Originally posted by sanjeevdas It is true that the levels were fairly low. However, the camera promptly locked focus with no hunting. It also didn't use the AF assist lamp. I don't know what the low levels light limits for K5 are before it will not focus. I was comparing it to my D7000 where I have shot hundreds of similar pictures of people in my backyard during parties with very few OOF. I do think one session is not enough and I need to do some more controlled tests, once I get some time.
Hi Sanjeevdas,
As I explained (and I do not know why) the k5 seems very capable of finding something to lock on to even if it is too dark to do so reliably, and in my experience, when it does this, it is always a FF result.
The K5 AF system is specified to focus down to -1EV with the FA 50mm f1.4. Note that the f1.4 part of this equation is critical to understand.
What it means is that if you are using a slower lens, say one that is f4.0 max aperture, the lower light limit for reliable focus is actually 3 stops higher than -1EV. This is true because the AF operation takes place with the lens wide open, and f1.4 lets more light into the AF system than f4.0. This is true of all cameras, BTW.
As for your Nikon, my experience with Nikon (we use them at work) is that it turns on the AF assist light very consistently in light that is actually not very dim (at least the models I have used at work do so). I am not sure why the AF assist on the K5 body does not always come on when it seems like it should, but it often does not. When I have the AF540 flash on the camera, it seems to turn on the AF assist on the flash much more consistently than the one on the body.
The only way to understand what is really going on is to get some data. By that I mean get some exposure data for the dim scenes, note the lens used and max aperture and so on. It is also useful to try and determine if the AF assist came on or not (I have not looked for this in EXIF, so I do not know if the assist status is reported or not?). This exposure data should be without flash as the camera sets certain values when using flash no matter what the non-flash exposure would have been (depending upon the mode and settings, of course).
Here's a flash shot from a reunion in a bar. Note that the ceiling is not white, so there was little bounce, it was full dark, and as can be seen in the background, the lights were tungsten. This was shot with the K5 and the AF540 on camera using a Demb bounce/diffuser, but I do not know if the AF assist came on or not (K5 w/ DA* 16-50 f2.8):
The K5 is capable of properly focused images like this in all of the normal low light and dimly lit scenes I have used it in, but it would not produce such images in the same conditions before firmware 1.03. If you cannot get similarly focused images, something is wrong, and one way or another, it can be corrected.
Ray