Not really replying to JCO, just tagging into the thread here. The students in my class usually don't quite get the difference in sensor sizes and the relationship to focal length until they see the circular photo towards the bottom of this page.
It superimposes three sensor sizes over the circular image projected by a lens. <http://www.shortcourses.com/use/using5-2.html> Once they see this, they get it pretty quick. GS George Sinos -------------------- gsi...@gmail.com www.georgesphotos.net On Mon, Apr 12, 2010 at 3:28 PM, J.C. O'Connell <hifis...@gate.net> wrote: > a 12mm lens on APS is not as wide as a 15mm lens on FF > hence, the A15mm wont perform as well on on FF or even > APS as a 12mm on APS. (in general). The problem is that > it takes to many elements which hurts the flaring reduction. > Cost and lens speed are also factors. I would bet the > DA 15mm outperforms the A15 on APS as the DA15 isnt > designed to cover FF like the A15 is so it can be tweeked > for Aps. > > -- > J.C. O'Connell (mailto:hifis...@gate.net) > Join the CD PLAYER & DISC Discussions : > http://tech.groups.yahoo.com/group/cdplayers/ > http://launch.groups.yahoo.com/group/cdsound/ > > > -----Original Message----- > From: pdml-boun...@pdml.net [mailto:pdml-boun...@pdml.net] On Behalf Of P N > Stenquist > Sent: Monday, April 12, 2010 3:52 PM > To: Pentax-Discuss Mail List > Subject: Re: Ultra-wide zooms > > > > On Apr 12, 2010, at 3:38 PM, J.C. O'Connell wrote: > >> High performance ultra wide zooms (UW) don't really exist. Go with a >> UW >> prime >> and even that wont match basic wide primes. >> >> -- > The DA 12-24/4 is reportedly comparable in performance to the DA > 14/2.8, although it's a stop slower. I've also read that it's actually > better than the A 15/3.5 at comparable FOV. I haven't compared it > directly to either, but I know from experience that it's an excellent > lens, capable of generating a nice, crisp double page spread at 12mm. > Good tool. > Paul > >> J.C. O'Connell (mailto:hifis...@gate.net) >> Join the CD PLAYER & DISC Discussions : >> http://tech.groups.yahoo.com/group/cdplayers/ >> http://launch.groups.yahoo.com/group/cdsound/ >> >> >> -----Original Message----- >> From: pdml-boun...@pdml.net [mailto:pdml-boun...@pdml.net] On Behalf >> Of >> David Parsons >> Sent: Monday, April 12, 2010 3:12 PM >> To: Pentax-Discuss Mail List >> Subject: Re: Ultra-wide zooms >> >> >> There are two common crops for dSLRs as compared to FF SLR, 1.5 >> (Nikon and >> Pentax) and 1.6 (Canon). >> >> Canon has a 1.3 crop on some of their pro bodies. >> >> P&S sensors are a whole other barrel of fish and there are many >> sizes, but >> they don't correlate because the lenses are not interchangeable. >> >> On Mon, Apr 12, 2010 at 3:00 PM, Keith Whaley <keit...@dslextreme.com> >> wrote: >>> P N Stenquist wrote: >>>> >>>> On Apr 12, 2010, at 8:48 AM, Keith Whaley wrote: >>>> >>>>> Bong Manayon wrote: >>>>>> >>>>>> Thinking of ... >>>>>> 1. Pentax DA 12-24 >>>>>> 2. Sigma 10-20 >>>>>> 3. Tamron 10-24 >>>>>> Am not into fish-eyes so those options are out. Any votes for or >>>>>> against any of those listed above? Thanks! >>>>>> Bong >>> >>>>> I don't think those focal lengths are 35mm-equivalent numbers. I >>>>> suspect they're double ~ such as the Pentax DA 12-24 is really like >>>>> a 35mm lens of 24-48mm focal length. Nice wide angle-to-normal >>>>> lens, >>>>> but hardly a fish-eye... >>> >>>> First, the conversion factor for angle of view is 1.5. >>> >>> Was Bong talking about a specific camera? I know we were talking >>> digitals, but, I thought each camera had it's own conversion camera. >>> In my limited experience, which does NOT include DSLRs, most cameras >>> differ a little as to what their 35mm equivalent is. I avoid the >>> uncertainty by referring to the owner's manual for each camera. They >>> always mention it... >>> >>>> So the 12-24 has the same _angle of view_ on an APS-C DSLR as an >>>> 18-36 would have on a conventional 35 mm frame. >>> >>> Cropping factor, or what I call the telephoto effect, brought on by >>> the size of the sensor. In other words, the ratio derives from how >>> much smaller the DSLR's sensor is compared to 35mm film size. >>> See: >>> >>> http://www.minasi.com/photos/dslrmag/ >>> >>>> However, the focal length is 12-24. That doesn't change, regardless >>>> of the format. Furthermore, it's not a fisheye on any format. It's a >>>> rectilinear lens. In other words, the optics make the verticals as >>>> true as possible given the size of the elements and the constraints >>>> of physical science. Paul >>> >>> Quite so. Thanks Paul. >>> >>> keith whaley >>> >>> >>> -- >>> PDML Pentax-Discuss Mail List >>> PDML@pdml.net >>> http://pdml.net/mailman/listinfo/pdml_pdml.net >>> to UNSUBSCRIBE from the PDML, please visit the link directly above >>> and >>> follow the directions. >>> >> >> >> >> -- >> Aloha Photographer Photoblog >> http://alohaphotog.blogspot.com/ >> >> -- >> PDML Pentax-Discuss Mail List >> PDML@pdml.net >> http://pdml.net/mailman/listinfo/pdml_pdml.net >> to UNSUBSCRIBE from the PDML, please visit the link directly above and >> follow the directions. >> >> >> -- >> PDML Pentax-Discuss Mail List >> PDML@pdml.net >> http://pdml.net/mailman/listinfo/pdml_pdml.net >> to UNSUBSCRIBE from the PDML, please visit the link directly above >> and follow the directions. > > > -- > PDML Pentax-Discuss Mail List > PDML@pdml.net > http://pdml.net/mailman/listinfo/pdml_pdml.net > to UNSUBSCRIBE from the PDML, please visit the link directly above and > follow the directions. > > > -- > PDML Pentax-Discuss Mail List > PDML@pdml.net > http://pdml.net/mailman/listinfo/pdml_pdml.net > to UNSUBSCRIBE from the PDML, please visit the link directly above and follow > the directions. > -- PDML Pentax-Discuss Mail List PDML@pdml.net http://pdml.net/mailman/listinfo/pdml_pdml.net to UNSUBSCRIBE from the PDML, please visit the link directly above and follow the directions.
