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01-09-2013, 06:46 AM   #1
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AF speed FA43 vs DA40

I currently have an FA43 and a K-x, which I love but have problems with AF hunting when it's dark. On most occasions it works ok, but inside at night I often have problems to get AF to lock. Especially when subject moves (people, children).

I'm considering to switch to a DA40XS just for the quicker AF (the limited would of course be nice but I can't justify the price difference). I can probably live with the slower aperture and unpixiedustness if the DA40 solves my dilemma. But will it? Has anyone compared this?

I was at a store today and got to try the DA40XS, but the store was well lit and though I noticed a difference in AF speed, I would really have wanted to try it in darker conditions. The seller wouldn't let me try it in their bathroom

Thanks for any help!

01-09-2013, 07:07 AM   #2
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I have the DA 40 ltd., and with respect to AF it's the best lens I've owned. Very decent performance even in low light--in my experience, better than the FA 50mm 1.4, whose AF was quite capricious.
01-09-2013, 07:24 AM   #3
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If your concern is AF speed, perhaps the DA40mm XS is better. However, if you are concerned with hunting, the FA 43 technically allows more light and shouldn't perform any worse.
01-09-2013, 08:04 AM   #4
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QuoteOriginally posted by JinDesu Quote
If your concern is AF speed, perhaps the DA40mm XS is better. However, if you are concerned with hunting, the FA 43 technically allows more light and shouldn't perform any worse.
I've read that micro contrast wide open can be more important than max aperture for AF in certain cases. However I don't know if this is the case here... FA43 should be sharp enough at f1.9 I guess, but maybe DA40 at f2.8 is sharper.

I'm concerned about hunting yes, not AF speed. But for moving subjects I guess more AF speed helps to lock faster and thus leads to less hunting. Am I thinking right here?

01-09-2013, 09:34 AM   #5
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That is true, if you are shooting a fast moving subject you will want a faster focusing lens.
01-09-2013, 02:24 PM   #6
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I'd be concerned that the loss of over a stop of light would make the AF sensor hunt more. K-5ii seems like a solution :-D
01-09-2013, 02:39 PM   #7
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QuoteOriginally posted by retroflex Quote
I currently have an FA43 and a K-x, which I love but have problems with AF hunting when it's dark. On most occasions it works ok, but inside at night I often have problems to get AF to lock.
Thanks for any help!
How is your AF set up? Which AF mode? Which focusing area?
These are questions to deal with first,
before you even consider switching lenses.

I only use center point AF.S on the K-x,
so I can point the camera at a contrasty part of the subject,
located at the sharpest point of the lens' image field,
and know that that is where it will be attempting to focus.

Try this first, to see if it helps, if it's not what you're doing already.
01-09-2013, 03:53 PM   #8
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I also use center point AF.S and recompose. I have set to not shoot until focus is locked.

01-09-2013, 04:28 PM   #9
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the AF of the 40 is fast, but in fact the f2.8 really helps to get good shots simply because of the bigger DoF.
The focus throw is also quite short and as such when the lens hunt, it takes less time to go from short focusing distance to infinity.
However, i simply suggest you to learn to play with catch in focus, instead of trading a gem by a ... Lesser gem
01-10-2013, 03:18 AM   #10
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Thanks everyone for your help!

And thanks for the advice aurele! I will definitely read up and practise on catch in focus to start with.
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