It will take me some time to go through all this. Thank you, for the detail. I printed off the drawing earlier, and its pretty close, if not exactly, my findings.
My "about 2mm" measurement includes the rear element mount frame, as thats the surface that gets hit by the mirror and what everyone is concerned about.
One qualification is the thickness of the EOS bayonet, one starts with. Mine are 8.23mm inward offset from the camera mount face, which may be different.
Another is where one assigns the 42mm register zero point in the FD lens. I think your right on it, according to my measurements, but who really knows?
My comments here are about the FD50L and maybe should be in the FD50L thread, but I think the method is the same as and related to the FD85L, given my supposition that the rear element in both lenses is the same distance from the sensor (to be confirmed). Matching the infinity sharpness and original spacings was a long iterative process. I made the rear element in a M42 thread frame, so as to be able to adjust the placement. If I threaded the rear element in (away from the sensor) far enough to have the 5D mirror clear it, the main lens group would be closer than original spacing and be close to touching the rear element. I push the rear element out toward the sensor, and the main group would need to be pushed out (away from the sensor) for an increased space from original. I always do initial conversions with 2 lenses, using one as a reference.
JimBuchanan wrote:
Another is where one assigns the 42mm register zero point in the FD lens. I think your right on it, according to my measurements, but who really knows?
A guy modified his 300D to accept FD lenses. He took his "Flange" base at the same point than the diagram above, and his body/lens combo is focusing to infinity correctly.
Overall, it makes sense: this is precisely where the body flange touches the lens mount. Done deal as far as I know.
Hope that helps,
Alex
PS: 42 is actually 42.14mm, and EF is 44.14mm. Still a 2mm difference :-)
I understand now. You start your measurments at the screw base of the lens body and get 10.4mm distance for the rear lens element. I get more than a millimeter more.
Besides the fact we are talking about 2 different lenses with a very similiar mechanical build, I just realized a big difference. You state your lens doesn't focus past 10 feet, neverless to infinity, and mine does. That would explain the different measurments we get. However, regardless of focus distance, the rear element placement never changes on the FD50L or FD85L.
JimBuchanan wrote:
You state your lens doesn't focus past 10 feet, neverless to infinity, and mine does.
My 85L focuses actually up to 10 meters (33 feet). Because: 1) I wanted to avoid mirror issues w/ the rear element and 2) wanted to keep the same original FD design (distance between rear element & last next group).
I saw in a different thread that adjusting the entire lens to gain infinity while not moving the rear element is actually a bad idea, since the last lens group could easily hit the rear element (convex/convex contact). What that means is to reach infinity w/ 85L one must either have a shaved mirror or to alter the original FD lens setup. I am not ready for either option yet.
JimBuchanan wrote:
That would explain the different measurments we get.
Not really. The 10.40mm is for proper infinity focus. The difference we get is because we are talking about 2 different lenses.
This might be the most interesting and treasured lens in my entire lineup, but it is definitely hurt by the mirror issue. As the rear lens position is not affected by moving the focus ring, I cannot even use the Live view mirror lock up trick on the 5d2 to counter the problem, as I can with the Rokkor. I can only hope one of you technically bright guys here eventually will have an epiphany...
ovredal73 wrote:
This might be the most interesting and treasured lens in my entire lineup, but it is definitely hurt by the mirror issue. As the rear lens position is not affected by moving the focus ring, I cannot even use the Live view mirror lock up trick on the 5d2 to counter the problem, as I can with the Rokkor. I can only hope one of you technically bright guys here eventually will have an epiphany...
AlexTokyo wrote:
PS: 42 is actually 42.14mm, and EF is 44.14mm. Still a 2mm difference :-)
Since film thickness is not zero, there are 3 film-to-flange distances and the one you are citing is the one from flange to pressure plate, which is the largest of the 3. The ISO film channel is 0.2mm so the flange to inner film rail distance is accordingly 43.94mm. Film can curl within that 0.2mm channel a bit and the focal plane of the lens is 44.00mm away from the flange in the hope that it will hit exactly where the emulsion is.
Film to flange figures thrown around on the net need to state in no uncertain terms where it is measured from to convey any meaningful information.
Things like the anti-aliasing filter and the microlenses may or may not have material thickness and refractive index, potentially changing the optical distance, but I presume Canon has accounted for that in the camera body's design, maintaining an optical distance of 44.00mm. The physical distance of the sensor as indicated on top of the camera body may not be the same.
cyberstudio wrote:
Since film thickness is not zero, there are 3 film-to-flange distances and the one you are citing is the one from flange to pressure plate, which is the largest of the 3. The ISO film channel is 0.2mm so the flange to inner film rail distance is accordingly 43.94mm. Film can curl within that 0.2mm channel a bit and the focal plane of the lens is 44.00mm away from the flange in the hope that it will hit exactly where the emulsion is.
Film to flange figures thrown around on the net need to state in no uncertain terms where it is measured from to convey any meaningful information.
Thanks for clarifying, this is an important point!
Not sure the maths are working precisely to get to 44.00 though, but that's not really critical: for practical purpose, since the only distance consistently given with tolerances by manufacturers is against the pressure plate, that's what I use for converting lenses (assuming film thickness is the same for everybody).
AlexTokyo wrote: No hope here. Just give up infinity focus & enjoy portraits shots, or fondue ones ...
I have converted FD 85mm/f1.2 ssc aspherical last year, it is doable to reach infinity at wide open ( samples are to be seen at my flickr).
The difficulties, was to fix the rear element with the EF mount and how to shave the mirror on 5D (precisions work is necessary to do it, due to width of the mirror)
If I see the pics from JimBuchanan, I guess it could not be fit into 5D body ( or I am wrong ?).
Should you reach this position, I am sure you 'll enjoy your lens and it is really a gem !.
Hope this helps.
My FD 85L is in limbo too. I was aware of the conversion issues for a Nikon mount and went ahead anyway. The rear element housing hits the inside of the body of the D700--haven't tested with other cropped cameras, but i did ruin a F3 machining the baffle and destroying the mirror ( the lens would mount but would hit the mirror ). As a consolation, I can use it on a Panasonic G1, but not my original intention.
The Nikon body needs severe modification for my lens to work properly. I'm close but not sure I want to shave the mirror of my D700.
Oh well--it's a hunk of glass with a f mount, and I can't use it...
wjlapier wrote:
My FD 85L is in limbo too. I was aware of the conversion issues for a Nikon mount and went ahead anyway. The rear element housing hits the inside of the body of the D700--haven't tested with other cropped cameras, but i did ruin a F3 machining the baffle and destroying the mirror ( the lens would mount but would hit the mirror ). As a consolation, I can use it on a Panasonic G1, but not my original intention.
The Nikon body needs severe modification for my lens to work properly. I'm close but not sure I want to shave the mirror of my D700.
Oh well--it's a hunk of glass with a f mount, and I can't use it......Show more →
I can definitely find it a new home (granted if the nikonF to eos adapter works as it should here) hahaha
Anybody here who has a lens layout drawing (cross section) or who could draw one?
I would be particularly interested to see what the distances are between the inner lenses at two different focus positions.
Is this one at infinity?
www.luciolepri.it/lc2/marcocavina/articoli_fotografici/TEST_85mm_f_1,2/02.jpg
m-a-x wrote:
Anybody here who has a lens layout drawing (cross section) or who could draw one?
I would be particularly interested to see what the distances are between the inner lenses at two different focus positions.
Is this one at infinity?
www.luciolepri.it/lc2/marcocavina/articoli_fotografici/TEST_85mm_f_1,2/02.jpg
As indicated in the diagram, the rear element is fixed and all the other elements move together when focussing. The amount of travel between infinity and 1 meter is roughly 1 cm.
I can only hope one of you technically bright guys here eventually will have an epiphany...
