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01-07-2010, 10:39 AM   #1
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PENTAX LX: exposure meter broken?

I have recently bought an LX. Very disappointingly the exposure meter is behaving strangely although the seller stated that the camera has been fully serviced in 2009 (provided an invoice)...
The problem is that he meter gives correct readings from 1.7 (50mm) to f4, but after that the reading remains the same (the meter does not react to further aperture change). Same on all my lenses, except for different focal lengths the reading stops at different aperture value. On my 200mm M lens the reading stops changing at f8 or so, for example. Tried moving with a finger the little aperture hinge on the LX's body mount--without the lens gives gradual change of expo values in all positions. The lenses are fine. The strangest part is that the meter does react to all changes in aperture values wile the "depth of field preview" lever is pressed (which normally gives a 2 stop down from correct reading). For example, if the shutter reading at f4 is 125th without the lever and 30th with the lever pressed, at f 5.6, the readings are 125th (instead of 60th) and the logical 15th respectively.
I have tried changing the batteries-did not help.
Has anyone experienced similar problems?
Thanks for any help in advance.

01-07-2010, 11:51 AM   #2
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I am a new member too. Welcome. When testing the unit for exposure and metering there must be film in the camera and a lens on it. And if you have done this then try moving the compensation dial and see if the led's jump around.
01-07-2010, 12:18 PM   #3
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Thanks for the welcome, same to you!

Yes,I did everything with film in the camera. When the compensation dial is moved, the leds jump around accordingly. But the diaphragm after f4 is not considered in these metered values. For example, I compensate two stops up and meter goes two stops down in the viewfinder, lets say from 250th to a 1000th. But if I rotate the diaphragm or not after f4 does not affect the reading at all. If it's on a 1000th, it'll stay there.
01-07-2010, 12:30 PM   #4
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The LX does not need film for metering. The reading is done via a secondary mirror behind the main mirror. The film is only needed for Auto-expsoure during the actual exposition, as then the same photocell takes the reading (when the mirrors are out of the way) off the film surface.

This sounds very much like a mechanical problem, not an electrical one. May be the aperture coupler is loose or something the like. Have you tried to put a film through the camera? If it is only a mechanical problem the expsoure should be alright when you use Auto, but obviously would be off when you do the metering manually. If the film is under-/overexposed severely in Auto mode, than the metering system has a malfunction. It could have something to do with the resitsor package under the ASA/DIN dial, which is a weak point, not only in the LX, but also in the MX. That should be repairable easily.

Ben

01-07-2010, 01:28 PM   #5
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With contact problem...before trying to open anything or ask to fix the problem by a technician, try to play with the dial(exposure compensation) for a long period of time...If it's a bad contact due to oxidation on the track...it can help.
The beast need to be used and abused...!-)Give it a try, you can't make anything wrong...

Nico

Last edited by mine.cola; 01-07-2010 at 02:06 PM.
01-08-2010, 06:25 AM   #6
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I stand corrected. Film needn't be in the camera for meter readings but does if you want to compare the shutter sound to the led indication in the finder. i.e. 1/15 to 1 sec. There could be any number of things causing this problem. From the lens to the meter follower.
01-08-2010, 06:25 AM   #7
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I contacted pentax, and they said that this is very unusual problem, and most likely there is something wrong with the "stop-down coupler" (roughly 2 o'clock on the body mount). To me it looks normal. I wish I had another LX to compare it to. Can someone please post pictures of that coupler on their LX? I would appreciate it very much.
01-08-2010, 07:31 AM   #8
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I looked at the stop-down coupler through the back door with shutter open. If I set the lens to f 22 before mounting it, the meter does give readings on on all stops when I go from f22 to f1.7, but once I start closing it back toward f22, the reading stops at f4 like I have already described. I can actually see this through the back, with shutter open. If lense mounted with f22 set, the coupler starts at very top. When opening, it moves all the way down, but when closing, stops at f4 and does not move until opened above f4 again.

What exactly is broken here?

01-08-2010, 11:20 AM   #9
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QuoteOriginally posted by dedmozaj Quote
I looked at the stop-down coupler through the back door with shutter open. If I set the lens to f 22 before mounting it, the meter does give readings on on all stops when I go from f22 to f1.7, but once I start closing it back toward f22, the reading stops at f4 like I have already described. I can actually see this through the back, with shutter open. If lense mounted with f22 set, the coupler starts at very top. When opening, it moves all the way down, but when closing, stops at f4 and does not move until opened above f4 again.

What exactly is broken here?
It is possible for the coupler lever on either the lens or the body to be damaged such that they slip past each other instead of engaging. It is also possible that the coupler on the body is jamming at about f/4. Either way, this is probably not something you want to mess with. I would also suggest that this may be an expensive repair. Erictn would know.

Steve
01-08-2010, 12:38 PM   #10
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QuoteOriginally posted by dedmozaj Quote
I looked at the stop-down coupler through the back door with shutter open. If I set the lens to f 22 before mounting it, the meter does give readings on on all stops when I go from f22 to f1.7, but once I start closing it back toward f22, the reading stops at f4 like I have already described. I can actually see this through the back, with shutter open. If lense mounted with f22 set, the coupler starts at very top. When opening, it moves all the way down, but when closing, stops at f4 and does not move until opened above f4 again.

What exactly is broken here?
That's probaly just a spring, that forces the coupler back into its starting position against the force of the lens' lever. May the spring is just aged or broken. Well, at leats that would explain such a behaviour. I don't think it is more serious.

Ben
01-08-2010, 12:52 PM   #11
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Yes, but without the lens the coupler returns back normally. Besides, when it stops moving the lens lever is not pressing on it anymore> it moves higher, and the coupler is supposed to follow it being pressed back by a spring.
01-08-2010, 01:17 PM   #12
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QuoteOriginally posted by dedmozaj Quote
Yes, but without the lens the coupler returns back normally. Besides, when it stops moving the lens lever is not pressing on it anymore> it moves higher, and the coupler is supposed to follow it being pressed back by a spring.
Well, that seems to underpin a dead spring or perhaps lack of lubrication etc. I don't think it is a death spell for the camera and would be repairable within sensible limits.

Ben
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