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
