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Marco
Tinkerer
Username: Marco
Post Number: 19
Registered: 10-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, June 30, 2010 - 11:57 am: | 
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I cannot remove the dust cap from my 24/2.8 chrome nose. Both cap and breech ring are stuck solid. Upon closer examination one of the cap lugs is visible but not protruding, suggesting careless handling. Cap is Canon original. f/stop and distance rings move freely.
No amount of reasonable wiggling will produce any movement of either. Before resorting to brute force I seem to have three alternatives: (a) removing (or just loosening) the two breech ring retaining screws, without knowing the effect or what to do afterwards; (b) setting the diaphragm ring to the green circle Auto stop, ditto.; (c) ask the forum for help.
I’d appreciate any guidance before resorting to (a) or (b) or else, excluding reaching for the sledge hammer. Many thanks in advance. |
Glenn
Tinkerer
Username: Glenn
Post Number: 793
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, June 30, 2010 - 03:15 pm: |
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By 'Canon original' I presume that your rear cap does NOT have finger grip serrations around the rear diameter? On this cap the three cap lugs are actually tapered wedges - in use the cap is prevented from rotating in the mount by a slot in the lug fitting over the lens locating pin, turning the breech ring jams the alloy ring onto the wedge sectioned cap lugs 'locking' it in place and preventing accidental rotation of the breech ring. When the cap has been positioned properly on the rear of the lens you can see equal amounts of all three lugs - obviously all the lug before rotating the breech ring and approx half of each lug when an unworn cap is secured.
Your problem arises because of two things - a/ over the years the wedge shaped lugs wear ever thinner and this eventually allows b/ the cap does not positively fit over the locating pin and rotates as you move the breech ring. Invariably this leads to one of the cap lugs over riding the location pin and jamming the breech ring solid. One should note that there are some new rear caps for breech lenses available on eBay etc, these are all correctly marked up Canon but unfortunately the lugs are not wedge shaped - obviously the pattern maker used a worn cap as his sample - these caps will lock up immediately they are used if not put on carefully!
To remove the cap you must hold the cap tight and turn the breech ring so that it rotates off the cap lugs - clockwise when viewed from back of lens. Ideally you need a couple of the plastic and rubber strap wrenches used to remove stuck filters. However you can make a couple of strap wrenches from a couple of length of 1/2"x1/2" hard wood and an old leather/plastic belt. A very small drop of thin oil placed at the interface of lug and breech ring can make things free up easier, from your description it appears that only one lug/ring interface is visible - obviously when the jam is not too severe there will be three interfaces to lube. Apply the drop of oil from the tip of a sewing needle. ( Purists should note that I always use decanted WD40 as my lubricant of choice for this type of job and I have come across a fair number of ham fisted collectors over the years!).
Your comments about the diaphragm and focus rings are superfluous - they have no bearing on the problem what so ever. |
Marco
Tinkerer
Username: Marco
Post Number: 20
Registered: 10-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, June 30, 2010 - 10:56 pm: |
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Thanks a lot Glenn for your very detailed analysis, diagnosis and recommendations.
When I said ‘original’ I only meant to make it clear that it was not a third party cap, without implying that lens and cap were born together (as an avid collector of second hand ware I have learned that you never know…). As the offending cap DOES have (5mm high) grip serrations around its rim, I now realise the reason for your comment. The cap on another BL lens I have before me has no serrations but the one on an nFD lens DOES. So, I seem to have an nFD cap on a BL lens, is this right?
Comparing both caps I notice that even if the lugs in both share the same diameter they are clearly of different and apparently incompatible design (are they? just why eludes me) though not enough so for a worn or chipped nFD one to fit a BL lens, as the present case would show.
f I have understood your comments and correctly identified visual differences in both caps (triple-notched BL vs. single-notched nFD), the intruding nFD cap is riding on the location pin of the BL lens. I am already decanting some WD40 for the next obvious phase, barring the hacksaw option. Will inform you and the forum in due course. Many thanks again!
Saving the classics from oblivion or the dumpsite is in itself a very pleasant activity. But being part of and benefitting from this generous community is even more rewarding. |
Agno3
Tinkerer
Username: Agno3
Post Number: 25
Registered: 07-2007
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, July 01, 2010 - 06:35 am: |
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Canon-brand FD caps, whether serrated or not, fit all breech lock lenses equally. It is the positioning of the cap that causes the problem you are encountering.
Once you get your cap off and wish to cap the rear of the lens, note that when properly positioned and pressed toward the lens very lightly, the breech lock ring will rotate. If you see this happen, go ahead and tighten the breech lock ring on the cap. It will come off easily. |
Glenn
Tinkerer
Username: Glenn
Post Number: 794
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, July 01, 2010 - 08:45 am: |
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Marco,
I had a feeling that you had a nFD (serrated) lens cap on a breech lock lens. Now Mark (Agno3) is quite correct in stating that the nFD cap will fit a breech lock lens and the cap can only be put into the mount in one position due to the key effect of the larger lug - just as in the nFD mount, but fitting a worn nFD cap to a breech lens always runs the risk of the combination jamming - the breech ring does not always rotate when the cap is pushed in, depends on the lube used on threads of alloy ring ( I like a fairly heavy grease on these threads so ring does not self rotate on my bL lenses).
You say that you can see part of one lug - correct? Is this the lug opposite the triangular position marker on the rear of the cap (this lug has a raised stop on its lefthand end, viewed from rear of lens and is longer than the other two lugs) and if so, can you see the end of the silver lens locating pin positioned in the lug's location slot? The locating pin can be hidden for two reasons, the breech ring has rotated enough to cover the pin or the cap has become misaligned and pin is under the lug. I am trying to ascertain the actual radial positioning of the cap in the rear mount - Is it correctly positioned, but due to sloppy fit/wear the cap has rotated clockwise (viewed from rear) in the mount, thus becoming jammed under the breech ring without releasing the breech ring lock that stops the ring from being turned. In this instance the breech ring will obviously appear to be jammed, only by forcing the cap to rotate anticlockwise will allow separation.
The aforesaid raise stop on the end of the longer lug can also get jammed under the breech ring, but in this case none of that lug will be visible - well only about 1/16" peeping out from under the ring so to speak. This really requires a well worn cap and a very ham fisted operator to achieve - in this instance the ring could be locked or unlocked. Clearly my comments on turning the breech ring in my first post are only valid if the ring stop is released. As this is impossible to actually see, you should always try turning the cap anticlockwise first unless the lens locating pin is clearly visible in the lug's slot.
As you have both BL and nFD lenses and correct caps I suggest you examine both closely and I think you will soon see the areas that can cause problems. Knowing these I think you will find the solution much easier than writing about it! |
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