auto focus question

[mudman]

on my K7 the I use AF-C mostly and find that with either the 18-250 or the bigma that is virtually impossible to getv it to focus on infinity, evenn if i spot focus on a point way into the distance.
my question(s) is/are:
does the focusing system use fuzzy logic? if it does could it explain the never reaching infinity problem.
i find this especially annoying with the 18-250 as i get unsharp detail at distances far greater than the 30 metres marked on the lens. or could it be having shake reduction on when camera on tripod?

[OzzieTraveller]

G'day Mudman

From experience with long lenses & big-zoom lenses ... just like any other lens it should ALWAYS focus to infinity. Sometimes I have had a lens that focusses "beyond infinity" - ha ha some may say, but I have had 500 & 1000 lenses where the focus collar went a shade beyond infinity, and it gave me the confidence to know when it was at its best focus

My current primary lens is a Leica 28-275 (much the same as yours) and it will tightly autofocus to infinity ... I can easily distinguish tree branches in a line of trees on a ridge line for instance. But when I go to manual focus, the manual-focus-aid thingy clearly shows that I can go 'beyond-infinity'

As to fuzzy-logic ... my understanding of most auto focus systems is that they are contrast based to a large extent, most dSLRs have phase-detect focussing, (perhaps another expert can outline this one), but even so - it should focus for you

Dunno whether this helps - hope so
Regards, Phil

[jibbonpoint]

or could it be having shake reduction on when camera on tripod?

I can only comment on this. I found that if I accidentally left the shake reduction on when on the tripod, I got shake. The instructions with the K10D are clear.

[kevinj]

I can`t comment on Pentax,some Canon IS lenses(older versions)will produce "shake" on a tripod,it doesn`t happen with my IS lenses,but I turn it off anyway.