----- Original Message ----- From: "J. C. O'Connell" Subject: [Norton AntiSpam] RE: RE: Using a Super Tak w/ istDS- A challange to the list?
> Dear Sir ( is that gentlemanly enough) , > You forgot to mention fstop used on the > 105 lens and I don't even think there is > such a thing as a K105/2.5 lens if I am > not mistaken. Pardon the typos. You've made a few yourself over time, I'm sure you understand. That would be an SMC Pentax 105mm f/2.8 lens at f/8. > > Secondly, have YOU ever used a constant > aperture zoom of ANY range that wasn't easier > to focus manually on the longer end than on the shorter > end? I haven't and this pretty much squelches > any argument to the contrary over this. Its just > simple differences in the DOF. The more DOF > you have, the harder it is to find the true > focal point because the DOF is masking it > to some extent and you don't pop in an out > of focus as quickly as you do with a longer > lens which has shallower DOF at the same > fstop and distance. I don't have much use for zooms, the only constant aperture one I own is a 70-210 f/2.8. Shel originally mentioned that he didn't see much difference in ease of focus between a couple of primes anyway, so why bring zooms into the discussion? There was a comment made that he (and I) didn't have more trouble focusing a medium wide angle lens than a short telephoto when stopped down to f/8, using an istDs (shel) and an istD (me). I am aware of the optical theory you are using for your assertion, I suspect that the difference in DOF between the two focal lengths isn't great enough to cause either Shel or myself a problem. I don't care if you disagree with what my eyes tell me or not, since what my eyes tell me is true. William Robb -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net
