K-5 AF Fine Adjustment with zoom lenses

[RockvilleBob]

I am a new K-5 owner and bought two zoom lenses, a Pentax DA*16-55 and Sigma 2.8 70 -200. I also rented a Pentax DA*300 for a trip this week. I just went through lens calibration. The DA*300 prime was dead on with no adjustment needed. Both the Sigma zoom needed adjustment for near focus and the Pentax DA* zoom needed adjustment for far focus. The problem I encountered was the the AF Fine Adjustment varied with the focal length of the zoom lenses for both the Sigma and the Pentax.

I've never done lens calibration before and it seems logical that this might be the case. I am just asking for confirmation that AF will vary across the focal length range of a zoom, since both the zoom lenses are new.

It appears a clear advantage of prime lenses is more accurate auto focus?
 

[blackcloudbrew]

I have no answers to you questions and actually have not tried much in the way of lens calibration on any of my DSLRs. I would ask why you felt that you needed to calibrate you lenses - other than you can do it?

[RockvilleBob]

Was having some difficulty with focus with the Sigam 70-200 zoom. Made the corrections and now focus is sharp but slightly different across the zoom range. I feel the small effort to do this paid a good dividend. The I looked at the Pentax DA* zoom - similar issue with similar result.

My sense is that if you pay about $1000 for a lens it is worth the effort to insure you get the best focus possible.

I also learned that perhaps prime lenses are far more accurate focus lenses over zooms. Probably common knowledge but I did not know this.

[blackcloudbrew]

Good reasons! I was just concerned that you were new to the whole DSLR game and were sort of obsessing over sharpness. Just starting out there are lots of other things to worry about than lens sharpness, in my opinion. Prime lenses have typically always been regarded a sharper than zooms although modern zooms are often as good as primes. The bottom line is that you sound happier with your adjustments. Works for me!

[RockvilleBob]

Started in the 70's. Just sold 3 Olympus OM bodies and lenses. Also sold MY Sony Alpha100 and lenses. I waited for the A77 and didn't like what I saw - it targets consumers looking for video and lacks many important photography features. The Sony Alpha900 is great but for $3,000 I got the k-5 and the two zooms. Very happy with the Pentax k-5 but a little fussy about focus. Thanks for your interest and response. I really feel the K-5 gives the best bang for the buck versus Nikon and Canon since they have to jack up their prices to cover their advertising costs.

[blackcloudbrew]

Got it and welcome to PentaxWorld!

The whole business of lens calibration is one that I've 1) sorta felt I should be worried about, 2) tried one time to work on with my K20d, 3) wonder how that would work with my shooting on my K5. The deal is that I have a lot of lenses, well more than the amount of lens calibration adjustments in my K5. With the K20d there was only one calibration setting for all lenses. So I tried it once with several of my most favorite lenses and felt that they were spot on. So, I've had a 'what me worry?' attitude since then. But sometimes I see softness in some images and wonder if it's me or the specific lens. It's usually me though.

So...that's my $0.02 on it.