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| Re: FD 85/1.2 SSC Asph. to EOS Guide |
The point of the spring:
It is continuly pulling the lever (name it Lever1 for clarity) on real aperture in one direction. So the lever (Lever2) you have to install on the aperture ring need to have accuracy only on the front edge, because it is the only mating surface.
Without the spring, two edges of Lever2 must mate accurately with Lever1 (i.e., two mating surfaces), and throughout the focusing movement of the lens. This could be difficult without adequate tools and rigid materials (me included), especially if Lever2 must be a female one.
With the spring in place, no matter Lever1 is male or female, you only need a narrow Lever2 with its front edge (the one facing Lever1) accurately shaped.
After messing with 17, 50L(still in progress), 85L, 135, 300L with nFD mount, and 55 Asp, 300 Fluorite (and a 24Asp is coming) with SSC breech lock mount, I think the breech lock versions are just slightly more difficult to work with. And it is only because I have to cut across the thick breech ring and sand off its internal threads to provide a cover behind the aperture ring! If there is another way to provide the cover then...
To accommodate the differences in EOS and FD flange distance:
The total optical distance (OD) of the attachment on the rear must be 3mm.
All I need to do is to trim down the nFD mount ring to about about 1.5~1.6mm OD. The OD of ring is 3mm orignially, but there is 0.5mm protrusion at the outer edge that presses against the aperture ring (to provide a nice feel of click for aperture changes). Then simply attached the M42-EOS adapter (1.5mm or less OD). Follow up with the built-in infinity adjustment of the lens.
2. Breech lock SSC:
The total OD of the attachment must be 2.5mm
Trimming the existing light baffle OD from 1.5mm to 1mm, fabricate a cover behind the aperture ring and install the M42-EOS adapter. Adjust for the infinity.
If you need to reduce the optical length further to make a M42 compatible lens, then you have to disassemble more to trim down the rear mounting surface for the SSC, while for the nFD you just ditch the nFD mount ring completely.
The aperture linkage that is needed to be done is quite similar in nature (though varies from lens to lens.)
Well, may be the twin balls of the SSC's aperture ring can be a hell to install right at the same time .
And, the 300mm F2.8L is more difficult to convert than the 300mm F2.8 Fluorite! Because in the L, the aperture assembly utimately is resting on the nFD's central baffle tube that is removed during the conversion. So you have to cut out the baffle tube and re-install it somehow. OTOH the aperture assembly of the Fluorite is a pretty ordinary one, just a very long ~ long lever is what is required to do the trick.