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02-04-2011, 07:52 AM   #316
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But that sounds like such a beginners mistake that I doubt Pentax (or anyone else) would do it.

02-04-2011, 11:43 AM   #317
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QuoteOriginally posted by jolepp Quote
IR having an effect here would fit: tungsten light has plenty of that and I understand that focusing for IR would mean front focusing for the shorter (visible) vavelengths (?). If this is the case a firmware fix might not cut it assuming the AF sensor is a simple stripe of wideband detectors as opposed to maybe multiple parallel stripes with different filters on them (?).
The FF problem isn't restricted to tungsten light on my K-5.

In fact I first noticed it while sitting in my car at night trying to focus on another cars license plate lit by my cars headlights. This was halogen light.
02-04-2011, 12:36 PM   #318
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QuoteOriginally posted by Smeggypants Quote
The FF problem isn't restricted to tungsten light on my K-5.

In fact I first noticed it while sitting in my car at night trying to focus on another cars license plate lit by my cars headlights. This was halogen light.
As in "Tungsten Halogen" light?
02-04-2011, 12:37 PM   #319
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QuoteOriginally posted by Wheatfield Quote
As in "Tungsten Halogen" light?
Yup, those would be the ones

02-04-2011, 12:45 PM   #320
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Halogen is indeed souped up tungsten (filament can be hotter thanks to that halogen in the bulb atmosphere), hence color temperature is higher, but it emits loads of IR just like the basic tungsten.
02-04-2011, 02:14 PM   #321
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mine has ff in any light source under ev 4 including daylight , but only if the dof is very narrow, any dof over 90mm will mask ff..
02-04-2011, 02:34 PM   #322
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QuoteOriginally posted by jolepp Quote
Halogen is indeed souped up tungsten (filament can be hotter thanks to that halogen in the bulb atmosphere), hence color temperature is higher, but it emits loads of IR just like the basic tungsten.
fair enough
02-04-2011, 08:18 PM   #323
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Hello,

My apologies - I have not kept track with this issue because I didn't have a K-5 and I kind of got the impression some people have experienced the issue, and others not.

But I am a new (and proud) K-5 owner, and I want to see if my K-5 suffers from this problem.

Is there a summary post that tells me how to replicate the issue, and what to look for?

I have taken some high ISO shots in low yellowish light (not tungsten though - it's those "energy saver" bulbs replacing incasdescents that gives off a "warm" light) - but I can't see any obvious instances of FF.

02-04-2011, 09:02 PM   #324
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OK - I think I found the previous "locked" thread.

From the first posting there, can I assume if I focus on eyes in low yellowish light on DA70mm Limited wide open (f2.4), then I have the FF issue if the eyes are not focused but the nose is?

I just tried that and the eyes are focused, and the nose is blurry. Does that mean I don't have the problem?

For reference, my serial number is 3950XXX.
02-04-2011, 09:08 PM   #325
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Some testing ideas and results can be found here: https://www.pentaxforums.com/forums/pentax-k-5-forum/129738-k-5-user-auto-foc...t-results.html.
02-04-2011, 09:42 PM   #326
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Thanks! That is a really good test!

I just tried it, and there's no FF for exposure times less than a second

For very dim conditions, where exposure time is greater than 2 secs, it appears there is some FF.


Now the really interesting result is when I repeated the test with my K10D, and discovered my K10D also has FF under the same conditions (2 sec exposure), and no FF for exposure less than 1 sec.

So my conclusion based on my two bodies is that the "problem" is not confined to the K-5 but also present on my K10D.

Since I've never encountered this problem in actual shooting conditions in the 3 years that I've owned the K10D (I would never shoot anything in light so dim even my eyes can't focus properly) I'm not too concerned about the problem.

If Pentax fixes it, great - I wonder whether they will fix it for my K10D as well? :-)

PS - my tests were done using the 43mm Limited, not the DA70mm Limited. I was using the DA70mm earlier, but think the 43mm might be better because it's f1.9. Also, I finally found a source of halogen light (my living room, which has dimmable lights).

Last edited by Christine Tham; 02-04-2011 at 10:16 PM.
02-04-2011, 09:57 PM - 1 Like   #327
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Okay, here's the *really* interesting results.

Repeated the test with a Canon EOS-1D Mark III with EF 135mm f/2 lens.

Under the same conditions

Less than 1 sec exposure - Canon also did not have FF (not surprised)

Over 2 sec exposure - Canon could not even lock into focus (!!!)

So, basically, the conditions under which the K-5 has FF are conditions under which the EOS-1D cannot even achieve focus!

Based on this, my feeling is the problem is not just limited to Pentax cameras - we are talking about a situation where even a pro camera cannot focus well.
02-04-2011, 10:10 PM   #328
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QuoteOriginally posted by Christine Tham Quote


So, basically, the conditions under which the K-5 has FF are conditions under which the EOS-1D cannot even achieve focus!

Based on this, my feeling is the problem is not just limited to Pentax cameras - we are talking about a situation where even a pro camera cannot focus well.
Well, lookie here, we have a breath of fresh air.
Christine, thanks for posting this. It's good to get comparisons like this to put things in perspective (something sadly lacking on this forum sometimes).
02-04-2011, 10:32 PM   #329
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One final thought on the issue.

It appears that Pentax does have an issue - but it's not an "AF malfunction" issue. The issue is that the Pentax is giving a false positive by claiming to lock on focus when the situation is such that the camera can't actually focus properly, and stops hunting when the lens is slightly FF.

The Canon EOS-1D under similar conditions is clever enough to say "Sorry, can't focus. You're out of luck."

So I can see two ways for Pentax to fix this "problem":
- implement the same solution as Canon - refuse to lock focus in low light.
- turn on the AF assist light (as in LV - which does allow the camera to focus correctly)

Neither are ideal fixes - the first solution may result in a batch of user complaints that the AF system is broken and cannot lock focus. The second may result in exposure metering problems (not sure, guessing).

So my preference is for Pentax not to make any changes and leave it as is, or maybe allow the option for the user to fine tune when the AF assist light comes on. But we are talking about conditions under which I would not normally shoot pictures (though I appreciate others may want to shoot under such conditions).
02-04-2011, 10:36 PM   #330
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QuoteOriginally posted by Christine Tham Quote
One final thought on the issue.

It appears that Pentax does have an issue - but it's not an "AF malfunction" issue. The issue is that the Pentax is giving a false positive by claiming to lock on focus when the situation is such that the camera can't actually focus properly, and stops hunting when the lens is slightly FF.

The Canon EOS-1D under similar conditions is clever enough to say "Sorry, can't focus. You're out of luck."

So I can see two ways for Pentax to fix this "problem":
- implement the same solution as Canon - refuse to lock focus in low light.
- turn on the AF assist light (as in LV - which does allow the camera to focus correctly)

Neither are ideal fixes - the first solution may result in a batch of user complaints that the AF system is broken and cannot lock focus. The second may result in exposure metering problems (not sure, guessing).

So my preference is for Pentax not to make any changes and leave it as is, or maybe allow the option for the user to fine tune when the AF assist light comes on. But we are talking about conditions under which I would not normally shoot pictures (though I appreciate others may want to shoot under such conditions).
Thanks for the work Christine; I suspected this might be the case - thanks for confirming...and I agree a "fix" is unnecessary.

Perhaps it is now time for the two baying bloodhounds - Don and Rupert - to test their K20Ds (if they are capable of the task) to see how they perform.
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