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12-19-2013, 10:31 AM   #1
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Sigma 18-50mm f2.8, or Tokina 28-70mm f2.8?

Recently on ebay I've been seeing two lenses that I'm keen for:

Sigma 18-50mm f2.8 (continuous) and Tokina AT-X Pro 28-70mm f2.6-2.8.

I currently have the Tamron 28-75 f2.8, and the front focusing issues it has makes it only useful on my K-01. (It front focuses at different rates at different zooms and it's impossible to correctly dial in with the K-30's microfocus adjustments). I'd really like to have a f2.8 zoom that will work on my K-30 and K-x....

I do really like the range of the 28-75, but I do occasionally find myself needing 18mm. 50mm is often not enough for me though. So either way I'm making a sacrifice. So what it's going to come down to for me is, which is the sharper lens wide-open? The Sigma or the Tokina? (Note, I only care about center sharpness)

Charles.

12-19-2013, 10:40 AM   #2
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How about one of the 17-70mm lenses? Though, they might be a little more expensive. Btw, your sig says you already have a couple lenses in that range. DA L 18-55mm, F 35-70mm, Tokina 35-70mm, Signa 28-105mm..
If I were you, I would instead invest in more primes, like an (ultra) wide angle.
12-19-2013, 10:47 AM   #3
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I have a Sigma 18-50 f/2.8 constant, the first version (67mm filter, non-macro), and it's been good for the relatively low price I paid for it used. However, I find it is better on my K-01 than on my K-x, in terms of focus accuracy. So while this is only my own experience, it sounds similar to yours with your Tamron 28-75.
12-19-2013, 10:55 AM   #4
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Forget what's in my signature, it hasn't been updated in forever. Besides, I only have one in that range that is 2.8 constant aperture. I really, really need one that works on my K-30, the Tamron just doesn't, and the prices for the Sigma and Tokina are excellent. $500 for a lens is out of my budget right now.

Charles.

12-19-2013, 11:20 AM   #5
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QuoteOriginally posted by ChopperCharles Quote
Forget what's in my signature, it hasn't been updated in forever. Besides, I only have one in that range that is 2.8 constant aperture. I really, really need one that works on my K-30, the Tamron just doesn't, and the prices for the Sigma and Tokina are excellent. $500 for a lens is out of my budget right now.

Charles.
I personally would go with the Sigma. I use 18mm much, much more than I use 70mm.
However, if you never shoot anything wider than than 28mm, then that makes your choice easier
12-19-2013, 11:48 AM   #6
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At this point, it's a toss up between which I want more, 18mm or 70mm. I just want the sharpest wide open, and I'll work around the focal length restrictions.

Charles.
12-19-2013, 11:49 AM   #7
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Charles,

Be aware that there are multiple versions of the Sigma 18-50 f/2.8 constant zoom. The original one has a 67mm filter size. The revised version has a 72mm filter size and is labelled "macro" because it can focus slightly closer. In addition, many users claim that the macro version is sharper than the original, because of a different optical formula used. Nevertheless, the original version is the lightest and most compact of the Sigma 17/18-50mm f/2.8 constant zooms.

I've been happy with my non-macro Sigma 18-50 but it's definitely not that sharp wide-open, and from what I've read, trails the Tamron 17-50. But stop it down to f/4 and it really starts to shine. I use it more outdoors than indoors but can use it indoors in a pinch, especially with a flash. For utmost sharpness I slap on a prime lens but for convenience snap shooting, the Sigma 18-50 has been a nice and inexpensive workhorse.

According to this Member at this post:
https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/92006-if-no...tml#post937697

QuoteQuote:
I still have the old (pre-macro, pre-HSM) Sigma 18-50/2.8 and will keep it. Not only because my own DA 16-50 also fell apart a while ago and I want a backup at hand, but also, because it is much smaller and has less distortion. In terms of sharpness and contrast, the Sigma can easily hold its own, compared with the DA.
So wow, he has compared his copies of the DA* 16-50 and the first version Sigma 18-50, and thinks Sigma is its equal in terms of sharpness and contrast! That's reassuring to hear.

Here are some more helpful threads on this lens:
https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/131837-foll...macro-hsm.html
https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/6177-sigma-...2-8-macro.html
https://www.pentaxforums.com/forums/10-pentax-slr-lens-discussion/29276-sigma...ro-anyone.html

Good luck!
12-27-2013, 01:11 PM   #8
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Well, I decided to send my Tamron 28-75 off for an adjustment. $140 is cheaper than any of the other options -- that is, if they're able to actually get it right, AND they don't try and screw me with the "you must have dropped it" bullshit.

Charles.

12-28-2013, 10:13 PM   #9
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Well, this may be a stretch, but have you thought about the Sigma 'C' 17-70 mm f/2.8-4 ? I've read that the lastest (3rd gen) is actually pretty good. I haven't seen one myself (there are no Pentax stores in SoCal that stock anything).
12-29-2013, 10:08 AM   #10
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I must have constant f2.8 aperture, unfortunately.

Charles.
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