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12-18-2010, 08:14 PM   #1
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Auto focus at altitude.

I'm on vacation in bolivia right now. In la paz, which is at around 3600 meters. The plan is to head upto about 5000 meters.

Tonight the auto-focus was acting up pretty badly on distant objects (close to infinite focus range). This is on a k5 and a 16-50 2.8.

My laptop hasn't been handling the altitude very well (who knew hard drives need sufficient air pressure).

I was wondering if the autofocus on dslr's are affected by altitude. I found a few hits on google that hint toward this.

Any ideas?

12-18-2010, 09:42 PM   #2
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I can't imagine how altitude would affect anything.
12-18-2010, 10:23 PM   #3
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It's probably the temperature affecting the AF. Check the K5 and the lens manual for suggested working temperature.

I ever had this problem as well when I went for vacation to Mt. Buller, Victoria.

It's not only camera or lens, any electronic devices has temperature limit.
12-18-2010, 10:30 PM   #4
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I have not used my K-7 above 1,000 m but I do not think that the ambient pressure has a lot to do. I cannot see any physical explanation. The temperature and moisture contents might have some impact however... but Steve Kroeger used his K-7 up to 6900 m and he did not have problem:
K-7 and Steve Kroeger climb Aconcagua (6962m)
Steve Kroeger mit der Pentax K-7 auf dem Aconcagua | - Fotografie Nachrichten

By the way, the lens on the K-7 was the DA18-250mm.... It says a lot about this classical all-around lens.

12-18-2010, 10:48 PM   #5
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Dutch - If you are using all 11 focus points, try narrowing it down to just 5 points. It may help with distant objects.

12-18-2010, 10:53 PM   #6
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I've taken my K-x up to the top of Mauna Kea at ~4200m/13800 ft in sub-freezing temperatures, and I noticed nothing unusual about the AF, screw-drive or Sigma HSM.

Last edited by Cannikin; 12-18-2010 at 11:00 PM.
12-19-2010, 02:08 AM   #7
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I have used a *ist and the K200D at 20,000 feet - unpressurised aircraft. No problems.
12-19-2010, 02:59 AM   #8
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The AF may act up if the battery is nearing depletion. Maybe that's the case here.

12-19-2010, 04:56 AM   #9
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Could it be the low humidity was causing more static charge than usual? Some weeks ago both my 40D & K-m were frozen due to very dry air and the huge amount of static charge building up on my body due to the clothes that I was wearing. Once I earthed myself, they went back to normal.
12-19-2010, 05:58 AM   #10
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thanks for the advice guys, I'll try things out again today.
12-19-2010, 09:15 AM   #11
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I don't know about altitude, but cold has never been a problem for me...

I've never hiked higher than 6000ft but last winter I used my k20d in -40C temps with no problems, and last week was using my K5d in -18C and everything was fine.

12-20-2010, 04:32 PM   #12
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QuoteOriginally posted by wlachan Quote
Once I earthed myself, they went back to normal.
Off the topic, did it hurt a lot, how long was the spark?. 10 kV/cm. roughly, would be cool to know how ESD hardened the Pentax's are.

Cheers, Mike.
12-21-2010, 01:15 AM   #13
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I'v had my K20D, K10D, and istDS out for hours at a time on Haleakala (10,000 ft or 3,048 m), Hosmer Grove (6,800 ft or 2,072m) and Mauna Kea. Never had any problems. Haven't been up there with my K7, but I did use that camera on my recent trip to the south rim of the Grand Canyon (7,000 ft or 2,133m average). All of those except for Mauna Kea are lower that where you're at.

I think hard drives require an air cushion for the read/write heads to "float" properly above the drive platters. A google search seems to bear this out and wikipedia indicates that this is around 3000m. Going higher requires a sealed drive. Without the cushion, they are more susceptible to head crashes causing damage to the heads and the platters (losing data).

Perhaps there are parts in the K5 that are sensitive to atmospheric pressure? Say some sealed components like the AF sensor? Then again, wasn't there a guy that sent his K10D to the edge of space on a weather balloon?
12-21-2010, 05:39 AM   #14
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Nice discussion. But let's "earth" it in another way

The most likely cause for imprecise focus with far distant subjects is missing subject fine contrast due to atmospheric disturbances. With a 16-50mm, I would focus something contrasty 100m away and then use this focus at infinite distance.

But that's just an idea. But air pressure would be my last choice when searching for a cause.

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