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06-04-2013, 03:02 AM   #1
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Pentax FA 50 1.4 mechanical play

Hello!

I'm using a FA 50 f/1.4 lens for about 5 years now, and I'm very happy with the image quality it delivers. It's my primary lens, and thus has travelled quite a bit - and suffered. The cylinder which contains the lenses and extends or retracts while focusing is suffering from quite significant mechanical play. It was already evident when I bought the lens, but it became worse. Now I'm using the lens in manual focus on a Pentax MX, and the play makes focusing rather hard as the cylinder containing the lenses can "flip", thus shifting the image slightly (though not knocking it out of focus).

I showed the lens to a local repairman, who in a failed attempt to open the lens lost 2 of the three screws which hold the decorating ring in front of the primary lens, and made an estimate I just can't afford (additionally, I wouldn't trust him my lens any more :P) . (I did pay 120 Euro in a clearance sale 5 years ago for the new lens, I'm more than surprised seeing how the price increased over the last years! - unfortunately, repair costs of ~100 Euro are just out of reach right now.).

I found several guides how to disassemble a FA 50 f/1.4, I've got JIS screw drivers and thus think it should be possible to solve the problem on my own. (...The crucial part seems to be to mark the position of the helix which guides the moving cylinder when disassembling as the thread has multiple entries.)

-> I will need new lubricating grease when putting back together the lens - in fact I hope that new grease might solve entirely the mechanical play. Can you advice which product to use and where to buy it?
-> Looking through other disassembly guides, I did not find any retaining ring / screw which might cause mechanical play when loose - do you have any advice if there might be other reasons for the play than issues with the lubrication? I never dropped the lens, thus I guess I can exclude significant internal mechanical deformations.
-> Do you have any suggestion where I might find spare screws that got lost during the "professional" (...) attempt to remove the play? You find a picture of the missing screws attached to this post.

Would be great to get some pieces of advice. As soon as I know how to proceed exactly and which lubricating grease to use, I'll keep you informed about the progress and of course post pictures of the disassembly.

Best regards,
Rapfl

http://dl.dropboxusercontent.com/u/9718909/IMGP5659.JPG




Last edited by Rapfl; 06-12-2013 at 03:46 AM.
06-07-2013, 09:22 AM   #2
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fixed.

Hey,

i took apart the lens and fixed the problem.
There are two spacers which keep the extending cylinder containing the optics in two rails of the exterior lens housing (see figure below). There was a gap of about 1mm between the spacer and the rail on each side, causing significant mechanical play when focusing. I could easily loosen the screws holding the spacers, moving them further out, and then tighten the screws again. Luckily, I did not have to take apart the helicoid.

There are several posts in this forum of users who experienced the FA 50 to separate in two halves during use ( see e.g. https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/76666-wtf-my-...-my-hands.html ) - and some users point out that most probably these spacers jumped out of their rails during focusing. As it is a rather simple operation to take apart the lens to reach these spacers ( see e.g. https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/197889-fa50-d...djustment.html for a detailed guide ) I guess that it seems to be a good idea to check, when you are experiencing mechanical play just as I did, if these spacers are still there where they should be.

I am still looking for a broken FA 50 1.4 lens for spare parts (my local repair shop cant find the screws any more which I showed in the first picture (...), I already contacted Pentax, but there are no spare parts available any more.)

http://dl.dropboxusercontent.com/u/9718909/lens.JPG



Have a good day,
Rapfl

p.s.: @moderators: it might be a good idea to move this thread to the lens sub-forum, as the problem is solved and the explanation - i guess - would be better "stored" in the lens sub-forum.

Last edited by Rapfl; 06-12-2013 at 03:46 AM.
06-07-2013, 10:23 AM   #3
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I'm glad you could fix the original problem.

Thanks for sharing your solution.

Regarding the screws: I have a feeling that this may not help, but shouldn't this be the problem of your local repair shop? The person who cannot find them, should organise a replacement for you. Anything else seems wrong to me.
06-07-2013, 10:45 AM   #4
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Thanks for your feedback. You might be right that I could have been more persistent to get back the screws... (of course I won't let him look after my lenses any more :P) but as I didn't pay for his try to open it (and most probably would not have even if he fixed the problem...) I can't really ask him to get me a new lens or look for spare parts himself :-/


Last edited by Rapfl; 06-14-2013 at 03:14 AM.
06-08-2013, 12:49 PM   #5
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I have not tried it, but I would assume, if you have an old lens at hand or find an old Pentax lens lens for cheap in a thrift store or on the flea market, you might be able to scavenge matching screws. Also, if you get the exact size of the remaining screw (diameter, thread pitch, length, and screw head form) you might find an independent supplier, like Micro Tools: Micro-Tools Europe Tools | Miniature Tools for Camera and Watch Repair

Ben
06-12-2013, 03:45 AM   #6
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Thank you very much for this reply. Though I think it's a non-standard screw -
do you know any lens which attaches in a similar way the decorative ring around the front lens?
(FA 50 1.7 ? F 50 1.4/1.7 ? A 50 1.4/1.7?)

I only have access to the parts list of the FA 50mm.

http://dl.dropboxusercontent.com/u/9718909/IMGP5734.JPG



[metric scale, the distance from 0 to 1 equals 1 cm \approx 0.39 inch]

http://dl.dropboxusercontent.com/u/9718909/Screenshot.png


Last edited by Rapfl; 06-12-2013 at 04:16 AM.
06-12-2013, 02:36 PM   #7
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Hi Rapfl

Unfortunately I don't know any lens with the exact same screw type. So your first step would be to measure the screw size and thread. Lens screws tend to conform to homebrewn "standards" and are often not metric or even common imperial sizes (as UNC). But often one can find a standard size which is a close-enough match, to be useable. For a short thread (just a few turns), a slight difference in thread pitch is often acceptable. If you cannot measure the pitch yourself go to a good hardware store in your town or city and they will sure help you. Otherwise a precision mechanical workshop could also be helpful.

The screw head is of the flat head type. The only problem I see is to find a screw with the unthreaded part just below the head. But you could simply use a standard threaded screw and put a short tube (aluminium or plastic or even a short piece of shrink sleeving over it. That part of the screw is for centering the decorative ring without damaging it (which the sharp threads could do).

Hope, these hints help.

Ben
06-13-2013, 11:59 AM   #8
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The F50/1.7 has the same screw, same place. Ben's suggestion about a sleeve might work. I have a small stash of screws from a few broken SF series cameras that come in handy, but not all lens screws are common in cameras. For example, the mount screws are particular to lenses.

06-14-2013, 03:13 AM   #9
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QuoteOriginally posted by Just1MoreDave Quote
The F50/1.7 has the same screw, same place. Ben's suggestion about a sleeve might work. I have a small stash of screws from a few broken SF series cameras that come in handy, but not all lens screws are common in cameras. For example, the mount screws are particular to lenses.
Thank you very much for your replies!
Knowing that also the F 50 1.7 has the same screws certainly increases my probability to find original spare parts.
Otherwise I'll improvise just as Ben suggested.
08-15-2013, 07:49 AM   #10
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I just read this as I am trying to fix a FA50/1.4
IF OP hasnīt found the screws yet, you might want to look into cheaper autofocus lenses like F35-80, FA80-200 or FA kit lenses... They all probably have them!
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