sigma 18-35 review

[Larry Colen]

Pentax forums did a review of the 18-35:

Skipping to the conclusion:
http://www.pentaxforums.com/reviews/sigma-18-35mm-f18-dc-hsm-art/conclusion.html

From the start:
http://www.pentaxforums.com/reviews/sigma-18-35mm-f18-dc-hsm-art/introduction.html

tl;dr:
Amazing lens, incredible sharpness but nasty purple fringing and lousy
autofocus performance.

[Darren Addy]

Don't think you have accurately "summed up". From the article linked:
"Excellent aberration control with very low amounts of purple fringing"
and
"Perfectly accurate autofocus, regardless of aperture, when using
Contrast Detect AF (Live View)"
but using the viewfinder autofocus was inexplicably awful (at least on
the sample of lenses PF tested).
I wonder if this is something that could potentially be fixed via
lens firmware?

The thing I like the least about sample images I have seen from this
lens is the bokeh. I do not agree with the review in the bokeh
department. I think this lens has weird bokeh.

Post by Larry Colen
http://www.pentaxforums.com/reviews/sigma-18-35mm-f18-dc-hsm-art/conclusion.html
http://www.pentaxforums.com/reviews/sigma-18-35mm-f18-dc-hsm-art/introduction.html
Amazing lens, incredible sharpness but nasty purple fringing and lousy
autofocus performance.
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[Larry Colen]

Post by Darren Addy
"Excellent aberration control with very low amounts of purple fringing"
and

OK, I guess I misread the section:
http://www.pentaxforums.com/reviews/sigma-18-35mm-f18-dc-hsm-art/aberrations-and-flare.html

Verdict
There's really not much more to say - Sigma may have garnered the
industry's attention with the recent lenses they've released in their
Global Vision lineup, but they have still proven substandard at
mitigating flare.

And the pictures they had right above where showing purple fringing on
the FA77.

Post by Darren Addy
"Perfectly accurate autofocus, regardless of aperture, when using
Contrast Detect AF (Live View)"
but using the viewfinder autofocus was inexplicably awful (at least on
the sample of lenses PF tested).
I wonder if this is something that could potentially be fixed via
lens firmware?
The thing I like the least about sample images I have seen from this
lens is the bokeh. I do not agree with the review in the bokeh
department. I think this lens has weird bokeh.

I'm very intrigued by this lens. Since I do a lot of low light indoor
photography, the zoom range could be incredibly handy.
But, with my poor eyesight, I need fast accurate autofocus.

Post by Darren Addy

Post by Larry Colen
http://www.pentaxforums.com/reviews/sigma-18-35mm-f18-dc-hsm-art/conclusion.html
http://www.pentaxforums.com/reviews/sigma-18-35mm-f18-dc-hsm-art/introduction.html
Amazing lens, incredible sharpness but nasty purple fringing and lousy
autofocus performance.
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http://pdml.net/mailman/listinfo/pdml_pdml.net
to UNSUBSCRIBE from the PDML, please visit the link directly above and
follow the directions.

[Bryan Jacoby]

no phase detect AF system
is designed for an 18mm f1.8 lens.dc-hsm-art/aberrations-and-flare.html

That's true, but at the same time dpreview had no complaints about AF
performance with this lens on Nikon (but they did have problems with
Canon).

What do you think of the AF at more typical apertures, say f/2.8?

[Bryan Jacoby]

Sorry, I wasn't clear. What I meant was does the AF performance seem
adequate/typical in the context of the depth of field one gets at
f/2.8 (for a more fair comparison with other fast zooms).

Actually, I think the aperture used for TTL AF is set by the AF
system, not the lens. So while it's true that the lens is open to
f/1.8 during focusing, I think it's effectively only focusing at f/5.6
or f/2.8 depending on which camera and AF point you're using.

TTL AF is always performed with the lens wide open regardless of the
taking aperture.