Hi, I asked a somewhat similar question a few months ago. One of the more knowledgeable list members offered this response:
=================================== Longer focal lengths generally take more time to focus than shorter because there's more travel to deal with in the focusing mount. Internal focusing lenses focus more swiftly than displacement focusing lenses, front element focusing lenses often focus faster than internal, etc. It's a matter with several dimensions: the available power at the focus servo drive, the individual lens' particular focus throw and friction in its drive mechanism, and the AF discriminator's interaction with a particular lens' contrast and resolution when wide open. =================================== I have a 77mm but have not compared it directly to either of the other FA lenses you have lenses. One thing you can do to speed up auto focus is to set the lens manually to approximately the distances you'll be working at. Going from the closest point to out near infinity will take longer than if the lens was set to some middle point. Shel "The smallest feline is a masterpiece" - Leonardo da Vinci > [Original Message] > From: Jarek Dabrowski > I've recently bought a 77mm Limited lens - what a black beauty! > Today I compared the AF to my other lenses. And I am concerned about > AF speed - it is noticeably slower than with FA 50/1.4 and FA 35/2. [...] > I compared it on two cameras (PZ1 and *ist DS) - with the same results. > Can anybody, having the 77, set me at ease? The one I bought was the > last one in the store - in case of the return I won't be able to > compare it to another one (but my marriage will probably be saved...). -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net
