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02-13-2008, 04:16 PM   #1
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Pentax 17-70/4 or Tamron 17-50/2.8?

I hope I can get others' opinions on how to make the choice between the two lens.
At least it's not easy for me.

02-13-2008, 04:35 PM   #2
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Or Sigma 17-70/2.8-4.5? Most people rate it well.
02-13-2008, 05:01 PM   #3
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Neither lens is available right now. The Tamron is almost certainly closer to release, and is very well regarded in other mounts. The Pentax 17-70/4 is an unknown, and no release date has been announced.

That being said, both lenses serve different purposes. One trades speed for a longer reach, and the other does the reverse. It comes down to what you want to do with it. If you need the speed, the Tamron is a no-brainer between the two (although there are also the Pentax 16-50/2.8 and Sigma 18-50/2.8 that cover the same range). If you need the reach, the Pentax would be a better choice (but who knows when it will be available ?).

The aforementioned Sigma 17-70/2.8-4.5 is somewhat of a hybrid between the two lenses you mention. It only real disadvantage is that it is not a constant f/2.8 lens (but it would be humongous if that was the case). It is otherwise a very solid performer, for a very reasonable price.
02-13-2008, 06:11 PM   #4
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Popphoto has reviewed the 17-50 and rates it highly:
Lens Test: Tamron 17-50mm f/2.8 XR Di II AF - - PopPhotoSeptember 2007
Also, you might want to consider the Sigma 18-50/2.8 Macro. Unlike the Tamron, it already comes in the Pentax mount and is in the same price range as the 17-50 is in other mounts. Popphoto also has a positive review of this lens as well:
Lens Test: Sigma 18-50mm f/2.8 EX DC Macro - - PopPhotoMay 2007

Another place you might want to check for feedback on the Tamron and the 2 Sigmas is http://www.slrgear.com.

HTH,
Heather

05-25-2008, 11:49 PM   #5
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Got the Tammy and it great.. The Pentax range though is very tempting.. Considering this lens will perform as the 16-45mm.. I might consider it.. The range works for me.. The only thing that stopped me from getting the Sigma was the QC..
05-26-2008, 03:44 AM   #6
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I got my Tammy from Japan via ebay. It seems sharp to the edges as per reviews. For around C$440 shipped, I love it. As good as it is I wouldn't like to vote for it over the Pentax, as the 17-70 hasn't been tested thoroughly in English yet (as far as I'm aware). But as the cheapest SDM for Pentax, it's bound to gain a lot of support.
I'd imagine both would be very nice.
05-26-2008, 03:48 AM   #7
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You have to choose between faster aperture and extra reach. Decide which is more important to you.
05-26-2008, 10:03 AM   #8
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QuoteOriginally posted by ftpaddict Quote
You have to choose between faster aperture and extra reach. Decide which is more important to you.
+1 for this!

05-27-2008, 04:05 AM   #9
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Just recieved my Tammy 17-50. Slight vignetting wide open at 50mm. Gone stopped down at all. Cant reproduce vignet any other way. Underexposes often up to .7, havnt figured out the pattern yet. Havnt noticed any bad focaus issue yet.
Very happy with the purchase.
05-27-2008, 04:17 AM   #10
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Really happy with the Tamron 17-50 over here, very sharp indeed.. but it also underexposes bye 0.7-1.0 but if it's constent it's okee

but really nice lens for it's price!.. and preforms better then the sigma 16-50 and 17-70..(IQ, sharpness to corners and stuff)

cheers
05-28-2008, 03:01 AM   #11
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Did a quick test

It front focuses a wee bit at 50mm and 35mm, then jumps to crazy front focus by 17mm. Heres the shots.
Since the frame isnt filled by the chart at 17mm, I put it up against a Sigma 18-50 3.5-5.6 to check that the ff wasnt attributed to that.

17mm overview and close crop followed by 35ish overview and crop.
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05-28-2008, 03:04 AM   #12
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Tammys 50mm over view and crop followed by the Sigma. The Sigma also faired better on the other focal lengths as far as focus goes (even taking into account DOF)
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05-28-2008, 03:10 AM   #13
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Also noted. Underexposure is about constant through focal lengths, though not exactly constant.
Sharpness is great in correct focus.
Bummed about the wide angle focus since i wanted it mainly for wide. But cant do much about it (assuming this isnt a design feature of every copy) becuase I mailordered it from BHPhoto.

Also tested a FA50mm 1.4 under the same conditions. Needless to say that thing is the best. And absolute killer at 2.8, wow.
10-01-2010, 03:31 AM   #14
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Pentax 17-70/4 vs Tamron 17-50/2.8 vs Pentax 16-50 vs Sigma 18-50/2.8 and Sigma 17-70

As stated before, first descision is whether you want reach, speed (or both).
.
For me speed, although nice is not a big issue, if i want to use a fast lens, I will use a prime which usually beats the fastest zooms easily. At the moment I have smc 55/1.8, smc-f 50/1.7 smc-a 24/2.8 and in screw mount 35/2.0 and 80/2.0 lenses. I'd love to add a faster 24 though.
If you can't take the time to change lenses and cannot carry a second body with the other lens and therefore definately want your zoom-lens to be fast, the descision is clear. For those, I think the Pentax is the better choice, it has a slightly longer range to the wide-angle side (On film I always preferred the angle of view of the 24mm (16mm on APS-C) more pleasant than the more common 28mm (18mm on APS-C, for me a 24mm(16mm) therefore is a must. It also means ith will perform better at 18mm. The Tamron however is also god and much cheaper. For me however the fast zoom which is much larger, brings too much weight and has an immense (Ø77mm) filter-thread, thus raising the price for filters enourmously.
.
Image quality is another factor, the longer the zoom-range is usually the lower sharpness and the more difference between the ends and the optimum focal length (usually in the middle). With the Tamron 17-50, Pentax 16-50 and Pentax 17-70 I expect this not to be a big issue.
As vignetting, sharpness and most other lens faults tend to disappear when closing the aperture and most shot are not made wide open, I tend to give lower weight to these as to distortion. When shooting on film, It is impossible to correct this and although this can be done fairly good with digital processing, that only applies if the distortion is barrel-type or pincushion-type. Many lenses, (especially wide-angle-zooms) tend to have a combination (aka wave-type) which is nearly impossible to remove.
.
I have seen pictures, mostly from tests, where distortion is plain awful and therefore for me it is a break-point. It is however inherent to zoom-lenses, all zoom-lenses have it, either more or less. That is the price to pay for choosing a zoom-lens.
.
For me the zoom range of 17-70 is nearly ideal (starting at 16 would be perfect).
Thus if distortion is not too big, I'd go for the Pentax 17-70 which much better than the (cheaper) Sigma, has a constant aperture and is smaller.
Currently I have no idea whether the distortion of the 17-70 is too large for me or not, I have found few reviews of this lens and can't really compare because I don't have the distortion percentages for my Tokina 28-80/2.8 and smc-A 35-105/3.5 (my favourite zoom for film, digital equal would be 24-70, I use it together with smc-A 24 (hence starting at 16mm would be perfect) to compare with. If distortion is too much, my 1st choice would be the 16-45/4.0

Last edited by KX-Digital; 10-01-2010 at 03:39 AM. Reason: unfinished
10-01-2010, 07:22 AM   #15
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Hmm. I bet the OP made his decision a couple of years ago, but I agree about the Pentax.
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