Archived posting to the Leica Users Group, 2014/02/21
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]I agree with Paul, the lens opens slightly during focusing. It does not stop down. On Fri, Feb 21, 2014 at 12:58 AM, Paul Roark <roark.paul at gmail.com> wrote: > The Sony a7r focuses at approximately the the f-stop it is set at; it opens > what looks like maybe a half stop more than the shooting aperture. You can > look at the front of the camera and see the iris opening just a bit when > it's focusing. It does not open all the way to wide open (f/2.8 for the > 35mm FE) for easier focusing and brighter viewing. > > So, the a7r is unlike any modern SLR I am aware of. The typical SLR stays > wide open for viewing and focusing, and then stops down for the shot. With > an electronic viewfinder, the viewfinder is just as bright no matter how > closed down the iris is, as long as the exposure (iris, shutter and ISO) is > on the mark. As such, half the reason to have the iris open (viewing) is > eliminated. The other reason SLRs have the iris open when focusing is to > have the DOF very shallow, so it's easier to focus. However, this raises > the issue of focus shifting when the iris shuts down. Sony gave Zeiss one > more variable to forget about (relatively). Since the focusing is being > done at close to the shooting aperture, Zeiss is free to allow focus > shifting as needed to meet other design parameters. > > This is another example of the extent to which the optics and electronics > are being designed as a package. So, one irony of the Sony is that while > it's able to use legacy glass, it is also going to have optics that are > more tied to the camera than in the past. As such, I think Zeiss will be > able to produce sharper lenses for less money than could be done when they > had to worry about focus shift issues. > > Note that there is an interesting possible future solution to the vibration > -- have the iris do it all. It can be both iris and leaf shutter. Some > compact cameras do this. However, you'd lose legacy glass compatibility > and some very high speeds. I would not be surprised to see some lenses > with a leaf shutter option. They are the smoothest shutters. > > Paul > www.PaulRoark.com > > > On Thu, Feb 20, 2014 at 10:19 PM, Frank Filippone <red735i at verizon.net > >wrote: > > > Paul says it does stop down before it AF, Sonny says it stays open during > > AF... Specifically with the same 35mm FE lens > > > > ???? I am confused..... > > > > Frank Filippone > > Red735i at verizon.net > > > > > > > > > > _______________________________________________ > > Leica Users Group. > > See http://leica-users.org/mailman/listinfo/lug for more information > > > > _______________________________________________ > Leica Users Group. > See http://leica-users.org/mailman/listinfo/lug for more information > -- Regards, Sonny http://sonc.com/look/ Natchitoches, Louisiana 1714 Oldest Permanent Settlement in the Louisiana Purchase USA