Here's the LensAlign I made .... thanks to xbow for the graphics.

Now I've noticed a strange behaviour with my replacement K-5. I put my sigma 30/1.4 on it and it focussed spot on in daylight without any AF fine tuning. Cool! - it also focussed spot on at EV2 ( most of the time ) - Also cool.

today, after making the SmegAlign I decided to calibrate my lenses. I put my FA50/1.4 on and that needed no adjustment either. Cool!

I then put another lens on which did need some adjustment. so after turning on AF adjustment and calibrating this lens, I then put the Sigma 30/1.4 back on and it was really back focussing. It needed a +5 to calibrated it again. The same happened with the FA50/1.4 which needed -10 to calibrate it.

A bit flabbergasted by this I reset the AF fine tuning and turned it off. Both the Sigma 30/1.4 and the FA 50/1.5 showed back focus and front focus respectively and the need the +5 and -10 to correct them


So it seems that simply turning the AF Fine tuning on does something permanent to the AF system, which even a reset won't cure.

I'm taking delivery of my 2nd K-5 tomorrow so I'll be sure to test this again with the new camera.

note: this was all in daylight and was nothing to do with any front focussing in low light. In fact the front focussing behaviour with the replacement K-5 is working fine ( most of the time ) with the sigma in daylight and EV2. AFing with 103 in low light is still inconsistent.

Ive never heard of those terms before, thanks for bringing it to my attentions,

after a quick google with results at this very forum..it turns out that the lens is a varifocal design.... obviously the aussies aint got a clue about what they are selling!!, as the ets I was told to do.. wouldst work, and shouldn't work

great forum , many thanks for the very helpful advice

Hi Tommo,

I think a Google search will show that this lens is notorious for focusing issues across many brands with FF on the wide end being common.

In addition, even very good zoom lenses will not hold perfect focus at all focal lengths. It is also usually not going to give good results on most any zoom to focus at one setting and zoom to another without a re-focus at the new focal length, but you probably already know this.

I adjust my zooms one of two ways:

Best focus where I use it the most.

Best focus at the longest focal setting as the wide end will be more forgiving of a focus error.

BTW, I have a Sigma 18-50 f2.8 that isn't a bad little lens, but it REALLY doesn't want to focus properly on the K5. It was always ok on my K10 and K20. This makes me wonder about what data the camera is reading from the lens chip and if the Sigma lenses need an update for the K5?

Sigma is pretty good about re-calibrating and re-chipping products if needed, so it might be worthwhile to contact them about the lens.

Alternately, you could just buy a DA* 16-50....

Ray

I will try, but my priority is taking real life photographs rather than exact scientific study

Frankly for real life analysis such accuracy isn't needed.

As Ray wrote, this (different focus error at wide and tele end) is quite common with some Sigma lenses.

Since these are parfocal lenses (as practically all IF lenses are), ...

Tommot, just have your lens calibrated by Sigma service (they'll need you cam too since they'll calibrate the lens to your body). As Ray wrote, this (different focus error at wide and tele end) is quite common with some Sigma lenses. The local Nikon guys always advise to visit the Sigma repair center for calibration right after purchasing the lens

By the way, my DA17-70 and 16-50 also exhibit this to some extent: when shooting things farther than 3-5 meter away (e.g. cityscapes, landscapes, etc) with focal length under approx 20mm the cam (both K-m and K-5) usually doesn't get perfect focus, it's slightly off. Not evident in screen size, but you can see it in 100% pixel peeping. Since these are parfocal lenses (as practically all IF lenses are), I just turn the zoom ring to the middle range (or to the tele end), lock focus, then zoom back to wide end and take the picture. This gives perfect focus even when pixel peeping I guess wide fov making objects quite small and Pentax's oversized AF sensors might be the culprit.

Understood. It would just be useful to see how the K-5 compares to the K20D. I really don't know whether V1.03 made it catch up or not.


Why did you built the SmegAlign then?
What was wrong with the flat charts if you are not too fussed about accuracy?

Frankly, I believe a cheap print of a regular focus chart is safer to use than an XYZ-Align which might be misaligned itself (Ray Pulley's seemed a bit out of shape in his shots) and to which the camera is not exactly aligned to. An XYZ-Align holds the promise of a more precise adjustment but only if the setup is done with great care.

yep Im gonna do that...they have to send it to sydney...be away for 10 days they reckon..I might send my 70-200 sigma with it too, as that has alway been soft at F2.8..perhaps a calibration will help that too ?

by the way...does anyone know whats done during these calibration ..is it a mechanical job or just electronic fixing ?

Because the Smeglaign is easier to mount on a flat surface ( more ergonomic ) and I wanted a little bit more consistency and accuracy than just chucking a piece of A4 paper around.

I doubt that you have achieved more consistency and accuracy if you are not including a careful alignment of the SmegAlign to the camera. Believe it or not, chucking a piece of A4 paper around is more forgiving regarding perfect alignment.

Ash
It's always been soft , sharpens up at f4 though

Ash
It's always been soft , sharpens up at f4 though

Actually after a couple of hours of mass calibrating today . I tried both the SmegAlign, A4 focus sheet and actually taking pics of real world stuff, I found the real world stuff was the best in calibrating the lenses.

Which also proves all those popping on my initial tests in the OP of this thread wrong.

I'm happy. I have two new K-5s which focus accurately with all my lenses down to EV2 and below.