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01-15-2009, 11:45 AM   #1
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AF speed - F50/1.7 vs FA50/1.7

Has anyone tried both? Is there a significant difference in autofocus speed? Also potentially curious about the 1.4 versions of each lens...

01-15-2009, 11:57 AM   #2
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one is 0.007 seconds slower than the other, the latter are 0.002 seconds faster then the than the former, and the one that you really want to get is 0.003 seconds faster than all of them.
01-15-2009, 12:01 PM   #3
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QuoteOriginally posted by Gooshin Quote
one is 0.007 seconds slower than the other, the latter are 0.002 seconds faster then the than the former, and the one that you really want to get is 0.003 seconds faster than all of them.
I really want to get the F because I somehow find its dated plasticky 80's looks endearing. It's also cheaper, but some older AF stuff has a bad reputation for being slow and inaccurate so I think this is a valid question
01-15-2009, 12:19 PM   #4
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QuoteOriginally posted by Erik Quote
I really want to get the F because I somehow find its dated plasticky 80's looks endearing. It's also cheaper, but some older AF stuff has a bad reputation for being slow and inaccurate so I think this is a valid question
autofocus speed is 2 parts

camera side, and lens side

lens side, what affects focus speed the most is focus throw, (how much you rotate the focus ring between min and infinity focus) the longer this is (in degrees), the longer the screw drive will have to turn it, this is simple physics

also weight of the moving parts playes a roll, but rather insignificant when it comes to small lenses like a 50

this is partially why the current DA prime lineup are so fast to focus, their focus throws are non existant, unfortunetly this makes them ass for manual focusing.


then camera side there is the AF sensors and how much light/contrast it gets, the faster the lens the more light hits it, easier to determine contrast, esp in low light situations.


so, you have two lenses, both are 1.7, both are 50mm so the internal design is probably nearly identical, both are used on the same body, and both are driven by a screw drive

you tell me, which you think is going to be faster, and for comic relief refer to my first post.

01-15-2009, 12:28 PM   #5
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QuoteOriginally posted by Gooshin Quote
so, you have two lenses, both are 1.7, both are 50mm so the internal design is probably nearly identical, both are used on the same body, and both are driven by a screw drive

you tell me, which you think is going to be faster, and for comic relief refer to my first post.
I realize all this. However, I do not KNOW that the focus throw is identical between the two, and not even that the optical formula is identical or nearly so, which is why I asked in the first place. I've never held either lens in my hand and I want to make an informed decision. "No, there is probably no significant difference" would have sufficed if that's all you have to say, but I was really more looking for answers from people who have USED both lenses on the same camera.
01-15-2009, 01:15 PM   #6
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First of all, i've only had the F50/1.7, so i wont be comparing to other 50's.
Subjectively judging, it was the same as kit (18-55 I), the only difference is 50 being much more louder. Duno if mine was weared out already (looked perfect from outside), but the whole asambly seemed kind of loose. I could even see the lens "shift" some times a little bit. So, it isnt reallly good in some quiet places, where you would like to discretly shoot without flash. Will get everyones attention, when the AF roars and shakes to focus.
I've heard, that the FA's have shorter af throw comparing to F's, thus having faster but less accurate focusing.
What is certain, that the 1.7 versions are much more sharper at wide apertures.. 1.4 has much more chromatic aberations and are softer, wich feels kind of odd for a prime.. but thats what you have to accept for that famous creamy bokeh.
I had no problems using 1.7@f1.8..2 outdors. Excellent.
AF wise, sharpness is more important than brightness. Is the speed difference significant? I doubt it.
01-15-2009, 01:20 PM   #7
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I've had a F 50mm 1.7 and have a FA 50mm 1.4 , there's no difference in focus speed between those two lenses.

I highly doubt the F and FA 50mm 1.7 have any mechanical differences between the two of them -- but I have no authority on that assertion.
01-15-2009, 01:58 PM   #8
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Alright guys, thanks for the responses! Looks like I'm probably going with the F50/1.7 at some point in the future when I have the dough. Noisy AF is not a problem seeing as I mostly take pictures of trees and things like that and I don't think they'll care

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