On 15 Jun 2001, at 22:07, Cotty wrote:
> But - what happens when you squeeze a metal aperture ring? Answer,
> nothing. The fact it is metal means that it holds its shape. When you
> squeeze a plastic/poly-something aperture ring, it changes shape from a
> true circle, very very slightly, but just enough to cause the lens mount
> metalwork underneath to act like drum brake on the aperture ring. The net
> result is that the more you squeeze, the less it wants to turn.
> Unfortunately, the less you squeeze, the less it also wants to turn
> because of the small spring-loaded ball dropping into the tiny detents,
> giving the aperture the 'clicks'. Brilliant Catch-22.
I thanks that the problem stems from the fact that Pentax adapted a design
with was originally intended for manufacture from metal to a plastic without
changing the design simply to preserve visual integrity in the lens line. The
new Mamiya 7 lenses (read expensive) all have plastic aperture rings, the
difference is that the physical design of the rings is such that it is plain to
see that there will never be any problems with distortion or binding. They
were made much deeper than wide so they are quite rigid and they actually
feel quite good to use. So I am not put off by plastic components as long as
they are engineered with respect to their properties.
Cheers,
Rob Studdert
HURSTVILLE AUSTRALIA
Tel +61-2-9554-4110
UTC(GMT) +10 Hours
[EMAIL PROTECTED]
http://www.ozemail.com.au/~distudio/publications.html
-
This message is from the Pentax-Discuss Mail List. To unsubscribe,
go to http://www.pdml.net and follow the directions. Don't forget to
visit the Pentax Users' Gallery at http://pug.komkon.org .
