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Prism Diagonal

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#51 grendel

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Posted 29 January 2012 - 02:50 PM

oh and when I use a diagonal its always a prism one - I even have a .965" / 1.25" hybrid prism diagonal.
Grendel

#52 EastAnglian

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Posted 29 January 2012 - 07:43 PM

Max I have to say that with that pier and a 1250mm f/l scope near the horizon I am standing my 6'4" on the step next to the pier, and when looking at the zenith 'straight through' I am sitting on the step with the eyepiece just a few inches from the pier and quite low really. but the mount is really super steady on that 1/2" thick 6" diameter cardboard pier - that weighs in at about 20lbs.
Grendel

Hi Grendel!
From my home position I can't observe anything near horizontal, and due to atmospheric conditions, don't do anything serious below thirty. Using that info as a starting position, actually diminishes the up/down eye movement considerably. I like to sit when I observe, preferably almost recline, so a comfortable astonomers stool with notched risers in fairly small increments, within safety limits should suit me fine. I hear what you're saying about closeness to pier, and will either make a simple alt/az balanced mount with large altitude projection, or just simply not observe at zenith. On that note, re your other post, although I'm going to give it a go in not using a diagonal, I have to say that I've never seen a hybrid .965/ 1 1/4" PRISM diagonal; where did you get it?
Cheers
Max

#53 grendel

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Posted 30 January 2012 - 04:43 AM

I picked both mine up from telescope house - in their box of odds and ends, one is a 45 degree hybrid diagonal, the other a standard diagonal. not even sure what brand they are. maybe I just got lucky or they took a standard .965 diagonal and happened to have a 1.25 eyepiece holder that fit the same thread.or a standard 1.25 and had a .965 nose that fit the thread - never really thought about it much, it was just available when I went in and asked - just £10 each from the bits box too.
Grendel

#54 EastAnglian

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Posted 30 January 2012 - 08:57 AM

Very nice too! I have a couple of standard plastic bodied mirror type, but haven't seen a prism in this configuration.
Cheers
Max

#55 Sarkikos

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Posted 30 January 2012 - 10:36 AM

FWIW, a couple years ago I experimented with five different prism and mirror diagonals on my ST80 (80mm f/5 achromat). The diagonals included 1.25" and 2" mirror diagonals, dielectric and otherwise. I used several 1.25" prism diagonals, correct image and reversed image, BAK4 and BK7. I did not see any improvement in CA correction using any of the diagonals.

Recently I acquired a 70mm f/12.9 achromat. I might try the experiment again using all the 1.25" diagonals. Maybe a prism diagonal will improve the slight CA in this scope?

Mike

#56 EastAnglian

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Posted 30 January 2012 - 11:01 AM

Hi Mike,
That's a very interesting experiment you did there. I for one would be very interested to hear the result, if you do something similar with the new scope. It's not often that anybody has such a comprehensive set of diagonals to do such a test.
Cheers
Max

#57 grendel

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Posted 30 January 2012 - 04:33 PM

I just dug my two hybrid prism diagonals out and took some pics, the 45 degree one is a meade and has what is obviously an adaptor thread for the 1.25" eyepiece holder.
the other looks like it might have the same, but I couldnt unscrew it.
Grendel

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#58 grendel

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Posted 30 January 2012 - 04:34 PM

and the two.
Grendel

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#59 grendel

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Posted 30 January 2012 - 04:47 PM

a bit of research shows a 'Meade Diagonal Prism #917 Hybrid' with the 90 degree diagonal and
'Meade Hybrid Erecting Prism #931' with a 45 degree prism
so obviously they were made - both are on clearance at telescope house in the uk for £37
Grendel

#60 EastAnglian

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Posted 30 January 2012 - 06:05 PM

Hi Grendel!
Many thanks for taking the pics, and doing the research! The numbers are particularly useful.
Cheers
Max


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