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Angenieux 25-250 EF Vignetting on S35 sensors


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#1 Tristan Newton

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Posted 11 July 2016 - 07:22 AM

Hi,

 

I've got an Angenieux 25-250 T3.9 in EF mount that for some strange reason is vignetting badly on a c300 MKII and an Amira in both 4K and 2K.

 

Last time I tested it there were no issues on the long end on a full frame (5D) nor M4/3 camera across the full focal range.

 

As far as I understand the EF flange distance is 44mm regardless of camera which suggests something very odd is happening with the mount. Panavision Australia fitted and tested it a while back and it *was* fine.

 

Has anyone experienced anything strange like this happening? In terms of my options to fix it, should I switch it back to PL?

 

Thanks very much for your help!


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#2 Satsuki Murashige

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Posted 11 July 2016 - 03:26 PM

Can you post some frame grabs of the vignetting you are experiencing? That would help.

Have you tested the lens on a Super35-sized sensor before? Just because the lens covers Micro 4/3s doesn't mean it will cover S35. I would suspect the lens was originally designed to only cover Academy 35 at best, not the larger S35 format. But maybe Panavision adapted it for better coverage? You should probably call and ask them. Very strange that you are also experiencing vignetting in 2K crop mode on those cameras, you would expect crop mode to eliminate vignetting and coverage issues.

If you are not having problems holding focus throughout the zoom range or reaching infinity focus, then I would not suspect a flange depth issue. You are using a lens support with that lens, correct?
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#3 Tristan Newton

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Posted 11 July 2016 - 10:37 PM

Hi Satsuki,

 

Thanks very much for your feedback.

 

Panavision used the lens on F35 relatively recently with no issues, however I suspect the problems cropped up after it was switched to EF. Not my preferred mount, but I got it for a good price.

 

An ex Panavision lens tech confirmed it should cover an image circle of 28mm on the wide, and 32mm on the long end. It was setup properly, but sadly I wasn't present for the tests (a skilled DoP carried it out). However as you said, it was designed for Academy 35.

 

Best guess is there are issues with the mount in this case. I know it'll cover RED 4K so I suspect it will be better if I pass it on to someone who can use it.

 

Thanks again

 

Tristan


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#4 Gregg MacPherson

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Posted 11 July 2016 - 11:12 PM

Looking at the old Panavision docs for frame dimensions,  the diagonal on S35 extracted/transmitted frames are 27.3/27.5mm.  So it looks like your image circle should cover that.  But if you have vignetting with the cropped 2K frame your adapter has to be the problem, you think?


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#5 Tristan Newton

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Posted 11 July 2016 - 11:51 PM

Hi Gregg,

 

Thanks very much for looking into that for me.

 

Was that the T3.9 or the newer HR version?

 

Almost certainly the adapter is the issue...which makes no sense as it worked fine in the past. As far as I know the EF mount hasn't suddenly changed spec.

 

Best option I think is to sell it off and suggest the buyer switch it for the more reliable PL.

 

Thanks 


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#6 Tristan Newton

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Posted 11 July 2016 - 11:52 PM

Sorry Gregg I misread your message.

 

The sensor size diagonal on the c300 and Amira I'm pretty sure are a bit smaller than s35 so the adapter is almost certainly the issue.


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#7 Dom Jaeger

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Posted 12 July 2016 - 12:00 AM

I've measured the image circle of an Angenieux T3.9 25-250 and at close focus it goes well under 28mm, more like 27mm. If you keep the focus past about 6 ft the image circle should remain above 28mm.

 

I'm not sure how the mount could cause vignetting, given that EF is used for full frame 35mm. Is the zoom vignetting at all focal lengths and distances? Are you using a mattebox or anything at the front of the lens that could be the culprit?

 

I'm sure the guys at PV Sydney could sort out the issue if you took it in.


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#8 Tristan Newton

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Posted 12 July 2016 - 12:13 AM

Hi Dom,

 

Thanks very much - I actually was going to contact you directly but Neil at Lemac confirmed what you said.

 

As I mentioned to Satsuki, above I wasn't present for the tests - but the DoP was experiencing a significant vignette across the entire zoom range and even at 2K.

It certainly made no sense to me at all. The only thing I could think of was the flange distance was somehow greater than 44mm due to the lens-camera mount not engaging properly. He claimed his AC (an ex lens tech) said that these older zooms were designed for Academy and not s35 (true), and would vignette 25-30mm focal range - and you still had bad fall off/corner performance in low light.

 

Panavision installed the EF mount years ago and the person I got it from left PV a little while back. Mystery to me what's going on. I'll pick up the lens tomorrow and try and get my hands on a camera test it myself.

 

Thanks again


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#9 Dom Jaeger

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Posted 12 July 2016 - 01:17 AM

If the flange depth was off the zoom would no longer hold focus, and I can't see that causing this issue anyway. But something weird is going on if there's a constant vignette.

 

If you're in Melbourne you're welcome to drop in to Cameraquip and I'll give it a quick look over.


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#10 Tristan Newton

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Posted 12 July 2016 - 01:22 AM

Thanks very much for your kind offer Dom.

 

Tested very recently on a GH4 m43 with EF adapter and was nice and sharp at 1080p - no issues I could find. Obviously sensor is much smaller, but still no issues with either the mount nor the optics/mechanics.


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#11 Satsuki Murashige

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Posted 12 July 2016 - 01:33 AM

Gregg is asking about the the vignetting you experienced in 2K cropped mode on the Amira and C300 Mk2, which should be similar to 16mm sensor size. It just seems weird that you would still have vignetting under those conditions unless the EF adapter was cropping the image somehow.
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#12 Tristan Newton

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Posted 12 July 2016 - 01:38 AM

Hi Satsuki,

 

I've tested in on a GH4 1080p (~20mm diagonal) and there were no issues at all - so the problems on 2K crop on the Amira made no sense to me. Its looking more and more like operator error. I'm yet to find out if it was tested at the minimum close focus of ~6ft.

 

Thanks again


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