination of subject distance and focal length you use.
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#7 Satsuki Murashige

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Posted 30 April 2007 - 11:08 PM

I have an HVX project coming up that requires soft to completely out of focus backgrounds on dialogue coverage.

You've probably already thought of this, but what about setting up a large gel frame with a very light diffusion like Hampshire frost and putting that behind your subjects? Or if that would make too much noise, then a large piece of Plexiglas with vaseline smeared on it.

Or a custom tilt/shift lens setup? That would probably be a bigger headache than diopters.

Or you could simply use a telephoto adpater/converter on the lens - boring, but probably the most practical solution.
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#8 Chris Keth

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Posted 01 May 2007 - 09:42 PM

Or you could simply use a telephoto adpater/converter on the lens - boring, but probably the most practical solution.


That won't work either. Those converters just change the focal length. To get the framing he wants he'll ahve to just get farther away from the subject, putting the depth of field right back where it was when he was closer without the converter.
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