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General Astronomy >> Beginners Forum

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Classic8
professor emeritus


Reged: 04/12/06

Loc: Naperville, IL, USA
Re: RACI finder scope new [Re: Haas]
      #5834465 - 05/01/13 01:52 PM

Has anyone tried using a GLP attached with velcro? That way you wouldn't have to hold it - not sure if I can get it lined up well enough but it just has to be close. Then the finder would just be needed to confirm I'm on the right star, and for starhopping from there. Plus the laser could be removed quickly.

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Tony Flanders
Postmaster
*****

Reged: 05/18/06

Loc: Cambridge, MA, USA
Re: RACI finder scope new [Re: Haas]
      #5834485 - 05/01/13 02:00 PM

Quote:

Holding a laser through my finder scope seems impractical to me. How could you ever tell that you're holding that laser parallel to the finder scope?




When you shine something backward through a telescope, magnification works in reverse. So any error in alignment of the laser is divided by 9 in a 9x50 finderscope. Certainly good enough to get your initial fix on the sky.


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Haas
sage


Reged: 11/22/12

Loc: Wis., USA
Re: RACI finder scope new [Re: Tony Flanders]
      #5834495 - 05/01/13 02:05 PM

Quote:

Quote:

Holding a laser through my finder scope seems impractical to me. How could you ever tell that you're holding that laser parallel to the finder scope?




When you shine something backward through a telescope, magnification works in reverse. So any error in alignment of the laser is divided by 9 in a 9x50 finderscope. Certainly good enough to get your initial fix on the sky.




I guess I'm not understanding. Why would you be shining the laser backwards through the scope? It wouldn't shine to the sky, it would shine in your eye, no?


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TexasRed
scholastic sledgehammer


Reged: 05/17/11

Loc: East Texas
Re: RACI finder scope new [Re: Haas]
      #5834572 - 05/01/13 02:46 PM

Quote:

Quote:

Holding a laser through my finder scope seems impractical to me. How could you ever tell that you're holding that laser parallel to the finder scope?




I guess I'm not understanding. Why would you be shining the laser backwards through the scope? It wouldn't shine to the sky, it would shine in your eye, no?




Remember that most finderscopes are just small refractors. When you shine the laser into the eyepiece at that back, the light will come our of the objective lens at the front and into the sky, showing you where the finderscope is pointed. You won't need to center the laser or hold it rock steady or perfectly parallel to the finderscope. You just need to point it into the eyepiece of the finderscope to get a green line going into the sky in the same direction as the finderscope.


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Haas
sage


Reged: 11/22/12

Loc: Wis., USA
Re: RACI finder scope new [Re: TexasRed]
      #5834581 - 05/01/13 02:53 PM

Quote:

Quote:

Quote:

Holding a laser through my finder scope seems impractical to me. How could you ever tell that you're holding that laser parallel to the finder scope?




I guess I'm not understanding. Why would you be shining the laser backwards through the scope? It wouldn't shine to the sky, it would shine in your eye, no?




Remember that most finderscopes are just small refractors. When you shine the laser into the eyepiece at that back, the light will come our of the objective lens at the front and into the sky, showing you where the finderscope is pointed. You won't need to center the laser or hold it rock steady or perfectly parallel to the finderscope. You just need to point it into the eyepiece of the finderscope to get a green line going into the sky in the same direction as the finderscope.




So, if I have the laser tipped at a slight angle through the finder scope, it will still come through the scope the same as if I were not tipped?


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Thomas Karpf
Carpal Tunnel


Reged: 02/09/09

Loc: Newington, CT
Re: RACI finder scope new [Re: TexasRed]
      #5834700 - 05/01/13 03:57 PM

Quote:


If you don't like craning your neck to look through your finder or point your scope in the right general direction, just try shining a green laser pointer into the eyepiece of the finder.




It'd be a lot more precise if you just shined the laser pointer through the eyepiece of the scope, right?


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GlennLeDrew
Postmaster
*****

Reged: 06/18/08

Loc: Ottawa, Ontario, Canada
Re: RACI finder scope new [Re: Thomas Karpf]
      #5834760 - 05/01/13 04:42 PM

If one were to aim the laser even so badly as to just skim the field edge (25 degrees off axis fir a 50 degree apparent field) the beam would still point in the sky to a point at the edge of the true field. As long as light gets out the front, you're still hitting somewhere in the finder's FOV. It's not hard to obtain pointing into the eyepiece to within 5 degrees, and 10's a doddle. at 9X, that's to better than a degree on the sky. If one were to get really ICD over it, an adapter could be made up which slips over or abuts the eyepiece so as to obtain very near axial alignment.

Thomas,
As I mentioned in my previous post, with a scope the magnification expands the beam to the point of diluting its photon flux, making it more difficult to see. At 100X, for example, a 1mm beam (which is just about as small as you get) expands to 100mm.

But then the pointing accuracy is much better, if one is uncertain of using the finder for this purpose.


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Haas
sage


Reged: 11/22/12

Loc: Wis., USA
Re: RACI finder scope new [Re: GlennLeDrew]
      #5834766 - 05/01/13 04:45 PM

Quote:

If one were to aim the laser even so badly as to just skim the field edge (25 degrees off axis fir a 50 degree apparent field) the beam would still point in the sky to a point at the edge of the true field. As long as light gets out the front, you're still hitting somewhere in the finder's FOV. It's not hard to obtain pointing into the eyepiece to within 5 degrees, and 10's a doddle. at 9X, that's to better than a degree on the sky. If one were to get really ICD over it, an adapter could be made up which slips over or abuts the eyepiece so as to obtain very near axial alignment.

Thomas,
As I mentioned in my previous post, with a scope the magnification expands the beam to the point of diluting its photon flux, making it more difficult to see. At 100X, for example, a 1mm beam (which is just about as small as you get) expands to 100mm.

But then the pointing accuracy is much better, if one is uncertain of using the finder for this purpose.





Now I understand. So, it's not perfect, but still gets you withing the range of just a nudge or two.


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GlennLeDrew
Postmaster
*****

Reged: 06/18/08

Loc: Ottawa, Ontario, Canada
Re: RACI finder scope new [Re: Haas]
      #5834809 - 05/01/13 05:03 PM

Just to clarify. The idea is to use the laser to know where the finder is *roughly* aimed. Then when putting eye to finder, you already know you're in the ballpark and can rely on getting your bearings immediately.

It's not necessarily to be expected that this will get you to within the main scope's field right off the bat. But you can, with due care.


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newtoskies
Pooh-Bah


Reged: 07/15/12

Loc: SE Ma.
Re: RACI finder scope new [Re: Haas]
      #5834946 - 05/01/13 06:17 PM

oh great, now I am thinking for buying a laser to point through the finder scope. Very cool info fellas, thanks.

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Haas
sage


Reged: 11/22/12

Loc: Wis., USA
Re: RACI finder scope new [Re: newtoskies]
      #5835002 - 05/01/13 06:50 PM

LOL, I know. I had my mind set on a RACI, now I'm thinking about laser also.

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newtoskies
Pooh-Bah


Reged: 07/15/12

Loc: SE Ma.
Re: RACI finder scope new [Re: Haas]
      #5835025 - 05/01/13 07:04 PM

Me too Haas. Been looking at RACI's and trying to find the green laser pointer. I had seen them before, but now that I am interested in it, I can't find them..lol

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Haas
sage


Reged: 11/22/12

Loc: Wis., USA
Re: RACI finder scope new [Re: newtoskies]
      #5835029 - 05/01/13 07:07 PM

Quote:

Me too Haas. Been looking at RACI's and trying to find the green laser pointer. I had seen them before, but now that I am interested in it, I can't find them..lol




I'm looking at one here, but don't know if I should be looking at others or not. This is the only one I've found so far.

http://www.telescope.com/Accessories/Telescope-Finder-Scopes/pc/3/49.uts


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Grandpa Jim
old fogey
*****

Reged: 08/04/12

Loc: GREAT AMERICAN DESERT
Re: RACI finder scope new [Re: newtoskies]
      #5835267 - 05/01/13 09:27 PM

Quote:

Me too Haas. Been looking at RACI's and trying to find the green laser pointer. I had seen them before, but now that I am interested in it, I can't find them..lol




http://www.scopestuff.com/ss_lasre.htm

http://www.scopestuff.com/ss_sfind.htm


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Haas
sage


Reged: 11/22/12

Loc: Wis., USA
Re: RACI finder scope new [Re: Grandpa Jim]
      #5835277 - 05/01/13 09:36 PM

I have to admit something here, maybe irrational, but here goes. One thing that scares me with the laser pointers is, what if I'm pointing out at a star, or moon, or anything else, and that just happens to be an area where an airplane comes into the same line as the laser? I don't want to be in trouble for being accused of deliberately pointing a laser at an airplane. Silly fear, or legit? Of course it wouldn't be on purpose, but accidents do happen.

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Kunama
professor emeritus


Reged: 10/22/12

Re: RACI finder scope new [Re: Haas]
      #5835627 - 05/02/13 03:24 AM

in response to a few comments of the RACI being hard to get to on an Eq mounted Newt, the Stellarvue has a rotateable diagonal to allow a better angle if the scope rotation causes the focuser to be difficult to access.

It also fits beautifully into the Takahashi finder bracket and probably many other brackets, by simply removing the diagonal then installing the finder tube and lastly refit the diagonal. See pic below on my TSA120 in the Tak bracket.



I did have to paint the Stellarvue to better match the Tak TSA, but the benefits of not bending my arthritic old neck to odd angles are well worth it:



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GlennLeDrew
Postmaster
*****

Reged: 06/18/08

Loc: Ottawa, Ontario, Canada
Re: RACI finder scope new [Re: Kunama]
      #5835631 - 05/02/13 03:33 AM

For the brief time a laser is used, statistically speaking an aircraft will be intercepted in its beam at almost vanishingly small probabilities.

I mean, think of it. A plane might subtend an angle of 2 arcminutes. That amounts to an area of 0.0000085% of the 180 degrees of the celestial hemisphere. What do you think are that chances of accidentally illuminating a cockpit?


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Haas
sage


Reged: 11/22/12

Loc: Wis., USA
Re: RACI finder scope new [Re: GlennLeDrew]
      #5835863 - 05/02/13 09:30 AM

Quote:

For the brief time a laser is used, statistically speaking an aircraft will be intercepted in its beam at almost vanishingly small probabilities.

I mean, think of it. A plane might subtend an angle of 2 arcminutes. That amounts to an area of 0.0000085% of the 180 degrees of the celestial hemisphere. What do you think are that chances of accidentally illuminating a cockpit?




I dunno, I'm a little leary going strictly by chance, even when the odds are in my favor. Ever hear the joke, "when it's a 50/50 chance, there's a 95% chance I'll pick the wrong one"? That's me!
I'm fairly close to the Milwaukee airport too. I think I'll try the RACI, and if I still have issues, then I'll give the laser a whirl.


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newtoskies
Pooh-Bah


Reged: 07/15/12

Loc: SE Ma.
Re: RACI finder scope new [Re: Haas]
      #5835921 - 05/02/13 10:01 AM

Haas I was looking at the Orion one too, after my comment above. I hadn't realized they were that expensive. I'll just get a RACI first, then wait for when the budget allows for another toy.
I have the RIGEL finder but only used it once. LP here so the Rigel didn't help me much....yet.


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Haas
sage


Reged: 11/22/12

Loc: Wis., USA
Re: RACI finder scope new [Re: newtoskies]
      #5835954 - 05/02/13 10:19 AM

Quote:

Haas I was looking at the Orion one too, after my comment above. I hadn't realized they were that expensive. I'll just get a RACI first, then wait for when the budget allows for another toy.
I have the RIGEL finder but only used it once. LP here so the Rigel didn't help me much....yet.





LP= ?

Nevermind, just dawned on me "light pollution".

Edited by Haas (05/02/13 10:20 AM)


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