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09-28-2012, 03:07 PM   #1
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Can FA Lenses Cover FF Dimension + SR Movement Distances?

Sorry if it's answered before, but I just wondered, when an FF sensor is moved in both axis (say +-4mm) for SR, could FA lenses image circle can cover FF sensor size plus +-4mm, any ideas?

09-28-2012, 03:14 PM   #2
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Being that the FA Limiteds were made too be as compact as possible(and made before SR came along), I'd say no they probably wouldnt cover FF Dimension + SR Movement Distances
09-28-2012, 03:17 PM   #3
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Ooh boy, if that so, the conclusion would be for an FF camera a new lens line is needed or big&heavy 645 lenses must be used on FF right? Another saying FF dream is stuck with the in-body SR.
09-28-2012, 03:22 PM   #4
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You could find out by putting 35mm lenses on a medium-format camera and taking some snaps!

In any case, from a business standpoint, it's desirable for the answer to be "no" so that a brand-new line of full-frame lenses would have to be marketed, and perhaps that's why this seed was planted. On the other hand, given that only the corners of the frame are critical, I'm sure that in general most of Pentax's full-frame lenses give you plenty to work with.


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09-28-2012, 03:33 PM   #5
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QuoteOriginally posted by Adam Quote
You could find out by putting 35mm lenses on a medium-format camera and taking some snaps!.
Who makes a K-mount to 645 adapter? I know you can put a 645 lens on a K-mount, but not the other way around. It would never focus.

But it is an excellent idea just to test image circle. Which medium format camera can you put K-mount lenses on?
09-28-2012, 03:45 PM   #6
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I think an easier way to do it, if anyone's inclined to do this test (I'm not), would to take a K-mount extension tube and mount it in a small box, with the mount 45.5 mm from a translucent sheet of some kind -- like a sheet of thin paper or transparency film with accurate sensor-size outlines printed on it and centered.

Then you can just hold this thing up in reasonably bright light, move the focus/zoom mechanisms around, and see what happens to the image circle in comparison to the printed outlines.

Obviously this wouldn't help too much to figure out things like vignetting or edge-to-edge sharpness (except to the extent you could eyeball it), but it would indicate the overall size of the image circle projected by a lens.

I tend to think all of the mainstream current and past FF lenses would pass this test.
09-28-2012, 04:00 PM   #7
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See falk's comments here:
https://www.pentaxforums.com/forums/pentax-news-rumors/107970-k-rumors-report...ml#post1117001
09-28-2012, 05:51 PM   #8
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4mm sounds like an awful lot, from whence does this figure come?

09-28-2012, 07:11 PM   #9
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QuoteOriginally posted by maxfield_photo Quote
4mm sounds like an awful lot, from whence does this figure come?


How much movement does the Sony A900 require? Looks like at least 3mm.
09-28-2012, 08:25 PM   #10
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I don't think it would be something to worry about. Image circle is not an absolute cutoff and both the FA 35 and the FA 77 have negligible vignette on 35mm film. (Those are the two FA lenses I own and I shoot them both on film as well as digital.) I would expect NO vignette attributable to SR for vertical movement and little, if any, in the horizontal dimension.


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Last edited by stevebrot; 09-28-2012 at 08:56 PM.
09-29-2012, 12:27 AM   #11
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I wouls say that SR is possible on FF with FA lenses. I don't think more than +- 0.5mm is needed for 4 stops of SR on FF.
09-29-2012, 01:07 AM   #12
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QuoteOriginally posted by maxfield_photo Quote
4mm sounds like an awful lot, from whence does this figure come?
I've said (say +-4mm) which means it's just my imagination, if someone knows the true distance please let us know.

My simple logic says if there is even a slight vignetting exists without SR, with SR movement, that existing vignetting will increase at the opposite side of the SR movement in that particular exposure period.

Last edited by cbaytan; 09-29-2012 at 03:15 AM.
09-29-2012, 04:09 AM   #13
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QuoteOriginally posted by Quicksand Quote
I think an easier way to do it, if anyone's inclined to do this test (I'm not), would to take a K-mount extension tube and mount it in a small box, with the mount 45.5 mm from a translucent sheet of some kind -- like a sheet of thin paper or transparency film with accurate sensor-size outlines printed on it and centered.

Then you can just hold this thing up in reasonably bright light, move the focus/zoom mechanisms around, and see what happens to the image circle in comparison to the printed outlines.

Obviously this wouldn't help too much to figure out things like vignetting or edge-to-edge sharpness (except to the extent you could eyeball it), but it would indicate the overall size of the image circle projected by a lens.

I tend to think all of the mainstream current and past FF lenses would pass this test.
Your idea is pretty good, but I would add one or two things. First, do this at infinity focus, because as you increase magnification it is likely the projected image circle also increases, and second, photograph the illumated circle. To do this it should be a tissue paper with concentric reference circles drawn on it. Use a photo editor to measure greyscale value. That will give you an accurate assessment
10-01-2012, 09:56 PM   #14
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As Falk (falconeye) posted multiple times, SR simply does not represent an issue for an FF sensor.

Even for a four stop advantage in SR, you need less than 1mm overhead in the image circle.
10-02-2012, 08:32 AM   #15
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QuoteOriginally posted by Class A Quote
As Falk (falconeye) posted multiple times, SR simply does not represent an issue for an FF sensor.

Even for a four stop advantage in SR, you need less than 1mm overhead in the image circle.
On top of that, I would be willing to turn off SR with my FA 77 LTD, A 50/1.2, K 28/2, Tammy 180/2.5 and F 28/2.8.
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