Good point, Vaughn. I plan on doing just that! I'll post in a couple weeks.
-Mickey
----- Original Message -----
From: "Vaughan Bromfield" <vaughan.bromfield@xxxxxxxxxx>
To: <olympus@xxxxxxxxxxxxxxx>
Sent: Sunday, March 18, 2001 8:18 PM
Subject: Re: [OM] mirror lenses......puzzling
> So far the only observed discrepency has been with the *meter* reading
> and viewfinder image, both of which may be fooled by the annular
> aperture in the reflex design. The actual image may not be affected at
> all: to find out, make some exposures with slide film, bracketing around
> the expected and indicated exposure, and see what happens.
>
> So go out and expose some film... please. It's the only way to
> definitively end the debate.
>
>
> Vaughan
>
> --
>
> > Date: Sat, 17 Mar 2001 12:58:59 +0100
> > From: Thomas Bryhn <thomas.bryhn@xxxxxxxxxx>
> > Subject: Re: [OM] mirror lenses......puzzling
> >
> > At 19:24 16.03.01 -0500, John Raymond wrote:
> > > I would say with the mirror the viewfinder appears to be
> > >atleast an f8 or slower. I am puzzled.
> >
> > That is puzzling. f/8 means you you loose 65-700f the light somewhere
in
> > the optical path. The mirror coatings would have to be *very* bad to
> > account for that, and this thing is only like 20 years old.
> >
> > >The confusion I have is that I have read from other mirror users that
this
> > >loss of light is common and the f stops are not accurately described on
> > >mirror lenses. I thought then I wasn't alone.
> >
> > Nothing is perfect, but I would assume a lightloss about 0.3 stops,
> > certainly nowhere close to 1.5 stops. Check out the measurements at
> > http://brashear.phys.appstate.edu/lhawkins/photo/mp-cat-tests.txt
> > The worst is the Vivitar 600/8 at f/8.9, and that's almost exactly 0.3
stops.
> >
> > > The only thing I can see possibly causing problem (this
> > >might be huge) is that the lens I have doesn't have the UV filter on
the rear
> > >end. I am not sure that it is part of the optical formula as it would
sit
> > >right against the last real element anyway.
> >
> > A missing *flat* filter will not cause lightloss, on the contrary, but
any
> > rear mounted filter should be part of the optical formula, as it
otherwise
> > will cause spherical aberration. You should always leave a filter in
there.
> >
> > >Also, the t-mount doesn't stop in accordance to the built in-non
movable
> > >tripod mount. If it were to be on a tripod I would have to tilt the
platform
> > >quite a ways to bring it to "flat".
> > >I have heard that some t-mounts can be adjusted to get this
alignment-maybe I
> > >have a bum t mount as well? : )
> > >I will also research this.
> >
> > A T-mount adapter will usually have an inner ring that can be rotated
after
> > losening 3 or 4 screws. Is it possible that your T-mount has a very
small
> > opening thereby causing serious vignetting? If not, take the whole thing
> > back to the shop or have another shop look at it. You've probably paid
good
> > money to have f/4.5, not f/8.
> >
> > >Thanks Thomas for your thoughts and any others who have responded or
will.
> >
> > You're welcome, hope you can sort this out! Now, if anyone knows of
another
> > fast mirror lens, a Celestron Comet Catcher, for sale, (500mm f/3.64)
I'd
> > love to hear about it.....
> >
> > Regards,
> > Thomas Bryhn
> >
> > ------------------------------
> >
>
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