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Looking for help with FD 55mm 1.2 SSC repair
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PostPosted: Sat Feb 03, 2018 7:20 pm    Post subject: Looking for help with FD 55mm 1.2 SSC repair Reply with quote

Hi, I have a FD 55mm 1.2 ssc (non aspheric) that I recently purchased that I am looking to repair, the lens was converted to EF mount by the guy I bought it from, and in order to make it clear the mirror on full frame cameras he altered the spacing of the front and rear groups. I can make a spacer on my lathe to fix it but I am having trouble determining the correct distance between the groups.

If anyone here has this lens and could measure the distance from the front lens to the rear lens with a micrometer or accurate calipers I'd be able to make the correct sized spacer.

Thanks, Aaron.


PostPosted: Sat Feb 03, 2018 7:49 pm    Post subject: Reply with quote

Welcome aphcl84

Fascinating mod. Hope you get your answer. I think you've asked best place!


PostPosted: Sun Feb 04, 2018 6:22 am    Post subject: Reply with quote

I have an FD 55mm f/1.2 SSC lens and also a set of 0.001" calipers. So you want the distance from the max point of curvature of the front element to the back element (which I believe is flat)?

I'm sitting here trying to figure out how your lens's previous owner changed the distance between the outside edges of the exterior elements. it seems to me that, if he were trying to miss a mirror, then he'd want to bring the back element in somewhat ("in" as in into the lens). Seems like it would mess up the optical formula though, and probably even change the point of focus. Good luck undoing what this guy did.


PostPosted: Sun Feb 04, 2018 3:03 pm    Post subject: Reply with quote

cooltouch wrote:
So you want the distance from the max point of curvature of the front element to the back element (which I believe is flat)?


Exactly that, he had machined off part of the flange that the rear group screws into so that the group was further away from the sensor and just cleared the mirror on a 5d II, as you say it introduced all sorts of abberations and changed the original focus distance. The good news is that I can simply make a brass spacer once I know the correct lens spacing and setting proper infinity focus is easy. Also since the conversion to EF mount was done somewhat poorly I've made a proper mount conversion to E mount since I will be using this on my A7II.


PostPosted: Sun Feb 04, 2018 4:04 pm    Post subject: Reply with quote

Okay I have some numbers for you.

Lens: Canon FD 55mm f/1.2 SSC, set to infinity.

Overall length of the lens at infinity: 2.255"

Both elements are recessed from their surrounding parts of the lens. The front is recessed by 0.151" and the back is recessed by 0.032". Put these two values together, then subtract them from the lens's overall length and we get 2.072" (or 5.263mm if you prefer). This is the length of the optical path at infinity.

At closest focus, the lens front moves out and the rear element retracts into the lens.

Overall length of lens at closest focus: 2.530"

As above, both elements are recessed. Front element's dimensions have not changed, so 0.151" recess.
The rear element recessed. The new measurement is 0.270". Put these two values together: 0.421" -- almost half an inch. Subtract 0.421 from 2.530: 2.530" - 0.421" = 2.109" (or 5.357mm). This is the length of the optical path at closest focus.

These numbers are the nearest I can determine with the tools at my disposal: dial calipers, accurate to 0.001", and a straight edge. I own a depth micrometer, which might have given slightly more accurate numbers, but I don't know where it is at the moment. We're still living out of boxes from our move.

I haven't compared the dimensions between the FD and FL rear flange collars that surround their rear elements. On my FL, this collar fits exactly into an M42 to EOS adapter I have. So, I've removed the breechlock ring and its associated stuff and now the M42 to EOS adapter can be bolted directly to the back of the lens. A no-damage conversion. Only thing left to do is to machine down the back flange of the adapter so as to set up the correct registration distance. Only problem is the back flange of that adapter is going to be very thin. I hope it's gonna work. I'll let y'all know when I get my mill back in service.

Anyway, I was thinking that, if the dimensions between these two lenses' rear collars is the same, it might be an easy way for you to do the conversion yourself. If you're gonna use another method, tell us about it. I have some FD lenses I wouldn't mind converting to EF.


PostPosted: Sun Feb 04, 2018 5:45 pm    Post subject: Reply with quote

The rear recess was measured from the light baffle correct? I should be able to get the spacing correct using that measurement.


PostPosted: Sun Feb 04, 2018 9:36 pm    Post subject: Reply with quote

I don't know what that piece is called. It's the ring of metal that is surrounding the rear element that has the aperture posts sticking out of it. It's a very slight step down from this ring onto the surface of the rear element -- 0.032" in fact.


PostPosted: Mon Feb 05, 2018 3:35 pm    Post subject: Reply with quote

I'm not sure what it's called either, but that baffle or whatever it's called is exactly 37.8mm from the film plane and so I can simply set the lens to the original infinity focus mark (I can see where the screws were originally) and I'll know how far off the rear group is. Thanks for all the help, I really appreciate it.