Wow! Thanks Tom ...This is a public forum. Jump in whenever you wish. Shel
> [Original Message] > From: Tom Reese > Shel Belinkoff asked: > > > BTW, what's the difference between F lenses and FA > > lenses? > > I'm not sure if this was directed at everyone or only to Dave Mann. > Please forgive my intrusion if you were speaking only to Dave. > > You got me curious so I did a Usenet search and I found this post to > rec.photo.equipment.35mm from someone named Bandicoot (which sounds > familiar): > > <BEGIN QUOTE> > > FA lenses are more recent, all of both types are autofocus. The F > lenses were introduced in 1987, the FAs in 1997. A few F lenses are > still in the range, notably the 17-28mm fisheye zoom. The F lenses went > with the KAF version of the K mount, the FAs with the KAF2 - as usual, > there is full interchangeability. > > When the FA lenses came in there were two main changes: one was to the > chip you mention (F lenses are 'chipped' too, but FA ones store a bit > more data)and the other was the introduction of the Power Zoom feature. > Most current FA lenses don't have Power Zoom, though the top ones > still do, and many of the current body range supports only a subset of > the PZ feature range - a few support none of the PZ features. However, > any Power Zoom lens can still be used on any body. > > The KAF mount and the F lenses can exchange a certain amount of data: > focal length (transmitted value changes in a series of steps as a zoom > lens is varied), lens-to-subject-distance, 'absolute' value of the > selected f-stop (including for variable-aperture zooms), and the > physical size of the lens (allowing for changes as it is zoomed and > focused). > > The biggest use of this information was for improved flash automation - > the focal length indication allows the body to warn you if you try to > use a built in flash with a lens having a wider angle of view than the > flash's coverage, and the lens size information enables bodies to warn > if the lens will block some of the light from a built in flash. The > distance information is also used to improve flash exposure accuracy, > and in some of the bodies that have picture taking 'modes' it varies the > programme line selected. > > Focal length also affects the programme line, with bodies (when set to > the default programme line) generally trying to avoid setting a shutter > speed slower than the reciprocal of the focal length in use. This is > done by storing the programme line in a chip in the lens - one for fixed > focal length lenses, up to three for zooms. > > The KAF2 mount and FA lenses exchange all of the above information and > also one other piece. The chip stores information on the lens's MTF > performance at different apertures - this makes it possible to select a > programme line - in bodies that support the feature - that will always > try to use the aperture that offers the best resolution. > > The other change that the FA spec. saw introduced was, as described > above, the Power Zoom feature. This offers a range of operational > options with lenses that support it - some of them very useful, others > less so. This is a whole topic in itself. > > Those are the key differences. There are also cosmetic differences: F > lenses are grey (early) or moderately shiny black (somewhat later), with > the long F* (ED) lenses being white. FA lenses are in the shiny black > (earlier) or either matt black or silver (later). FA* lenses are in a > hard silver coating that I think looks very nice on (relatively) smaller > lenses like the 24mm f2 and the 200mm f2.8 but am not so keen on when it > is used on the real biggies - like a 300mm 2.8 or 600mm f4. The FA > limited lenses, of course, are different again. > > The practical difference applies to the F* and FA* lenses. These have a > clutch that disengages the focusing ring - this means a 'real' focus > ring that gives good manual control for manual focus use can be built > in, because it can be disengaged so it doesn't turn in AF use. In F* > lenses it is a ring behind the focus ring that you pull back on, to use > the lens in manual focus you need to do this and switch the body to > manual. In FA* lenses you pull back on the focusing ring itself, and > can use the lens in manual just by doing this, even with the body left > on AF. I marginally prefer this latter method, but both work really well. > > <END QUOTE> > > I can't vouch for the information but nothing jumps out at me as being > incorrect and it seems to make sense. > > Tom Reese
