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Thread: Aligning the Finderscope

  1. #1
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    Question Aligning the Finderscope



    So I tried out my Newtonian for the first time last night. Must say we had exceptionally clear viewing conditions for being so close to the light-polluted city. I was trying to do a two-star align, which requires centering each of the stars in the finderscope first followed by centering each of them in the eyepiece. However, what I see in the eyepiece is not necessarily what I see in the finderscope. No matter how much I adjusted it, as soon as I go to the next star, it is out of alignment again.

    My question is how do I know that my finderscope is properly aligned so that whatever I see in the finderscope is at least going to appear somewhere in the eyepiece for every subsequent object I point to?

    I was trying to align with Sirius, for example. Sirius is a very obvious star, so it's hard to miss. When I centered it in the finderscope, it wasn't anywhere to be seen through the eyepiece. I had to move the tube around slightly and hunt for it, and eventually found it.

    Here's what I'm trying to infer from the situation: If you have the object in the eyepiece, it makes sense then to just adjust the finderscope so that the object is also in the middle of the crosshairs for the finderscope. Is this how everyone else does it? Maybe I just wasn't precise enough?

    Opinions, suggestions, and criticisms. Let it flow.
    Last edited by Ramsey; 10-15-2017 at 10:27 PM.

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    Default Re: Aligning the Finderscope

    Hi,

    Align your main scope and finder scope during the daytime using a distant recognizable object. This method is soooo much easier than trying to do it at night. For example, find a distant stop sign or lone tree on a ridge or a Cell antenna in your main scope by pointing it from the back. Once the object is centered in the main scope move to the finder and adjust it so that same object in the center of the finder. Then go back to the main scope to make sure it didn't move while you were adjusting the finder. Do this as many times as needed till everybody is looking at the same thing.

    Cheers,
    JT
    Last edited by jaetea; 10-15-2017 at 10:41 PM.
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    Default Re: Aligning the Finderscope

    If you have a Telrad finderscope mounted on a Dob Newtonian, then do this. Every night when I pull the scope out I find a really bright star that is unmistakable, put in my lowest power eyepiece and center the star in the low power eyepiece. Then I move to the Telrad. The Telrad has two small set screws that adjust the finderscope views, which need to place the centered star exactly in the crosshairs. Then I move back to the eyepiece views to be sure I didn't take so long that the view has changed. I repeat that process until it is perfect. You could then repeat with a higher power eyepiece but low power is all I need. It really is critical to do this every time, since the Telrad can shift when you take the cover off the scope and move it outside. Finding targets with an unguided Newtonian can be problematic and if you're a little out then you'll waste a lot of time.

    You mention a two star alignment technique, so presumably you are trying to set up a guided scope. There are extra steps for that process, though you always start by verifying and adjusting the finderscope to point at the same target as your scope.
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    Default Re: Aligning the Finderscope

    Quote Originally Posted by spelunkerd View Post
    If you have a Telrad finderscope mounted on a Dob Newtonian, then do this. Every night when I pull the scope out I find a really bright star that is unmistakable, put in my lowest power eyepiece and center the star in the low power eyepiece. Then I move to the Telrad. The Telrad has two small set screws that adjust the finderscope views, which need to place the centered star exactly in the crosshairs. Then I move back to the eyepiece views to be sure I didn't take so long that the view has changed. I repeat that process until it is perfect. You could then repeat with a higher power eyepiece but low power is all I need. It really is critical to do this every time, since the Telrad can shift when you take the cover off the scope and move it outside. Finding targets with an unguided Newtonian can be problematic and if you're a little out then you'll waste a lot of time.

    You mention a two star alignment technique, so presumably you are trying to set up a guided scope. There are extra steps for that process, though you always start by verifying and adjusting the finderscope to point at the same target as your scope.
    Sounds consistent. I'll try to do that. I guess it's an acquired skill really. But then again, I knew when coming into this that it wasn't going to be easy. Thanks, Spel.

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    Default Re: Aligning the Finderscope

    Quote Originally Posted by Ramsey View Post

    Here's what I'm trying to infer from the situation: If you have the object in the eyepiece, it makes sense then to just adjust the finderscope so that the object is also in the middle of the crosshairs for the finderscope. Is this how everyone else does it? Maybe I just wasn't precise enough?

    Opinions, suggestions, and criticisms. Let it flow.
    Ramsey,

    That's exactly what I do in my setup, only difference being that I use a camera instead of an eyepiece. The camera's viewfinder/liveview has got cross hairs so this helps to get the centering dead on. If your EP doesn't have crosshairs, you might be out just a tad bit, but it should still be in your FOV.

    Roger
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    Default Re: Aligning the Finderscope

    One thing to remember is that your finderscope has way less magnification than the eyepiece, so while your finderscope could be "in the spot" , your scope actually can't be off of it. A perfect aligments takes time and experience too. When align, use first the lowest magnification eyepiece and then switch to a middle and finally a high power.
    I always use Polaris because it "won't move" in the FOV. If you are going to set the scope before sunset, use an object on the ground that is far away from you.
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    Default Re: Aligning the Finderscope

    When centering a star in the eyepiece, if you don't have a cross-hair eyepiece (most newcomers don't), try defocusing the star till it fills or nearly fills the field of view. This will help insure the star is, in fact, centered. This is a good trick for centering alignment stars for your goto setup, too.

    Although it is easier to align a finder during the day you need the skill to do so under dark skies if the need arises.
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