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Steve_roberts
Tinkerer
Username: Steve_roberts
Post Number: 65
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, September 22, 2011 - 09:41 am: | 
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I have a problem with the focussing accuracy of my MX. I found this when doing some very shallow DoF work and the results were less than sharp. Focussing on an object about fifteen feet away, the lens distance scale is telling me that the object is further away than it is, a fact borne out by comparison with the same lens on other Pentax bodies, where the distance is indicated correctly. I believe the problem to be where the bottom of the mirror sits on the tab inside the lens throat on the film cassette side of the camera. There is a shiny witness mark on the tab and a corresponding tiny depression in the crinkly black paint on the underside of the mirror. By inserting a thin film between the two, I can restore the correct focus, but I'm sure there must be an adjustment. Near the tab (which is spring loaded for cushioning) there is a small screw with a slotted head. Might that be the adjustment? I can't imagine that any adjustment would be too far inside the camera, as it could only be set once the body and mount are assembled.
Further information: I'm unable to focus in the viewfinder at infinity - it's a shade off with various lenses and I've no reason to question the seating of the removable focussing screen.
Any help or suggestions would be much appreciated.
Best wishes,
Steve |
John_s
Tinkerer
Username: John_s
Post Number: 57
Registered: 07-2009
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, September 22, 2011 - 01:21 pm: |
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I can see the screw and tab on my MX, there's a good chance that the screw is for adjusting focus but I'm not inclined to try it as mine seems OK. I did a similar thing with a Nikon FM a while ago, the adjusting screw being on the opposite side but you could see what it did, unlike the MX where it seems to be happening inside. Hopefully someone will come up with a more informed answer. |
Steve_roberts
Tinkerer
Username: Steve_roberts
Post Number: 66
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, September 23, 2011 - 03:53 am: |
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Thanks John. I'm hoping that screw has some kind of cam or eccentric on the other end that acts on the mirror tab. Though I've looked hard at an exploded diagram of the arrangement, I can't quite make out what's going on in that area.
Best wishes,
Steve |
Don
Tinkerer
Username: Don
Post Number: 64
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, September 23, 2011 - 10:12 am: |
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From what I can see of the exploded views that I have, that screw should adjust the mirror angle. Can send a scan of the view if that will help. Lot of MX info here: http://www.mypentax.com/PentaxMX.html |
Steve_roberts
Tinkerer
Username: Steve_roberts
Post Number: 67
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, September 27, 2011 - 02:43 am: |
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Hi Don,
Thanks for your advice. I've seen a copy of the MX service manual, but the detail was too small to see what was going on. If you have something clearer than that, yes please, I'd very much like to see it. My email address is s3roberts[at]plymouth.ac.uk
Best wishes,
Steve |
Don
Tinkerer
Username: Don
Post Number: 65
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, September 27, 2011 - 06:14 am: |
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What I have is probably no different than from what you've seen. Screw appears to be linked to the linkage on the outside of the mirror box going to the cam that the mirror rests on. If it were me I'd give it a turn - can't say what direction & see what happens. Can't imagine Pentax not providing this model w/o means of mirror adj. Draw a pencil line from the screw slot onto the box to serve as a reference point. |
Don
Tinkerer
Username: Don
Post Number: 66
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Tuesday, September 27, 2011 - 06:23 am: |
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What I have is probably no different than from what you've seen. Screw appears to be linked to the linkage on the outside of the mirror box going to the cam that the mirror rests on. If it were me I'd give it a very slight turn - can't say what direction & see what happens. Can't imagine Pentax not providing this model w/o means of mirror adj. Draw a pencil line from the screw slot onto the box to serve as a reference point. |
