Archived posting to the Leica Users Group, 2012/06/11
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]I think it has to do with the type of AF sensors. A bit like microprisms the AF sensors "look" outwards in pairs. The angle they look outwards is to look through an F5.6 aperture "hole", this gives the best overall potential AF accuracy, since that is the slowest lens they are likely to "look" through. There are sensors which work through f4 apertures, and IIRC there are some which only work on f2.8, to increase autofocus accuracy, in high end cameras. It is entirely equivalent to rangefinder base length, the wider the sensors are angled outwards, the more accurate the focus (but the fewer lenses it is compatible with). With the old MF cameras if you wanted a microprism screen for slower lenses you had to fit a special, and I am sure everybody noticed how important it was to center your eye when using a slow lens so the microprism/split image didn't go half dark. This is equivalent to whether these type of AF sensors can work or not. The mirrorless cameras use contrast detect AF, rather than this type of sensor, so are slower focussing, but are not aperture sensitive (apart from needing adequate brightness). FD On 11 Jun, 2012, at 22:03, Bob Shaw wrote: > Oh, just remembered; autofocus no problem but no multipoint focus. But > then, it's about one bird or critter, so I don't have a problem with that. > Besides, I still don't get multipoint. Whatever happened to using DOF? > > > Bob Shaw > rsphotoimages at comcast.net > > > On Jun 11, 2012, at 1:49 PM, John McMaster wrote: > >> Something to do with the AF sensors, I think the new Nikons (D4/800(E)) >> are the first to AF at f8.0 >> http://www.dpreview.com/reviews/nikon-d800-d800e/15 >> >> john >> >> -----Original Message----- >> >> All I know is it says so in the manual and acts so in reality. I was >> disappointed, to say the least! Works fabulously on a tripod however... >> >> Bob Adler >> www.rgaphoto.com >> >> On Jun 11, 2012, at 11:15 AM, George Lottermoser <imagist3 at mac.com> >> wrote: >> >>> >>> On Jun 11, 2012, at 12:12 PM, Bob Adler wrote: >>> >>>> Not sure if you will be using it with the 2.8 or 4, but I'm pretty sure >>>> with the 4, auto focus does not work. >>> >>> I wonder why that would be the case - too dark at F8 - that would seem >>> odd say in sunlight? >>> >> >> _______________________________________________ >> 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