[kari]

I bought the K-x with the 18-55mm and 55-300mm kit lenses a while ago and am a bit disappointed with the shorter lens' sharpness, especially as I shoot landscapes quite often. The 55-300mm, on the other hand gives amazing results. So which of these lenses would be the best option?

Tamron SP AF 17-50mm f/2.8 XR Di II LD Asp.

Advantages:
Very sharp (according to reviews on this page)
f2.8 throughout the range.

Disadvantages:
Less reach
No OS
No Macro

Sigma 17-70mm f/2.8-4 DC Macro OS HSM

Advantages:
More reach on the long end
Macro
OS (means I can turn SR off, which is good as my K-x suffers from the 'mirror slap' issue)

Disadvantages:
CA at 17mm according to reviews
Lower score on reviews

At the moment I'm leaning towards the Sigma, because it's more versatile and would solve my SR issue at wide angles shooting vertically. But is it really the best choice? I could probably turn off SR on the Tamron too as it's a fast lens. Price wise they are basically the same (the Sigma is about $40 more).

[kari]

I also forgot to add that it would not be possible to return the lens once I've bought it (due to my current location) and that the Tamron seems to have front-focusing issues. Are the chances that you get a good copy significantly better with the Sigma?

[Ubuntu_user]

I can't speak for the Tamron, I can however speak for the Sigma. A very nice lens, indeed! Professional quality? No. But for how much you pay, it is a very good lens. I loved the working distance (up to 70mm). As for the copy I had, it was defect free. But I can't guarantee that you would get a good copy... Sigma has been known to have some QC issues.

Overall, I would definitely recommend the Sigma.

[anthers]

I have the Tamron and I've been very happy with it. The constant f2.8 is a big plus for me, and I find I can hand-hold it pretty well at slower shutter speeds. Mine is sharpest around f5.6 and between 20-50mm, although it is still perfectly usable at 2.8 and 17mm. It really comes down to whether you need 50-70mm on your wide zoom or whether you need f2.8 at the longer lengths.

In terms of production quality, I have seen both happy users and complaints from people with both lenses. I think I'd just pick whichever one seems to be the most useful and hope for the best.

[Tonto]

I have the sigma and was considering the Tamron at purchase. I agree with above two quite different lenses. Tamron would be a direct replacement for the kit lens if you are happy with the FL. It will enable you to shoot at higher shutter speed more often reulting in more keepers with less iso.
However if you want a walkabout lens the Sigma is hard to beat. I find even 70mm a tad too short but the lens covers alot of lens needs until I progress 2.8 at 17mm is great for indoor - it looks just fine! So is my subsitute low light lens.
Wide angle is great so unless I change lenses don't think I'll need a superwide. Macro ability is great so I won't need one for a while.
Overall IQ is great from what I've see so far, manual focus is good too which helps in macro/low light.
But both lenses are just ridiculously good value for money. You can't really go wrong. To add fuel to the fire have you considered a Tamron 28-70 2.8?
I f you plans involve a wide prime like the DA15 or a 10-20 then it may be worth a look, length AND speed.

[kari]

The 28-75 is too long for me at the wide end, and I can't afford a dedicated wide-angle at the moment.

However useful the Sigma may be, I think I will go with the Tammy. It's said to have almost prime-like quality, someone even said it's sharper at 50mm than their SMC A 50mm 1.7 (which I also have)

Just worried that the improvement over the kit lens will not be as noticeable with the Sigma and leave me feeling that I could have spent the money better.

[tubamatt]

Completely agree with you mate. I ordered the Tamron 17-50 today instead of the Sigma 17-70 because picture quality of the Tamron is better than the Sigma one and if your used to using your kit lens then the Tamron one would be the best choice I reckon.

[bdery]

If you need the speed, get the Tamron. Not much of a choice if constant f2,8 is needed. Otherwise, get the Sigma. It is a much better balanced lens, offering more bang for the buck.

[jimH]

I love my 17-50 Tamron! It's a great lens and here in the States it's got a 6 year warrantee.

[Jasvox]

The 17-50 is the best step up kit lens replacement going, in my opinion.

Jason

[planedriver]

have you considered the DA16-45? really great lens!

Andras

[Pablom]

OS (means I can turn SR off, which is good as my K-x suffers from the 'mirror slap' issue)

wasn't this thing solved by bending the battery contacts or something similar? I'm not sure about it but you might want to check that out.

[kari]

I haven't seen the shutter blur much lately with my K-x. Maybe just because I'm more careful when shooting vertically and because I don't mind using ISO 400 or 800 to avoid those shutter speeds. I decided on the DA* 16-50mm in the end! It's still in the mail so I can't report back on it.

[jimH]

I haven't seen the shutter blur much lately with my K-x. Maybe just because I'm more careful when shooting vertically and because I don't mind using ISO 400 or 800 to avoid those shutter speeds. I decided on the DA* 16-50mm in the end! It's still in the mail so I can't report back on it.

I'm sure you'll enjoy the lens, has a great reputation for IQ.