Backfocussing 35 mm macro limited

I bought a brand new Pentax SMC 35/2.8 macro limited on jan. 4 2011 from a shop near my home town. I want to use it as my ever reliable walkaround lens, like a 50 mm in the old filmdays. The 1:1 macro facility is an extra on my way for all small flowers, spiders etc.

But; infinity causes problems. With autofocus it's mostly OK, but on bleak rainy winterdays it'not. Things like windows and signs on buildings maybe 100-200 meters away are not sharp. Not even using 5.6 or 6.7 apertures with speeds up to 1/125. Using manual focussing things get worse; when I turn the ring until the mechanical stop at infinity, pictures are 100% out of focus. When I stop the ring, about 2 or 3 mm before the mechanical end, pictures are deadsharp even at infinity!
I returned the lens to the shop and have been waiting for 4 weeks now.

It's a Limited lens, meaning handmade, but does this hand belong to a drunk brain, or is backfocussing a 'normal' procedure at the Pentax plant?

I think you've just been unlucky, that lens is held in high regard around here.

In Europe, you would be within your rights to ask for a full refund or a replacement lens.

THe op is in Europe.

Yes, I know. I think he knows too, but your post doesn't help him with his lens issue. Mine hopefully did.

It just sounds as though the infinity focus setting is out - Pentax's repair bods should be able to fix that in an hour assuming it's anything like the FA 80-200mm I had to reset infinity on after cleaning fungus.

I would be more inclined to ask for a replacement and check it thoroughly before taking it away though. Not unreasonable to expect an expensive item to work perfectly from the box!

I had a similar problem with my DA35 limited. But I don't think it was the lens that was faulty.

Mine appeared to be back focusing only coming good above F4 even at infinity focus. However in my case it turned out to be my K10D that was back focusing.

I think this lens is very sensitive to camera focus alignment. This is probably because it is a macro and has the focus ring movement designed to maximise control over short distances. There is very little focus movement between 0.5M and infinity so I think it is susceptible to camera miss alignment at longer distances.

I'm now using a K-7 and the same lens is working perfectly on this camera.

Glyn

Thanks for all hypotheses. My only DSLR is the K200D. It never ever in 3 years showed focusing problems. I think the camera is OK. I hope to get my lens back soon and repaired. I will certainly test it thoroughly in the store!

The mechanical stop is usually set past infinity, to allow for shrinkage/expansion in extreme temperatures.

It has never showed focusing problems, but (according to your signature) you don't have any other f2.8 AF lenses. So maybe you didn't notice before because of the greater 'leeway' for focus accuracy at smaller apertures?

i had a 35mm da limited macro that couldn't focus all the way to infinity. it needed some readjustment due to some loose bits inside.

if you grab the focussing ring and try to wobble it, is there any play? i.e. not if you try to turn it, but if you try to push it up and down in the way that it's not meant to go. it should be pretty sturdy and stable. it should hardly move in that direction. if it does move, then you likely have the same problem that i did, and your lens needs to be repaired.