[Christine Tham]

So, I evebtually think that Christine's camera wasn't different but that she just didn't hit the intermediate region where the AF assist beam engages only once.

Falk,

Interesting theory re the AF focus light being triggered by the AF sensor - I'm inclined to think it is plausible.

However, my camera does behave differently from your theory. Once the AF light engages, it will engage until the completion of focus (even in EV2-3).

It's very hard to get the AF assist to come on, even in very dim light. I usually force it by cupping my hands in front of the lens, which then forces the AF assist light to fire.

Once that happens, the AF assist light has a "tendency" to continue to be engaged for subsequent shots, even when I raise the ambient light to as high as EV3.

To get the AF asist light to stop engaging, I have to raise the ambient light to EV4-5 at which point it will stop working, and continue not to work even if I lower the light back to EV1-2.

Interesting behaviour, and implies the camera has some control over the AF assist light, and it's not driven purely by the AF sensor readings.

[Mistral75]

(...)

I would be rather surprised to learn that 645D and K-5 share the very same physical module. It would cover maybe less than the inner third of the 645D frame only.

It's actually the case:

[Smeggypants]

One question: This problem has no effect on those who normally shoot in full daylight or use full spectrum bulbs for their modeling lights, correct?

Until they come to sell the camera of course

[Smeggypants]

Falk,

Interesting theory re the AF focus light being triggered by the AF sensor - I'm inclined to think it is plausible.

However, my camera does behave differently from your theory. Once the AF light engages, it will engage until the completion of focus (even in EV2-3).

It's very hard to get the AF assist to come on, even in very dim light. I usually force it by cupping my hands in front of the lens, which then forces the AF assist light to fire.

Once that happens, the AF assist light has a "tendency" to continue to be engaged for subsequent shots, even when I raise the ambient light to as high as EV3.

To get the AF asist light to stop engaging, I have to raise the ambient light to EV4-5 at which point it will stop working, and continue not to work even if I lower the light back to EV1-2.

Interesting behaviour, and implies the camera has some control over the AF assist light, and it's not driven purely by the AF sensor readings.

Maybe your Camera has a faulty AF assist light?

[bjan]

Dear Falk,

With all information gathered as per today. Do you believe in a firmware update that can fix the AF issue in the K5 or is the shortcoming from a dimension that we can only hope for the next generation of cams ?

Have a nice day

[Wheatfield]

One question: This problem has no effect on those who normally shoot in full daylight or use full spectrum bulbs for their modeling lights, correct?

My experience so far is that the K5 focuses perfectly in daylight or close to it down to ~ EV-2.
If you check the specifications for the camera, you will find that they are claiming AF down to EV-1 (according to the specs listed on DPReview, the spec sheet on Pentax imaging doesn't mention an EV base for AF).
One could argue that the AF is working as advertised, no matter what the wishful thinking of people is regarding miracle AF.
I wouldn't worry about resale value, the K5, like any other DSLR, is a disposable consumer electronic commodity. In a year, the new price will probably be 2/3 of it's launch price, and in 2 years it will sell for a few hundred dollars on the used market.
It would be this way if the AF worked as wished for or as specified.

[Smeggypants]

My experience so far is that the K5 focuses perfectly in daylight or close to it down to ~ EV-2.
If you check the specifications for the camera, you will find that they are claiming AF down to EV-1 (according to the specs listed on DPReview, the spec sheet on Pentax imaging doesn't mention an EV base for AF).
One could argue that the AF is working as advertised, no matter what the wishful thinking of people is regarding miracle AF.
I wouldn't worry about resale value, the K5, like any other DSLR, is a disposable consumer electronic commodity. In a year, the new price will probably be 2/3 of it's launch price, and in 2 years it will sell for a few hundred dollars on the used market.
It would be this way if the AF worked as wished for or as specified.

This is an insult to us K-5 owners who just want the AF to work in reasonable low light levels that can be expected of a camera of this ilk.

The K-5 has a proven faulty AF. Wanting this fixed is not wanting a 'miracle' AF.

[Gimbal]

My experience so far is that the K5 focuses perfectly in daylight or close to it down to ~ EV-2.

And my experience so far is that the K5 focuses perfectly in daylight or close to it down to ~ EV4.

[Ray Pulley]

My experience so far is that the K5 focuses perfectly in daylight or close to it down to ~ EV-2.
If you check the specifications for the camera, you will find that they are claiming AF down to EV-1 (according to the specs listed on DPReview, the spec sheet on Pentax imaging doesn't mention an EV base for AF).
One could argue that the AF is working as advertised, no matter what the wishful thinking of people is regarding miracle AF.
I wouldn't worry about resale value, the K5, like any other DSLR, is a disposable consumer electronic commodity. In a year, the new price will probably be 2/3 of it's launch price, and in 2 years it will sell for a few hundred dollars on the used market.
It would be this way if the AF worked as wished for or as specified.

Page 358 of the manual specifies the AF working range of EV -1 to 18.

Your camera works to within 3 stops of this apparently, and others reporting EV4 are 5 stops over the specified lower limit.

That's not even close by any stretch of the facts.

NOTE: if any of the 3 K5s I tried would have held even barely within DOF at 5.6 at EV2, I would still have one as that is just about what my K20 will do and it has the same specification as the K5

Ray

[Smeggypants]

And my experience so far is that the K5 focuses perfectly in daylight or close to it down to ~ EV4.

And my experience also so far is that the K5 focuses perfectly in daylight or close to it down to around EV4

[Ray Pulley]

Falk,

A question/observation or two for you:

The earlier specifications for AF (K10 and K20, etc) all had the same EV -1 to 18 range, but were qualified by a note that specified this at f1.4 ISO 100.

The K5 only specifies ISO 100.

Regardless, isn't the earlier f1.4 note a clue about the amount of light getting into the system, which in turn tells us a little about the conditions under which the range was set? No, we do not know the shutter speed based upon this spec, so we do not really know the specific answer to my question, but what if (in the typical Pentax way) this really means:

EV -1 to 18 ISO 100 f1.4 at shutter speed n
EV 0 to 18 ISO 100 f2.0 at the same shutter speed?
EV 1 to 18 ISO 100 f2.8 at the same shutter speed and so on until the minimum aperture opening of 5.6 is reached?

The point being that it is an indication of the range of the system based upon how much light it sees at max available aperture before exposure? This might explain the lens differences even if it does not explain why.

From what I can find, which only includes all models up to the K10, the Pentax service AF test is done with a dark hood using a target not that dissimilar to many that we commonly download and use at home at a color temp of 2856K, LV 11 or 12.

The newer models might be different but I could not find any information about this for them.

It might be interesting to setup similar conditions, zero your lens and then re-test for the FF in lower light of the same color temp.

Ray

[ursamajor]

I heard that the firmware will be available on 1st april.

[falconeye]

Dear Falk,

With all information gathered as per today. Do you believe in a firmware update that can fix the AF issue in the K5 or is the shortcoming from a dimension that we can only hope for the next generation of cams ?

Have a nice day

Appearently, a version 1.03 is imminent, promised to fix the AF low light issue. This is news from after this thread started. You'll find clues within it.

Falk,

A question/observation or two for you:

The earlier specifications for AF (K10 and K20, etc) all had the same EV -1 to 18 range, but were qualified by a note that specified this at f1.4 ISO 100.

The K5 only specifies ISO 100.

Regardless, isn't the earlier f1.4 note a clue

I cannot check right now. Are you sure you looked up the AF spec rather than the metering spec? I asl because I remember the metering spec contains a reference to the lens which is logical too.

[Christine Tham]

My experience so far is that the K5 focuses perfectly in daylight or close to it down to ~ EV-2.
If you check the specifications for the camera, you will find that they are claiming AF down to EV-1 (according to the specs listed on DPReview, the spec sheet on Pentax imaging doesn't mention an EV base for AF).

Wow if you can focus down to EV -2 that's pretty impressive!

The "EV -1" limit that DPR quotes is from page 358 of the manual (Appendix: Main Specifications):

Brightness Range: EV-1 to 18 (ISO100)

Interesting that the manual puts a caveat of ISO100 on the range, which would imply that the range could vary depending on ISO (although I don't see how ISO is relevant).

I was interpreting the limit of EV -1 as a "best case scenario" - in other words it's like inkjet manufacturers saying their printers can print "up to 8 ppm"

But if you can focus down to EV -2 that may imply Pentax was being conservative.

My limited experience suggests that under a reasonably white or neutral light, the camera can focus down to somewhere below EV 0, but in yellowish light it will start to exhibit slight FF from around EV 1-2.

The photo I took of the incandescent bulb in the torch however may suggest that the camera could FF at higher EVs under very yellowish light.

So posters who claim to notice problems at EV4 are probably right.

[Christine Tham]

Are you sure you looked up the AF spec rather than the metering spec? I asl because I remember the metering spec contains a reference to the lens which is logical too.

According to page 358 of the manual, the metering spec is "EV0 to 22 (ISO 100 50mm f1.4)"