I haven't received Chuck's email that James is replying to.
What I came across was that the MTO lenses were first built in the 50's or
perhaps even earlier. They were used on Russian cameras that had a pretty
short "flange back" distance. The first ones used a 39mm thread mount while
the later ones used a 42mm thread mount. Arasat is currently selling some
that cover a 6x6 image. Maybe the secondary mirror is larger than necessary
for 35mm ? ... blocks more light than necessary but allows the infinity to
be shifted without vignetting?
I don't know if the short distance is helpful/detrimental to spotting
scopes. The lenses have very little clearance between the large diameter
back of the lens and the camera. Maybe this is what the sites meant by
flange back distance(I took it to mean flange to film but ... sort of the
same thing). Some of the lenses have added an optical element but apparently
not all. People are putting spacers on them and re-adjusting the infinity
focus. In some cases it looked like the spacer was nearly 1/2 inch thick.
The prism housing / pop up flash on many newer cameras interfere with the
back of the lens. An old posting (perhaps to this mailing list) mentioned
that OM cameras with the shutter speed control on the flange presented a few
limitations ... using an OM-1 or OM-3 having an impossible to reach speed
control with a fixed aperture lens.
The link I posted led to some short comments about the founders of
Spiratone, Cambron, and others. I think I have a Cambron 400/8 or 500/8
refractor that had pretty good specs for a $50 lens. It was physically so
long that I seldom used it. I wonder if James bought his lens because it
received similar good reviews ...
-jeff
-----Original Message-----
From: James N. McBride
Subject: [OM] Re: 500/5.6 Rubinar / MTO Catadioptric lens
I had a Spiratone 400mm and it was a camera lens and not a spotting scope
format. I think most of their lenses used the t-adapter. /jmac
-----Original Message-----
From: olympus-owner@xxxxxxxxxx [mailto:olympus-owner@xxxxxxxxxx]On
Behalf Of Chuck Norcutt
I found this a bit confusing. I well remember Spiratone and bought a fair
number of things from them in the late 60's and early 70's. I also remember
the Russian MTO and also the stories that the Spiratone 500 mirror lens was,
in fact, an MTO lens.
What confuses me is your comment about adjusting the mirror to move the back
focus out to make it suitable for an SLR. The implication is that the MTO
is a spotting scope rather than a camera lens. Maybe you're right but I
remember the MTO and Spiratone 500's as T-mount lenses and thus designed for
SLR use from the get-go.
OK, all you oldies out there (most of you except Ali), which of us is
correct?
Chuck Norcutt
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