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12-20-2009, 08:01 PM   #1
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Auto focus: which is better K7 or K-X?

I know that single criteria judgements about cameras is not the way to go. However, with my K100D, the one main thing I wish it did better is nailing the auto focus quicker. It hunts a lot. If this criteria is important to me, which camera does a better job: the K7 or the K-X?

I understand the 55-300mm Pentax lens prefers manual focusing, especially with a 1.5X or 2.0X Kenko. But which camera is likely to do a better/quicker auto focus job with that lens if one HAD to use autofocus, the K7 or K-X?


Last edited by gfmucci; 12-20-2009 at 08:07 PM.
12-20-2009, 08:07 PM   #2
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K7 has the autofocus assist lamp, but both cameras seem rock solid on the autofocus front.

Much improved.
12-20-2009, 08:10 PM   #3
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QuoteOriginally posted by erickallemeyn Quote
K7 has the autofocus assist lamp, ...
The K-X does not?
I had a Sony f707 5 or 6 years ago that had an infra red focus assist lamp - it focused in pitch black. That was nice. That feature would definitely favor the K7 for me.
12-20-2009, 08:13 PM   #4
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nope. a minor annoyance with the K-x.

Unless you pop up the flash, but then its a 2-second strobe to focus. Very intrusive.

12-20-2009, 08:20 PM   #5
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How about focusing speed differences between the K7 and K-X WITHOUT using the focus assist lamp - when I'm using a longer lens where the lamp will not be of any value? Any thoughts?
12-20-2009, 10:49 PM   #6
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I have both... the K-7 is faster, but the K-x is quite fast in its own right. Easily faster than the K20D I used to own.
12-21-2009, 01:01 AM   #7
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I don't have both, but for less than the difference you can get a af360 flash that has an assist lamp in it....

I also have a k20d (and k10, and k110) and the kx is much faster than them.
12-21-2009, 06:32 AM   #8
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QuoteOriginally posted by gfmucci Quote
How about focusing speed differences between the K7 and K-X WITHOUT using the focus assist lamp
There are reasons to believe that K-m and K-x share the identical AF module. Both are believed to sit in between K20D and K-7 speeds.

Back in June, I studied AF speed of K-7 vs. K-m here:

Falk Lumo: K-7 and its precision autofocus


Moreover, the K-7 is supposed to have better AF accuracy in tungsten light.

12-21-2009, 11:15 AM   #9
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The K7 has more voltage to power the focus motor, so all else equal, it should win any comparison, if not necessarily by a lot.
12-21-2009, 02:22 PM   #10
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Thanks, everyone. It does sound like the K7 has a somewhat more robust auto focus system than the K-X. This appears to be the case in both the close range/dim light scenario due to its built in assist lamps, and in the distant, long lens scenario due to the stronger focus motor and increased focus points. Do I understand correctly?

Are the K7 focus points more precise than the K100D focus points, which seem to be approximations of the focus points. I wonder how broad (how wide an area) each focus "point" covers?
12-22-2009, 01:16 PM   #11
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According to digital camera review, the K-x AF acquisition is .04 of a second faster than the K-7. Interestingly the K-m/2000 comes in at 0.32 of a second. This is the only website I could find with AF timings for both cameras. I have no idea on their reputation.


Pentax K-x Performance, Timings, and Image Quality
Pentax K-7 Performance, Timings, and Image Quality
http://www.digitalcamerareview.com/default.asp?newsID=3858&review=pentax+k2000

Really nothing in it.

Tim.
12-22-2009, 01:45 PM   #12
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It is a tough question to answer in general because it also depends on the lens. For example, with a screw drive lens there may be a big difference because as Marc says, the power output is higher on the k-7 body-drive AF motor. With an SDM lens, there may be no difference, because the motor is in the lens.

Focus speed is all relative though, and while significantly improved from the k20d, it has a way to go I think. Has anyone else seen this youtube video of k-7 vs 7D focus speed? The lenses are not the same, but it does show that our mount has a way to go to catch up in the AF speed race. If I could ask for one thing to change about the k-7 it would only be a significant improvement in the SAFOX. For the lenses, a ring-SDM. Then I would be really happy. The Pentax mount excels in all other areas though.

[YT]http://www.youtube.com/watch?v=ngUcQUchHEU[/YT]

Last edited by PentaxPoke; 12-22-2009 at 02:00 PM.
12-22-2009, 05:24 PM   #13
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QuoteOriginally posted by PentaxPoke Quote
It is a tough question to answer in general because it also depends on the lens. For example, with a screw drive lens there may be a big difference because as Marc says, the power output is higher on the k-7 body-drive AF motor. With an SDM lens, there may be no difference, because the motor is in the lens.
I'm interested in focus performance with the following lenses:
Pentax 50mm 1.4 FA
Pentax 55-300 mm
Pentax 12-24mm
Pentax 18-55mm
12-22-2009, 06:01 PM   #14
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QuoteOriginally posted by PentaxPoke Quote

[YT]http://www.youtube.com/watch?v=ngUcQUchHEU[/YT]
Wow, the Canon is a beast... and that's against pentax's fastest focusing body.

Now when will the 5Dii come down to 2000$?
07-16-2010, 01:24 PM   #15
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QuoteOriginally posted by erickallemeyn Quote
nope. a minor annoyance with the K-x.

Unless you pop up the flash, but then its a 2-second strobe to focus. Very intrusive.
The lack of AF assist lamp is a MAJOR annoyance. I looked really stupid last week, when my $1000 equipment was incapable of taking pictures in the dark. The cheap P&S cams did the job, them

PS: I found this thread from a web search engine.
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