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retrofocus lens


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#1 Lee Young

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Posted 09 June 2007 - 10:08 PM

I was just wondering how to use retrofocus lenses. I have a 10mm angenieux lens that goes under this title. Is the depth of field table for this lens the same as what I would see on another 10mm lens? Is it always set on infinite focus? If I had a depth of field of 10 feet where would it start and end? Thanks for any help you can give me. I wasn't able to find it anywhere else.
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#2 Laurent Andrieux

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Posted 10 June 2007 - 05:26 AM

On my point of view, the fact it's a retrofocus doesn't matter. Use the DOF tables or calculators just the same as a normal lens.
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#3 Stephen Williams

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Posted 10 June 2007 - 05:59 AM

On my point of view, the fact it's a retrofocus doesn't matter. Use the DOF tables or calculators just the same as a normal lens.


Hi Laurent,

As most wide angle lenses are retrofocus & long lenses are of telephoto design, standard DOF tables will work fine.

Stephen
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#4 Charles MacDonald

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Posted 10 June 2007 - 07:45 AM

Hi Laurent,

As most wide angle lenses are retrofocus & long lenses are of telephoto design, standard DOF tables will work fine.

Stephen

Retro focus really means that the lens has a backfocus distance longer than the focal length. for example many cameras have a flange to film distance on the order of 40-50mm, which allows for things like viewers and the shutter. so to have a lens of say 10mm it must actually be of the retro-focus design to allow for the needed space. (They often will look like the front eleiment is a negative lens).

As far as the film is concerned it is as if the lens was phyicaly closer than is posible.

In the case of telephotos, they do the oposite so that a 6 inch (150mm) does not have to be phyicaly 6 inches from the film. ( I have an old c mount 6 inch lens, and it looks impresive with a long alluminum barrel)
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#5 Daniel Madsen

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Posted 10 June 2007 - 08:04 AM

Retro focus really means that the lens has a backfocus distance longer than the focal length



I would call this an inverse telephoto design.
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#6 Stephen Williams

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Posted 10 June 2007 - 08:06 AM

I would call this an inverse telephoto design.


Hi,

It's the same thing.

Stephen
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#7 Lee Young

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Posted 10 June 2007 - 08:18 PM

my question is sense there is no selective focus, where does my depth of field start from. This may be a very naive question, but I am not use to a lens that does not have focus selection. I am assuming that I treat it like infinity focus?
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#8 Charles MacDonald

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Posted 10 June 2007 - 08:52 PM

my question is sense there is no selective focus, where does my depth of field start from. This may be a very naive question, but I am not use to a lens that does not have focus selection. I am assuming that I treat it like infinity focus?


You have a lens without a distance scale?

these are sometimes found on "consumer" cameras. Some of the old Keystones come with a fixed focus lens at about f 3.5 or so. the idea is that the Depth of Field will cover you for most shot sin the "snapshot" range, 8-10 ft, and still not make the background too Blurry.

On a wide angle, that range can be from a few feet out.
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#9 chuck colburn

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Posted 10 June 2007 - 09:48 PM

Hello Charles,

The Angenieux 10mm made for 16mm use was a fixed focus lens. So was the 5.9mm.

Chuck
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#10 Charles MacDonald

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Posted 10 June 2007 - 10:03 PM

The Angenieux 10mm made for 16mm use was a fixed focus lens. So was the 5.9mm.


that makes sense, in that the depth of field would be from very close to infinity at most settings.
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#11 Patrick Neary

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Posted 11 June 2007 - 06:25 AM

my question is sense there is no selective focus, where does my depth of field start from. This may be a very naive question, but I am not use to a lens that does not have focus selection. I am assuming that I treat it like infinity focus?


I was always under the assumption that a lens like the 10mm retrofocus was set somewhere near its wide-open hyperfocal distance (about 8 or 10 feet?)...
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#12 chuck colburn

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Posted 11 June 2007 - 12:41 PM

I was always under the assumption that a lens like the 10mm retrofocus was set somewhere near its wide-open hyperfocal distance (about 8 or 10 feet?)...


I use to fudge the infinity collimation on those lenses. That is I adjusted it just shy of infinity to the point that I knew it would reach it even wide open.
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