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06-01-2012, 08:55 PM   #1
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Kr + Tamron 70-200 2.8

I've seen a lot of threads about K5's using the Tamron 70-200 2.8, but haven't seen one for the Kr. Does anyone know if the lens' performance makes a difference with whether you use it with a Kr or a K5? I'm really more concerned about the AF performance of the lens.

I just got one myself. I've had it less than a week and due to a ridiculously busy work schedule (that seemed to start the day UPS dropped off the lens) I've only had a chance to try it out twice. Both times have been indoors and outside when the sun is almost completely gone.

I've noticed some focusing issues with the lens. From reading up on the lens already, this seems to be the major complaint about it. I'm not ready to complain about the lens just yet though. I think it's pretty safe to say that the fact that I've only used it twice merits the possibility that I still haven't learned how to use it properly. I've noticed that its autofocus is very hit or miss. Both times I've used it I've had low light and used a high ISO (up to 6400).

I do have to mention that when the autofocus gets it right, the images are incredibly sharp, even at 2.8. I don't think it's front or back focus, some images are spot on.

My questions are:

1) Are the low light focusing issues normal? Is it the same as with other lenses that will struggle with lower light? Don't all AF lenses struggle with low light?
2) How can I get more accurate shots with this lens? I figure there's got to be some quirks to learn about it.
3) Are there any other tips that would help me with this lens?

I will probably use this lens 70 percent of the time for stationary subjects (mostly people), but would like to use it for pictures of my kids (when they're playing) and for sports. I know that Sigma would have been the better option for sports, but the 1300 dollars is way out of my price range and I liked the image quality from the Tamron more than the image quality from the Sigma.

Thanks again for any help you guys can offer.

06-01-2012, 09:07 PM   #2
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No issues on k-x - loved it actually.
06-02-2012, 06:30 AM   #3
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f/2.8 is a full stop wider than the kit lens at its longest zoom. At this aperture, the depth of field (depth of focus) is more shallow than anything the kit lens can produce. And where you are most likely to shoot wide open is in low light situations. Based on your post, at smaller apertures the camera's auto focus is good enough for the subject to fall in the deeper DOF, but perhaps not at f/2.8. I would recommend checking and perhaps tweaking your auto focus specifically for your new lens.

There is a 'sticky' on this site on how to do that, and while it is good, it also relies on a fairly expensive piece of equipment that you are likely to use exactly once. There is a much less expensive way to accurately perform fine adjustments to auto focus. I wrote about it here:
https://www.pentaxforums.com/forums/pentax-k-r/177901-best-procedure-adjust-a...ml#post1857120
06-02-2012, 07:10 AM   #4
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QuoteOriginally posted by reivax Quote
My questions are:

1) Are the low light focusing issues normal? Is it the same as with other lenses that will struggle with lower light? Don't all AF lenses struggle with low light?
2) How can I get more accurate shots with this lens? I figure there's got to be some quirks to learn about it.
3) Are there any other tips that would help me with this lens?
1) All AF systems need light to focus. All the AF lenses I've used struggle with low light. I find that I actually get better wide-open dim AF performance on my K20D with my F35-70/3.5-4.5 than with my FA50/1.4 -- likely due to the zoom's thicker DOF.

2) For more accuracy, shoot in brighter light. For more sharpness, stop-down a little. DOF at 200/2.8 is razor-thin, especially when the subject isn't far off. The point you think you're focusing on might not be the point your camera is using.

3) In low light, MF often beats AF. Learn the MF tricks: Prefocus. Don't rush. Wait for Focus Confirmation. With SR on, follow the 1/FL rule. Boost ISO to get an adequate shutter speed. High-ISO noise can be fixed in PP; misfocus or motion blur, can't.

06-02-2012, 10:08 PM   #5
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Actually, 2.8 is two stops faster than the kit lens at full zoom
06-03-2012, 08:29 AM   #6
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I wanted this lens desperately and decided to rent one before buying. I had previously bought a lens on impulse and ended up selling it 4 months later after I found I never used it.

What I found is the more I used a mono-pod or tripod the better shots I got irregardless of light but especially in low light. The only thing I could figure, the lens is so
heavy that hand holding it wasn't a real option for me if I wanted dead on focus and sharp images especially at the longish end.

It's a good lens if you'r into weight lifting. :-)
06-03-2012, 10:23 AM   #7
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QuoteOriginally posted by RioRico Quote
For more accuracy, shoot in brighter light. For more sharpness, stop-down a little. DOF at 200/2.8 is razor-thin, especially when the subject isn't far off. The point you think you're focusing on might not be the point your camera is using.
Thanks. I hadn't really considered how thin the DOF would be at these longer ranges with 2.8. That might be a part of the problem.

Now I'm curious, if I'm shooting indoors or in low light without a flash, would 2.8 really be a useful aperture above 130mm? I don't mind bumping up the ISO, but I worry that the DOF might be too thin to be useful. One of the reasons I really wanted this lens was to have those extra stops for low light situations. I'm concerned about situations with groups of people or maybe shooting a sport. Should I be concerned about not being able to get usable shots? Or will I probably be fine?

QuoteOriginally posted by geru2000:
What I found is the more I used a mono-pod or tripod the better shots I got irregardless of light but especially in low light. The only thing I could figure, the lens is so
heavy that hand holding it wasn't a real option for me if I wanted dead on focus and sharp images especially at the longish end.
Yeah, I shoot hand held 99% of the time. I think it's time to take that monopod out of the closet. That lens does get heavy pretty quickly.
06-03-2012, 10:53 AM   #8
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QuoteOriginally posted by reivax Quote
Now I'm curious, if I'm shooting indoors or in low light without a flash, would 2.8 really be a useful aperture above 130mm? I don't mind bumping up the ISO, but I worry that the DOF might be too thin to be useful. One of the reasons I really wanted this lens was to have those extra stops for low light situations. I'm concerned about situations with groups of people or maybe shooting a sport. Should I be concerned about not being able to get usable shots? Or will I probably be fine?
Birders and sports toggers love those longer faster lenses. DOF is thinner with closer subjects, thicker with further ones. The basic DOF guidelines:

* For thicker DOF: shorter focal length and/or tighter aperture and/or greater distance
* For thinner DOF: longer focal length and/or wider aperture and/or closer distance

One way to beat thin DOF, especially with any action, is machine-gunning, spray-and-pray. Use Continuous drive mode and fire off a string of shots. At least one may be good, eh?


Last edited by RioRico; 06-03-2012 at 12:38 PM.
06-03-2012, 12:21 PM   #9
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QuoteOriginally posted by RioRico Quote
Birders and sports toggers love those longer faster lenses. DOF is thinner with closer subjects, thicker with further ones. The basic DOF guidelines:

* For thicker DOF: shorter focal length and/or tighter aperture and/or greater distance
* For thinner DOF: longer focal length and/or wider aperture and/or closer distance

One way to beat thin DOF, especially with any action, is machine-gunning, spray-and-pray. Use Continuous drive mode and fire off a string of shots. At least one mya be good, eh?
Hahaha. I will definitely use a combination of "machine-gunning" and "sniping" until I get more comfortable with the lens. Thanks for the advice.
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