#5999 Jun 18, 2001
--- In ap-ug@y..., thefamily@c... wrote:
> Is there a way to make an optically excellent Amici> diagonal; or
> is there a way to unreverse the fiels L/R in a refractor using a
There are a couple of mirror solutions which do not require the
precise roof tolerance of an Amici prism. The first is using half an
EMS unit from a binoscope at www.binoscope.com . This method is
described in the Nov 1982 S+T magazine. Unfortunately this would be
outrageously expensive and may require more backfocus than you
have...unless you get another 9" f/15 to use as a twin :-)
Go to www.williamoptics.com under "What's New". There is a new
accessory "super erect mirror diagonal" which has a spec of 1/8 wave.
This is a pure guess but I believe this diagonal will use a similar
two mirror scheme as the EMS unit above. You would have to test it,
of course to see whether it was the claimed accuracy.
#6000 Jun 18, 2001
In a message dated 6/18/2001 8:34:19 AM Pacific Daylight Time,
> My 9" f/15 shows erect images, reversed left and right
Actually, the scope itself shows up and down as well as left to right
reversed, same as any Newtonian. When you put a star diagonal in the back,
the diagonal reverses the up-down only to give you right side up viewing but
a mirror image. Same is true of any Cassegrain used with a star diagonal.
As far as I know, there are no good Amici prisms. To make a precise sub-arc
second Amici requires a lot of fine hand labor. One of my industry sources
charges upwards of $1000 for a precision Amici prism, glass only. The only
way I know how to do this right is to use two very high quality flat mirrors
and place them at a specific angle to mimic an Amici optical path. I believe
someone in Japan has done this, but can't recall who.
[Non-text portions of this message have been removed]
#18636 Sep 5, 2003
Whoops -- I am late to this discussion, so please forgive if this is
redundant. What is the best choice of amici prism for use with a
Traveler. Intended use is mostly (90% plus) for terrestrial viewing. I
noted the new Williams 2-inch amici, but they are unsure whether it
works with the Traveler...
#18638 Sep 6, 2003
the william optics work on the traveller, but clear aperture is no more than
on the Baader T2 amici and the Baader have for shure the better optics
Markus ----- Original Message -----
From: "Paul Saffo" psaffo@...>
Sent: Saturday, September 06, 2003 2:39 AM
Subject: [ap-ug] amici diagonal
> Whoops -- I am late to this discussion, so please forgive if this is
> redundant. What is the best choice of amici prism for use with a
> Traveler. Intended use is mostly (90% plus) for terrestrial viewing. I
> noted the new Williams 2-inch amici, but they are unsure whether it
> works with the Traveler...
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#18641 Sep 6, 2003
> What is the best choice of amici prism for use with a
> Traveler. Intended use is mostly (90% plus) terrestrial.
> I noted the new Williams 2-inch amici, but they are unsure whether
> it works with the Traveler...
Hi Paul -
Here's my eight cents on one of my favorite subjects...
The Williams prism is by far the best choice for your intended
purpose. I've been using one with a Traveler for the past year and I
was using a similar unit for years before that.
For me, the issue is the 45. viewing angle, not obtaining an image
that's correct left-to-right. I've never understood birders who
think a mirror-reversed view is inadequate. (I won't go so far as
Sue French, who, according to Alan, doesn't even care if the ducks
are swimming upside down. I mean, there IS a certain aesthetic
involved. (Fun suggestion for Mr. French - flip the TVs in the house
over and see if she's fine with that, too.))
The ergonomic benefits of a 45. view are the true selling point for
me. Easier on the neck; easier to share; lower, better balanced
scope. The optical trade-offs are minimal if you stick to the
magnification range typically employed by traditional spotting
scopes. If I go above 50x I always switch to the 90. mirror diagonal
as high-power targets are likely to be stationary anyway.
It's true that the clear aperture of the Williams prism is about 31
mm but any vignetting that results from use of eyepieces with wider
field stops such as a 35 panoptic is hardly objectionable - more to
the point, how useful is 17x for terrestrial use? I seldom use
anything longer than a 22 nagler during the daytime. It gives me 28x
with a 3. field and has a field stop diameter of... 31 millimeters.
The Baader 90. prism might very well be a bit better optically but I
still doubt it could be free of annoying aberrations at planetary
magnifications and I would find it about as useful tits on a bull.
What i COULD use would be a good 2" PORRO prism that would provide a
quality straight-thru view up into middle-high terrestrial
magnifications. Anyone know of such a beast?
By the way - get yourself a Wimberley mount.