I think, my second SIGMA lens is getting defective

LaFoto · Jul 15, 2008

When I looked at the photos I took in Hamburg last Saturday, at first I thought "oh dear, in some the focus is not right", to only later see that they look blurred only IN PART - and now I fear my second Sigma lens is getting defective (the first would - after some time - "fall into focus" or "fall out of focus", just as it pleased, randomly, and I had no influence over it).

Again, not every photo shows the blurred part, but some do.

In horizontal frames it is in the lower right, and in vertical photos in the upper right corner:

Any idea what might cause this? Any idea what could be done ABOUT it? Will I need to get myself a THIRD lens of the kind (no money for anything better than that one!)?

BoblyBill · Jul 15, 2008

Interesting... I haven't seen anything like that before. I couldn't tell what would cause that unless one of the many pieces of glass has shifted out of place, but the problem with that theory is the lens would act more like a lens baby and have a tilted focus plane or something like that. I would suspect that it was a finger print or something like a rain drop on the lens. Have you shot with it since and found a similar out of focus area?

LaFoto · Jul 16, 2008

Yes, I used it all day long on Saturday, and the "surrounding" photos to these three examples are ok :shock: ... a finger print would show in ALL of them until I wipe it away. But it is to be seen in some (only these three, to be honest) and not seen in others. So also I was thinking some glass inside had shifted, but this can't be???

tirediron · Jul 16, 2008

Well duh.. some ****er's gone and drawn on your front element with a great big red grease pencil. That's what pushed the elment out of alignment!

Seriously, that's an odd one; I don't think it's an element issue, as it would be out whack on the otherside of the image too. It looks exactly like the same effect I see out here (Gulf States) quite often shooting in high humidity when the's still a skin of moisture on one part of the lens. Is there any chance that you got some moisture on the outer element for those images?
What lens is this?
If you remove the lens from the camera and site down the glass with the apeture wide open, do you see anything that looks out of place? Is there any unusal noise or time-lag for the auto-focus?

LaFoto · Jul 16, 2008

Oh, I would need to re-read all your thoughts and test it when I'm back home from Hamburg Airport, to where I'm now taking my favourite model and her friend so they can fly to England to spend two weeks in Oxford. I'll then do all you suggest to see where this field of blurriness could have come from (and yes, some were taken from a boat, and some after heavy rain).

Battou · Jul 17, 2008

If you look at it, it occures in the same spot, that lower right hand corner of the frame. If tirediron's first assessment is correct and it's moisture on the lens, I would advise wiping it down between shots when shooting under moist circumstances.

If the second is correct there is a possibility of fungus, A result of regular and or prolonged exposure to high humidity and dark storage. This would warrent a send out repair. The lens is still useable with fungus but it eats away at the coating on the glass so it's best to get it taken care of ASAP. If it is fungal growth and it's effecting images this considerably it will be visable as you site down the glass with the apeture wide open.