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Super35 with Normal 35 groundglass?


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#1 christian mann

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Posted 11 November 2011 - 11:05 AM

I was wondering why excactly one has to recenter the lens port when changing from normal35 to super35 or the other way round?
And what would it look like if I recenter the lens port for super 35 but use a normal 35 groundglass? Or shooting normal35 and using a super35 groundglass.....?
And what is the reason for changing the bridge plate again?

Thanks for some input!
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#2 Francesco Bonomo

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Posted 11 November 2011 - 12:46 PM

I was wondering why excactly one has to recenter the lens port when changing from normal35 to super35 or the other way round?


Because although the film negative size is the same, Super35 uses a larger and recentered gate, needed because its frame occupies the space on the negative that was used for optical soundtrack.
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#3 David Mullen ASC

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Posted 11 November 2011 - 12:50 PM

Depends on the lens, for some prime lenses, if they fill the Super-35 frame entirely without fall-off, then the only problem with leaving them centered for Academy is that the lens flares are a little off-centered.

But if there is some corner fall-off, then the off-centered lens will show it more on one side.

It's a bigger problem with zooms since as you zoom in and out, the image will be drifting slightly to one side, so the operator would have to compensate. And zooms tend to have more corner fall-off too. And more flares as well, which will be off-centered (i.e. if you put the sun in the center of the image, the lens flares won't be centered around it.)
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#4 Francesco Bonomo

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Posted 11 November 2011 - 12:51 PM

(this diagram should make it easier to understand. The grey area in the picture is the one used for the optical soundtrack, see how Super35 extends in that area, so it needs to be recentered)

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  • 187px-super35_and_techniscope2.png

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#5 Dom Jaeger

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Posted 11 November 2011 - 07:30 PM

As well as the corner fall-off, flares and zoom tracking that David mentioned, any pin cushioning or barrel distortion will also be more pronounced on one side if the lens is off-centre, as will any lens deficiency that gets worse towards the edges such as chromatic or spherical aberration (typically exhibited when a lens is wide open).

Many older lenses only just cover the Super 35 frame, so if they are not centred they may actually vignette on one side.

Using a ground glass that does not match the lens port position simply means your frames lines will be off.

The bridge plate needs to be recentred because the rails support accessories such as matte boxes and lens supports that need to be centred to the lens.
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#6 christian mann

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Posted 12 November 2011 - 03:24 AM

great answers! now it all makes sense again.
thanks to all of you!
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