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11-03-2009, 04:25 PM   #1
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smc PENTAX DA Star 55mm F1.4 SDM SUPER SLOW Auto Focus with K-7

Hi, I just bought the smc PENTAX DA Star 55mm F1.4 SDM lens, but I've noticed the AF is SUPER SLOW, much slower than the 4 times cheaper smc PENTAX DA 18-55mm F3.5-5.6 AL WR lens.

I do not get it, this lens is supposed to be the TOP of the line, super fast Lens, maybe I have to configure something within the camera ?, please feedback, previous experience, I am paying a top price here, thanks

11-03-2009, 05:18 PM   #2
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The DA55/4 does appear to be slow if you are timing it by racking the AF from near to far and seeing how it does. In actual use it is fairly quick.
You are paying for a superb optic, not a blisteringly fast AF on this lens.
11-03-2009, 05:24 PM   #3
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Notice the focus throw on the 18-55 compared with that of the *55.
You'll appreciate the accuracy in focusing in your results.
11-03-2009, 05:25 PM   #4
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QuoteOriginally posted by Wheatfield Quote
The DA55/4 does appear to be slow if you are timing it by racking the AF from near to far and seeing how it does. In actual use it is fairly quick.
You are paying for a superb optic, not a blisteringly fast AF on this lens.
And it does take a while to get used to SDM if this is your first lens with it. Kinda took me by surprise when I got my 50-135. Take Wheatfield's suggestion and see how it focusses on real - life subjects. It's a fantastic lens!!!!! (debating on getting that or just save for a k-7).

11-03-2009, 05:28 PM   #5
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Did you compare shooting the same scene with both lens? What aperture were you shooting? f1.4 vs a 3.5?

If you shoot at wide aperture, the camera need to make sure the focus is correct, and usually a bit slower in finetuning the focus before confirmation is given. The focus throw is slightly longer on the 55 compare to your kit lens. AF speed is to do with the focus throw, as well as the weight of the lens elements + the focus mechanism. SDM might not focus faster than the screw driver.

I had the DA* 55mm for a week, so I can share my experience with you. Its a super fast lens, as you said, which means lots of light. Not super fast in auto focus, but I didn't find it super slow in my use. I guess the user expectation + subject type determine whether it matters or not.

Most people will buy that lens for low light or portrait work. I don't think its suitable for tracking moving object, and the DA limited series lens are more suitable in doing that. Those lenses AF very fast.
11-03-2009, 05:32 PM   #6
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Thanks, I am planning to buy the smc PENTAX DA 40mm F2.8 Limited lens for motion pictures and as an all purpose lens, from what I've read the AF is one of the fastest available today in a pancake lens,
11-03-2009, 05:32 PM   #7
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Thanks, I am planning to buy the smc PENTAX DA 40mm F2.8 Limited lens for motion pictures and as an all purpose lens, from what I've read the AF is one of the fastest available today in a pancake lens,
11-03-2009, 05:38 PM   #8
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SDM lenses are slower as a general rule than screw driven lenses. They are much quieter though

11-03-2009, 05:42 PM   #9
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wtf?

https://www.pentaxforums.com/forums/pentax-dslr-discussion/78677-slow-af-pent...-sdm-lens.html


edit: thank you mods for clearing that up

Last edited by yeatzee; 11-03-2009 at 10:53 PM.
11-03-2009, 05:43 PM   #10
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QuoteOriginally posted by brosen Quote
Hi, I just bought the smc PENTAX DA Star 55mm F1.4 SDM lens, but I've noticed the AF is SUPER SLOW, much slower than the 4 times cheaper smc PENTAX DA 18-55mm F3.5-5.6 AL WR lens. I am using the Pentax K-7 camera with Firmware 1.02

I do not get it, this lens is supposed to be the TOP of the line, super fast Lens, maybe I have to configure something within the camera ?, please feedback, previous experience, I am paying a top price here, thanks
Its a top of the line "portrait" lens... not a sports lens. Plus SDM is known to be slow.

In Canon land their kit lens has faster AF than the 85mm F1.2 ($1800).

Its not an excuse just a fact of life. If you want fast AF you should not buy the 55mm F1.4.
11-03-2009, 06:53 PM   #11
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QuoteOriginally posted by kunik Quote
In Canon land their kit lens has faster AF than the 85mm F1.2 ($1800).
LOL, even super slow doesn't do justice to the canon 85/1.8 especially the first version, but as was said bigger heavier elements in an optically faster lens can often result in slower AF performance..
11-03-2009, 07:17 PM   #12
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I merged the two duplicate threads.
11-04-2009, 05:43 AM   #13
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A lot of focus speed has to do with a combination of the size of the lens and the length of the focus throw. The Da* lenses are bigger lenses, with more glass to move. The DA 55 has a long focus throw as well. Helps to get you exactly where you need to be when shooting wide open, but certainly doesn't get you there fast. If you are interested in fast focus primes, I would suggest either the DA 40 or 70. They are very quick.
11-04-2009, 05:49 AM   #14
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You mean the DA 40 or 70 Limited Pancake ?
11-04-2009, 12:14 PM   #15
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Those are the only DA40 and DA70 there are. "Pancake" is just a slang term some people use to describe these lenses; it's not part of the official name of the lens. "Limited" is part of the official name, but still, it's pretty common to leave that word out when referring to the lens, as it's not like there are both Limited and non-Limited versions of these (or any!) lenses that we'd have to worry about confusing.
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