"Broken Back" lenses

guardian · Joined: 18 Mar 2009 Posts: 1749

The title is pretty lame. I don't really know how briefly to describe what I'm talking about, so I'll try to explain:

Not so much for shorter focal length MF lenses. But for longer focal length MF lenses which are physically on the long side, and especially for long MF zoom lenses:

I have several such lenses now with "broken backs". The lens, when fully extended, wobbles on its axis. If you hold both ends and try, you can wiggle the lens back and forth axially. Mounted on a camera body, the lens "droops" slightly. The section to section connection points of these lenses, which should be solid, are instead loose.

I hope that explanation is sufficiently clear. If so, I have two questions:

What event in the lens's past caused the "broken back"?

Was it perhaps caused by the lens having been mounted on a camera body which was dropped? If so, I can tell you I'm not finding any other indications of dropping on my "broken back" lenses.

Are "broken backs" caused by a manufacturing or design deficiency?

The "broken back" lenses I own arrived that way. I've not (so far, at least) ruined a previously-good lens by dropping it. So I'm at a loss to know what causes the "broken back" condition. I also have been at a loss to be able to repair any of my several lenses with this kind of damage.

Do you know what causes this "broken back" condition? Have you ever successfully repaired a lens in this condition?

philslizzy · Joined: 07 Aug 2012 Posts: 4748 Location: Cheshire, England

I'm not sure exactly what you are referring to but I had a wobbly lens on a rangefinder that was making the photos blurred, I found that the ring holding the rear element in was loose. I tightened it up and everythings perfect.

guardian · Joined: 18 Mar 2009 Posts: 1749

Thanks. I realize what I am asking is not entirely clear. It's difficult to explain, but:

All lenses have some segmentation, or sectionalization, to them. Short focal length lenses have shorter segments. I've not encountered this on short f/l lenses.

The segments, or sections, of any lens in proper order connect smartly with adjoining segments. There is no looseness or "play" when the lens is right.

But I've brought in several lenses, all physically longer, where the segments are not tightly connected as they should be, or (I'm sure) as was the case when the lens was new.

Naturally I've looked at these lenses in hope of tightening them up. So far, at least, I've not been able to find a way to do that with any of them.

As I wrote in the OP, these are second hand lenses so I don't know what event gave rise to the loosening between segments or sections. If the lenses were dropped, perhaps there was stretching (i.e., bending) of a metal flange (internally), or something of that nature.

From the paucity of responses I have to conclude other MF lens fans are not running into this problem to the extent I am. Let me say:

I envy your good fortune!

I'm not proficient at disassembly and/or repair of the larger lenses. I'll most likely have to sacrifice one in an effort to get inside and (try to) discover what's going on.

philslizzy · Joined: 07 Aug 2012 Posts: 4748 Location: Cheshire, England

You explain it well, but if you haven't experienced something like that its a little hard to get your head round. Maybe that explains the lack of responses. Its been a quiet evening, perhaps when the Americans get on line there may be some replies.

The ring I'm referring to is a slotted ring round a lens element. The one I repaired was easy to see and reach, no opening up the lens to get at it.

Another thing you may look for are screws in the barrel, many are hidden under the grip. If the focus grip is rubbery material you ought to be able to lift it off or at least roll it back. There may be grubscrews that need tightening. Not rocket science and easily done by someone with good eyes and a pair of hands. And a mini screwdriver

mo · Expire: 2016-07-30

Can you focus through the lenses at all?

guardian · Joined: 18 Mar 2009 Posts: 1749

jaecarlos714 · Joined: 06 Jun 2013 Posts: 17 Location: Portland, Oregon

I had a Vivitar 200mm with same issue. Problem was loose screws holding the barrel to base. Required complete disassembly to get to loose screws and tighten. Great learning experience and now I'm no longer afraid to take a lens apart.

visualopsins · Expire: 2025-04-11

Welcome jaecarlos714

I have seen:

Set screws around the barrel. (Most common in my experience)

Fixing screws inside the barrel.

Barrel segments that screw together. (Second most common)

guardian · Joined: 18 Mar 2009 Posts: 1749

Gerald · Joined: 25 Mar 2014 Posts: 1196 Location: Brazil

norland · Joined: 10 Aug 2013 Posts: 165

Discrepancy between the interlocking focus-threads is unlikely to be so severe as would cause the "broken back" symptoms.
I have a Yashica 300mm which has such a problem....
Indications are that some internal fastenings have come partly undone -- but its focus action is not at all sloppy.