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Re: [OM] A.I. Gigapixel Test -Bill

Subject: Re: [OM] A.I. Gigapixel Test -Bill
From: Jan Steinman <Jan@xxxxxxxxxxxxxx>
Date: Mon, 17 Sep 2018 09:57:26 -0700
> 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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