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11-19-2010, 07:52 AM   #1
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Quick question on Tamron 17-50mm vs Sigma 17-50mm

I currently have the Tamron 28-75mm f/2.8 lens, which I LOVE, and is a great walk-around lens and an incredible portrait lens. However, sometimes I need a wider angle, so I was planning on buying the little brother of my lens, the Tamron 17-50mm f/2.8.

But now Sigma has complicated things by releasing a new 17-50mm f/2.8 with an HSM motor and optical stabilization. The silent HSM would be nice, and the stabilization sounds like it might be more effective than my K-x sensor-based stabilization, but I really don't NEED either of those features. Since the IQ seems to be similar between the two lenses (with the Sigma having less CA at wide angles), I am still inclined to go with the less-expensive Tamron (approx $150 - $200 less). The Tamron also has the warranty advantage with 6 years vs 4 years for the Sigma.

However, I have one question that could make the difference. One nice thing about my 28-75mm lens is that in addition to the constant aperture, it maintains constant focus as you zoom in and out. I have found this to be especially useful when recording video. I don't know if there's a technical term to describe such a feature, but I have heard the lens referred to as a "true zoom" since it maintains focus.

Does anybody know if either the Tamron 17-50mm or Sigma 17-50mm maintains focus as you zoom in and out?

Any other feedback on the Tamron vs Sigma would also be appreciated. Thanks!

11-19-2010, 08:07 AM   #2
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I have the Tammy 17-50 f/2.8 XR Di II and I don't believe, by design, that it's parfocal (term for maintaining focus while zoomed). It does sometimes change focus between zooming from max to min and vice versa. Not much - it's very slight. I don't shoot video with my dslr, so it's never posed a problem for me.

I can't speak for the Sigma and whether it is parfocal or not.
11-19-2010, 08:53 AM   #3
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Those 2 zooms have quite a bit of overlap. Howzabout the 12-24 or similar? Of course now there would be a small FL gap, but you get some actual wide angle.
11-19-2010, 09:38 AM   #4
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QuoteOriginally posted by SpecialK Quote
Those 2 zooms have quite a bit of overlap. Howzabout the 12-24 or similar?
I should have explained my plan. I have been using the Tamron 28-75mm f/2.8 most of the time, and used the Pentax DA 55-300mm when I needed more reach. I kept my 18-55mm kit lens and use it when I absolutely need the wider view.

My plan is to sell my Tamron 28-75mm and my Pentax 55-300mm and replace them with the Tamron (or maybe Sigma) 17-50mm f/2.8 and the Sigma 50-150mm f/2.8.

I already sold the 55-300mm on eBay for $357 (not bad, considering I picked it up on Craigslist for $150). The 55-300mm was actually a decent portrait lens for me, so I was sad to see it go. You can see some of the images I captured with it on the completed eBay auction:

Pentax lens DA 55-300mm f4-5.8 ED k-x k-r k-7 k20d k10d - eBay (item 130450659766 end time Nov-08-10 17:14:20 PST)

I also sold a Sigma 18-125mm that I basically got for free but almost never used (I guess superzooms just aren't for me).

I'm having a hard time parting with the 28-75mm lens, but I just can't afford to keep it if I'm buying the 17-50mm and the 50-150mm. I have a home studio where I take a lot of portraits, and the 28-75mm has been perfect for that. I'm not sure whether I'll be using the 17-50mm or 50-150mm more in the studio. In a perfect world I would keep the 28-75mm in the studio, and take the 17-50mm and 50-150mm out with me.

As you can see, I'm torn.

I was briefly considering the Pentax 50-135mm f/2.8 instead of the Sigma 50-150mm f/2.8, but it seems like the Sigma has almost equal picture quality, but focuses faster. It is also slightly less expensive and has a 4-year warranty, vs 1-year for the Pentax. With all of the anecdotes I've encountered about the SDM failing on the Pentax 50-135mm, I'm nervous about spending so much on a lens with a 1-year warranty.

Eventually, I might add the Sigma 10-20mm to my collection, but it might be a while before I can convince my wife that I REALLY need another lens.

11-19-2010, 10:34 AM   #5
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I sent an email to Tamron and to Sigma asking if their 17-50mm f/2.8 lenses were parfocal or varifocal. For Tamron, I asked specifically about the non-VC version of the lens. While I was at it, I also asked Tamron if they had any plans to release their new stabilized 70-300mm lens in a Pentax version. It seems to have excellent image quality, and the IS on my K-x seems to be less than stellar at long focal lengths.

Tamron responded within 15 minutes.

Here is Tamron's reply:

Hi Edgar,

The 17-50 is parfocal. Unfortunately there are currently no plans to introduce the new 70-300 VC for Pentax. Please let me know if you have any questions!

Regards,

Customer Service
Tamron USA, Inc.
10 Austin Blvd.
Commack, NY 11725
631-858-8400

Last edited by Edgar_in_Indy; 11-19-2010 at 10:41 AM.
11-19-2010, 01:08 PM   #6
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This is the response I just got from Sigma reference the new 17-50mm f/2.8:
Thank you for your interest in Sigma products.

The lens is a varifocal lens.


Desiree Gaige
Customer Service/Technical Support
Sigma Corporation of America

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