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Canon FD (non breach) 300mm f4l aperture stuck wide open.
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PostPosted: Wed Apr 29, 2020 8:12 pm    Post subject: Canon FD (non breach) 300mm f4l aperture stuck wide open. Reply with quote

Ok so the title says most of it. I discovered the issue today when I went to put my 2x-A extender on. Aperture adjustment was working fine, then just got stuck.

I took the lens off and did the trick to text the blades (turning the back element and moving the aperture lever. The blades open/close fine when I do this.

However whenever I mount the extender on, actually even when I don't now, the blade either stay stuck where I set them in manual mode, or open wide when the extender is attached.

I feel like I am missing something stupidly simple, but I have tried everything. I assume the mechanism isn't broken as it works when I push the two pins down and twist it into forced manual mode.

I am at a complete loss, this is a wonderful lens and looks like it would be $200-300 to have it repaired. I am really hoping someone here has some sage advice for me.

Massive thanks in advance to anyone who can help.


PostPosted: Wed Apr 29, 2020 10:42 pm    Post subject: Reply with quote

You might like to try adding the extender and then mounting it to your camera, and see if the problem persists.
Canon FDs need to be mounted for the aperture to operate
Tom


PostPosted: Wed Apr 29, 2020 10:56 pm    Post subject: Reply with quote

no dice when mounted, but it works when I trick it into being on a cam and manually operate the aperture lever and the blades move (so they aren't technically stuck).

I cannot find ANY oil etc on the blades, they are so pristine looking. I am really hoping that the springs aren't bad.

I have mounted to both canon (native mount) and my sony a7ii via a novaflex adaptor and I can't get it to do anything.

I am really hoping this lens isn't shot...


PostPosted: Wed Apr 29, 2020 11:13 pm    Post subject: Reply with quote

Oldhand wrote:
You might like to try adding the extender and then mounting it to your camera, and see if the problem persists.
Canon FDs need to be mounted for the aperture to operate
Tom


oldhand, I have tested another FD 55mm 1.2 and it works fine. So now I am super concerned as the 300 isn't at all cheap to have fixed.


PostPosted: Wed Apr 29, 2020 11:19 pm    Post subject: Reply with quote

Yes, it does sound like the lens needs help.
Sorry to hear that.
I had a 300/2.8 lens defungused and it was not cheap.
Tom


PostPosted: Sun May 24, 2020 12:13 pm    Post subject: Reply with quote

A couple of years ago I bought a Canon FDn 300mm f4 lens with stuck wide open aperture diaphragm blades. The blades suffered from a common issue in FD lenses, ie oil migration onto the leaves of the diaphragm mechanism (not always easy to spot). As I had addressed this problem before in other lenses I decided to strip the lens to effect a cleanup.

First step was to remove the front section of the lens barrel. The frontmost element unscrews together with the lens hood. The next flared shaped section of the barrel was more difficult. Pulling back the rubber sleeve material around the focus ring revealed a diagonal cutout channel in the ring when slowly rotated exposed three sets of (2) tiny grub screws close to the front. Incidentally the focus ring surface beneath the rubber sleeve was saturated in oil. Each grub screw needs to be loosened, not removed. Then the barrel section next to the focus ring needs to be unscrewed and this gave me the most difficulty as it was screwed on extremely tight, I thought the threads might be seized or corroded. Eventually I managed to release the threads by improvisiing a clamp and using a heat gun to expand the metal. Once this element is off, the plastic 'tub' holding the aperture diaphragm can be removed after unscrewing a screw also ensuring the rear set of grub screws are sufficently loosened. The whole tub can be rinsed several times in isopropyl alchohol or lighter fuel, left to dry then reassembly can begin. Worth a try if you have the tools and patience.