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09-18-2012, 02:20 PM   #1
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Does sigma HSM lens improve AF accuracy on the k5?

So I was reading the in depth comparison between the 2 sigma and 1 pentax 17-70mm lens.
The AF review suggest that both the sigma has the fast and reliable focus, while the pentax lens has a pretty low rating on it.
So I was wondering, does HSM offer a different method of focusing on the camera?

Anyone who own both pentax and sigma HSM lenses, what is your experience on AF?
I tried to search this topic on the forum but couldn't find any.
If the HSM really does make a difference on AF accuracy, I am getting either the 17-70mm, or the cheaper 18-50mm HSM from sigma... (I just sold my DA 18-55)

09-18-2012, 02:42 PM   #2
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I have one Sigma HSM lens and one Pentax SDM lens. Both are pretty big lenses, but not otherwise strictly comparable (one is a 70-200, another is a 300).

I find the Sigma HSM very nice and it does seem to deliver a good, confident AF. But I have no complaints about the SDM lens either. Both seem fast to lock and hold AF.

If you shoot low contrast scenes, shoot scenes busy with detail, use all 11 points all the time, shoot in very low-light, use a UV filter etc, SDM/HSM probably isn't going to make much difference to how the AF performs though.
09-18-2012, 02:51 PM   #3
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thanks for sharing your experience rawr.
i have only been using pentax lens (18-55mm, 55-300mm, DA 35/2.4, pentax-f 35-70mm), and similar to others in the forum, i occasionally suffer focus issue.
and yes i know finding more contrasted spot will improve focus, but it still suffers much more than my xz-1 point and shoot.

all of these lens use screw drive to focus, after reading the comparison article makes me wonder if the problem is on the screw drive.
and as i know, HSM improves focusing speed and noise, so i am thinking if it improves on accuracy too...
does tamron lens offer similar feature? if so what is the function call in their term?
09-18-2012, 03:40 PM   #4
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QuoteOriginally posted by telly0050 Quote
thanks for sharing your experience rawr.
i have only been using pentax lens (18-55mm, 55-300mm, DA 35/2.4, pentax-f 35-70mm), and similar to others in the forum, i occasionally suffer focus issue.
and yes i know finding more contrasted spot will improve focus, but it still suffers much more than my xz-1 point and shoot.

all of these lens use screw drive to focus, after reading the comparison article makes me wonder if the problem is on the screw drive.
and as i know, HSM improves focusing speed and noise, so i am thinking if it improves on accuracy too...
does tamron lens offer similar feature? if so what is the function call in their term?
Tamron has PZD motors.

09-18-2012, 03:50 PM   #5
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QuoteOriginally posted by telly0050 Quote
does tamron lens offer similar feature?
As far as I know, all Tamron lenses for Pentax (17-50, 28-75, 70-200 etc) are screw-drive. Some of the newly announced Tamrons have HSM-like AF, but they aren't available for Pentax (yet).

SDM/HSM help the lens sometimes find focus better than screw drive because the lens mechanism is able to move back-and-forward faster as the camera PDAF tries to get an AF lock.

So SDM/HSM may certainly improve the speed with which you get a good focus result. In particular, I notice a difference when shooting fast-moving subjects like wildlife or sports. But for shooting static scenes (people, landscapes, whatever), I notice no difference between screw-drive and SDM/HSM.

In other words, while SDM/HSM may make your AF faster, and thus boost your keeper rate in the real world, HSM/SDM may not technically make your AF any more accurate, I think. If you tested HSM/SDM vs screw-drive in the lab for their contribution to AF accuracy against a static test chart, they would probably perform the same.

Last edited by rawr; 09-18-2012 at 03:58 PM.
09-18-2012, 03:51 PM   #6
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QuoteOriginally posted by Eulogy Quote
Tamron has PZD motors.
Only on their very latest lenses, which aren't available for Pentax.
09-18-2012, 03:58 PM   #7
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I don't think the motor will affect the accuracy of the AF much, but it will affect the sound it makes and how fast it is. The actual AF accuracy is a combination of various factors (which is why the K-5 allows lens-specific focus adjustment)
If you want better focusing accuracy I would suggest finding out about AF point size (it is not as small as the red overlay in the viewfinder) and maybe thinking about a focusing screen (which will not affect AF, but it will allow you to see if the focus is where you want it to be). You might also want to look into lens adjustment, because some lenses might not be calibrated the same as the camera.
Focusing is one of the hardest parts of photography and a hard skill to hone. Mistakes with metering can be fixed in post processing (to an extent), photos can even be cropped for better composition, but focus is forever.
Oh, also, in some photos I thought I had focusing problems or that the lens was not very good, but then I realized it was camera shake (long shutter, big focal length).
09-18-2012, 04:11 PM   #8
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QuoteOriginally posted by Na Horuk Quote
I don't think the motor will affect the accuracy of the AF much, but it will affect the sound it makes and how fast it is.
LensRentals.com - Autofocus Reality Part 3B: Canon Cameras

New AF motor designs provide for more consistent AF accuracy when used with newer AF systems. The movement of the elements is more accurate and more consistent in new designs.

I have only used the DA*55mm (slow) and the DA* 200 (decent). I ended up buying the Sigma 50mm F/1.4 over the DA* 55mm and the HSM Sigma is very fast and very quite. The Sigma 85mm F/1.4 is not as fast 50mm, but compared to the 85L it is pretty quick. I think the screw drive LTD lenses are pretty fast, but they have pretty short movements. My 31mm LTD is pretty snappy and AF has been very consistent.

09-18-2012, 09:25 PM   #9
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QuoteOriginally posted by telly0050 Quote
So I was reading the in depth comparison between the 2 sigma and 1 pentax 17-70mm lens.
The AF review suggest that both the sigma has the fast and reliable focus, while the pentax lens has a pretty low rating on it.
So I was wondering, does HSM offer a different method of focusing on the camera?

Anyone who own both pentax and sigma HSM lenses, what is your experience on AF?
I tried to search this topic on the forum but couldn't find any.
If the HSM really does make a difference on AF accuracy, I am getting either the 17-70mm, or the cheaper 18-50mm HSM from sigma... (I just sold my DA 18-55)
I had the Sigma 18-50 f2.8, and I think it is a screwdrive, but I am not 100% sure of that as I sold the lens some time back. For the price, it was a decent lens, and quite small for a f2.8 design. Others do not seem to have had the same luck with this lens that I did, so maybe getting a good copy is hot or miss?

I recently bought the Sigma 17-50 f2.8 HSM and the Sigma 50-150 f2.8 HSM and have owned the DA* 16-50 f2.8 and the DA* 50-150 f2.8 for quite some time.

While I have years more time with the DA* lenses, here is my experience so far:

The Sigma 17-50 is not faster to AF than the 16-50. It is just as quiet and smooth, however. I think it is optically better than the 16-50, quite sharp and punchy with less distortion. Of course, it is 1mm less wide too. In testing for AF fine tune, the lens was just about perfect, but I see no accuracy benefit so far over the DA*.

The DA* 50-135 is just a sweet lens optically, but just as slow as all of the other SDM lenses (IMO). The Sigma 50-150 HSM is noticeably faster to AF than the DA*. It too is quite sharp and a solid performer, perhaps not quite as good as the DA*, but pretty good. It too was spot on my my AF fine-tune testing, but once again, I do not see any accuracy benefit over the DA*.

I have not owned the DA 17-70, and I really wanted that lens as a walk-around lens, but a co-shooter had 2 copies, and both just were not sharp anywhere in the frame or zoom range. There have been many similar reports of less than sharp results with that lens, so I never bought one.

If you are looking for improved AF accuracy, I'm not sure that the lenses you listed will make a significant difference, although any given lens could be more accurate than another just due to tolerances.Things like higher CA wide open, or lower contrast wide open (mainly design issues) can result in one lens "design" being more or less accurate at AF than another.

If you have the opportunity to do so, I would buy the one you are most interested in from somewhere you can easily return it and test the accuracy to see if it makes any difference in your images.

Ray
09-18-2012, 10:33 PM   #10
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I have two Sigma HSM lenses and don't find the K-5 AF any more or less accurate compared to Pentax screw and SDM. You do have to check/adjust the phase detect AF accuracy for each lens first though -- this has helped improve AF accuracy a lot. You should also understand the characteristics of each lens and the K-5 AF system itself.

I like HSM, it's quiet and quick. The SDM in my 60-250 is as quick as HSM; the DC in my 18-135 quicker, but some of my AF screwdrive lenses are quickest, e.g. DA 40 and DA 70.

Practice and experimenting with the AF system greatly helped me. I've also used the screwdrive DA 55-300 and monopod at soccer games with good IQ and AF results.

A quick focusing lens will help you catch the moment. But the short answer is, in my experience with the lenses I have, screw/HSM/SDM/DC drives in proper working condition do not influence the K-5's AF accuracy. So I'm surprised that the reviews you refer to blame the drive type for focus issues.

Last edited by Gray; 09-19-2012 at 02:23 AM.
09-19-2012, 08:19 AM   #11
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thanks guys for sharing your generous experience.
so it seems like HSM doesn't really provide much benefit on AF accuracy.
i guess i will just stick with the one i am interested in..
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