K-r Autofocus performance update..not good

Started Nov 26, 2011 | Discussions thread
OP Barry Fitzgerald Forum Pro • Posts: 29,888
Issue is present regardless of lens

ico66 wrote:

I have combination Kr and 17-50 tamron. There are some problems with AF in low light. I sow that tamron is litle bit darker than kit lens. At same speed kit lens give half stop slower f-stop than tamron 17-50. The lenses of 17-50 are with biger diameter than 18-55, which means that relatively tamron is darker than kit.

Problem is the kit lens has a lot of issues too so it really doesn't matter what lens you use, Pentax or any other maker.

I suppose that in spot were is phase dedector the light is now enough for exact measuring of distance. This is reason contast AF to be more precise than phase AF. The combination of camera and exact lens is important. It is possible to calibrate camera with fine AF adjustment but this metod work at diferent focal length in diferent change so it is no comfortable.

It is possible to make calibtration of lens but this is expensive and you need good workshop.

On this one well if you calibrated the lens and body to AF perfectly in low kelvin light, it would be miles off in other lighting conditions. There are no obvious signs of big misfocus issues with the 17-50 and K-r in other light..there are none with the 90mm f2.8 either.

Both miss and quite badly in this specific lighting condition so calibration can't help you. This is probably why there isn't a solution as yet available to users

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