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Sorry, Alf, for the missing rear element .
But I did measure its diameter to be 36.15mm (glass + metal ring). I think the metal ring is permanently fused to the glass, and the whole thing screws in its carrier in the back plate of the FD mount. The diameter of that carrier is 37.4mm.
Anywhere, I noted that the quality of my images focused at infinity is a bit softer at the right side. Given that I centered the rear element and the M42 adapter by simple eyeballing, this may be the cause. I measured at 0.2mm out of center for the M42 adapter relative to the main lens.
Therefore I stripped them down, and recentered carefully with caliper this time, and this showed more even image quality at the different sides of frame.
There is haze overall at f1.2, which is largely gone at f2.0 (At very long distance there does have some real haze due to air pollution in Hong Kong.) Notes that the depth of field does not cover the entire image!
At f2.8 the whole image is reasonably sharp. It continues to improve at f4.0.
I forgot to add:
I also tried to increase the protrusion of the rear element towards the mirror. I have removed the original metal plate and just glued the rear element (with its metal ring) to the M39 adapter, with careful centering. Then the M39 adapter ring is filed down 0.8mm. Now if I screwed in the rear element too much the mirror would hit the edge of the element's metal ring.
I finally settled to 1.3mm protrusion over the M42 mount, making the total distance of element to EOS flange to 6.96mm. Thus it is just 0.5mm off from its original FD configuration.
Edited on Oct 17, 2009 at 10:03 AM · View previous versions