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01-16-2011, 03:58 PM   #91
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Like I said, my camera AFs fine for all pics I have tried, right down to the light level where the AF beam comes on.

So I don't think there is an issue.

Why there should be an issue between F1.x and F4, but not at F4+, I don't understand. I would have thought that light is light... how can the AF system tell between say F2 and F4?

But there will always be an issue with low light level AF because the AF assist beam works only for near targets. To AF on a building 100m away you would need a 100W lamp

There is simply no general solution to this - for any camera. AF will never work if there isn't enough light.


Last edited by peterh337; 01-16-2011 at 04:08 PM.
01-16-2011, 04:07 PM   #92
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For f=2.8 EV 4 would be:

0.5s @ISO 100,
1/4s @ISO 200,
1/8s @ISO 400,
1/15s @ISO 800,
1/30s @ISO 1600,
1/60s @ISO 3200,
1/125s @ISO 6400

(EV 0 by definition is 1s f=1 @ISO 100)
01-16-2011, 04:12 PM   #93
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QuoteOriginally posted by Smeggypants Quote
Just wanna confirm that my New K-5 , got it yesterday, is suffering very bad FF in low light

S/n 39xxxxx V1.02
What sort of light (tungsten?)?
01-16-2011, 04:28 PM   #94
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QuoteOriginally posted by jolepp Quote
What sort of light (tungsten?)?
Well a mixture of tungsten an computer monitor.

I've just tried a shot from the bedroom window into the street which is lit by sodium lamps. I focussed on a high contrast iron gate about 100feet away and got severe Front Focussing. manual focussing or using the Live View focus worked fine and was spoton. My K20D is also spot on with the same lens ( sigma 30/1.4 )

I've found my Pentax FA50/1.4 is also Fro Focussing under same conditions.

I wish we'd get some official response about this problem. I've contacted my supplier about it and hopefully I'll get a reply tomorrow ( monday )

01-16-2011, 04:34 PM   #95
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QuoteOriginally posted by peterh337 Quote

Presumably going to say ISO 400 sidesteps the issue, and on the K5 there is not a lot of difference in IQ between ISO 100 and ISO 400... in most situations where the shutter is open for 1s, IMHO.
Using a higher ISO makes no difference. My last test shots were al at a higher ISO. For example shooting into the street was 1/15 - F/1.4 ISO3200 - Around EV0. My K20D can AF this no problem.

QuoteQuote:
It could be cured in firmware, for near objects, by making the AF light come on at a higher illumination level.
Sure but it's a bodge job.
01-16-2011, 04:38 PM   #96
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QuoteOriginally posted by peterh337 Quote
Like I said, my camera AFs fine for all pics I have tried, right down to the light level where the AF beam comes on.

So I don't think there is an issue.

Why there should be an issue between F1.x and F4, but not at F4+, I don't understand. I would have thought that light is light... how can the AF system tell between say F2 and F4?

But there will always be an issue with low light level AF because the AF assist beam works only for near targets. To AF on a building 100m away you would need a 100W lamp

There is simply no general solution to this - for any camera. AF will never work if there isn't enough light.
This kind of general talk is irrelevant.

There is a specific issue with some K-5s where you get severe Front Focus in low light and possibly when that low light is red/orange weighted.

I've been following these theads for a while. I only got my K-5 on Friday and have found I have the problem. My20D has no problem focussing under the conditions.

If a K20D can do it then there's every reason to expect the K5 to do it. Which means there is a solution. What that solution turns out to be it remains to be seen. I hope it's a firmware job as I don't want to have to return the camera for a replacement and be without it for sometime.
01-16-2011, 04:38 PM   #97
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I photograph flamenco dancers. I used to shoot on Tmax 3200 with a Leica at 1/60 sec and f2, pushed if necessary. Now I am using a K-7 and a K-5. In one restaurant I frequent the K-7 would work at 1/60 sec, f2, and ISO 6400, noisy with the histogram to the left but usable. The last few days I tried the K-5 at 1/60 sec, f2, and ISO 12800, an EV of 1 according to PhotoME. The noise structure of the K-5 at 12800 appears to be the same as that of the K-7 at 3200, which definitely helps my flamenco shots. However, I am throwing out about 3/4 of my pictures because the focus is off. I don't use the focus assist light because it's going off 200 times in a 30 - 45 minute show could bother the dancers and irritate the restaurant patrons. I am going to try to calibrate the lenses I use in this environment at EV 1 (down a long dark corridor). It may be that I am expecting too much and that most cameras would have focus problems in this environment. The Leica was so good in this respect.
01-16-2011, 04:48 PM   #98
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QuoteOriginally posted by peterh337 Quote
Like I said, my camera AFs fine for all pics I have tried, right down to the light level where the AF beam comes on.

So I don't think there is an issue.
YOu mean don't think there is an issue with your camera?


QuoteQuote:
Why there should be an issue between F1.x and F4, but not at F4+, I don't understand. I would have thought that light is light... how can the AF system tell between say F2 and F4?
Now this is interesting.

I just took two test shots at roughly EV2


The first was 1/40 f/1.4 ISO12800

The second was 1/40 f/4.0 ISO1600


The front focussing is still there at both apertures.


Last edited by Smeggypants; 01-16-2011 at 04:58 PM.
01-16-2011, 04:51 PM   #99
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Heh, as it is now the AF assist light may sabotage an attempt to fix the problem by AF fine adjustment: the other day I was trying to take pictures (with flash) in a dimly lit room (tungsten-like fluorescents) where the assist light sometimes kicked in and sometimes not. When it did, there was less FF and so too much adjustment (I guess I could disable the assist light to avoid this).
01-16-2011, 04:52 PM   #100
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QuoteOriginally posted by cpk Quote
I photograph flamenco dancers. I used to shoot on Tmax 3200 with a Leica at 1/60 sec and f2, pushed if necessary. Now I am using a K-7 and a K-5. In one restaurant I frequent the K-7 would work at 1/60 sec, f2, and ISO 6400, noisy with the histogram to the left but usable. The last few days I tried the K-5 at 1/60 sec, f2, and ISO 12800, an EV of 1 according to PhotoME. The noise structure of the K-5 at 12800 appears to be the same as that of the K-7 at 3200, which definitely helps my flamenco shots. However, I am throwing out about 3/4 of my pictures because the focus is off. I don't use the focus assist light because it's going off 200 times in a 30 - 45 minute show could bother the dancers and irritate the restaurant patrons.
Yes exactly the reason not to use the assist light.

QuoteQuote:
I am going to try to calibrate the lenses I use in this environment at EV 1 (down a long dark corridor). It may be that I am expecting too much and that most cameras would have focus problems in this environment. The Leica was so good in this respect.
A short term fix is to note the calibration required to get focus in low light and change the calibration in the camera, but my Sigma 30/1.4 is FF A long way I doubt +/- 10 would accommodate it. Something else to research.

Again my K20D has none of the problems reported here.
01-16-2011, 04:53 PM   #101
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QuoteOriginally posted by jolepp Quote
Heh, as it is now the AF assist light may sabotage an attempt to fix the problem by AF fine adjustment: the other day I was trying to take pictures (with flash) in a dimly lit room (tungsten-like fluorescents) where the assist light sometimes kicked in and sometimes not. When it did, there was less FF and so too much adjustment (I guess I could disable the assist light to avoid this).
Yup

I'ev already programmed a user mode with it disabled precisely for shooting situations where it would annoying to subjects
01-16-2011, 05:14 PM   #102
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QuoteOriginally posted by peterh337 Quote
...
Why there should be an issue between F1.x and F4, but not at F4+, I don't understand. I would have thought that light is light... how can the AF system tell between say F2 and F4?
...
I don't think the issue is directly related to the aperture used. It is just that it becomes relevant with smaller apertures where DOF gets thin enough for the focus error to matter.
01-16-2011, 05:49 PM   #103
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QuoteOriginally posted by Wheatfield Quote
Why try anything? If your camera works, enjoy it.
If you don't want your camera to work, then keep making the conditions it has to work under more and more extreme until it fails.

Because determing that not all bodies have focusing issues would indicate that this is a body specific hardware issue and that those who are waiting for a firmware fix may be out of luck and should consider warranty service.

I think this is the type of participation is important to the community and should not be questioned / discouraged.
01-16-2011, 05:52 PM   #104
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QuoteOriginally posted by Smeggypants Quote
There is a specific issue with some K-5s where you get severe Front Focus in low light and possibly when that low light is red/orange weighted.
I don't think the color has anything to do with the FF issue. I've been shooting concerts with lots of different lighting colors, and even when the whole scene was lit in green I had the same severe FF.
01-16-2011, 05:59 PM   #105
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QuoteOriginally posted by PhilippeG Quote
I don't think the color has anything to do with the FF issue. I've been shooting concerts with lots of different lighting colors, and even when the whole scene was lit in green I had the same severe FF.
Ahhh OK. That's helpful
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