Originally posted by Wheatfield One thing to remember is that whether they fix the AF or not, the camera is still useable several stops below the AF.
AF in this camera is rated to EV -1 (and appears about 4 stops off of that in critical close focus situations), but the sensor is capable of giving very usable images as low as EV-3 to EV-4.
Here is a handy exposure chart that I reference to quite frequently when I want to know what a particular EV value relates to in the real world.
Ultimate Exposure Computer
You posted a quite nice picture of a red bird on the "how long for a k6" thread. I figure that shot is ~EV 7.5 or so, which is well within the range of the K5 AF to operate accurately. A couple of stops less light though and you might want to keep an eye on your AF.
Also, if you aren't doing close ups and if you can stop down a bit, and the AF inaccuracy will be masked somewhat by DOF.
As with most things on the internet, this particular issue, while there and quite a fail for Pentax, does not render the camera useless, to a certain extent it is another thing blown out of proportion by single performance metric users. Were it that big a deal, it wouldn't have taken two months to find it given the manic penchant the members of this forum have for finding every possible flaw with their equipment.
What I think is of greater gravity is the bounciness at 1/15 second. I suspect more shooters will be affected by this than by any low light AF problems.
Wheatfield,
While there is some truth in what you are trying to say it is completely beside the point.
To start with I am pretty sure that the K5 specifications as advertised by Hoya/Pentax do not state that the AF will fail completely at EV 3-4 or so and that the camera will be all but unusable at the specified lower limit of the AF operating range.
Many (like me) did not buy a K7 because the DR and noise performance was not an upgrade over the K20, and in fact was not competitive. The K5 IQ is class-leading and well worth the upgrade as long as you do not need to ever shoot an image below EV 3-4. While one can certainly make use of the DR of the camera in many situations other than lower light, there are many shooting situations where the excellent noise performance of the K5 allows me to choose a higher ISO and therefore a higher shutter speed or larger DOF in a low light situation. Not so if the camera cannot focus properly in this light.
The K5 even ruins situations where you might choose a flash to light the scene as the camera will front focus whether you have a flash on or not. In fact, I first noticed significant FF in a room on Christmas eve where I was shooting with bounce flash. I have been shooting in this room on Christmas eve for decades with many different Pentax bodies, and focus has never been an issue. My normal setup in this situation is ISO 400, f 5.6, and this was NOT enough DOF to mask the FF. I had to dial in all of the AF adjust to get properly focused images.
There is no way I can shoot the K5 in a typical indoor wedding reception, also a situation I have had little trouble with using other Pentax bodies. The K20 might have been slow to lock focus in low light, but it either gave up or locked at a good focus even if slow.
Why would one need a good SR mechanism to be able to shoot hand-held images at slow shutter speeds (normally lower light situations) if the camera cannot properly focus in this situation?
I note your concern over blur at 1/15 sec. Many situations where this blur might appear are going to be low enough light levels that the mis-focus is going to make any shutter blur a non-issue.
I'm also not sure I will be able to get a good focus in a studio lighting situations lit by the modeling lights on my flash banks.
Lastly, the problem is not an either/or issue. The camera shifts towards FF as the light is reduced, which can limit use of shallow DOF wider apertures even in higher light levels. In addition, I have some lenses that need AF adjustment in good light for FF. These lenses have very litle room for further adjustment, which means in lower light, I cannot use them at all.
No, I think that there are many situations where users will see this in the images they are trying to capture, even one as simple as a child's indoor birthday party, and the real fear is that Hoya will neither acknowledge the issue nor fix it, just like SDM failures and shutter blur.
Ray