Converting a FDn 500mm f/8 to EF mount - a project

Discussion in 'Canon EOS' started by scrivyscriv, Jun 9, 2009.

  1. I just started working on converting my FDn 500mm f/8 CAT telephoto into an EF mount - not really big news, been done before, but I'm sure a few people will be interested in seeing it.
    KEH had an as-is Tamron 28-200mm for US$8, so I snapped it up, along with an order for a few other miscellaneous things I needed, to cannabilize the EF mount.
    The FD 500mm came off of Craigslist local in Memphis - the guy had a 17mm f/4 and the 500mm f/8 listed for fifty bucks each! I jumped on it but someone had already bought the 17mm. The 500mm has some spots inside; not completely sure if they are fungus or dust. I can't tell if it affects performance since I've never really used a lens like this before. Anyway, I tripod mounted it and held my EOS camera up to it for shots that look like this:
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    But I wanted a more permanant mount. Here is what I've gotten so far :
    [​IMG]
    Bunch of shims under this EF mount from the Tamron lens!
    [​IMG]
    The FD mount is pretty simple, but a little more complex than EF.
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    The EF mount loosely placed on the 500mm.
    I haven't drilled the aluminum EF mount yet since that's going to be the most precise job. Will post more photos of the process and through the finished lens :)
     
  2. awahlster

    awahlster Moderator

    Moving this to the EOS forum as it's more appropriate for that forum
     
  3. Yes, the FD folks, quite understandably, are not too keen on this kind of thing!
    I have seen reports of successful conversion of the (FD) TS35 to EF mount, and, as with the Reflex 500/8, there is no stop-down machinery to complicate things. These two, and possibly also the 8mm fish-eye of which I believe the same is true, would usefully fill gaps in the EF range. What would be really cool would be to get hold of a focus-confirmation EF mount that could be burned with the f/8 aperture of the lens!
    Anyhow, good luck, and keep us posted on progress.
     
  4. Updates:
    Finished with it. The EOS mount isn't very compatible with the FD mount because of the screw locations. You basically have to drill straight down through some of the bayonet mount - If the mount had a smaller internal circumference, you'd have more room to drill and countersink to have a secure mount.
    However it does achieve infinity! And beyond! I get a little OoF blur when focusing on clouds - !
    [​IMG]
    [​IMG]
    A few shots taken through it... They are at ISO 3200 and right around or a little under recommended hand held shutter speed.
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  5. Well done, Robert! Could you post some 100% crops, please, with details of the body you are using. Also, what level of metalworking equipment did you find it necessary to use?
     
  6. Re-fitting the mount doesn't take much metalwork experience. It's not hard, especially since the mount I used was made of aluminum.
    I'm going to rework the mount by adhering a layer of epoxy around the inner circumference of the EF mount (with a paper towel tube, or similar, as a mould) to give more drilling room. The screws need to be countersunk in the bayonet mount.
    Here are some tripod mounted shots.
    Made with a 20D at 400 ISO with MLU.
    [​IMG]
    100% crop below:
    [​IMG]
    Full shot @ ISO 3200:
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    100% crop:
    [​IMG]
    And here's a (handheld) 100% center crop from an above picture (ISO 3200)
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    Handheld 100% corner crop at ISO 3200 (yes, I know it's a 1.6x camera...) :
    [​IMG]
     
  7. Thanks, very interesting. Image quality obviously is a bit limited, and the peculiar bokeh created by all mirror lenses is apparent on both the bird shots. That said, for your outlay you have obtained good value and created something genuinely useful. I used to have the Sigma 600/8 mirror lens in EF mount, but found it very disappointing (despite its reasonably good reputation among lenses of that type). The Canon 500/8 certainly looks better.
     
  8. I haven't been very satisfied with the way the EF mount is secured to the lens, so I've been working up some drawings of an adaptor. I just sent them to a machine shop so I'll find out within a few weeks how it turns out (pun intended). It's a one-piece piece of aluminum, turned to spec. It's basically a shim to give the EF mount a flush platform to mate up to, with a flange to allow the EF mount to screw in using stock EF screw locations.
    This is the full drawing with specs. The total thickness spec is actually .126", not .100" as printed on the drawing. Even at .126" high, I believe this adaptor will still permit infinity focus. As mentioned above, I am getting past-infinity focus with the current setup.
    I intend to buy a chip for AF-confirm and EXIF data from one of the eb*y shops - AF-confirm won't work at f/8, but the EXIF data and "finished" appearance of the chip will be nice.
    [​IMG]
     
  9. Also, here area a few images taken with the current non-machined setup - IQ is excellent!
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