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Please Help - Vignetting on my Ultra prime 16mm

R

Ram charan

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Hey guys,

I just bought an alexa xt recently. I decided to shoot open gate with my 16mm UP. I just realized the image circle of UP 16mm is smaller in proportion to the sensor size of alexa and the vignetting was common with 16mm.

But, I have been told that shooting on a 2.39:1 aspect ratio scope does not give you the vignette within the scope. But I still had vignetting within the scope. So I borrowed my friends 16mm and THEY HAD NO VIGNETTE within the scope.

Why does my 16mm alone give a vignette? In fact mine were newer lenses.

I tested both the lenses with the same ISO,Aperture and shutter. The camera was fixed and exposure was the same. Both had perfect focus (No back focus), But one thing which I did notice was that mine had a wider frame than my friends older ultra prime ( around .5 to 1mm difference).

Please help me out , because most of the DP's shoot in open gate and I dont want any complaints regarding the vingetting.

Thank you
 
What type of lens does your friend have? different lenses have different image circles. if your friend has an ultra prime 16mm then thats strange. if he has a different lens it because its a different lens.
 
Yes..Its the same ultra prime 16mm. I know. Its very strange. And yes, the client called back and reported the vignetting problem. :( . Does this mean I wont be able to use my 16mm on alexa open gate anymore? Or do we have a solution ?
 
Yes. That was my last resort. But once it goes to arri and gets serviced , its no longer a new lens, Well ,not atleast for my clients.

I'll drop a mail to arri and see what they have to say.
 
ALEXA in 4:3 mode needs a lens capable of delivering an image circle around 30mm. In Open Gate you need 33.5mm. Your Ultra Prime 16mm delivers a 33mm image circle so you are probably getting slight vignetting on the corners of your frame. Every lens is a bit different even when they should technically be the same. You may be able to solve this problem by asking ARRI to adjust your UP16 lens so that it "becomes" a 16.5mm which would in turn slightly increase your image circle and hopefully eliminate the vignetting.
 
Hey Adrian. Yes, I am aware of the image circle size. But would arri really do that? Change the focal length? Considering how insanely expensive they are, how is it fair to produce a "bit different" lens each time? Now that bit difference cost me 4 days of my lens rental. I am really pissed at arri right now! To verify it once again, I tested it with another 16mm which is newer than mine and it had no vignette (within the 2.35 scope)!

Just sent a huge mail to arri. Lets see what they have to say.
 
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