"soft left edge" but not "soft right edge"

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RolandRB - 09 Apr 2007 11:41 GMT

This has been puzzling me a while now. I guess it applies to MF as
well as digital where I have seen it and somebody here will have an
educated opinion on it (not so for the digital or 35mm groups). That
is, why do lenses often show a soft left edge but not a soft right
edge? Assume this applies to zooms as I have no experience of it for
primes.

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dadiOH - 09 Apr 2007 13:50 GMT

> This has been puzzling me a while now. I guess it applies to MF as
> well as digital where I have seen it and somebody here will have an
> educated opinion on it (not so for the digital or 35mm groups). That
> is, why do lenses often show a soft left edge but not a soft right
> edge? Assume this applies to zooms as I have no experience of it for
> primes.

Never seen it so can't say but I'd suspect your film plane is not flat
and/or perpendicular to the axis of the lens. You might want to check
the pressure plate.

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dadiOH
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RolandRB - 09 Apr 2007 14:17 GMT

> > This has been puzzling me a while now. I guess it applies to MF as
> > well as digital where I have seen it and somebody here will have an
[quoted text clipped - 6 lines]
> and/or perpendicular to the axis of the lens. You might want to check
> the pressure plate.

It's actually digital cameras I am noticing this on with fitted zoom
lenses. I asked the question here because I know it will go unanswered
(sanely) on the digital and 35mm groups. Maybe the problem goes
further than this and extends to MF. They are the "perfect image"
crowd if there ever was one so it might get noticed by them also.

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Karl Winkler - 09 Apr 2007 18:40 GMT

> > > This has been puzzling me a while now. I guess it applies to MF as
> > > well as digital where I have seen it and somebody here will have an
[quoted text clipped - 12 lines]
> further than this and extends to MF. They are the "perfect image"
> crowd if there ever was one so it might get noticed by them also.

There was someone asking about this in one of the digital groups
except that the bottom of the frame was soft while the top was sharp.
The general consensus was that the sensor was not mounted properly or
had become out of alignment. It could also be that one of the lens
elements in a zoom is not collimated properly. For that to be the
case, that element could not rotate when the lens is focused or
zoomed, otherwise the soft area would move around the frame.

-Karl
http://www.karlwinkler.com
http://www.giovanniquartet.com

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RolandRB - 10 Apr 2007 09:57 GMT

> > > > This has been puzzling me a while now. I guess it applies to MF as
> > > > well as digital where I have seen it and somebody here will have an
[quoted text clipped - 22 lines]
>
> -Karlhttp://www.karlwinkler.comhttp://www.giovanniquartet.com

Oddly enough, on the "blur index" graph on this page it can have one
edge more blurred than the other for the Sony DSC-R1 lens.

http://www.imaging-resource.com/PRODS/R1/R1A6.HTM

This has taught me to stop the lens down by one stop at least next
time I am doing landscape with that camera.

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dadiOH - 10 Apr 2007 14:39 GMT

>>>>> This has been puzzling me a while now. I guess it applies to MF
>>>>> as well as digital where I have seen it and somebody here will
[quoted text clipped - 32 lines]
> This has taught me to stop the lens down by one stop at least next
> time I am doing landscape with that camera.

The page says,

"...when we look at the R1's optical test results, we see graphs so
good that they're almost boring. Sharpness across the frame and across
the aperture and focal length range is almost perfect, as shown by the
exceptionally low and uniform blur numbers."

so I don't really see that your question/problem has been resolved.

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RolandRB - 10 Apr 2007 16:00 GMT

> >>>>> This has been puzzling me a while now. I guess it applies to MF
> >>>>> as well as digital where I have seen it and somebody here will
[quoted text clipped - 41 lines]
>
> so I don't really see that your question/problem has been resolved.

If you play with the interactive blur chart then at the widest
aperture you can get some very non-perfect results.

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george - 09 Apr 2007 19:52 GMT

>> > This has been puzzling me a while now. I guess it applies to MF as
>> > well as digital where I have seen it and somebody here will have an
[quoted text clipped - 12 lines]
> further than this and extends to MF. They are the "perfect image"
> crowd if there ever was one so it might get noticed by them also.

I've never seen that before. The probable causes that come to mind are:
1) Film pressure plate (or sensor for digital) not perpendicular to the lens
mount meaning that either:
a) pressure plate or sensor needs to be adjusted; or,
b) lens mount needs to be adjusted
2) Incorrectly collimated lens

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