> From: Moose <olymoose@xxxxxxxxx>
>
> On 9/16/2018 9:48 AM, Jan Steinman wrote:
>>
>>
>> let you create lens profiles for lenses that were developed before profiles
>> existed, like my OM Zuiko stable.
>
> Ah, yes, that's the one I've encountered in a few apps. One person's opinion,
> after careful comparisons - LensFun is
> significantly poorer than PTLens and DxO's lens profiles. PTLens is cheap and
> also allows creation of new profiles. You
> take the test shots, he makes the profile. Very responsive, according to
> Chuck and others. There are already profiles
> for most OM wides on FF, which is where I first used it. PTLens is an
> independent, one man show, so should fit your
> criteria. His profiles are actually slightly better than DxO for some ?4/3
> lenses.
Thanks for that info. I'll look into it. When trying to get rid of CA in the OM
21/2, LensFun was the only one I came across.
>> In particular, fast-wide legacy glass is known for excessive CA in the
>> corners and edges.
>
> As Philippe says, that's mostly not an issue with a 4/3 sensor, as the
> outside zones are cropped off.
My understanding is that the CA is an artifact of a lack of "telecentricity" in
retro-focal lenses, which all SLR wides are.
Whatever the cause, I see it in all the OM fast wides I've tried on a 4/3rds
sensor. (18/3.5, 21/2, 24/2, 28/2, and 35/2. Not an issue with the 55/1.2 or
longer. Haven't tried it with the 40/2 or the various 50s.)
I had been planning to use the 21/2 for astrophotography, until I discovered
the stars in the corner were purple/green streaks. That started me off on a
hunt for profiling software.
That was what caused me to sell off my fast-wides in a fit of "won't work-ism."
Having discovered focal reducers (which only came into being with Micro
4/3rds), I'm now regretting that.
> I WANT those aberrations for some of my Alt photography. They weren't there
> with my OM lenses on ?4/3
Odd, that. Have you looked for point light sources in the corners? Which OM
wides were you using that didn't have CA on 4/3rds?
>> You can manually correct for that in your favourite photo editor, or create
>> a LensFun profile and let your open-source-based photo editor do it for you
>> automagically.
>
> Well, not quite automagically, as they can't know what MF lens you used. You
> do have to tell it.
True, that.
I set up my EM-1.2 to embed the appropriate manual lens info. I just wished
that it had more than ten slots for different manual lenses. With focal
reducers and teleconverters, I could easily use four times that many entries.
I MORE than wished it were different: I sent the Oly engineering group a long,
detailed message on how they should handle manual lens EXIF data, with minimal
engineering effort and minimal changes to their menu system. They sent me a
nice note, thanking me for my input, but it hasn't shown up in the two updates
since. :-(
Jan
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