[Anvh]

Would the k-5 be better than the k-x when using super fast lenses like the 55 1.4?

The opening is larger on the AF of the k5 if I recall correctly.
So it well fashion more from fatter lenses.

[JinDesu]

The opening is larger on the AF of the k5 if I recall correctly.
So it well fashion more from fatter lenses.

Well, that bodes well for my obese lenses

[crewl1]

K-5 AF performance is better in my experience than K-x.

The ability to micro adjust each lens in the K-5 will improve accuracy on some of your lenses also.

Low light has the AF assist light on the K-5 that is not on the K-x.

If you can swing it I would hang onto the K-x as a backup because for what they are selling now it is better to keep it, and the sensor is IMO just as nice as the K-5 for most uses.

[pero]

I've had a K-5 for about a month and a K-x for 15 months. So far I'm not that happy with the AF of the K-5. In good light and easy to focus subjects it's no problem, but indoors it seems rather random, especially in bulb light. When the green assist light has gone off I've not found that it actually helps the focus. The same goes for manual focus using the green hexagon indicator. It's a bit hit and miss. To be fair the problem seems worst with "difficult" lenses such as an A 50/1.7 and a 15/4 Limited. But I've never found any issues of the kind with my K-x, with any lense.

It might be that I had higher expectations with the K-5 and therefore it disappoints me a bit, perhaps I'm scrutinizing the pictures more carefully. But the AF is in my experience not a reason to buy it. Having said that, I'm very happy with it in every other respect, it's a great camera and I don't regret buying it (the high ISO performance is nothing but stunning). And I guess there are always variations between different copies of the same model.

[wildweasel]

I got my kx in Oct of 2010, and my k5 in Dec of last year and can say, at least as far as my examples are concerned, the k5 is significantly faster and more accurate, in all lights. The difference is especially noticeable in low light; where the kx hunts around the focus point before deciding on the wrong part of the composition, the '5 just locks on. The difference does vary somewhat from lens to lens, with the 35/2.4 showing least variance in speed between the two cameras.

[pero]

Edit to my own post above (#19): I should have said that those experiences are from using center focus point only. I never use the auto select focus points so I've no experience there.

[DownhillGR]

there are videos in youtube showing focus speed of both cameras. Although k5 seems extremely fast i can tell you by owing a kx that it's focus speed is absolutely great. Of course lenses always play a major role in focus speed and accuracy. But i can tell you that those numbers in the technical booklet about k.x are real.

now if you are intrested in technical details here they are:
Pentax K-5 Camera Performance - Full Review
Pentax K-x Camera Performance - Full Review

actually kx seems a bit faster in numbers. I don't know about k5 as i've never used one but i think that k-x is one of the best bargains pentax ever made!!!

if you want just for the fun of it, check this out...

Canon EOS 60D Camera Performance - Full Review

twice the price twice the delay... feel free to check out similar nikons....

but the bottom line is that k5 is much much much better camera than k-x when it comes to ease of use and custom settings...

[gflauti]

Thanks for answers!