Thread: Full frame lenses on smaller sensors

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  1. #1 Full frame lenses on smaller sensors 
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    What happens with IQ when using a lens build for a large sensor, but used on a smaller one?
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    Depends on the difference in image circle size between lens and camera.

    But to generalise, on the plus side, you're usually only using the "sweet spot" in the optics - the centre - so no IQ compromise. Of course, this is on a lens-by-lens basis.

    On the minus side, you may be wasting optical potential, by having much of the optics unused. Also, you may end up with a much (physically) larger lens than an equivalent focal length designed for that camera. If a lens is designed for a smaller image circle, then it's easier to design it to be faster and lighter/smaller than an equivalent focal length for a larger image circle.

    For example - a 17-120mm f/2.8 lens designed for 1" sensors can cost $300 and be 120mm long, 70mm front diameter and weigh 300 grams. An equivalent focal length zoom (17-120mm f/2.8) for super35 may cost $30,000 and be 260mm length, 114mm front diameter and weigh 3 kilograms.

    That said, I've been collecting some Mamiya Sekor C medium format lenses with an image circle of 70mm to use on my URSA Mini which needs and image circle of 29mm. The advantage is I'm using the sweet spot in the optics. Also, and sensor sizes in cameras get larger, my glass will be able to cover those cameras, so it's a long term investment. For such large image circle, the lenses are very small and compact. But they are generally not very fast f/2.8 to 3.5 with only one really fast lens at f/1.9. But the characteristics of the lenses are beautiful.
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    ^-- Says it ALL.
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    I wouldn't generalize regarding that 'sweet spot'. There are vintage lenses which are struggling at the wider end to maintain sharpness and a flat image plane at the same time.
    So, the manufacturers made a balance between center sharpness and edge sharpness where neither is optimal (at least when wide open). As already said above by Trispembo, it's a lens-by-lens thing.
    Last edited by Nomad; 08-06-2017 at 07:36 PM.
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  5. #5  
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    Quote Originally Posted by Nomad View Post
    I wouldn't generalize regarding that 'sweet spot'. There are vintage lenses which are struggling at the wider end to maintain sharpness and a flat image plane at the same time.
    So, the manufacturers made a balance between center sharpness and edge sharpness where neither is optimal (at least when wide open). As already said above by Trispembo, it's a lens-by-lens thing.
    Yes I'd agree with Nomad.

    The idea of the center of the lens being used doesn't quite apply. I think the idea has leaked from having a APERTURE that is down a couple of stops that DOES use the center of the lens, but as I understand it's a different optical outcome to crop the lens. In some ways I guess you don't use the full correction of the glass if the lens is "aspheric" for example.

    And having a larger projected image means a lot more light bouncing around between the back of the lens and the sensor. It means you can get unusual flares or just veiling flares that mean reduced contrast.

    In the film days, it was a common idea to get 35mm format lenses when shooting super 16, but again, similar problems. Weird flares and it really didn't seem to make any visual difference. But plenty of people still did it.

    In the way that a speed booster can improve the image by some metrics by reducing the projected image, if you're going to other way to crop into it...I'm not sure it means it's better...

    JB
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  6. #6  
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    Quote Originally Posted by trispembo View Post
    That said, I've been collecting some Mamiya Sekor C medium format lenses with an image circle of 70mm to use on my URSA Mini which needs and image circle of 29mm. The advantage is I'm using the sweet spot in the optics. Also, and sensor sizes in cameras get larger, my glass will be able to cover those cameras, so it's a long term investment. For such large image circle, the lenses are very small and compact. But they are generally not very fast f/2.8 to 3.5 with only one really fast lens at f/1.9. But the characteristics of the lenses are beautiful.
    Are you on PL or EF mount? I'm looking for a good Mamiya Sekor C MF to EF mount adapter. Which one are you using with the Ursa?
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    Quote Originally Posted by EYu View Post
    Are you on PL or EF mount? I'm looking for a good Mamiya Sekor C MF to EF mount adapter. Which one are you using with the Ursa?
    My UM is PL, so I'll be replacing the mounts to PL.

    They are currently with a lens tech being de-clicked. Once that's complete, I'll remove the original mounts, and send them to c7 adaptors, who'll then send a replacement PL mount for each lens + shims.

    Currently I have a locking Mamiya 645 to EF adaptor from c7 which is pretty good. However, not all of the lenses lock, so I'm not very satisfied with that solution. The PL mounts will mean zero play, so the best possible solution.
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  8. #8  
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    Quote Originally Posted by John Brawley View Post
    And having a larger projected image means a lot more light bouncing around between the back of the lens and the sensor. It means you can get unusual flares or just veiling flares that mean reduced contrast.
    That's a good point - extra projected image could cause unwanted results. I'll have to keep a close eye on that when I start using Mamiya 645 lenses on my URSA MIni.
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  9. #9  
    Senior Member kgimedia's Avatar
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    I've also seen some discussion about Medium and Large format lenses not being as sharp as smaller format lenses. The theory is that the larger negative requires less enlarging later so it didn't need to be a sharp and precise.
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  10. #10  
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    Quote Originally Posted by kgimedia View Post
    I've also seen some discussion about Medium and Large format lenses not being as sharp as smaller format lenses. The theory is that the larger negative requires less enlarging later so it didn't need to be a sharp and precise.
    You may be right, but I've only had experience with Mamiya Sekor C.

    On the tests I've done with Mamiya Sekor C 645, they are plenty sharp. But what is even more enticing about these lenses - apart from the excellent build quality, small form factor and future potential - is the character. Beautiful resolves on digital sensors, and the smoothest bokeh I've ever shot with.

    There's some discussions about it here on BMCUser:
    http://www.bmcuser.com/showthread.ph...Mamiya-Sekor-C

    And lots of discussion about it here:
    http://www.reduser.net/forum/showthr...t=mamiya+sekor

    Mamiya Sekor C are currently the only medium format lenses that Duclos offer as a cinemod.
    https://www.ducloslenses.com/pages/mamiyapl

    Discussion about that cinemod here:
    http://www.reduser.net/forum/showthr...t=mamiya+sekor
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