Archived posting to the Leica Users Group, 2013/01/06
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Hi Mark, Yes, it's an f4 lens. Sweet spot, per the manufacturer is between f8-f11. My testing shows f11.3 is best and very little degradation from diffraction at f/16. I found the GG not to be reliable on these technical cameras with medium format backs. I had been using the ground glass, which, though it looked sharp, often was not. These sensor are so remarkably flat that even being off 1/100mm will cause out of focus images. That's why Alpa allows users to shim the piece that holds the digital back onto their cameras to be adjusted with shims by 1/100mm. Other digital technical cameras allow you to adjust the focus point of each lens to the back. The manufacturing tolerance of the back's mounting plates are not within this range. The difference between my traded in back and this back was .1mm (the back had to be positioned .1mm closer). It takes a bit of time getting the distance just right, but no worse than testing film (actually, a lot easier; no densitometer needed!). Best, Bob On Sun, Jan 6, 2013 at 11:11 AM, Mark Rabiner <mark at rabinergroup.com> wrote: > I don't know what's the optimum f stop of the lens f11? > Would f8 or 5.6 be a tad sharper and with the tilt still get from your feet > to infinity? What did it look like in the ground glass before you stopped > down? Its an f4 lens? > I thought the point of a tilt is to not have to stop down so much but use > the optimum f stop of the lens you want to not the one you have to to get > DOF? > > > On 1/6/13 1:35 PM, "Bob Adler" <rgacpa at gmail.com> wrote: > > > Why? > > I think the point of the practice was to practice getting sharp from my > > feet to the beginning of infinity. What purpose would wide open serve? > If I > > want a faster shutter speed, I could always increase the ISO. About 400 > is > > usable on this back. > > So curious about your comment... > > Thanks for taking a look, Mark. > > Bob > > > > On Sun, Jan 6, 2013 at 9:37 AM, Mark Rabiner <mark at rabinergroup.com> > wrote: > > > >> Would be interesting to see how wide open you could have shot this > thing. > >> Looks great! > >> > >> > >> On 1/6/13 3:40 AM, "Bob Adler" <rgacpa at gmail.com> wrote: > >> > >>> Nice day down by Carmel just hanging out. Went to Pt. Lobos for a lunch > >>> (windy and wet) and a walk. Saw this and thought I'd practice my tilt > >>> technique. 3 images with back shift, stitched and cropped. About a 45 > >>> minutes to set up and nail the focus. About 45 minutes of exposing. > >>> > >>> > >> > http://gallery.leica-users.org/v/rgacpa_HI/20130105-Pano1-PtLobos.jpg.html > >>> > >>> Please look large. > >>> Seems to work well. Hope you enjoy... > >>> Bob > >>> > >>> Techie stuff: > >>> Alpa Max > >>> Alpa 50mm Rodegon HR SB34 with polarizer > >>> Alpa 7deg 17mm T/S adapter (about 1.4deg tilt) > >>> Alpa 17mm Extension > >>> PhaseOne IQ160 > >>> f 11.6 @ ISO 50 and about .5 sec. > >> > >> > >> > >> > >> -- > >> Mark William Rabiner > >> Photography > >> http://gallery.leica-users.org/v/lugalrabs/ > >> > >> > >> > >> _______________________________________________ > >> Leica Users Group. > >> See http://leica-users.org/mailman/listinfo/lug for more information > >> > > > > > > > > > -- > Mark William Rabiner > Photography > http://gallery.leica-users.org/v/lugalrabs/ > > > > _______________________________________________ > Leica Users Group. > See http://leica-users.org/mailman/listinfo/lug for more information > -- Bob Adler