Dented filter ring on lens

[Rachel]

Any tips on how to "straighten" the filter ring on a lens? It's a Mamiya M42 lens that came with a scrap 1000DTL that a friend gave me. The lens is in nice shape except for the filter ring which is flattened on one edge. Thanks for any advice.

[kiev4a]

Rachel

I have had SOME luck using a wooden block with a half circle cut out of it that closely matches the curve of the filter ring. I lay the bent edge in the cut out and then use a wooden dowel with a rounded end (and a small hammer) to try to tap out the wrinkle to match the cut out. You have to be VERY careful. If the area has much of a bend it tends to break off rather than return to the original shape. MicroTools sells a device designed specifically to straighten bent filter rings but unless you do a lot of it the price probably can't be justified.

Wayne

[PeterW]

Hi Rachel:

Any tips on how to "straighten" the filter ring on a lens? It's a Mamiya M42 lens that came with a scrap 1000DTL that a friend gave me. The lens is in nice shape except for the filter ring which is flattened on one edge. Thanks for any advice.

You can pay a lot of money from Micro Tools for a tool which they say will do the job, but if you've got access to a band saw, or know someone who has, try this link for a home-made no-cost tool. It's the same method that Wayne used.

www.kyphoto.com/classics/filterringtool.html

I'm not sure of you have to join the forum to access the above link, but if you do it's free, and worth joining. It's full of info from very helpful and friendly people, and the searchable archives go back several years.

I made the tool and it worked very well on one lens, a filter screwed in with no problems. But with another lens the dent removal looked successful but a filter went tight after half a turn. It wasn't till a friend lent me a thread chaser with the correct thread pitch to clean up the burrs on the threads that a filter would screw in.

If you can't borrow a thread chaser, a finishing tap with the correct thread pitch can be used instead. Naturally, almost the only metric pitch thread I hadn't got in my tool cabinet was the one I wanted, that's why I had to borrow a thread chaser. The diameter of the tap isn't all that important so long as it isn't too small. To use it (or a thread chaser) you put the tool on an undamaged part of the thread close to dented part and then run it round by hand so that it cleans up any burrs on the damaged part. The thread pitch is very fine, so light pressure and several passes is better than trying to clean up the thread in one push. A tap holder (tap wrench) comes in useful to get a proper grip on the tap.

Both lenses were light alloy metal-bodied. I don't know if it would work on a plastic-bodied lens.

Hope some of this helps. Good luck!

PeterW

[mickeyobe]

Rachel,

I repaired a bent filter ring a couple of weeks ago.
My method was much the same as Wayne's and Peter's except, being lazy, I did not cut a curved base on which to rest the lens.
Instead, I used a flat piece of soft wood, pine to be exact. Instead of shaping a dowel I used a chopstick. I placed the small end of the chopstick against the dent, not the rounded long side as one might expect. The lens was held in place on the pine board with a big blob of plasticine.
With a small hammer I tapped very lightly on the large end of the chopstick, going very slowly and gently and testing the filter ring frequently with an appropriately sized filter.
It only took a few minutes to correct the problem. The repair is still visible, but barely.

Mickey

[Rachel]

Thanks guys. That gives me something to think about.

Peter I was able to access that article and I've made a copy of it for future reference. I'll have a closer look at that site as well.

[nikonbob]

Peter

Just out of curiosity, what is the metric thread pitch for the chaser?

Bob

[PeterW]

Bob:

Just out of curiosity, what is the metric thread pitch for the chaser?

If I remember rightly I think it was either 0.75mm pitch or 32 TPI. There's not a lot of difference, I think 32 TPI is about 0.8mm pitch, but the difference is enough to make a filter bind, even on four or five threads. My friend, who used to be a machinist, took the filter into work and measured very carefuly with an optical thread gauge before lending me the chaser, as four or five threads isn't really enough to be certain using a 'saw-tooth' type hand gauge.

It was probably 32 TPI because I have a 15mm diameter 0.75mm pitch tap which I could have used. It was a Schneider lens from the 1950s, and at that time many old-established German optical makers still used Imperial thread pitches from the days in the early 1900s when they were almost a world-wide standard for microscope threads. The Leica thread mount from the 1920s to the start of the M series was 39mm diameter by 26 TPI. From about the 1960s I believe most gradually changed to using DIN Standard metric pitch.

PeterW

[herron]

Rachel:
I've used both methods...tried the wooden form first...got frustrated at the results and bought the Micro-Tools tool...works fine, and my worktable humor went up considerably!

[Rachel]

herron said:

Rachel:
I've used both methods...tried the wooden form first...got frustrated at the results and bought the Micro-Tools tool...works fine, and my worktable humor went up considerably!

Ron, I had a look at the Micro-Tools (Europe) site and it would cost me about £43 (inc P&P) so probably not economical for me. Thanks for your comment.

[nikonbob]

PeterW

Thank you for the useful info on thread pitch.

Bob

[casualcollector]

Always wondered why the Leica was 26 TPI instead of one mm!

[nikkortorokkor]

Hmmm, 26 TPI BSC (British Standard Cycle Thread) is used on bicycle axles and steering tubes and Raleigh bottom bracket shells (the rest of the industry used 24 TPI BSC there). The Germans also used BSC on their bikes, and millions of low-end bicycle hubs still use the 3/8, 26 TPI BSC axle rather than an M9x1 or M10x1.

After the horror of the 1970s it is sometimes difficult to remember just how influential British engineers and manufacturers were during their Halcyon days.

Dragging myself back on-topic, I too have a badly dented filter ring on the Phenix 205E (Yes, I dropped it - Doh!). I'll attempt the methods suggested here and document my progress.

I have a feeling the Phenix's ring will split, but I also have a less damaged ring on a Yashica J (not my fault this time) so I may be able to demonstrate what can and can't be done.

[nikkortorokkor]

As threatened, here is documentation of my first attempt at filter thread straightening.

The dent:


The repair jig:


The female form is cut from a piece of softwood (Pinus Radiata), the hole saw was, happily, about 2 mm bigger than the OD of the filter ring.

Unfortunately my timber shed contains only softwoods. I have some experience in cold working metals and suspected that it would be difficult to make a male form to punch aluminium into shape from softwood. What is needed is a very concentrated, controlled force. I tried a couple of different timbers, and neither was hard enough to make a small enough form that would transfer sufficient force before deforming itself. The obvious solution was to use some aluminium bar stock. I selected some 3mmx12mm gradeless bar that I had handy. This stuff is sourced from hardware stores and is very soft, easily softer than a filter ring, I guessed.

I cut about 15cm (6") of bar and filed the end to a curve roughly matching the inside of the ring. After a few judicious taps with a light hammer the filter ring achieved an acceptable shape and the end of the male form had acquired the thread off the ring: so my guess about relative hardness was correct.

Though not perfect, the ring was good enough for me to unscrew the lock ring with little difficulty. I think that I've slightly overdone it, that the dented section is now slightly proud, but this is preferable to the opposite when it comes to filter binding. I haven't yet run a tap or thread cleaner over the job.

The repair:


The caveat
I know that none of the older hands need to be reminded of this, but maybe a few other novices should know - on a fixed lens rangefinder like the Phenix, this operation is fraught with risk. If the lens is not sufficiently supported by the female form the interface between the lens and body is easily damaged.

With the Phenix, I found that the best method was to hold the female form firmly in a woodworking vice in such a way that the camera body was supported by the bench and the lens was supported in the form. Thus, the force was concentrated on the filter ring and not transmitted to the lens/camera interface. For anyone not used to cold working metal, I'd definitely recommend starting on a junk camera or even better, junk detachable lens in order to work out how much force is necessary.

[John Parry]

Well that worked Michael!!

How many filters have you got for those rangefinders??

Regards - John

[nikkortorokkor]

John, it's one of those funny things.

I don't have any 'special' screw filters for my cameras, just skylights and UVs. I do have a Cokin system from my Nikon days, but no adaptor rings that happen to fit any of my meagre collection of Rokkor lenses. Come to think of it, I think I have a 55mm Cokin ring, so I could use my NDs on the Hi matic 7 - I honestly think that is the only combination of filters and lenses I have that's useful. I can't imagine trying to use my ND grads (the only other Cokin filters I have) on a rangefinder!

To tell the truth, I fixed the ring on the Phenix because looking at it really pi..I mean, cheesed me off. A past sin continually haunting me.

When I bought it, I did like the fact that the Phenix had a lens mounted meter and so was filter compatible without a bunch of calculations. Unfortunately, the filter is as useful as tits on a bull, so I'm going hand held and will still have to do the adding and subtracting if I want to use B&W and filters. I have the Phenix completely in bits now and am thinking of easing assembly by just leaving the wires off the metering, it really is that dodgy. Then again, I can't really see myself relying on the Chinese brick now that I have the Hi Matic 7.

Sort of a filter I s'pose is the Sun Widenet wide adaptor that I'm experimenting with on the Hi Matic 7. I'll have a film finished soon so we'll soon see how well it works.