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Gez
Tinkerer
Username: Gez
Post Number: 36
Registered: 09-2007
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, September 10, 2008 - 08:36 am: | 
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Has anybody experience in accessing the iris blades of the 'new' style FD 35mm 2.8 lens?
I removed the decorator ring plus the 3 screws that secure the filter ring and expected the front lens cell to come off as in the 50mm 1.8, but apart from a well glued ring that appears to be holding the front element there is nothing obvious to shift. The inner barrel doesn't seem to unscrew either.
Any ideas? |
Glenn
Tinkerer
Username: Glenn
Post Number: 414
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, September 12, 2008 - 11:17 am: |
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Your description would indicate somewhat messy DIY handywork - half a tube of contact adhesive to hold the name ring in!! As I have stated before; the official Canon repair 'notes' are really an 'aide memoir' for the technician, and as such can be somewhat sparse in detail. The one for this lens is very sparse indeed. I do not have this lens, but I think you will be able to work it out with the lens in front of you. What is not clear however, is if you remove the focus ring before the optical group. My guess is that this is a typical 50/1.8 construction, hence the optics come out before the focus ring is removed.
At whatever stage the focus ring is removed; you must rotate it to infinity and then scribe a datum onto the ring and the helicoid, before removing the three screws. In all the other wide angles, you can only see the helicoid when the optical group is removed. So I would think the procedure is as follows:-
Remove name ring.
Remove the three filter ring retaining screws and lift off ring.
Remove inner retaining plate.
Lift out optical cell/elements.
Remove focus ring as per above.
The optics seem to sit in a 'funnel' shaped baffle, which in the notes appears to just lift out. All the wide angle notes refer back to the 50/1.8 detailed repair notes when guidance is needed. So I do not think you will have much of a problem.
Your problem, will be removing the mess that has bonded in the inner retaining plate
Make sure your scribe datum lines on the iris assembly and inner helicoid - so you can replace in exactly the same location. If you do not, the f values will not be correct. Also only remove the iris assembly holding screws, and not the two that hold the iris housing front and back plates together. |
Gez
Tinkerer
Username: Gez
Post Number: 37
Registered: 09-2007
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, September 12, 2008 - 02:07 pm: |
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Glenn, many thanks for your detailed instructions.
Fortunately I didn't have to remove the focusing ring and having slept on the problem realised that the glue wasn't holding the optical cell in place, it just appeared to do so. The cell is sitting a 'funnel' as you describe, held in place by the filter ring, though a much tighter and precision fit than in the lightweight 50/1.8. On carefully removing the cell the iris assembly was visible and secured by 3 screws. I made a measurement of the aperture at f16, about 2mm., lifted the unit out and flush cleaned 4 times with lighter fluid without further disassembly. The trick on reassembly seems to require holding the blades open while securing the screws. All seems OK! perhaps beginners luck, anyway it has given me confidence to tackle some of Canon's heavyweights.
Thanks again. |
Glenn
Tinkerer
Username: Glenn
Post Number: 416
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, September 13, 2008 - 09:54 am: |
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As you have found out, the assembly tolerances are much tighter on the more 'expensive' optics. There are far more matched optical pairs in the element groups, and the groups have obviously been pre-assembled on an optical bench - spacer thicknesses are specific to a particular lens. If you try swapping individual elements and spacers in the f2 wide angle series - to replace a damaged front element say - the resolution of the bitsa will be nothing like the originals. In fact it will be between rubbish and barely acceptable.
In your repair: As long as you measure the iris diameter at a known f number, do not separate the iris assembly by mistake, reassembly is normally a simple matter. Obviously if you need to strip the iris assembly, you do this when the assembly is out of the barrel and on a flat surface. You do not have the individual blades falling all over the place, and reassembly is a simple reversal. I have been known to 'oil up' an unknown iris assembly prior to dismantling - just to keep the blades and any spacers stuck together, when separating the blade cage.Better to see how the manufacture placed the parts, than spend a frustrating time working it out! |
Gez
Tinkerer
Username: Gez
Post Number: 38
Registered: 09-2007
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, September 21, 2008 - 12:55 pm: |
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Well, this lens appears to be made using composite material, at a guess glass fibre in a resin matrix. The front optical cell seems to be a sealed unit with no retaining rings or spacers in evidence. That's OK as there is less to worry about.
I followed the procedure all the articles recommend and measured the aperture diameter at f16 before and after the work, but the iris assembly doesn't seem to have any provision for such adjustment. I just cleaned the unit and replaced it without any disassembly. How would I go about adjusting the iris if that was necessary?
I next hope to tackle a Canon FD 50mm / 1.4, breechlock that has been 'serviced' by a 'professional'. His less than expert attentions have resulted in an uneven iris opening and some oil creeping back! |
Glenn
Tinkerer
Username: Glenn
Post Number: 426
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Sunday, September 21, 2008 - 06:52 pm: |
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The iris adjustment is somewhat crude in the nFD lenses. If you had examined the iris assembly closely, you would have notice that the holes for the retaining screws are oversized. To adjust diameter of iris, you set the aperture ring at the f value for which you have the actual factory spec diameter. Slightly loosen the retaining screws, insert a drill shank of the required diameter in the iris and then gently close the iris blades onto the shank by rotating the whole iris assembly. This is rather awkward unless you have three hands! So you mount the drill shank vertically on a piece of board, then place the lens barrel over the upright shank. This then allows you to rotate the iris assembly with one screwdriver, and then tighten the retaining screws with a driver held in the other hand.
The 1.5/50 and the 2.8/35 were basic optics that used a simplified construction. Some parts were made from precision molded engineering plastics to keep costs down. The only work I have carried out on the 2.8/35, is to replace the lens mount - so I cannot comment on how the optical cells are built up. However the parts list does not indicate any spacers in the assembly. In fact none of the basic/cheapest nFD lenses use individual spacers, only plastic moldings. A good example of the extreme cost cutting used on the nFD series of optics. |
Gez
Tinkerer
Username: Gez
Post Number: 39
Registered: 09-2007
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, September 25, 2008 - 02:58 pm: |
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Glenn, have you any experience servicing the iris of a Carl Zeiss Jena Flektogon 35mm / 2.4?
I did a search on another forum (not as august as rangefinderforum!) and came up with some instructions that involve removing the mount and focusing collar, in fact a full strip-down. This doesn't seem right. Any ideas? |
Glenn
Tinkerer
Username: Glenn
Post Number: 432
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, September 25, 2008 - 05:06 pm: |
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Gez,
Sorry, no I have no experience of this lens. However from experience with the medium format Jena lenses, the full stripdown could be the correct procedure for this lens. |
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