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12-27-2011, 11:29 AM   #1
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Try for another Tamron, or give the Tokina a shot?

I have a Tamron 28-75 f2.8 which I never use. The autofocus is not at all reliable, and I cannot fix it to what I consider "acceptable" with the in-camera microfocus adjustment. The focus lock varies from wide to tele, and also based on the distance of the object from the camera. When the photos are in focus, they're really sharp even at f2.8. But that's when they're in focus.

I've been told I just got a bad copy, and I'm a little leery of replacing this with another Tamron 28-75 now... I will be buying online, so I don't want to have to go through a bunch of copies before I find one that doesn't suck. So I was looking into the Tokina ATX 28-70 f2.8, the SV version. Anyone with a copy of the Tokina, can you comment on the autofocus reliability? What about sharpness at f2.8? Finally, what's the minimum focus distance? If you own the Tokina, would you recommend it?

Thanks!

Charles.

12-27-2011, 12:04 PM   #2
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Have you considered a second hand FA* 28-70/2.8?

That's my fav lens, never let me down and focus has always been spot on with the K10D through the K-5.
12-27-2011, 12:17 PM   #3
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I had the same problem with a used Tamron 28-75/2.8 I picked up this year and since it was only 3 yrs old, used the 6 yr warranty to get it calibrated free and without sending my camera with it. Now the variance from 28mm to 75mm is small enough that I can just use the AF adjust at 50mm and thats it, even at f2.8.

Funny, I know a member with the Tokina who was asking me about buying my Tamron so HE could get proper AF. I recommend a calibration if thats all it takes to put you back in love with the Tammy. I dont know what it costs if out of warranty.
12-27-2011, 12:28 PM   #4
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I bought the Tamron second-hand, and the warranty is not transferable and I have no idea if it's still in warranty anyhow... I could look into a calibration though.

Charles.

12-27-2011, 12:29 PM   #5
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The FA is $1200 used. Thanks, but that's way out of my budget.

Charles.
12-27-2011, 01:16 PM   #6
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You might also consider the Sigma 24-70mm f/2.8 EX DG Macro. The seem to run around $300 used and I am quite happy with mine so far. The lack of quick shift focus is a bit annoying but I don't think the Tamron or Tokina have it either. The lens's main weakness is flare if you shoot across the sun, but I've seen the same complaint about the Tokina and so far it hasn't been an issue in my shooting. I think close focus is around 1:4 at 70mm. The HSM version is another option but it is quite a bit more expensive.

Sample photos on several systems:
Flickr: Sigma 24-70/2.8 EX DG MACRO
12-27-2011, 01:36 PM   #7
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1:4? What's that in inches? The Tamron is nice because minimum focus distance (at all focal lengths) is 6". I will look into the Sigma as well... wouldn't mind the extra 4mm on the wide end actually.

Charles.
12-27-2011, 02:50 PM   #8
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Have you tried posting sample pictures to demonstrate your focus issues? I know it fashinable and commn to b,ame lenses, but all it takes is a few minutes reflectin on how AF actually works to realize there is next to nothing that could could possibly cause a *lens* (as opposed to a camera, or to the user) to misfocus. The only credible physical explanations ever given would be very easy to test for using a somple focus test chart. One potential physical cause would cpshow focus getting worse as you stopped down, meaning it would never be a problem wide open, and the DOF would mask the problem as you stopped down, so it would never be a problem in practice. The other potential physical problem would cause images to focus differently depending on the starting position of the focus - whether it started focused in front or or behind the target. And in this scenario, the effect would be undetectable unless you started from close to minimum or close to infinity and the ring needed to turn a long ways to get to its final position. A subsequent refocus woild result in perfect focus.

Unless you have controlled tests showing one of those two effects, or another plausible theory as to what could actually be going on physically, I submit your problem is actually either with your camera, or, more likely, with your technique.

12-27-2011, 04:10 PM   #9
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QuoteOriginally posted by ChopperCharles Quote
I bought the Tamron second-hand, and the warranty is not transferable and I have no idea if it's still in warranty anyhow... I could look into a calibration though.

Charles.
Ah..thats why I mentioned that my aquisition was used also. Officially maybe not transferable, I never read to find out, but I emailed tech support to get an RMA# and checked with the seller who said it was fine to use his name if needed so I included both our names on the return address as well as a copy of the original receipt to prove it was less than 6 yrs old. They had no issues with my email or address not matching the invoice. YMMV, but if you need to know anymore then PM me please.
12-27-2011, 07:58 PM   #10
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Marc, you might believe that nothing could possibly be wrong with a lens to cause it to misfocus. I've had others try and push that rhetoric as well, but it just doesn't hold water. I've used focus charts extensively to set the microfocus - yes, I used them correctly too - and I could dial in adjustment for one specific set of conditions. 70mm at 12 inches, for instance, but then moving to a different set of conditions (28mm at 2 feet, 70mm at 6 feet, 40mm at 2 feet, whatever) all required VASTLY different microfocus settings. VASTLY. Using the focus charts in natural outdoor lighting, 30 degree angle, the tamron would front focus as much as 11cm in some cases, as little as 3cm in others. (as indicated on the chart). The microfocus adjustment is a static adjustment, it just can't account for a range like that.

I don't have problems with the autofocus on my SMC-F 50mm f1.7, and it has a MUCH narrower depth of field. I don't have these issues with ANY other lenses I own, only the Tamron gives me fits. I find myself using my 35-70mm f3.5 if I need a walkaround zoom, because it is nearly as sharp as the tamron and it always nails focus dead to rights. I can't rely on the Tamron to do that. I've missed too many shots with the Tamron, even at smaller apertures. It just does not focus accurately. (and do note that Tamron QC and the focusing issues are well documented on the internet, so it's not just me)

Anyhoo, I contacted the previous owner and he emailed me the original transaction receipt. I will see if I can have it fixed. Out of warranty it's $140 to have it serviced, so even if they don't honor the warranty that's still right around what I'd lose selling it with a focusing problem.

Charles.
12-27-2011, 08:09 PM   #11
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QuoteOriginally posted by ChopperCharles Quote
1:4? What's that in inches?
Reproduction ratio. Actually 1:3.8, vs 1:3.9 quoted for the Tamron. Supposedly the Tamron focuses down to 33cm and the Sigma to 40cm, so not a huge difference.
12-27-2011, 08:42 PM   #12
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33cm? That's 13 inches... I think you're mistaken on that number, I just pulled out my Tamron and at 28mm it focuses at right around 7 inches. At 75mm it focuses at 5.5 inches.

Charles.
12-27-2011, 09:26 PM   #13
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I picked up that number from Tamron's literature: Tamron Canada DSLR Photo Lenses - TAMRON 28-75mm f/2.8 Pentax Di A09P 104A09P CANADA -

Keep in mind it is measured from the sensor and not the end of the lens. Using your method the Sigma focuses to 6 inches at the wide end and 7 at the long end.
12-27-2011, 11:07 PM   #14
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Okay, that makes sense then. Wasn't aware it was distance to the sensor... the specs for my P&S (Pentax RZ10) lists a 1cm minimum focus distance, and that's obviously from the front of the lens to the object, and that is just how i assumed it was measured for dSLRs as well. (and honestly, it's the measurement I care about, after all! )

Charles.
12-28-2011, 07:02 PM   #15
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QuoteOriginally posted by ChopperCharles Quote
Using the focus charts in natural outdoor lighting, 30 degree angle, the tamron would front focus as much as 11cm in some cases
If your camera ever focuses 11cm from where it tried to, the camera, not the lens, is hopelessly misadjusted. But I'd have to see a picture to believe that ever happened.

QuoteQuote:
do note that Tamron QC and the focusing issues are well documented on the internet, so it's not just me
Had the Internet been around in 1400, you'd have found the flatness of the earth well documented as well, so I'mnot impressed by that as a line of argument. I realize I am in the minority in thinking about this logically, but no one ever takea me up on this challenge, so I have still yet to see evidence that a lens can misfocus in any way other than the ways I described, with the effects I described.
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