I also agreed PTLens is a useful tool, for distortion correction it shows
the power in complex distortion, for simple barrel or pincushion I can do it
with PS easliy. I do not correct distortion unless there is straight lines
in the image and which look uncomfortable, chance is little with the 4/3
lenses I used so I haven't consider a separate tool for distortion
correction.
21/3.5 do have high field curvature close-up but the Olympus 18/3.5, 21/2,
24/2 and 28/2 all have close focus correction, the field curvature are very
low but with very high linear distortion though.
C.H.Ling
----- Original Message -----
From: "Moose" <olymoose@xxxxxxxxx>
> C.H.Ling wrote:
>> PTLens looks interesting but I see some problem for shots at different
>> focus
>> distance, like the Zuiko 18/3.5, it has very slight pincushion distortion
>> for distance object but high barrel distortion at close distance.
>>
> Huh! Who knew. Gary's test showed no linear distortion at 1:40. I've not
> noticed any at infinity, but then I don't usually shoot subjects where
> slight pincushion would show.
>
> I don't think I've ever shot anything really close with the 18 or
> 21/3.5s. I know some images posted here some time ago showed the 21/3.5
> to have high field curvature close-up, So I wouldn't tend to use them
> for that purpose.
>
> I'll admit to cheating with PTLens on occasion. IF your image doesn't
> have an EXIF, which is easy enough to erase in a copy, you may choose
> any camera/lens combo you like. I've simply shopped for a lens with
> similar distortion to the image I have and used it.
>
> It's pretty quick, as the preview shows the effect immediately. Not
> necessary for straightforward pincushion or barrel, which many apps
> handle nicely. But with what Chuck calls moustache distortion, finding a
> match can be better.
>
> Another option is a plug-in that lets you select three points on a
> horizontal line to correct the line - but I have for the moment lost
> track of it.
>> Distortion may not be very critical for 4/3 system. Most 4/3 lenses have
>> very low distortion. ...
> I was making no comment about 4/3 lenses. I was replying to a specific
> request in a post for distortion correction software that covers 4/3
> lenses.
>
> Moose
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