Grrr... lens misery

Irritated with my ability to take pictures with my digital camera in the
way I used to with my Praktica, I got the old SLR out and tried to make
some repairs.

I stripped and cleaned the 50mm prime lens, but now, for some reason,
the aperture setting doesn't seem to be fed back to the light meter
properly (the camera is a Jenaflex AM-1, with three contacts on the body
for the aperture setting from the lens). Another lens works just fine.

I dismantled the lens again and gently swabbed the carbon track with
swicth cleaner. The contacts travel along the track, and all seems
normal there, but the full travel of the aperture ring only produces a
very small movement of the light meter inside the viewfinder.

Any suggestions? It's odd that the aperture information only gets back
to the camera a bit, either than completely or not at all.

Daniele

In article , Lionel
wrote:

A scarier possibility is that you've
degraded the track while cleaning/disassembling. You might try calling
a camera repair business & sweet-talking them into telling you of any
common 'gotchas' that tech's run into when working on those lenses.

That would be my guess; bad contact would probably produce no reaction
at all. Also, In my young and foolish days I myself destroyed a
variable resistor by "cleaning" it improperly. God help you getting
parts for the old "electric" Praktica lenses.

"D.M. Procida" wrote

I stripped and cleaned the 50mm prime lens, but now, for some reason,
the aperture setting doesn't seem to be fed back to the light meter
properly (the camera is a Jenaflex AM-1, with three contacts on the body
for the aperture setting from the lens). Another lens works just fine.
I dismantled the lens again and gently swabbed the carbon track with
swicth cleaner.

A few likely culprits:

o The metal brush/contact/finger/thingy that slides along the carbon
is bent and isn't really touching the carbon. The carbon probably
isn't really carbon but conductive plastic. There should be a
small amount of pressure there. Be sure the brush is smooth where
it touches and that it touches squarely so the contact area is as
big as possible. Bend carefully. The carbon wearing through
[if the conducting element is really carbon] is a problem with the
very cheap controls used in pocket radios, but should not be a
problem with a quality design like a lens.

o I am not sure on this lens if the brush or the carbon strip is
the one that moves, but in any case the moving ring has to make
electrical contact back to the lens - find what does this and check
it is working right.

o The pads/pins on the lens aren't wired correctly to the lens brush
& carbon - something is loose or broken.

o If the lens has pins then one of the pins may not be springing
back and forth and is hanging-up.

If you have (or can borrow) a resistance meter (also called a DVM or
VOM or multimeter) then check the resistance between the pins at
both ends of the aperture motion: something should change in a
logical manner. Use the lens that works as a model so you know what
the readings should be. Be aware that one of the electrical contacts may
be the lens mount so you need to measure mount to pin.

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

D.M. Procida wrote:

I stripped and cleaned the 50mm prime lens, but now, for some reason,
the aperture setting doesn't seem to be fed back to the light meter
properly (the camera is a Jenaflex AM-1, with three contacts on the body
for the aperture setting from the lens). Another lens works just fine.

I dismantled the lens again and gently swabbed the carbon track with
swicth cleaner. The contacts travel along the track, and all seems
normal there, but the full travel of the aperture ring only produces a
very small movement of the light meter inside the viewfinder.

It turned out to be a soldered connection to the head of one of the
three pins which make the electrical contact with the body. Once I'd
resoldered that it was fine.

Now the only faults left are depth-of-field preview slider which jams
(somewhere deep inside the camera - I don't think I'm going to tackle
that myself) and the back which springs open at wholly random intervals.

Thanks for the various suggestions, by the way.

Daniele