I didn't make a blanket statement, I made a statement relating to the original of the thread which was about SLR lens focusing. Also, this is a PEN TAX forum, and Pentax does not make RF cameras so there can be no confusion there either. You specifically mentioned the Pentax DSLR as your test camera too for your "tests". jco
-----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Shel Belinkoff Sent: Tuesday, November 14, 2006 2:39 PM To: Pentax-Discuss Mail List Subject: Re: Using a Super Tak w/ istDS- A challange to the list? Yes, I know that - however, JCO and others did not differentiate between RF lenses and SLR lenses. They made blanket statements. My comment was intended to show that there are enough variables that a blanket statement is foolish. Shel > [Original Message] > From: Adam Maas <[EMAIL PROTECTED]> > To: Pentax-Discuss Mail List <[email protected]> > Date: 11/14/2006 11:21:18 AM > Subject: Re: Using a Super Tak w/ istDS- A challange to the list? > > Shel, > > I'll note that focusing with SLR's and RF's is quite different. RF's > lose focusing accuracy with longer/faster lenses (Where this happens > depends on the effective RF baseline length) while SLR's lose focusing > accuracy with slow/wide lenses. Experience with focusing a Leica M lens > does not cross over to focusing a SLR lens. > > -Adam > > > > Shel Belinkoff wrote: > > John, > > > > There was no "original contention." What started all this was my comment > > that I found the ST 105/2.8 easy to focus when stopped down to f8.0 > > when used with the istDS. It was just a simple comment reporting my > > personal experience with a specific lens on a particular camera, and > > my pleasure in > > finding how nice and easy it was to use an old screw mount on the istDS. > > No contention that this experience is/was transferable to other > > people, cameras, lenses, situations. Later I tried the 35mm/3.5, > > and found it about as easy to focus. Just another comment reporting > > my experience, with > > that lens, on the same camera. I guess my ignorance of the laws of physics > > and the science of focusing must have skewed my experience. I just didn't > > know that longer lenses are easier to focus. Had I known that, > > perhaps my > > experience would have been colored by that knowledge, and I'd have > > found the 105mm easier to focus than the 35mm ;-)) > > > > Neither Bill nor I contended that our experience would be true for > > other lenses, other situations, other cameras, nor were we trying to > > refute the > > laws of physics. However, JCO, and now Mr Papenfuss, Ph.D., > > PPSEL-IA, claim that longer lenses are always easier to focus, > > although Mr Papenfuss > > at least has the good sense to add a rather long list of qualifiers > > to his > > argument. > > > > Never did I think that this thread would get so contentious, and > > that it would run for so long. And now Mr. Papenfuss, Ph.D., > > PPSEL-IA has joined > > the fray and gotten things going again. All the scientific evidence > > and book learnin' in the world cannot change the experience Bill and > > I had, regardless of what the laws of physics says. Of course, Mr. > > Papenfuss was > > careful to qualify the heck out of his comment, which is as it > > should be, > > because there are numerous variables in the real world, which, > > unfortunately for some people, is where we have to live, work (and > > photograph) these days. > > > > Now, were we to try the test in a lab, eliminate all variables, use > > scientific measuring tools, remove the human element, it may be that > > the 105mm lens could be proven to focus easier or more accurately > > than a 35mm > > lens. > > > > It's also interesting to note that some fast, long lenses are notoriously > > difficult to focus well or quickly, and that wider lenses are easier > > to focus. A case can be made using the Leica M75/1.4 or the Leica M 90/2.8. > > For many people both lenses require a lot of practice to focus accurately, > > and focusing a 28mm lens is much easier for many, if not most, Leica > > M users. So, where does that fall into this "discussion." Oh, > > wait, no one > > said anything about rangefinder lenses ... they are the exception to > > the laws of physics and scientific testing and discourse. > > > > Shel (a man of no letters) > > > > > > > > > >>[Original Message] > >>From: John Francis > > > > > >>> Everything else being equal (aperture, contrast, resolution, > >>>helical gear cut, etc), a longer focal length (e.g. 105mm) will have a > >>>higher "focusing sensitivity" than a wide angle (e.g. 35mm). That's > > > > just > > > >>>plain physics. > >> > >>But that still doesn't necessarily make them easier to focus, which > >>I believe was the original contention. In fact in at least one way > >>it makes them harder to focus - it's too easy to overshoot, or to > >>focus on the wrong place (especially if you are trying to pre-focus > >>in anticipation of a moving object coming into your composition). > > > > > > > > > > > > -- > PDML Pentax-Discuss Mail List > [email protected] > http://pdml.net/mailman/listinfo/pdml_pdml.net -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net
