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08-12-2010, 05:14 PM   #16
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Mmmmm…. three words for ya- buy a flash.

No prime will perform any better than what you have there at those light levels/shutter speeds.

08-12-2010, 05:29 PM   #17
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From the first pic, it looks like you just barely missed focus. His shirt looks more sharp than his eyes, which would give a much better general impression of sharpness.

The others it's harder to tell... they just look oof, rather than soft.

Try taking more test shots outside?
08-12-2010, 11:27 PM   #18

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A proper copy of the Tamron 28-75/2.8 should be plenty sharp even at f2.8.
Can you compare against some other lens you have (you mentioned the DA70)?

My own test shots against a A50/1.4
100% center crop

A50/1.4 @f2.8

Tamron 28-75/2.8 @ 50mm f2.8

The Tamron is just a wee bit less sharp, but its wide open, while the 50/1.4 has been stopped down to f2.8.
I don't even think the difference will mean anything in real photos.
08-13-2010, 06:29 AM   #19
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My comparison shots with the FA 50/1.4 were pretty similar to the ones posted. I wonder if there is an AF issue - a bit of FF - if this is the lens or the camera or the combo. I don't think the FA 50 has this issue, curious about the DA 70. Is this common with 3rd party lenses as opposed to pentax? If I go into debug to fix it, will it affect my other lenses?

08-13-2010, 12:59 PM   #20
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QuoteOriginally posted by tbirdas Quote
The baby picture looks good to me, the other two not as much.
Second looks like motion blur combined with being slightly oof (most cameras will FF in tungsten light, and that's not something you adjust away but rather live with and compensate for). Last one looks fine, except DOF is so shallow that barely anything you care about is in focus. But the parts that are in focus look as sharp as can be expected with any lens given the conditions. So overall, I'd say these pictures illustrate the points I made earlier very well - it's not about the sharpness of the lens, but the difficulties inherent in low light photography.
08-13-2010, 01:11 PM   #21
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Thanks everybody, it is reassuring to get opinions form people that are more experienced than me in photography.
Maybe I should return the 70mm limited without opening the box, I am afraid I may keep both!
08-19-2010, 06:17 PM   #22
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well the 70mm limited came...size is certainly great. First few shots under same lighting conditions with 28-75 show only a minor improvement with the 70mm. More to follow, but if the trend continues, I suspect the problem has been my unrealistic expectations.
08-20-2010, 09:51 AM   #23
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Well, a little of that, but again, mostly it's just a matter of technique. Both lenses are capable of far better results than what you posted, even in low light. But you have to get focus right, and you have to be careful to combat blur from camera shake and subject motion.

08-21-2010, 04:16 AM   #24
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The more I use the 70mm limited the more I like it. The pictures are a bit sharper at 2.8, perhaps due to more accurate focus. Is it be because of Pentax vs 3rd party lens? The Tamron seems to still FF just a little bit indoors while the Pentax is spot on. I am even more puzzled now. I forgot to mention that I have a used copy of the older Sigma 17-70 which seems to be fine. I am thinking more and more I should return the Tamron and keep the 70mm limited. Final tests will be this weekend in better light conditions.
08-21-2010, 07:27 AM   #25
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For your stated purpose (kids and general indoor photography) 28mm may well not be wide enough - when I'm doing this sort of stuff, I tend to use my kit lens at 18mm and 55mm, and rarely anywhere in between.
08-01-2012, 02:59 AM   #26
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Found this thread today and it is just the same question I am currently brooding over. I have the Tamron 24-75mm and used it for my portrait shoots so far. The outcome seems great to me but I have no comparison to prime lenses like Da 70mm, DA 40mm or 50mm 1.4. What I'm asking myself is it worth investing into one of those primes or stay with the Tamron? The problem I had recently was while shooting a couple at 24mm wide open with available light. Almost each picture was too soft for my perception not comparable with the following samples.
I attach some pictures made with the Tamron so you have an impression of what I am talking about. Pictures are taken at f 7.1 - f 8.0, 1/100 - 1/125s with my K7

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