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11-07-2010, 06:26 PM   #16
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QuoteOriginally posted by yusuf Quote
I recently got the 28-75mm and I have been happy with it as far as IQ goes. However, in low-light, the lens hunts a lot in auto-focus, sometime so long that I've missed some beautiful shots. AF is fine in day-light though. I Googled about it and found that this is typical with this lens.

Now since I am eying on Tamron 70-200 f2.8 too, I suspect that it will be even slower in focusing than 28-75mm. Can someone used both comment on relative focusing speed? is Sigma HSM significantly better?

I am using it with K-x.
I think that focus speed is more a function of the camera, rather than the lens. After all it's the camera sensors that are determining the focus and not the lens. The lens is only reacting to the camera's ability to lock on to a focus point.

I also think that "front focus" and "rear focus" that I frequently see blamed on a particular lens are also a function of the camera sensors, rather than a particular lens.


Last edited by jimH; 11-07-2010 at 06:31 PM. Reason: add comment
11-07-2010, 07:09 PM   #17
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QuoteQuote:
JimH: I think that focus speed is more a function of the camera, rather than the lens. After all it's the camera sensors that are determining the focus and not the lens. The lens is only reacting to the camera's ability to lock on to a focus point.

I also think that "front focus" and "rear focus" that I frequently see blamed on a particular lens are also a function of the camera sensors, rather than a particular lens.
I think your analysis is spot-on. And just imagine the even more likely event for focus problems when the lens is made by one company, and the camera by another? Pentax has a hard enough time getting its own lenses to focus properly, and this is vital to their bests interests. Getting a Tamron lens to focus properly on a Pentax body is not necessarily in their best interests. ")
11-07-2010, 08:06 PM   #18
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QuoteOriginally posted by philbaum Quote
....
But here's a trick that may help you, it certainly helps me.

I went to the custom menu and disabled half-shutter focusing. I then enabled the AF button for focusing. .....
That helped me too...many times what I thought was focus hunting was actually caused by minor subject motion or my moving the camera for minor re-framing.

Dave

PS A slightly different question is how a particular lens (given high contrast and wide aperture) can be prone to focus hunting since the optics and decision making involved are in the camera; all the lens need do is move. I guess if the lens doesn't move reliably in response to camera demands (like maybe it overshoots) hunting can result.
11-08-2010, 02:52 PM   #19
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QuoteOriginally posted by jimH Quote
I think that focus speed is more a function of the camera, rather than the lens. After all it's the camera sensors that are determining the focus and not the lens. The lens is only reacting to the camera's ability to lock on to a focus point.
Just did a non scientific experiment. I tried each lens on my K10d focusing between a close object and a far one. I then tried the same on my daughter's K-x. The K-x was definitely faster at locking in on focus.

11-11-2010, 07:36 AM   #20
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Yesterday i received my new tammy 70-200. I can say that until now i couldnt find a speed problem. I own a K7 and i suppose the camera is working pretty good with the lens..
I was not sure for my choice, between the tamron and the sigma. Anyway i am interested more in the Optical Quality and for Nature photography and i took the risk.. ( plus it was cheaper then the sigma )

Did some shots today..i can definitely say its the fastest zoom lens i own, i was really impressed and had the feeling i can shoot action as well. Anyway time will tell, i still didnt check the pics on my Monitor This baby will be my Companion for my New Zealand trip, together with the sigma 8-16, pentax 16-45 and sigma 105 macro!
11-11-2010, 07:38 AM   #21
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Awesome, I also plan to get one. Would love to hear your experience about this too - https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/121853-tamron-...naccuracy.html
11-11-2010, 07:56 AM   #22
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QuoteOriginally posted by yusuf Quote
Awesome, I also plan to get one. Would love to hear your experience about this too - https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/121853-tamron-...naccuracy.html
ok i will post my opinion, when i tested thoroughly
11-11-2010, 12:41 PM   #23
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Carrying your 70-200 with you on an overseas trip? You're keen.
Might have to do some pack marching prior to the trip to build your strength and endurance up to be able to lug all your gear around...

11-11-2010, 02:12 PM   #24
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QuoteOriginally posted by Ash Quote
Carrying your 70-200 with you on an overseas trip? You're keen.
Might have to do some pack marching prior to the trip to build your strength and endurance up to be able to lug all your gear around...
its not too much weight all the lenses..but i am thinking if its worth taking the tripod..2.4 kg, maybe taking only the monopod

i checked the pics, didnt see a problem with focusing..the pictures were pretty sharp

here is a link with 6 pics
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