Re: amici diagonal


Jun 18, 2001

 


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#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

> diagonal?



Hi Jim:



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.



Derek



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#6000 Jun 18, 2001

In a message dated 6/18/2001 8:34:19 AM Pacific Daylight Time,

thefamily@... writes:



> 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.



Roland Christen





[Non-text portions of this message have been removed]



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#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...

-p



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#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@...>

To: ap-ug@yahoogroups.com>

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...

> -p

>

>

>

> To UNSUBSCRIBE, or for general information on the ap-ug list

> see groups.yahoo.com/group/ap-ug

>

> Your use of Yahoo! Groups is subject to docs.yahoo.com/info/terms/

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>



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#18641 Sep 6, 2003

Paul asks:

> 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?



Rob Hunt



By the way - get yourself a Wimberley mount.







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