Canon FD 300mm f4 access to aperture unit

<p>Hi, anybody have experience of disassembling a Canon FD 300mm f4 lens for cleaning. I acquired one of these lenses with the aperture stuck wide open presumably due to oil migration onto the diaphragm blades. No amount of shaking or working the aperture ring will loosen it up.<br>

I have successfully stripped down 100mm and 28mm FD lenses for internal cleaning, working in from the front. However the 300mm seems very different in construction. The front element drops out after unscrewing the retaining ring, but underneath that there is no further ring or retainer to remove. The front part of the lens barrel forward of the focusing ring has three small grub screws which I have loosened in the hope that this part unscrews together with the front lens block, but despite using a strap wrench there is no sign of it budging.<br>

Any suggestions will be greatly appreciated!<br>

Kokon</p>

<p>Only suggestion would be to pick up a FD telephoto repair manual. I have a few and can tell you that assembly and disassembly of FD telephoto lenses is quite different from other focal lengths.</p>

<p>If your 300/4 is a New FD model, it has internal focusing, and you really don't want to mess with any of the internal element assemblies. They require special calibration equipment to put the lens back into spec after any work has been done with them.</p>

<p>If you really want to work on this lens, I recommend that you approach this from the rear of the lens. You'll have to remove the mount and then use a lens spanner to remove the rear elements. You'll also have to remove the lever arms for the actuator mechanism out of the way, and this can get tricky, especially with long lenses. After all this, it should expose the iris blades. It may be possible to clean them while they remain in the lens, but if so, make sure you clean the element just in front of the blades very well, since cleaner and other stuff will fall on it.</p>

<p>My recommendation, however is you ship your lens off to Ken Oikawa. He's a retired Canon tech. He does great work, is reasonably priced and has a fast turn around. He doesn't do the Internet, though, so you'll have to call him.<br>

Here's the most recent contact info I have:</p>

<p>Ken Oikawa<br /> 28288 West Worschester Rd<br /> Sun City CA 92586<br /> 951 246 9136</p>