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Portholing? can i get some help


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#1 Zachary Baney

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Posted 28 June 2008 - 02:04 PM

I have recently been discussing what portholing (dark center and brighter center) is and how it pertains to digital photography and cinematography.

From what I understood it is mostly caused by the size up the rear element. digital sensors are inherently more reflective than the emulsion of film. I was told that if the rear element is too small then the rear element will reflect light bouncing off sensor and create a hot center. If the rear element is larger than the sensor then this problem will not ocur.

If this is true then I assume that rear element size/coating in the primary differnce with digitally optimized cine lens

This all makes sence to me except the fact that digital still lens often have very small rear elements and do not exhibit portholing. at least from what I can tell. Havnt really tested that statement however.

could someone tell me if I am completely wrong or at least clarify why dlsr lens have resilien to portholing
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#2 Stephen Williams

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Posted 28 June 2008 - 02:09 PM

Hi,

Digital optimized lenses are telecentric, with film the angle that light hits the film is unimportant.

Stephen

I have recently been discussing what portholing (dark center and brighter center) is and how it pertains to digital photography and cinematography.

From what I understood it is mostly caused by the size up the rear element. digital sensors are inherently more reflective than the emulsion of film. I was told that if the rear element is too small then the rear element will reflect light bouncing off sensor and create a hot center. If the rear element is larger than the sensor then this problem will not ocur.

If this is true then I assume that rear element size/coating in the primary differnce with digitally optimized cine lens

This all makes sence to me except the fact that digital still lens often have very small rear elements and do not exhibit portholing. at least from what I can tell. Havnt really tested that statement however.

could someone tell me if I am completely wrong or at least clarify why dlsr lens have resilien to portholing


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Visual Products

Metropolis Post

Media Blackout - Custom Cables and AKS

Rig Wheels Passport

CineTape

Aerial Filmworks

Willys Widgets

Abel Cine

Broadcast Solutions Inc

The Slider

FJS International, LLC

Technodolly

Opal

rebotnix Technologies

Ritter Battery

Tai Audio

Paralinx LLC

Wooden Camera

Glidecam

CineLab