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02-04-2011, 10:44 PM   #331
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QuoteOriginally posted by jthommo Quote
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.
Aw, c'mon, man. Leave the K20D alone, will ya?

02-04-2011, 10:47 PM   #332
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QuoteOriginally posted by jthommo Quote
Thanks for the work Christine; I suspected this might be the case - thanks for confirming...and I agree a "fix" is unnecessary.
I just realised I should have qualified my statement. I have assumed that all K-5s behave like mine - it may well be that there are K-5s out there that have FF even in situations where mine didn't.

If that is the case, Pentax *may* have an issue with *some* units where the camera fails to lock focus when it should have.

However, I suspect the issue is also lens related - different lenses let in different amount of light - I have tested using the 43mm Limited - it may be that a lens that lets in less light will cause the camera to not auto focus properly in brighter conditions.

So my qualified statement is - if a K-5 performs at roughly the same level as my K-5, then I don't believe a "fix" is required or necessary. However, I cannot speak for all K-5 units out there.
02-05-2011, 12:22 AM   #333
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QuoteOriginally posted by Christine Tham Quote
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.
I take it you did your tests at 100 ISO?
02-05-2011, 12:23 AM   #334
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QuoteOriginally posted by Christine Tham Quote
I just realised I should have qualified my statement. I have assumed that all K-5s behave like mine - it may well be that there are K-5s out there that have FF even in situations where mine didn't.

If that is the case, Pentax *may* have an issue with *some* units where the camera fails to lock focus when it should have.

However, I suspect the issue is also lens related - different lenses let in different amount of light - I have tested using the 43mm Limited - it may be that a lens that lets in less light will cause the camera to not auto focus properly in brighter conditions.

So my qualified statement is - if a K-5 performs at roughly the same level as my K-5, then I don't believe a "fix" is required or necessary. However, I cannot speak for all K-5 units out there.

Gee, are you gonna cop a hiding...LOL

02-05-2011, 12:36 AM   #335
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Oh, Christine....

Recant your faith in the god Pentax and his son K5 before the inquisition find you
02-05-2011, 05:01 AM   #336
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QuoteOriginally posted by Christine Tham Quote
I just realised I should have qualified my statement. I have assumed that all K-5s behave like mine - it may well be that there are K-5s out there that have FF even in situations where mine didn't.
...
However, I suspect the issue is also lens related -
...
The thing is that some do not suffer from front focus in low artificial (tungsten) light and some do. Whether this means that there are defective and good units out there or that the conditions for this to occur are quite specific (or both or something else altogether ) we don't really know. Like the more general FF/BF issue this could be something that occurs (or not) with the combination of a specific copy the K-5 and the lens used.

Faster lenses, of course, should enable AF to work in murkier conditions as AF is done aperture fully open.

I have had this hamper my use quite a bit as this time of year at least my shooting is mostly confined inside (where the most interesting thing tends to be people ), and much of that is in artificial light. In practice this means using my Tamron 17-50mm 1:2.8 at f=2.8 (typical: ISO 3200 t ~ 1/30 - 1/60) so DOF is kind of narrow; it is annoying to discover that something that would have been very nice otherwise e.g. has the tip of someone's nose in focus and eyes a bit soft, especially so when the k-x did not have similar problems (or in fact made this sort of thing possible for me with its low ISO capability). I guess I could always put in a proper focusing screen and get some more MF lenses and see how that works out, but I'd prefer AF working at least as well as it did with the k-x. Of course, I might do well to pick some less convenient targets, but that is another matter.

Last edited by jolepp; 02-05-2011 at 07:53 AM.
02-05-2011, 05:53 AM - 1 Like   #337
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QuoteOriginally posted by Christine Tham Quote
However, I suspect the issue is also lens related - different lenses let in different amount of light - I have tested using the 43mm Limited - it may be that a lens that lets in less light will cause the camera to not auto focus properly in brighter conditions.
It is indeed dependent on the lens used, try a normal zoom lens at the wide end on normal indoor distance around 2m. The scene could be a typical dinner, my k5 will lock instantly but will FF with around 0,5m. And it is not pitch dark but around EV 4. Easily hand holdable at iso 1600.

Add a little more light and it's suddenly spot on. This is what I'm complaining about, not a few mm in total darkness.
02-05-2011, 10:24 AM - 1 Like   #338
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QuoteOriginally posted by Christine Tham Quote
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...
What kind of test lists a less than 1 sec. and a greater than 2 secs. exposure only?

Without ISO and f-stop, how would one determine if you were shooting in EV1 to EV4 (where the problems are reported). Furthermore, what kind of lighting source are you in, as tungsten light is thought to either cause or increase the problem.


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).
The K-5 should refuse to lock in EV2 to EV4? Why? The K-5 lists all the way down to EV -1... (I believe accurate EV2 to EV4 is what is wanted).

Did you know that EV 7-8 is offices and commercial environments,
--------EV 5-7 is a nicely lit home (day ~6-7 and evening ~5),
--------EV 3-4 is a dimly lit home (evening),
--------EV 1-2 is a poorly lit home or area.

Do you understand if EV 2-4 (mood type lighting that many people enjoy shooting in) has front focus, even if you use a flash it will still be front focused unless your f-stop is higher.

My K20D can focus accurately in EV 2-4 at f2.0 with a narrow depth of field. If the Canon EOS-1D Mark III can't, that's too bad for Canon...

So now, with a better sensor on the K-5 than the K20D, Pentax is supposed to say sorry, can't do EV 2-4 now.


QuoteOriginally posted by Christine Tham Quote
I just realised I should have qualified my statement. I have assumed that all K-5s behave like mine - it may well be that there are K-5s out there that have FF even in situations where mine didn't.

If that is the case, Pentax *may* have an issue with *some* units where the camera fails to lock focus when it should have.

However, I suspect the issue is also lens related - different lenses let in different amount of light - I have tested using the 43mm Limited - it may be that a lens that lets in less light will cause the camera to not auto focus properly in brighter conditions.

So my qualified statement is - if a K-5 performs at roughly the same level as my K-5, then I don't believe a "fix" is required or necessary. However, I cannot speak for all K-5 units out there.
So the shots were maybe in the wrong lighting condition, and you don't know the EV in which you were shooting in. Yet your qualified conclusion is it works well and a fix is not needed because some other cameras didn't work either.

Am I supposed to respect this type of analysis and believe many other posters are wrong or got bad K-5's, and the front focus issue doesn't exist if you get a good K-5? Finally, I have yet to see good examples in EV 2-3 with tungsten lighting at f2.8 from anyones K-5 that focused correctly.



Last edited by betaPhoto; 02-05-2011 at 11:29 AM.
02-05-2011, 10:47 AM   #339
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QuoteOriginally posted by Gimbal Quote
It is indeed dependent on the lens used, try a normal zoom lens at the wide end on normal indoor distance around 2m. The scene could be a typical dinner, my k5 will lock instantly but will FF with around 0,5m. And it is not pitch dark but around EV 4. Easily hand holdable at iso 1600.

Add a little more light and it's suddenly spot on. This is what I'm complaining about, not a few mm in total darkness.
According to some, your'e either wrong or expecting too much.
02-05-2011, 01:25 PM   #340
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QuoteOriginally posted by jthommo Quote
Thanks for the work Christine; I suspected this might be the case - thanks for confirming...and I agree a "fix" is unnecessary.
You think the low light FF issue on my K-5 shouldn't be fixed?


QuoteQuote:
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.
Your childish and offensive comment in bold aside and I suggest you grow up, I have both a K-5 and a K20D and my K20D has no problem focussing down to light levels well below where the assist light comes on, on the K-5. while the K-5 exhibits FF below EV4.
02-05-2011, 01:27 PM   #341
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QuoteOriginally posted by Christine Tham Quote
I just realised I should have qualified my statement. I have assumed that all K-5s behave like mine - it may well be that there are K-5s out there that have FF even in situations where mine didn't.

If that is the case, Pentax *may* have an issue with *some* units where the camera fails to lock focus when it should have.

However, I suspect the issue is also lens related - different lenses let in different amount of light - I have tested using the 43mm Limited - it may be that a lens that lets in less light will cause the camera to not auto focus properly in brighter conditions.

So my qualified statement is - if a K-5 performs at roughly the same level as my K-5, then I don't believe a "fix" is required or necessary. However, I cannot speak for all K-5 units out there.
I've never heard such utter rubbish.
02-05-2011, 01:43 PM   #342
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QuoteOriginally posted by Smeggypants Quote
I've never heard such utter rubbish.
Why don't you just go out and have some fun taking pictures with the great cameras you have??
02-05-2011, 02:07 PM   #343
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QuoteOriginally posted by Smeggypants Quote
I've never heard such utter rubbish
Someone takes the time to run a test, qualifies her results with "I cannot speak for all K-5 units out there", and all you and beta can do is run her down because her results don't match yours? Talk about "childish and offensive".
02-05-2011, 02:30 PM   #344
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QuoteOriginally posted by bikecoboss Quote
Someone takes the time to run a test, qualifies her results with "I cannot speak for all K-5 units out there", and all you and beta can do is run her down because her results don't match yours? Talk about "childish and offensive".
Christine Tham's results don't mean anything, because we have no idea what they are. The only thing we know for sure is that she is happy with her K-5. That' great.

But to say there isn't a problem without any respectable test, and to further say Pentax has nothing to fix because of her tests is ridiculous!
02-05-2011, 02:41 PM   #345
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She said she thinks that if all K-5's are like hers, there's nothing to fix. She carefully qualified her conclusions, I'm sorry if you can't or won't understand that.
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