John Coyle wrote: > I have a similar Sigma lens, the 18-35 ASP, and while I have not noticed > anything in the viewfinder, I have had some recent shots where the focus > was just a little off. These were all shots taken in low light, using the > RTF, and with no other focussing aid than the AF system. I wondered > whether it was down to low-contrast making it harder for the camera > to auto-focus, or whether, because I was shooting towrds the wide end > of the lens, some other factor was coming into play, such as a mass > of fine detail and no large tonal differences?
I have similar experiences when it comes to AF with wideangle zooms. I experienced the same problem with my old Tokina 20-35, but I've not yet had the Sigma in a situation which will really test it. The thing that caught my attention with the focusing "error" I described in my original post, was that it appeared to be deliberate and changed consistently as I set different apertures, even though all the autofocusing was, of course, performed with the lens wide open. I have now got the negs from the test film I shot in the back garden, and I'm scanning as I type. It will be interesting to see how the Sigma at 24mm compares with my FA 24-90 at 24mm. For the purposes of the test, I accepted the focus that the camera gave me. I think I'll do some tests soon to compare the camera's focus (with apparently-deliberate error) to my best effort, and see if I can tell the difference on film. Graham -- [EMAIL PROTECTED] - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
