Specific advice on a lens problem, please

[ucci]

It is not always easy to admit you are a dead set drongo and in desperate need of being led by the hand and helped. But in my case I am willing to do so.

Okay, so here is the problem.

I have a couple of tamron AF 70 to 300 F/4-5.6 lenses for a canon. "But why have two," did I hear the class smartie ask? Well, I did tell you I was an idiot, didn't I?

So, it happened like this. I bought my first one a few years ago. And it was a lens I really loved. My absolute favourite. But then one day whilst zooming with it instead of zooming in and out the lens simply unscrewed itself from the camera frame. Which was a bit unnerving for an old chap. As this problem became the norm I went back to the large camera store franchise where I bought it and was advised by some sincere, smiling salesperson, who would have to know all about these things, that it would probably far cheaper to buy a new one than send off the old one for assessment and advice on its 'repairability.' And before I could scratch my bum to think about this my much loved wife, in her usual pragmatic way, said it was no problem and promptly bought me a replacement. Which made me as happy as a pig in poo. Until recently when this second lens started to unscrew itself as well rather than zoom. So this time I was more cunning. I went to a different camera store in another town and sought a professional opinion which was, " Hmm it shouldn't do that." I took much comfort in this observation as even me, being a total klutz in these matters, had already worked this out.

The thing is that I tried these two lenses on a 7D and a rebel 1000D frame with the same end result of both lenses screwing off rather than zooming. So at the moment both lenses are sitting on a shelf gathering dust. I have a range of other canon lenses and they lock on both frames quite well and firmly.

So, once you have ceased you uncontrolled sniggering at an old man's stupidity, can any one please give me some advice on this? Can these lenses be realistically salvaged or would I just be throwing good money after bad? Though I really like this particular lens I feel that probably it would be pushing my luck to ask Mrs Ucci for a third one. She would say 'go for it,' I know. But I would feel terribly guilty if I did. Well, for a short time, anyway.

I do have a Sigma 500 mm lens for zoom work but it is such a huge heavy monster and not one which one can whip out for a quick, hand held, close up. Takes me all my time to lift it up onto a tripod. The 300 mm I found excellent for these sorts of sudden, one of, hand held shots, that are fleetingly 'get it now or it is gone for good.'

Any advice on this would be much appreciated.

And while we are about it. Another question. Does anyone have an opinion or experience with the Olympus OM m5 camera? Any feed back on this would be appreciated.
Cheers
Old Ucci

[Ken MT]

For non Australians

drongo - Australian slang: A "no-hoper" or fool. Derives from a racehorse of that name in the 1920's that never one a race out of 37 starts.

Recruits to the RAAF in WWII earned the nickname "drongos".

(Nothing to do with the class of bird -- drongo)

"You've really mucked that up, ya drongo!"

[jcuknz]

Without knowing the lens or how it fits together I would think that the zoom part of it has siezed up and needs a 'lube job' done on it. I am suprised that it unscrews itself off the camera because there should be a locking pin on/in the camera to stop the rotation which also needs inspection. If you fixed the camera mounting stuck pin problem the zoom might work with some effort ... which is not something I would advise ... better is for Mrs Ucci to agree to a camera repair mechanic checking out the lens for you.
I think you need to ask as to what kind of lubricant is suitable for the locking pin and I simply do not know. It is something you might be able to do yourself but the lens itself should go to the repair shop.

By 'rotating off the camera' I imagine you mean a part turn to free the lugs rather than the several turns rotation if the mounting was an older M42 version with a thread like a large screw? I believe the 7D has an EOS type bayonet lens mount?

The other thing will comes to mind is perhaps the tamron lens has an adaptor to EOS bayonet on it base which could be locked on better to stop the unwinding. In coming off the camera does it come off completely leaving the camera with its EOS bayonet mount? as when you take off the other lenses you have** These maybe silly questions but I am trying to think of possibilities that might be occuring, however wild and inprobable. I have a horrible thouight that maybe the Tamron doesn't mate up with the camera pin and relies purely on friction to stay on the camera and so when the zoom siezed up it easilly rotated to disengage from the camera.

Hope these thoughts are of help and I don't think you come under the heading of drongo

** I was using my Pentax lens on my Canon DSLR and to do this I had a thin collar [ M42 to EOS adaptor ] which accepted the lenses M42 screw mount but bayonet fitted to the camera with the camera's locking pin to stop the third of a turn rotation to come off again. The collar rotated several turns to come off the lens but only a third of a turn to come off the camera .... hence my question.

[Stagecoach]

Two lenses the same having the zoom seize up, suspicious.

Ken it's a bit unclear from your description what is unscrewing. If you are referring to the camera/lens mount when you align the lens in the mount and then turn it to lock it does it 'ckick'?

Or as I am not familiar with canon mounts these days when mounting it does it feel the same as your other lenses?

Grahame

[davidedric]

Can't help the OP directly, but I can comment that I have had the same lens on a 600D body for a couple of years without problem. There is certainly no separate adaptor on the lens. All very odd.

[ucci]

Thank you all for your comments. There seems to be some lack of clarity in how I have described the mechanics of the problem. The lenses actually should twist on with half a turn and lock on to the frame. But it doesn't and when 'zooming' the lens it tends to twist off as well as zooming out and disengages from the camera body. Normally when putting the lens on at the end of the locking twist one can 'feel' the lens locking on to the camera. This is not happening. It is obviously a lens problem as both the lenses will not lock on to 2 different camera frames where as I have no problems with several other canon lenses locking into place. It just seems strange both lenses exhibit the same problem. And to have them looked at they have to be sent away to a specialist shop as the problem seems well beyond the ken of the 'experts' in the camera specialist stores.

Oh well, it's back to the drawing board I guess. Thank you all for your helpful feed-back comments

[Manfred M]

From the way you have just described things, it sounds like a fairly minor repair / lubrication issue as all that seems to be happening is that yor lens is not locking when mounted. Somehow the spring-loaded locking pin is not moving freely enough to engage. This could be caused by any number of things, including an issue with the lens mount on the camera (this it unlikely the cause, as other lenses are mounting properly and the lens is showing the same issue on another camera body). I would look at getting the lenses repaired.

I would never ask a camera salesperson about repairing a camera; their primarly role is to sell you more gear, not to repair you existing equipment. This certainly seems to have happened in the case of the first camera shop you visited...

[GrahamS]

Make sure that you are attaching the lens with the correct alignment - red dot to red dot and then twist to "click". The locking pin is in the lens-mount flange on the camera body (it's a body, not a "frame) and is spring loaded. Spring tension should insert the locking pin into a corresponding cavity on the mount on the rear of the lens. If this is not happening, the pin and cavity are not aligned or the cavity on the lens is filled with foreign matter (unlikely). Just a thought.

Incidentally, it is possible to mount some lenses "upside down" in which case the mount lock will not engage.

[ajohnw]

Some times the bayonet fit is a little tight so it can be hard to full engage the lens. This shouldn't happen and is a reason to immediately return the lens if the "click" isn't apparent. I had a Soligor (yuck) lens many years ago like that. The fitting was badly machined. It might be worth looking to see if there is any fraze etc or a slight bend or bent corner - one way of tightening loose fittings. I have also used well worn FD lenses in an adapter on m 4/3 that didn't lock easily.

Grapham made a good point too. I certainly have had none camera brand lenses that appear to fit the wrong way round.

I suspect the "unscrewing" is down to inertia but I would have thought that would need a very loose fit - humorously - maybe you should zoom the opposite way.

John
-

[Rita]

I have no suggestions for your first issue but I do have an Olympus omd em5. I totally love it!
I use it with the kit lens and also a macro.....waiting with a lack of patience for my zoom to be
purchased.

[Stagecoach]

Ken,

If you have a magnifying glass do the following;

Carefully look at the hole in the lens mount which the pin is designed to go into. Are there any burrs on the edges? Is there any marking on the surface around the hole showing rubbing where the pin has sat?

[William W]

If the two Tamron Lenses are for Canon, then they are an EF Bayonet Mount.
The lens will have the MALE bayonet and the Camera has the FEMALE bayonet.

BUT – the LOCKING PIN which holds the lens in position on the camera has the OPPOSITE orientation.

That is to say on the locking pin is MALE on the camera body and is retracted by the locking pin release button, seen here on this 400D:



***

On all EF (and EF-S) Bayonet Mount Lenses and Accessories there is the FEMALE recess for this locking pin to engage, seen here:



***

If the problem is only with these two lenses, then the first thing that you should check is if there is any foul or crud in those recesses on the two lenses preventing the locking pin to engage.

The next thing you should check is that you are rotating the lens to a FULL ENGAGEMENT, such that the locking pin does engage into the lens’s recess for it.

The second problem is not so uncommon especially with a lens that is not often used – one must rotate the lens until the soft “click” of the pin dropping in, is heard.

***

It is not possible to mount an EF Lens upside down or otherwise – i.e. it is impossible to engage the bayonet such that the lens is flat on the camera mount, without first BOTH the Red Alignment Dots being lined up, together.

WW



Addendum:

What Grahame wrote, too, have close look - I was finding my photo files when he was writing.

[Stagecoach]

Ken,

In addition to checking the 'pin' hole also check the edges of the bayonet flange protrusions. It is these that determine how far the lens rotates before being mechanically stopped.

Personally, if the lens was mine and I did not want to send it back to Tamron I would remove the bayonet ring having done the checks I mentioned and either de-burr around the hole and retry and if this did not work using a dremel remove a very slight amount of material from the bayonet lugs that determine the stop position.

I suspect the bayonet ring is a part that may be purchased fro Tamron at a very reasonable price and easily fitted by yourself.

[ucci]

Thank you all for your most helpful advice. It is very much appreciated. Lens to repair shop is the go, as it seems as if the pin lock system just won't work for the tamron lenses, even though it works just fine for several canon lenses and a Sigma 500mm zoom/

[AB26]

Hi Ken,

Now that my uncontrolled sniggering has seized and I have wiped the tears from my eyes I can see Manfred is probably hitting the nail on the head.

Have you checked the mount on the lens side for any dirt or other obstruction preventing it from turning far enough to reach the correct position to lock? If that little hole on the lens side and the pin on the camera side do not align perfectly it will not lock into position.
I suppose the lenses did lock in place when they were new. You are probably missing a very minor little issue, preventing the locking to take effect.

Ken I know other people like you and having them around a fire with a beer in hand is dangerous. Laughing till you drop, into a fire, is no joke at all. Thanks for that, you made my day.

[Manfred M]

Thank you all for your most helpful advice. It is very much appreciated. Lens to repair shop is the go, as it seems as if the pin lock system just won't work for the tamron lenses, even though it works just fine for several canon lenses and a Sigma 500mm zoom/

This can always be an issue with any third-party lens. Reverse engineering a part may mean that the tolerances / specs might be off by a bit versus what the OEM is using. Sometimes simple manufacturing tolerances or changes can cause issues, especially with a precision machined part.

The problem very much reminds me of issues I had with my first SLR. The lenses used the M42 threaded mount (a.k.a. Praktica-Pentax mount). While screwing a lens into a camera body gave you are really solid mating between the two components; there were issues with it. Attaching a lens took time; one really did not want to damage the len or lens mount by applying too much force and cross-threading the lens mount.

The other issue is that the lens was really held in place by friction; so when shooting outdoors in cold weather, the lubricants in the lens became more viscous, and it was all too easy to unscrew the lens while focusing, much in the way you are describing what is happening with your lens. One ended up developing a technique of holding the lens in place while focusing, so that it did not loosen up.

[AB26]

Ken,
Have you checked all those little screws on the "back plate" of the lens? Are they all flush with the back plate?