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From: bob on 16 Feb 2010 14:23
On Mon, 15 Feb 2010 19:52:00 -0600, John Sheehy <JPS(a)no.komm> wrote:

>Rich <none(a)nowhere.com> wrote in
>news:Kr6dnZdC_fO56PrWnZ2dnUVZ_sednZ2d(a)giganews.com:
>
>> Forget Dpreview's recommended B.S. It's just them selling glass for a
>> manufacturer. Even ones that don't advertise on the site now are
>> fetted because of the potential for advertising down the road.
>>
>> These test figures are horrible, absolutely horrible. They are so
>> bad at 250mm that you could literally shoot with a good 135mm prime
>> lens and get as much detail as the longer f.l.!!!
>>
>> http://www.dpreview.com/lensreviews/sigma_18-250_3p5-6p3_os_c16/page3.a
>
>Come on now, rich. Are you really surprised that a zoom with that much
>range for a fairly large sensor (it's easy for 1/1.8"), at a low price, is
>compromised at one extreme?
>
>The 135 with the crop will have coarser "grain" and coarser demosaicing
>artifacts. Maybe if you meant with a TC ... but remember the reasons for
>using zooms.


here is the ISO 12233 test for this lens, compared to others.
http://www.the-digital-picture.com/Reviews/ISO-12233-Sample-Crops.aspx?Lens=101&Camera=453&Sample=0&FLI=0&API=3&LensComp=490&CameraComp=474&SampleComp=0&FLIComp=5&APIComp=3
From: John Sheehy on 16 Feb 2010 17:59
bob(a)myhouse.com wrote in
news:u4sln5d0d3abb6m9hp52a7ncovq2uod5vs(a)4ax.com:

> here is the ISO 12233 test for this lens, compared to others.
> http://www.the-digital-picture.com/Reviews/ISO-12233-Sample-Crops.aspx?
> Lens=101&Camera=453&Sample=0&FLI=0&API=3&LensComp=490&CameraComp=474&Sa
> mpleComp=0&FLIComp=5&APIComp=3

That's pretty bad. That wasn't even within my assumed range of
possibilities. Is this typical for this lens, do you know? CA starts
right near the center, and it is so strong that each color channel is
severely radial-blurred. I don't know if there are any good CA corrections
which work by promoting to more than 3 color channels, as three color
channels are too few, really to correct extreme CA. The 135 f/2 compares
quite favorably at 270mm with a 2x TC.

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