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Old August 9th 07, 06:12 PM posted to rec.photo.equipment.35mm
Nicholas O. Lindan
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Posts: 1,227
Default Pentax 50mm A lens

[50mm f1.7 Pentax-A]
It's pretty clear that the lock on the aperture ring mechanism is
faulty, and gets stuck just before f11. It can be moved past this by
holding down the lock button (though I can hear a metallic click as it
goes past).
The lock button should stay down until the ring is in the A position,
but it rises after f8. What are the chances of having this repaired at a
reasonable cost, or even of doing it myself?


I am not a Pentax-A expert, but if it is like other bayonet mount lenses
then
removing the shiny mounting ring from the back of the lens by removing 4 (or
so)
screws should let you slip the aperture ring from the lens.

Cover your workplace with a fluffy white towel to catch any dropped or
sproinged
parts - look out for little ball bearings used to generate the 'click' on
the
aperture ring.

The good news would be that something slipped and fitting it back (possibly
with
a little gentle corrective bending) fixes everything.

The bad news is that something inside has broke in two. The most cost
effective
solution is to remove the whole lock-button assembly/parts - the lens
aperture
won't lock but the lens is perfectly useable.

The original grease should be fine for reassembly. If the motion is grating
then
there may be bits of sand in the grease or the grease needs re-distribution.
If you need to lubricate (and you don't have the proper lubricants) then
dipping
a toothpick in 10W-30 engine oil and touching it to parts that need lubing
is
the best 'kitchen table repair' solution. Don't use
WD40/LPS25/3in1/household oil:
they all turn to goo in a month or so.

Advice worth price charged. I take no responsibility for anything that goes
wrong
[but, like everyone, expect full credit for anything that goes right].

--
Nicholas O. Lindan, Cleveland, Ohio
Darkroom Automation: F-Stop Timers, Enlarging Meters
http://www.darkroomautomation.com/index.htm
n o lindan at ix dot netcom dot com