On 24 Apr 2005 at 20:24, Shel Belinkoff wrote: > You're right of course. I just didn't understand what Cory was saying on > the first and second round, but when he finally rephrased the statement I > got it. Anyway, my style is not to do math to figure out what result I'll > get from a lens. The old fashioned way of sticking it on the camera, > looking through the finder, and making a few exposures seems to work pretty > well > for my needs.
I agree, for general photography the math may be unnecessary however if you are creating multi-image panoramas or other technical work like distortion correction the math does matter. > Plus, there's something of a flaw in just using math to determine the AOV > ... while a lens may be nominally rated at a particular focal length, it > may not in actuality be that focal length. Depending on the actual focal > length of the lens the difference may be significant. I agree that lenses don't always measure to be the FL that they are said to be however from my empirical testing most of my wide angles have been very close to the mark. > ... if you recall, not long ago Cotty put up some pics made > with lenses of similar focal lengths that seemed to show a greater difference > than would have been expected had the nominal FL of the lenses been precisely > as > indicated by the manufacturer. I do recall if they were lenses from the same manufacturer I'd have been concerned but I wasn't too surprised at his results, I believe that I have owned the same models of lenses. The other thing to consider in this type of caparisons is that the tests were performed using a cropped frame. This shouldn't make a difference however some lenses exhibit more distortions than others and the apparent AOV can change significantly as the image is cropped. It's difficult to explain but picture a lens with bad barrel distortion. When an image from such as lens is corrected to eliminate the distortion the centre of the image will contract. If the image was just cropped from that section alone it would give the impression of a wider AOV. IOW the FL and its suggested AOV may only be true for a full frame view. > While it's nice to know how to figure out all these technical things, I > feel that nothing beats making a photograph to get to the truth when it > comes to lenses and all their characteristics. Sure, as soon as David N and I get together again I'll set up a little real world comparison shoot-out between his Zenitar 16mm and my A16/2.8 and A15/2.8 and put them up for anyone who is interested to see. Cheers, Rob Studdert HURSTVILLE AUSTRALIA Tel +61-2-9554-4110 UTC(GMT) +10 Hours [EMAIL PROTECTED] http://members.ozemail.com.au/~distudio/publications/ Pentax user since 1986, PDMLer since 1998
