Are your numbers given for "effective focal length at 1:1" taking into account that at 1:1 you are normally at twice the infinty focal length on a non-pseudo zoom macro lens?? for example, when you state that the A50/2.8 is effectively 55mm @1:1, do you mean that its actually 27.5mm if at infinity or do you mean that its effectively 110mm (55mm if at infinity)??? jco
-----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Digital Image Studio Sent: Saturday, December 09, 2006 10:21 PM To: Pentax-Discuss Mail List Subject: SR effectiveness at 1:1 macro? Since I don't often shoot long lenses one of the most attractive things about SR to me is the potential to make more use of available light in my macro photography. However thinking about this and the relevance of FL in the degree of correction that's applied got me shinking about effective FL at close subject distances. Studying my macro lens arsenal it appears that at their maximum magnification apparent focal length can be quite different to their infinity FL. My A*200/4 Macro appears to be effectively 137.5mm at 1:1 mag, so the change in diagonal AOV through the focus range is from 8.08° at infinity to 11.74° at 1:1 magnification. My Voigt Lanthar 125/2.5 is effectively 95mm at 1:1, my FA50/2.8 is 48.75mm at 1:1 and my A50/2.8 is 55.5mm at 2:1 Given this knowledge I can dial in the effective FL on my manual lenses so that SR is optimized when I'm working at or close to 1:1. My question is does the SR system compensate for FL change when using later lenses where manual input of the FL is not available? Obviously with the shorter FL lenses it of minimum significance as FL doesn't change dramatically but with longer lenses where shake is magnified it would be preferential if the system either compensated for FL change or allowed manual FL entry. I know it's being critical but I didn't spend all that cash on my macro lenses with a view to not getting the very best out of them ;-) -- Rob Studdert HURSTVILLE AUSTRALIA Tel +61-2-9554-4110 UTC(GMT) +10 Hours [EMAIL PROTECTED] http://home.swiftdsl.com.au/~distudio//publications/ Pentax user since 1986, PDMLer since 1998 -- 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
