"William Hamblen" wrote in message
m...
On 2011-12-23, Michael wrote:

That kind of aperture setting was called "pre-set" as opposed to "auto"
(the aperture stayed wide open during framing and closed down to what
you set it at when you took the picture, doing so "automatically").
These lenses were very common in the 1960s and even the 1970s as low
cost alternatives to the "auto" lenses. I think they started to
disappear when lenses became automatic in the sense we think of them
today.

Old lenses were manual only (and of course rangefinder cameras did't use
automatic diaphragms for the most part), then you had pre-set lenses,
then you had semi-automatic lenses, then you had automatic lenses.
Semi-automatic lenses closed the diaphragm when you took the picture,
but you had to reopen the diaphragm after the shot. Pentax Auto Takumar
lenses always (I think) had a manual/automatic switch that you could
flip to have a completely manual lens to use on old cameras. Newer model
lenses often lack the manual/automatic switch. These tend to come from
the off-brand companies like Vivitar.

Bud


Third-party manufacturers- such as Vivitar, Tamron, Spiratone, etc- would
design lenses without a specific mount, and add a mount that fits a specific
camera. Tamron came up with the "T-mount" system that could be easily
interchanged by the user. A user could buy a T-mount adaptor for his
Canon/Nikon/Whatever, and buy T-mount lenses without a mount. Or if a user
had both a Canon and a Nikon, he could use the same T-mount lenses for
either camera by switching the interchangeable mount.
The third-party manufacturers often made preset lenses because each camera
type had different stop-down mechanisms. Camera "A" might push a pin forward
to stop down. Camera "B" might allow a spring-loaded pin to come out for
stop-down. Camera "C" (as in Canon) might push a pin to the left to stop
down. So to accomodate all the different stop-down systems, the third-party
manufacturers just ignored stop-down and made their lenses preset.

Preset lenses have fewer moving parts: no linkage to stop down; so they are
cheaper to design and manufacture. Thus they usually sell for less (or allow
a higher markup for a retailer!).

I've used preset lenses before. In fact, Canon made a 1200mm FL-mount lens
that was manual stop-down, not even preset. But that's not much of a problem
for a 24X lens as a tripod is required. If I were using a lens for
fast-paced work (like sports), I would not want a preset.


--
Ken Hart