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04-25-2018, 06:15 PM   #1
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Unusual Problem with FA 31

My FA 31 exhibits an unusual problem with my LX where the focus is off by at least 3 feet if I use the split screen as the focus point. If I use the distance scale, the focus point seems to be correct. When I attach it to my K1 and let it autofocus, it is dead on.

I was thinking it may be the focus screen, but shots with my FA 43 don't seem to be off.

A couple of examples where the focus point should have been obvious (it was the same thing with the entire roll)





Any ideas?

04-25-2018, 06:26 PM   #2
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Thumb print on rear element?


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04-25-2018, 06:28 PM - 1 Like   #3
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Four unlikely possibilities:

1. Diopter misadjustment on the eyepiece

2. Loose or miss-shimmed focusing screen

3. Loose element inside lens that jumps when the aperture is actuated

4. Missing/dead mirror bumpers
04-25-2018, 07:41 PM   #4
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Back focusing by a mile. Since it’s good on the K1, are you sure it was on the camera all the way?

04-25-2018, 07:52 PM   #5
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I have a feeling the camera was bumped or something in the bag. I did some experiments with four different lenses, the LX, ME and MG. Using a scale, all lenses were off a bit on the LX, and all were spot on with the other bodies.

A few months ago I had the LX CLA’d and I was getting great shots with perfect focus. I checked the diopter, but it’s the FA-1 finder and the adjustment is under it where it couldn’t be bumped.

I may have to run over to my repair man tomorrow to see what he thinks.
04-25-2018, 08:00 PM   #6
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We can deduce:

1. It is not the LX at fault (your 43 Ltd focuses fine), therefore the problem must be the lens.

However the lens works fine (on k1) when autofocussed.

Possibly a wobbly element that is held firm when the screwdrive is engaged ? Have you tried manual focus with the K1 ?

Give the lens a shake and let us know what you can hear ?

Edit...just seen your last post. So the 43 Ltd does not focus fine with the LX after all Possibly the mirror is not sitting properly and this is throwing your focus off. Did you have a "sticky mirror" syndrome addressed with the CLA ?
04-26-2018, 01:11 AM - 2 Likes   #7
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QuoteOriginally posted by photoptimist Quote
1. Diopter misadjustment on the eyepiece 2. Loose or miss-shimmed focusing screen
Both of these are probable causes of your woes.

QuoteOriginally posted by photoptimist Quote
4. Missing/dead mirror bumpers
Also a likely cause of a problem. If the angle of the mirror is unregulated focus errors can occur.

QuoteOriginally posted by twilhelm Quote
if I use the split screen as the focus point.
As I recall split prism focus aids are very sensitive to errors in focus screen alignment. Microprism collars are somewhat less sensitive.

QuoteOriginally posted by pschlute Quote
Possibly a wobbly element that is held firm when the screwdrive is engaged ? Have you tried manual focus with the K1 ?
Pentax screwdrive AF mechanism is not intended, designed or even capable of holding loose lens elements in place.
04-26-2018, 04:50 AM   #8
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QuoteOriginally posted by pschlute Quote
We can deduce:

1. It is not the LX at fault (your 43 Ltd focuses fine), therefore the problem must be the lens.

However the lens works fine (on k1) when autofocussed.

Possibly a wobbly element that is held firm when the screwdrive is engaged ? Have you tried manual focus with the K1 ?

Give the lens a shake and let us know what you can hear ?

Edit...just seen your last post. So the 43 Ltd does not focus fine with the LX after all Possibly the mirror is not sitting properly and this is throwing your focus off. Did you have a "sticky mirror" syndrome addressed with the CLA ?
I had thought the 43 was fine because I had used it last on the camera a few days prior and the focus was on. It never had the sticky mirror issue, I had the CLA done because the slower shutter speeds would stick.

Iím thinking you and Digitalis May have hit it with the screen being off.

04-26-2018, 07:42 AM   #9
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One fact that might help is that if a film SLR is back focusing, it means the optical path from lens-to-mirror-to-screen is LONGER than the optical path from lens-to-film. This happens if:

1. not enough shims

2. flattened or missing mirror bumpers

3. mis-adjusted mirror location

Problems 2 & 3 will also tilt the plane of focus (the top of the scene will focus closer to the bottom) although that may be hard to spot with a matte screen of the edges.
04-26-2018, 12:56 PM - 1 Like   #10
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So I just took it over to my camera repair man. He put the 31 on it and agreed it was out. He fiddled with the mirror a bit and told me the mirror was out of adjustment, likely from being dropped. (I'll have to have a talk with my son about this). I'll have it back Tuesday for $20 - 30.

On another note, he informed me he is only repairing cameras these days part time and plans to fully retire in the next couple of years. I'm going to miss having him right by my house...
04-26-2018, 01:39 PM - 1 Like   #11
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QuoteOriginally posted by twilhelm Quote
I'll have it back Tuesday for $20 - 30.
Woo! Hoo!


Steve
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