sigma 18-50 ex - problems! again! Anyone else experiencing!

Hi All,

this problem has turned me - a relatively young man into a doddering wreck!!

Despite fiddling with the software internals I still get bad back focus issues. Does anyone else have this lens?

Up to F4 seems the worst but then the bigger focus "net" seems to hide it.

Can anyone save me from constant fiddling - I just want to create art!!!

thanks again


James

Which camera body?
I had consistent back focus issues with the K10D (but didn't with the *ist-D). As it turned out, every lens back focussed and it was more apparent on wide apertures (like f/1.4). There's a thread on how it could be adjusted

You may find a tripod test with something like the focus test chart from http://www.focustestchart.com/ may help identify what's going on.

Matt

Hi Matt,

one day i'll have a word with the Queen and get you knighted as you are always a great help. Tried some of the links you mentioned last time and even tinkered with the af adjust. But can't get the blighter to work.

The prob is also when I switch to my lovely Pentax 70-320 it will not be calibrated.

When you use manual focus does it work the same - does the viewfinder "lie" to you?

Blue

sorry K10d

Matt,

Glad to see an evil Nikonian has provided the world with a very useful chart and an insightful writeup.

Thanks for passing it along.

I'm using it on manual focus Spotmatic, Super Program and P30 bodies with my 50mm Macro prime, to see how well the mirrors are adjusted.

'Course, it's my failing eyesight replacing AF in these tests

Maybe I'll see if I need new glasses.

Oh, boy - new lenses! (Any way I can get them )

LOL @ the knighthood

Not sure what you mean?? Did you mean the 80-320? There are other issues that can occur with the 80-320 - especially not being able to focus on infinity. But that's another story

The AF calibration on the K10D is camera wide and applies to all lenses. It's only the K20D that has lens-specific calibration

* If ALL lenses back focus then you can adjust the focus for the K10D as described.

* If only the Sigma BFs then that's another story!

* It's not that the VF looks wrong, it's that the focus-assist on MF and the AF are out by the tiniest fraction. To be honest, I couldn't actually see the difference in the viewfinder at all! (To calibrate you have to go through the process of taking a shot, zooming in, changing the AF, taking another shot etc etc. You can't setup using the VF!!)

A bit more concrete information would help a lot
Matt

Thanks Matt.

Lens is the Sigma 18-50mm ex dc.

I did a test with a ruler and tried to focus on one point. The lens appears to focus on my chosen number (always 16cm - don't know why I choose this)
but will always on the photo show as focused on 17cm.

I always compare the depth of field to the span of a net. At the weekend I took outdoor shots on a an aperture of F4 and these were also out of focus. Where the focus was, was impossible to see.

thanks again

Blue

Blue,
You MUST use something like the Focus Test Chart NOT a ruler. You cannot be absolutely sure that the centre focus point is accurately aligned.

The FTC has a thick black bar in the middle that you focus on at 45 degrees. There are ruler markings at the far right and left edges that will show the focus. But the camera needs something completely unambiguous to lock onto. Download the chart, print it out and try with that

Matt

ok will do!!

thanks again

Blue

Heres a couple of tests i performed just recently, just to give you an idea

https://www.pentaxuser.com/forum/viewtopic.php?t=6979