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03-22-2011, 04:45 PM   #1
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Sigma 24-70mm f/2.8 EX DG HSM vs. DA* 16-50mm

Had an opportunity to rent a couple of lenses for an upcoming shoot....rented a Sigma 24-70mm EX DG HSM and a Pentax DA* 16-50mm f/2.8. I need a lens in this range and was thinking about the 16-50 to complement my (broken) DA* 50-135mm...but also thought I'd try the Sigma (again)...I'd rented the Sigma for a wedding last fall and really liked it but didn't have anything to compare to. Figure with the "rep" of the DA* 16-50 that it would be a good comparison albiet at slightly different focal length ranges. I already have the DA Limited 70 2.4 which is my "sweet" lens but if the Sigma worked out, perhaps I'd sell the Limited 70.

Prior to a shoot I always spend about half a day getting the micro AF adjustment dialed in....I've learned the hard way that this adjustment is critical if you really want to nail the focus. Usually I start out with "gross" adjustments (0, 5, 10) to find the ballpark (it's almost ALWAYS a + adjustment with my K20D).....so I did the same with these two lenses.

I found two interesting things.....first off, the Sigma simply blew away the DA* 16-50 in terms of sharpness (I was at f/2.8 on both lenses). I've heard the 16-50 is soft wide-open so I'll probably run another test tomorrow at f/5.6 which is normally what I shoot at. I picked 35mm and 50mm to check out and compare against since these focal lengths overlapped for each lens.

The other thing was that as I was naming and labeling the best candidates for focus, I noticed that in every case the sharpest focus was also the largest image in terms of file size (I was shooting JPEGs for this instead of my usual RAW/DNG). After thinking about it, it made some sense that possible the sharpest overall photo would also be the "least compressible" since there'd be more detail (in theory). I'll probably get a chance to check that out as well again tomorrow when I go from the gross adjustments to the finer adjustments.

Before anyone comments, yes, I know that the Sigma is a full-frame lens vs. the "cropped" DA* lens.....maybe that points to the fact that on a cropped sensor, the full frame lens is likely to perform better? In my case though, I wasn't looking at corner sharpness where the FF lens might have an advantage but was simply looking at my LensAlign target right in the center.

03-23-2011, 11:49 AM   #2
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Update.....fine-tuned AF adjustments

Update:
I just completed my fine AF adjustment tests and even threw my DA Limited 70mm in the mix to see how it faired against the Sigma @ 70mm. For my final tests I decided to stop down one stop from wide open which put me at f/4 for the two zooms and f/3.5 for the DA Limited. I figured this is closer to the aperture range I typically use (f/5.6) but would still give me shallow enough DoF for my focus tests.

Results:
* The Sigma 24-70mm f/2.8 IF EX DG HSM easily out-performed the Pentax DA* 16-50mm at all focal lengths with the exception of 24mm where it was a draw....stands to reason as this is the extreme end of the Sigma but still mid-range for the DA* 16-50.

* The Sigma showed little-to-none "purple fringing" compared to the Pentax. Chromatic aberrations stuck out pretty bad on the Pentax even in the center of the image.

Sigma @ 70mm vs. DA Limited 70mm f/2.4....
* The DA Limited has a *slight* edge in outright shaprness but...
* The Sigma was superior in terms of purple fringing/chromatic aberation compared to the DA Limited. Once again, the DA Limited showed signs of chromatic aberration even in the center of the image.

Conclusion:
The Sigma 24-70mm really impressed me, enough that I'm likely to purchase one sooner than later and even sell my DA Limited 70mm. The sharpness of the Sigma is too close to call compared to the DA Limited while purple fringing was non-existant making my DA Limited 70mm redundant and even inferior to the Sigma...and I can't believe I'm even saying that as my DA Limited has always been my favorite lens in my bag.

Just to avoid confusion with other similar Sigma lenses, here's a link to the exact lens I tested: Sigma lens
03-23-2011, 11:57 AM   #3
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Thank you for your analysis.
03-23-2011, 12:07 PM   #4
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Great! I always heard the Sigma 24-70 HSM is a nice sharp lens. The old 24-60 is similar.

03-23-2011, 12:38 PM   #5
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Hmmm, that's interesting.

The Sigma doesn't have such a good reputation, either from what I've read.
But this didn't come from the Pentax crowd but Canon and Nikon.
May have been to other FF lenses.

It is said to have huge flare issue along with low contrast, general softness on the short end and only mediocre performance overall.

But your results don't surprise me. Firstly it is a FF lens so it should beat the Pentax (image center crop for the Sigma) and secondly I don't find the Pentax' perfomance overwhelming.
Would I have known about its weaknesses before, I probably wouldn't have invested in the Pentax.
To be fair, my copy has to be one of the earlier ones and I bought it used.

But AF speed and accuracy and resolution especially in the borders highly disappointed me.
If it wasn't the only sealed lens there is...

So...pictures to prove your text?
03-23-2011, 04:02 PM   #6
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QuoteOriginally posted by Egg Salad Quote

It is said to have huge flare issue along with low contrast, general softness on the short end and only mediocre performance overall.
I would say both the Sigma and the Pentax lens suffered from some flare....but the Sigma didn't have the Stigma of color fringing on top of that.

QuoteQuote:
So...pictures to prove your text?
Glad you asked....I'll follow-up with some pix.

Terry
03-23-2011, 05:10 PM   #7
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Photo samples

Here's a link to the photo album I just created that has screen shots from Photoshop with the images at 200% view plus an image showing my focus test setup.

Lens test album
03-23-2011, 05:17 PM   #8
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does the new Sigma 17-50 interests you? or does the Sigma 24-70 focal length suits you more for your use?

03-23-2011, 05:26 PM   #9
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One other thing, in my original post regarding my initial "gross" AF adjustments, I alluded to the fact that the image with the best focus also seemed to be the largest in file size.

This held true with my "fine" adjustments as well..largest file size = best focus. I'm telling you, it was no fluke....3 different lenses, two different brands, multiple focal lengths....and in EVERY single case file size equaled best focus.

What also was interesting is that the focus adjustments at the various focal lengths was exactly the same for each focal length *regardless* of which lens it was....

Pentax 16-50 @ 24mm: +0 to +2
Sigma 24-70 @ 24mm: +0 to +2

Pentax 16-50 @ 35mm: +0 to +2
Sigma 24-70 @ 35mm: +0 to +2

Pentax 16-50 @ 50mm: +6 to +8
Sigma 24-70 @ 50mm: +4 to +6

Pentax DA Limited 70mm @ 70mm: +6 to +10
Sigma 24-70 @ 70mm: +6 to +10


This suggests two things to me:

1) Micro AF adjustment is focal length dependent....the longer the focal length, the more adjustment required (btw, my lens-to-subject distance was fixed in these tests).

2) Micro AF adjustment is more a function of the camera body than any peculiarities of a particular lens...how else do you explain at a given focal length, the AF adjust was similar? While this is not exactly a huge sampling of lenses by any means, given the variety of brands and lens designs presented here, again, I think these findings are statistically significant.

OK, I'm DONE with lens testing for a while....time to go SHOOT!



Terry
03-23-2011, 05:33 PM   #10
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QuoteOriginally posted by Pentaxor Quote
does the new Sigma 17-50 interests you? or does the Sigma 24-70 focal length suits you more for your use?
I think the 24-70mm suits me better for a couple of reasons...

A) I already have the DA 12-24mm so any thing less than 24mm is redundant...and I really like the 12-24mm...nice lens....I can't imagine "wanting" the 16/17-24mm range of a different lens when what I have is already so good. OTOH, maybe I should compare the sub-24mm range on the DA* 16-50 that I'm renting to see if how it compares to the 12-24mm? But the DA* 16-50mm was underwhelming to me in so many ways that I don't think I'd consider it.

B) I'm shooting a lot of people photos, portraits and outdoor nature nudes and I think the 24-70mm on my K20D's cropped sensor is a good fit (effective 36-105mm). Normally I would never go wider for people photos but I would find myself wanting more than the 50mm the Sigma 17-50 and Pentax DA* 16-50mm have to offer.


Terry
03-23-2011, 05:38 PM   #11
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QuoteOriginally posted by Egg Salad Quote

The Sigma doesn't have such a good reputation, either from what I've read.
But this didn't come from the Pentax crowd but Canon and Nikon.
May have been to other FF lenses.
Of course, Sigma has TWO 24-70mm lenses.... I actually already own the other/older one that I've had on my Sigma SD9 (Foveon chip dSLR). I can tell you that it is not a very good lens in my opinion...but I've never been sure if that was more a function of the lens or of the SD9.

This 24-70mm HSM lens that I rented for this test appears to be a completely different/new design and, at least as it compares to the DA* 16-50, it seems to be very good....even comparing the Sigma @ 70mm to my DA Limited 70mm, it compares favorably.

tw
03-24-2011, 03:10 AM   #12
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Thanks for sharing.
I have the sigma 24-70f2.8 ex, but not the da*16-50.
Use it all time for indoor portraits. A bit heavy but great lens.
03-27-2011, 04:30 AM   #13
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If micro AF adjustment is lens dependent then what you experienced sounds logical.
If it is some sort of calibration error then the effect will increase/decrease with the lens elements moved apart - like it happens with a zoom lens.
I recently calibrated my lenses but only at the longest they offer. Adjustments may be over the top for shorter focal lenghts but DOF is usually more forgiving also so I guess this is the best way to use it.

To the tests:

I couldn't see a huge difference between Sigma and DA70 - only the edges are better on the DA70. Surprising.
Can't really see a difference between the DA* and the Sigma in the sharpness test shot, either...
"LENS ALIGN" looks better on the Pentax DA* shot but the lower part does with the Sigma.

Colour fringe tests are slightly unfair because the DA* adwell as the DA70 are more overexposed but still the Sigma beats both Pentaxes which seems legit.

The 400% crop isn't that telling but the bottom part looks far better with the Sigma. At this magnification it's not representative I guess.

So in the end the Sigma simply is a great lens.
I was reffering to the newer HSM version also but this surely proves this lens is in no way inferior to the OEm offerings.
Nikon's 24-70 will much likely perform even better but you can't use it on a Pentax so it doesn't really matter anyway.

Hmm, I could get the Sigma selling my DA* but then I also had to get something for the short end...
03-27-2011, 05:38 AM   #14
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From what I've seen the bokeh of the Sigma 24-70mm HSM isn't very good. I was set to spend the money in this when it came out, but after seeing the photozone reviews and a bunch of shots of fliker I said no.

Sigma AF 24-70mm f/2.8 EX DG HSM (FX) - Review / Test Report - Analysis
Sigma AF 24-70mm f/2.8 EX DG HSM (DX) - Review / Test Report - Analysis
03-27-2011, 07:42 AM   #15
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I've read the same review...several times.
Unfortunately when the Pentax was reviewed they didn't check the bokeh characteristics.
Since I own that lens I can say I don't find it overwhelming, either. So it may not be a huge downgrade.
Above F/4 its bokeh is really nice but even if the Sigma's was worse I could live with that given the other things the Sigma does better.

Only 3 things stop me from getting the Sigma and selling my 16-50: it is not sealed and the 16-50 is my only sealed lens. Frankly, the times I actaully needed the 16-50's sealing are countable with one hand but still the feeling of having it is calming.
One thing Pentax is really better at is coating front elements - the Super protect is almost a miracle - so hard to get smudgy unlike my Sigma lenses which are also harder to clean.
Reason 3: the gap that would occur without the 16-50...8mm to 24mm is too much.
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