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How to Align your Finderscope without Embarrassment
Submitted: Thursday, 10th April 2008 by Michael Viset

I admit to buying a cheap eBay Telescope, with an equally cheap finder scope.  I resolved the finder scope problem with the plywood Finder scope mount for cheap eBay telescopes and a $39 red dot rifle scope, also from eBay.

So now to align them. 

Problem

The instructions that came with the telescope say to focus the telescope on a distant object in the daytime, then focus the finder scope on that.  I presume this is also how the “experts” do it?

The problem is that like many of us I live in suburbia.  Without leaving my back yard, I have trouble finding a sufficiently distant object,  A neighbour’s TV aerial was as distant as I could get without going out on the street.  I didn’t want to look like a dork. 

I’m no astrophysicist but something told me that there would be an error if you align the finder scope and the telescope on a nearby terrestrial object (that’s one on the land) vs an almost infinite object, being the celestial body (that’s one in space).  My plywood finder scope mount brought the two even further apart, so the error would be accentuated.  But the point of making the rigid plywood mount with red dot was to allow greater ease and precision of alignment of the two, so I had to find a better way. I was determined to not to leave the anonymity of my backyard to do this alignment.

Concept

I came up with the idea to use “parallel alignment” rather than distant object alignment.  The experts probably have better terminology for this, and do it all the time, but this is a beginner’s guide.  The concept is to:

  1. Measure the orientation and distance between the main scope and finder scope
  2. Duplicate this on paper, marking which one is which.  This is the “target” paper
  3. Attach the target paper to a solid object (fence, car, house) a reasonable distance away, at the same approximate height as your telescope.  You don’t have to leave your backyard so you don’t have to look like a dork. 
  4. Focus the main telescope on the “Main” mark
  5. Adjust the finder scope to the “Finder” mark. 
  6. If you have the initial measurements and angles right on paper the alignment should be close to perfect for an object an infinite distance away
Result

I did the measurements with a ruler, and I would say they are within 1 cm, but not more accurate than that – try measuring it yourself!  actually put the target on the fence across the road, maybe 30m away, but my telescope never left the back yard, so my anonymity is still preserved.

When I eventually did point it at something several kilometres away I was absolutely staggered as to how precise and steady the alignment was.  It was right on, even with the 4mm cheap eyepiece that came with the telescope.

This telescope is potentially to be used by school kids, and the mount was possibly to be removed for varnishing to make it look pretty.  My teacher friend and I hastily wrote the attached procedure out and copied the alignment marks in case a student or colleague had to realign the finder scope. 

The word “Main” is upside down and inside out so it appears right way up in the “main” scope.

Finder_scope_alignment.jpg

Click to Enlarge
Target sheet
Finder_scope_alignment.jpg 155.88 KB
Full size target sheet
Application

I used it for the plywood “Cheap Telescope Finder Scope mount”, but I’d say it can be used for any telescope anywhere where you don’t want to or can’t practically focus on a distant object without effort or embarrassment. 

You will have to measure the angles and distances on your own telescope, and make up your own sheet.

The further away you can get the target and still see it then the more accurate it will be, but really, you don’t have to go past the short focus of your telescope.  Once you are parallel it doesn’t matter how far you go.

IIf the telescope is transported to a remote viewing site (eg these star parties I have read about) you would only have to mount the sheet temporarily 20m away, to quickly check and adjust the alignment.  A spirit level would make it even more precise.

Future?

If you wanted to be really clever you could make a permanent one up for your scope from plywood or cardboard, and use single red and yellow leds (Dick Smith, Jaycar – oh, and also eBay) for your target so it can be done in the night.

Project Cost

 – Almost zero
Satisfaction – Priceless!

Article by Michael Viset (Michael V). Discuss this article on the IceInSpace Forum.

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