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02-06-2011, 10:34 AM   #1
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k7 vs kx autofocus?

I was hired to do a birthday shoot last night and really noticed the how slow the autofocus on the kx really is. It work well and i got the job done but was wondering if upgrading to the k7 would provide noticeably faster autofocus. The venue had dim lighting so i know that was the problem but can anyone who has experience shooting with both cameras provide me with some feedback. I was planning on holding out till i could afford a k5 but a k7 for ~700 bucks used sounds pretty tempting. I would keep the kx as my secondary for high iso stuff and just need a fast autofocus camera as my primary.

TIA
jorge

02-06-2011, 10:57 AM   #2
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QuoteOriginally posted by boosted03gti Quote
I was hired to do a birthday shoot last night and really noticed the how slow the autofocus on the kx really is. It work well and i got the job done but was wondering if upgrading to the k7 would provide noticeably faster autofocus. The venue had dim lighting so i know that was the problem but can anyone who has experience shooting with both cameras provide me with some feedback.

I believe the K-x and K-7 are based on the same (SAFOX VIII) AF engine - the K-7 is bit more sophisticated (SAFOX VIII+) in that it has a tungsten light sensor (but I don't think it affects the AF speed only the accuracy under tungsten lighting)

Popular Photography does AF testing under different light levels and they do seem about the same



However you might consider this (no disrespect meant):

The old technique with manual focusing was to pre-focus and wait for the shot -
this can also be applied with AF cameras.

So unless one is shooting rapid sequences focusing speed tends to be mitigated (as long as it manages to lock)
- since there were many successful wedding and other professional photographers in the manual focus days
- and manual focus is substantially slower than AF.

Having said that, the posts I've read so far are both the K-r and K-5 seem to have faster AF (SAFOX IX, and +).

Last edited by UnknownVT; 02-06-2011 at 11:11 AM.
02-06-2011, 11:05 AM   #3
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i am familiar with zone focusing but i guess i feel that a machine could be better then me. maybe it is just my confidence level and my eye sight isnt the best. i have little practice with zone focusing but that is definitely a solution to any auto focus limitations. i did consider manual focus last night but i was shooting at f4 and f5.6, due to the low light, and didnt want to have out of focus images.
02-06-2011, 11:18 AM   #4
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QuoteOriginally posted by boosted03gti Quote
i am familiar with zone focusing but i guess i feel that a machine could be better then me. maybe it is just my confidence level and my eye sight isnt the best. i have little practice with zone focusing but that is definitely a solution to any auto focus limitations. i did consider manual focus last night but i was shooting at f4 and f5.6, due to the low light, and didnt want to have out of focus images.
Sorry I did not mean zone focusing - I meant focus and hold using the AF.

Pre-focus is to use the AF to focus on your subject using the half-depression of the shutter button -
then hold that half-depression and wait for the moment -
so that one is not reliant on trying to focus at the moment when one sees the shot.

The delay when pre-focused is dependent only on shutter lag -
with most dSLRs this is less than 1/10th sec - faster than human reaction -
whereas - as you see at lower light levels - AF can be as long as 1/2 to over 1 sec - long after the scene has changed.

02-06-2011, 11:30 AM   #5
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QuoteOriginally posted by UnknownVT Quote
Sorry I did not mean zone focusing - I meant focus and hold using the AF.

Pre-focus is to use the AF to focus on your subject using the half-depression of the shutter button -
then hold that half-depression and wait for the moment -
so that one is not reliant on trying to focus at the moment when one sees the shot.

The delay when pre-focused is dependent only on shutter lag -
with most dSLRs this is less than 1/10th sec - faster than human reaction -
whereas - as you see at lower light levels - AF can be as long as 1/2 to over 1 sec - long after the scene has changed.

oh, yea, i do that all the time. i focus lock on the subject and wait for the moment. the only real issue i had with the auto focus was when i tried to capture some candid moments and missed it due to the auto focus trying to lock.
02-06-2011, 01:21 PM   #6
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QuoteOriginally posted by boosted03gti Quote
the only real issue i had with the auto focus was when i tried to capture some candid moments and missed it due to the auto focus trying to lock.
Ha-ha! you and me both....

I shoot a lot in a lot more extreme conditions (very dark jazz club - where there are areas below the specs of the K-x AF and metering ranges!)

There are always moments like that -
but I have to learn to let them go -
unless of course they become very common (so far so good though)

I don't think there is any camera that can compensate for a lack of foresight/preparation on my part -
and IMHO I don't think there are that many dSLR that are that much faster than the K-x for real practical usage -
let's just take the grass is greener current top hot-shot dSLRs the CaNikon 60D and D7000 - with AF speeds that can be "envied"?



Yes, of course they are faster at the lowest light levels almost by a factor of 2x -
but does one really think even at their faster speeds of close to 1sec that one can capture a candid moment - after about 1 sec of seeing it?

and BTW even though the test results are not out yet -
I really don't think the K-r or K-5 are going to be that noticeably faster than those CaNikons......
AND please note: both the K-x and K-7 AF at LV (Light Level) 6 or brighter are already faster than those CaNikon hotshots.
LV=6 is f/4, 1/4sec @ ISO100 so it is not that bright......

Last edited by UnknownVT; 02-06-2011 at 03:10 PM.
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