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farmer kev
scholastic sledgehammer
Reged: 04/27/08
Posts: 814
Loc: Iowa, Sol IIIa
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Well I did a search of diagonals and didn't see anything like this but I still doubt its and original idea.
I would like to make a diagonal with an angle between the optical axis of 60 to 75 degrees for viewing with refractors pointing straight up. In the past fifteen years skyglow from nearby towns and the higher humidity of my current opserving sight plus my failing eyesight has rendered everything below 45 deg hard to view.
Before I go reinventing the wheel has this been done before?
Am I missing something that makes this a fools project?
My plan at this time is to make a 60 deg one that fits a 2" focuser and 1 1/4" eyepieces.
I had originally planned on making one 2" in and out but that takes a much larger mirror and would be much heaver and bulkier.
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Have towel, will travel.
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Moki
super member
Reged: 11/06/05
Posts: 349
Loc: Dallas, GA
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I've seen spotting scopes that have an angled eyepiece < 90 deg., on the order of 20 or 30 deg IIRC. They also have an image erection prism that you probably wouldn't need.
I assume you're considering the optical axis through the eyepiece at < 90 deg to the objective's axis. Don't see why it wouldn't work. You might want to mock something up first and try it to see how the "neck" angles work out, though. From what I've seen of how most refractors are mounted, a less than 90 deg angle at the eyepiece when near zenith would be hard on my neck, for sure.
What would be really cool (but not easily built, I suspect) would be to have the eyepiece mounted on a "turret" affair that would allow setting the angle to what ever is comfortable to you, even > 90 deg to the normal axis.
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"In questions of science, the authority of a thousand is not worth the humble reasoning of a single individual." Galileo
12.5" F5.3 Dob on EQ platform
8" F7 planetary Dob / EQ Platform
Current ATM projects:
Xtal-Controlled EQ platform motor drive
8" F6 Dob for club
Motorized focus for planetary
10" F6 Ultralight PushTo
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farmer kev
scholastic sledgehammer
Reged: 04/27/08
Posts: 814
Loc: Iowa, Sol IIIa
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Quote:
I've seen spotting scopes that have an angled eyepiece < 90 deg., on the order of 20 or 30 deg IIRC. They also have an image erection prism that you probably wouldn't need.
I assume you're considering the optical axis through the eyepiece at < 90 deg to the objective's axis. Don't see why it wouldn't work. You might want to mock something up first and try it to see how the "neck" angles work out, though. From what I've seen of how most refractors are mounted, a less than 90 deg angle at the eyepiece when near zenith would be hard on my neck, for sure.
What would be really cool (but not easily built, I suspect) would be to have the eyepiece mounted on a "turret" affair that would allow setting the angle to what ever is comfortable to you, even > 90 deg to the normal axis.
I have seen those spotter scopes listed with 45 deg diagonal, to my way of thinking they are 135 deg but thats just a POV proablem. However by their convention I'm talking about making a 105 or 120 deg mirror diagonal.
And yes I had thought about a diagonal that allow 30 to 45 deg of angle adjustment, might only be worth it for somebody with serious mobility issues.
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Have towel, will travel.
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jcjr
professor emeritus
Reged: 01/06/08
Posts: 563
Loc: TN, USA
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If DIY a diagonal, I think a >90 degree mirror would be an 'easier spec' because it would not have to be so long in the 'on axis' direction. And a <90 degree mirror would be a 'harder spec' because the mirror would have to be unusually long in the on-axis dimension?
With a 90 degree diagonal, the length (hypotenuse) of the mirror would need to be about SquareRoot(2 * (Width Squared)), so a 52mm width would need to be about 74mm long.
Which seems to bear out, given the size of this WO replacement dielectric diagonal mirror:
WO Dielectric Mirror
Just thinkin, one could use a mirror proper-sized for 90 degrees, and it ought to be 'plenty big enough' for any angle >90 degrees. For a <90 degrees diagonal, the mirror would need to be longer in comparison to its width.
I think a >90 degree diagonal would want more in-focus from the focuser, because it would need a longer optical path than a 90 degree diagonal.
Compared to a 90 degree diagonal, the >90 degree diagonal would have to move the eyepiece further away from the mirror to keep the eyepiece barrel out of the optical path. So if light travels further inside the diagonal, then obviously the diagonal would need to move closer to the objective?
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CPC 1100, C102SLT, SV F80, Meade 70 & 60 AZT
Q70 38mm, Pan24, Meade 5K 18mm UW, Axiom LX 15mm, Nagler 13T6, Axiom LX 10mm, Expanse 20mm, 9mm, 6mm, BO/TMB 5mm, 2.5mm
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DAVIDG
Pooh-Bah
Reged: 12/02/04
Posts: 1449
Loc: Hockessin, De
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You can simply put two standard 45 degree star diagonals together and just rotate them to any angle you wish. Here is a crude drawing that hopefully explains the idea.
- Dave
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Homemade 'scopes 8"f/7,6" f/5", 6"f/4, 4.25" Schief. 60mm Coronagraph,60mm H-alpha system, 4.25" White-light Solar Newtonian,solar spectroscope, 4.5" f/16 Schupmann Medial refractor, 14 Stellafane awards 7 in optics
Engineering = Taking what you have and making what you need.
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moron392
scholastic sledgehammer
Reged: 08/20/07
Posts: 808
Loc: Charlotte, NC
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just put in a 45* diagonal into your 90* diagonal.
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"If you've done something right, people won't be sure you've done anything at all."
http://www.freewebs.com/moron392/index.htm
60mm meade ngc60 refractor.
Meade 70AZ-TR (short one)
50mm homemade refractor (occasionally with a solar filter)
starblast4.5EQ
6mm,15mm expanse eyepieces
9mm meade Mh eyepiece,17.5mm Meade MA
nikon 7x35's
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