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01-27-2013, 10:06 AM   #1
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Focus Ring Dampening on Legacy MF lenses

Can someone explain how the focus ring is dampened on legacy Pentax manual focus lenses?

I have three a-series lenses with a varying amount of dampening (none of which are particularly well damped)

The 24mm a-series lens I just purchased has such a loose focus ring it it is bit hard to achieve focus. There is no resistance/dampening whatsoever.

Is this how these lenses were supposed to feel or is there something internally that control dampening/resistance that wears out over time?

Thanks!

01-27-2013, 10:36 AM   #2
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I am not 100% sure but I do not think there is any particular mechanism to damp it. Any I've taken apart just have the helical thread. The amount of 'dampening' is regulated by the grease on the helical threads. If things are too loose perhaps it can be re-greased?

Like I said, I'm not sure of this and if anyone else knows more I would love to be educated.
01-27-2013, 10:37 AM   #3
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The helicoid grease has probably dried out over time. Disassembly, cleaning and relubricating with a suitable grease is in order. Viscosity of the grease will affect the amount of damping.
01-27-2013, 10:44 AM   #4
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Basically, focus is achieved by sliding the optical barrel back and forth (back for infinity focus, forward for close focus). This is done via 3 helicoids (threaded brass pieces) with the first and the third turning in tandem. They are also reverse-threaded, so threading the middle piece in the first one also has the effect of unscrewing it from the third (and vice versa). This has the effect of transforming rotational movement (you rotating the focus ring) into longitudinal movement (different degrees of threading practically mean different distances from the film plane).
So basically this is the mechanical principle.
Now, in practice, these helicoids are made either from brass, aluminium or plastic, resulting in different amounts of friction between pieces. To minimize this friction effect, various lubricants are used (actually, they are not used for their lubricating properties, but for their shear resistance). As such, depending on the size and material of the helicoids, different damping greases are used. Some of these can also gum up, harden, spread or separate over time.
Of course, the lenses may be disassembled and regreased. It may be a tedious procedure, however, because the helicoids have more than one entrance, and they must be assembled in exactly the same way they were before, otherwise the lens will no longer focus properly.

01-27-2013, 10:46 AM   #5
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QuoteOriginally posted by Not a Number Quote
The helicoid grease has probably dried out over time. Disassembly, cleaning and relubricating with a suitable grease is in order. Viscosity of the grease will affect the amount of damping.
Okay figured this wasnt normal. Thanks. What should I expect regarding cost at a camera repair shop to regrease?
01-27-2013, 10:51 AM   #6
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QuoteOriginally posted by kcobain1992 Quote
Basically, focus is achieved by sliding the optical barrel back and forth (back for infinity focus, forward for close focus). This is done via 3 helicoids (threaded brass pieces) with the first and the third turning in tandem. They are also reverse-threaded, so threading the middle piece in the first one also has the effect of unscrewing it from the third (and vice versa). This has the effect of transforming rotational movement (you rotating the focus ring) into longitudinal movement (different degrees of threading practically mean different distances from the film plane).
So basically this is the mechanical principle.
Now, in practice, these helicoids are made either from brass, aluminium or plastic, resulting in different amounts of friction between pieces. To minimize this friction effect, various lubricants are used (actually, they are not used for their lubricating properties, but for their shear resistance). As such, depending on the size and material of the helicoids, different damping greases are used. Some of these can also gum up, harden, spread or separate over time.
Of course, the lenses may be disassembled and regreased. It may be a tedious procedure, however, because the helicoids have more than one entrance, and they must be assembled in exactly the same way they were before, otherwise the lens will no longer focus properly.
so maybe better to just leave it alone and deal with the sloppy focus ?
01-27-2013, 10:58 AM - 1 Like   #7
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Depending on the lens value, it may be or may not be worth the repair cost. Anyway, it is one of the more complicated repairs, because it involves almost complete disassembly. I cannot give you a price estimate, because I have greased my own lenses. Others may be able to tell you how much Eric Hendrickson charges, though.
Dampening is also influenced by the tolerances in the threads. By this, I mean that an A lens will always feel sloppier than a Takumar, and will require more grease to fill in the spaces between threads.
01-27-2013, 11:03 AM   #8
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QuoteOriginally posted by kcobain1992 Quote
Depending on the lens value, it may be or may not be worth the repair cost. Anyway, it is one of the more complicated repairs, because it involves almost complete disassembly. I cannot give you a price estimate, because I have greased my own lenses. Others may be able to tell you how much Eric Hendrickson charges, though.
Dampening is also influenced by the tolerances in the threads. By this, I mean that an A lens will always feel sloppier than a Takumar, and will require more grease to fill in the spaces between threads.
very helpful, thank you!

01-27-2013, 11:05 AM   #9
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You can get it cleaned and relubed by a pro. Focusing should be so easy you can practically do it with a single finger, but so tight it comfortably stays in place once you let go. A well-dampened focus ring can give new life to your lens and make it much more fun to use. Basically, it should be smooth as butter
An specialized photography store should be able to do this for you or at least point you in the right direction.
01-27-2013, 11:37 AM - 1 Like   #10
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QuoteOriginally posted by Na Horuk Quote
Focusing should be so easy you can practically do it with a single finger.
Personally, I prefer the stiffness of the focusing on the newer MF Zeiss lenses,
since I've lost prefocused shots with looser focusing lenses (like Limiteds)
after accidentally brushing the focus ring and changing the focus.
01-27-2013, 12:15 PM   #11
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QuoteOriginally posted by godwinaustin Quote
so maybe better to just leave it alone and deal with the sloppy focus ?
Depending on how much you paid for it, the Pentax-A 24mm is probably worth reconditioning to restore a smooth and properly dampened focus. Member kcobain1992 has indicated the main considerations. Doing the job personally is possible if you have the right tools (you can read the details on many posts in various forums - see, for example,the PF Pentax Lens Disassembly Database in the Pentax Articles).

I have restored several lenses with good success after going through a learning process, and I started with a relatively simple Pentacon. Only one helicoid reassembly gave me trouble (a Carl Zeiss Jena 50/2.8). The Pentax-A lens is not particularly complicated, so I think an experienced person should be able to do such a job in two hours; a technician perhaps one hour. Cost-wise, I think I'd expect to pay no more than $80.

- Craig
03-04-2013, 04:51 PM   #12
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Don't know if you're still looking for focus ring help or not,but there is a thread here https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/197807-repairi...ocus-ring.html
about 3 post down,with another link with photos.I also have an A lens 50 1.4 only with a tight ring,but I don't feel comfortable tearing into it.
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