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Is there a crop factor when....?


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#1 Aaron Hunt

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Posted 24 March 2016 - 03:00 PM

Hello, first time here on the site. I just shot an exposure test on a roll of super 16 on the Aaton LTR 54 with a Zeiss ARRI Super 16 Super Speed lens set. The guy I rented the lenses from muddled something about one of the lenses actually working out to being about twice the FOV of its actual focal length, and this has stuck with me. Is a 9.5mm lens built specifically for Super 16 cameras, not just that original 9.5mm FOV? Here is a still from the test roll that was shot using the 9.5mm lens, and since I've had this supposed crop factor bugging me, this doesn't seem to have nearly as much barrel distortion as I'd expect from a 9.5mm lens -- in fact it looks something more like an 18mm which would make sense if there were a crop factor.... But is there? It's driving me nuts! I am also using an adapter (if that's any factor). 

 

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#2 Adrian Sierkowski

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Posted 24 March 2016 - 04:18 PM

Crop factor only has meaning when matching equivalent FOVs on differing sensor sizes or film gauges. So your 9mm lens, if you wanted to mate the FOV on 35mm would be about an 18 (simplified math).

That said, if you're used to looking at 35mm (or APS-C) Focal lenghts, then yes, the 9.5mm on S16mm film would be very close to the image size for that given distance afforded by an 18mm on 35/APS.


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#3 Aaron Hunt

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Posted 24 March 2016 - 05:07 PM

Thanks Adrian. But then does the way that lens handle space/barrel distortion operate the same across all sensors/film? I understand that you'll be getting less or more of an image (the "crop" factor) depending on the sensor or film format, but just curious to know if the lens still operates consistently in terms of how it's handling space. 


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#4 Chris Burke

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Posted 24 March 2016 - 05:31 PM

With any given lens, they produce a certain size image circle. A lens purpose built for Super sixteen will produce an image circle that will cover that gauge.  concentrate on which format the lens is made to cover. So a 9.5mm lens that is made for S16 will look like a 28mm focal length for still 35mm or 18mm in cine 35 or APS. Lots of people get hung up on the "crop factor", it is confusing and actually rather misleading if you don't get how lenses relate to an imager. Forget crop factor.  If you know still photography focal lengths, with S16 if you multiply by 3, you get an approximate field of view to use as reference. Crop factor comes in when you use a lens intended for one format on another smaller or larger format. 


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#5 Aaron Hunt

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Posted 24 March 2016 - 06:28 PM

With any given lens, they produce a certain size image circle. A lens purpose built for Super sixteen will produce an image circle that will cover that gauge.  concentrate on which format the lens is made to cover. So a 9.5mm lens that is made for S16 will look like a 28mm focal length for still 35mm or 18mm in cine 35 or APS. Lots of people get hung up on the "crop factor", it is confusing and actually rather misleading if you don't get how lenses relate to an imager. Forget crop factor.  If you know still photography focal lengths, with S16 if you multiply by 3, you get an approximate field of view to use as reference. Crop factor comes in when you use a lens intended for one format on another smaller or larger format. 

Thanks Chris, for a while I just couldn't get my head wrapped around it... But putting it in the context of still photography focal lengths helped me do so. I really appreciate it.


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