At 12:08 AM 7/20/2002 -0500, John you wrote:
At 23:23 7/19/02, you wrote:
I would guess that your meter is fine. It may be that the SC lenses are
actually transmitting less light than the MC lenses. One of the benefits of
MC vs SC is supposedly better light transmission. As an example I have a
Soligor 200 f/2.8 that is really much closer to f/3.5 or so.
A better test would be to meter through the camera and shoot some slides
with the lenses to make comparisons. I suspect the slides will be similarly
exposed.
Jim Couch
The difference between SC and MC would not cause entire stops of
difference. To slow by an entire stop requires a 500ss in light
transmission! It's difficult for me to imagine a 1/6 stop difference, and
that's if the lens formulation is unchange. Lens formulations compensate
for losses in light transmission. Although the theoretical absolute
aperture diameter is focal length divided by the aperture f-number, in
practical lens design, absolute aperture diameters are adjusted to an
"effective" diameter to produce the required f-number.
But John, you are forgetting the photon wear factor. Since SC lenses are
subject to greater photon wear, often exacerbated by a silvernose and its
"dancing photon malaise," SC lenses frequently get somewhat rounded out on
the inside, like an old used up bearing. The effect of photon wear is to
create pits and caves to which the photons stray and lurk. This
incidentally is why the rubber focusing rings stretch and come off these
old lenses -- the "lurking photon syndrome." Photons should not be allowed
to lurk. It's dangerous. They work their way through the metal and things
then start to go wrong with the mechanics of the lens. Stuff starts
falling off -- focus rings, paint. Screws loosen. Nasty.
The reason the lenses seem OK with an OM-4 meter and not the OM-1 is also a
result of lurking photons. The OM-4, being newer and probably superior in
every way to the OM-1, can ingest lurking photon residue and mask its
effect for some period of time, although we are starting to see some of the
effects of using SC lenses on especially the older OM-4s now. But the
effect of SC lenses on OM-1s is unmistakable after years of this
unfortunate association.
We may see this effect even with OM-4s and MC lenses. The photon speeders
in MC coatings are certainly helpful in reducing the possibility of photon
wear and consequent lurking, but the best bet is simply to convert to
digital. The D/A converter in a digital camera simply scours photons! It
is still too soon to know the ultimate price to be paid for photo scouring,
but the prognosis is good because these cameras will all be in landfills
before the effect can even begin to be measured. Life is good.
Joel W.
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