Help auto focusing in low light

Hi the K10D seems to struggle quite bad in low light trying to focus in Auto mode is this normal and can a firmware fix it

Pete

Autofocus works by looking for contrast changes in specific strips of pixels (AFAIK), so in low light you are not going to get much contrast in those strips, therefore autofocus wont't work in low light. It's not a pentax thing nor a K10D thing, it's a limitation of the way such systems work. If you have a flash unit such as the AF360, there is a red illuminator which throws a grid of red light onto the object to allow the AF to work in almost totally dark conditions.

Lenses with smaller apertures are going to struggle even more. If your lens will only open to f5.6 it will have a lot less light to work with than say a f2.8 or f1.4.

Someone sells a cheap little attachment with a row of LEDs that help illuminate for focusing. But I think they are on all the time, so using the pop-up flash focus-assist or the 360/540 red spotlight is probably going to give better results as they are on only while the button is half-pressed.

We all struggle to focus in low light, not just cameras. It's because we use light to focus, and when there isn't any, we have a hard time doing it.

G

Hi Tim,

For reference Pete..

http://en.wikipedia.org/wiki/Autofocus

I tried this within an hour of getting my 360. Forget almost.. It works perfectly in total darkness.. perfect focus and exposure every time.. I just can't manage that in daylight..

Pete, until you get you get a 360 or 540 flash gun, you'll just have to focus manually when it gets too dark for the AF to work.

Cheers

Liam

Pete,
You can help the AF along a bit...

Switch the focus selector on the back to "Centre Only" - point the very middle of the viewfinder on something you can see has contrast and focus with that.

Personally, I find it much easier to use the custom function that disables focus-on-half-press-of-shutter and just use the "AF" button on the back

Generally I can get a focus in very low light if there's a spot of contrast (like the subject's eyes).

But, yes, low light = low contrast = difficulty in getting a focus lock.
And, no, it's not firmware fixable (ALL cameras have this problem in low light, perhaps to varying degrees). But Pentax have given enough custom options to be able to use the camera very, very sensibly.

Matt

another strategy is to use video lights....has obvious pros and cons...but works great with fast lenses.

Aw Liam, did you have go go and blow my cover as an expert (google/wikipedia) user?