What Type of Telescope Finder Gives the Best Results?

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Newtonian Telescope and Traditional Finder.
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Newtonian Telescope and Traditional Finder.

What Does the Finder Do?

The finder, or finder-scope, is an important part of your telescope.  It is a small, low magnification wide field telescope attached to your main telescope tube which is set-up so that the crosshairs that you see when you look through the finder's eyepiece precisely line up with the centre of the field of view of the main scope, even at medium-high magnifications.   When you sight an object through the finder you then switch your eye to the main telescope and the object should be close to the center of the field of view.  Finders feature on all kinds of telescope and are an essential aid to finding objects that are too faint for the eye to see.
Red-Dot Finer Types, Sadly in Common Supply.
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Types of Modern Finder Often Supplied...

Lots of modern telescopes have Red Dot finder types (left).
These won't show you anything you can't see with your eye.  But finding bright objects is easy.  Using both eyes open for ease of use, the red  dot you see when you look at it from 50cm or so stays in the same place even if you move your head a bit. 
These were designed to help Go-To telescopes sight on the bright stars they need to set-up.  Consequently, they didn't need to magnify or show anything that the unaided eye can't see.  Unfortunately, however, they became the 'cheap' option for beginner's telescopes but would help you locate bright objects only.  As you progress you'll want more than that!
Straight-Through 6 x 30mm Finder.
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Straight-Through 6 x 30mm Finder.

Traditional Finder Types.


The magnifying, light gathering finder
allows you to find objects that are too dim for the eye to see. 
For example, if you were wanting to observe M27, 'The Dumb-Bell Nebula', in Vulpecula you would be best advised to have a light-gathering, magnifying finder.  To find this Messier Object without a finder needs a bit of estimation and luck.  The 6x30mm finder would show it as a small fuzzy blob that can be put on the cross-hairs.

A 6 x 25mm Right-Angle Finder.
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A 6 x 25mm Right-Angle Finder.


Some telescopes come with a right-angle finder.  This has a diagonal mirror to re-direct the light from the main lens to an eye-piece that is in the same direction as the telescope's eyepiece.  These are usually found on Newtonians (and some SCTs).  This type of finder can be tricky for the beginner as the telescope is pointing at 90 degrees to the line of sight of the observer.  A little practice may be in order to get used to this strange feeling to begin with.  But they perform well.
Zennox 70mm Refractor and 15mm Finder.
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Zennox 70mm Refractor and 15mm Finder.

Size - An important consideration.

Some telescopes are supplied with finders that are woefully small for the telescope they serve.  A finder of at least 25mm is recommended, and 30mm is much more desirable for 150mm telescope.  A 40mm or 50mm finder-scope is more suitable for 200mm reflectors and larger. 
If you think about the light gathering power of successively larger telescopes. They will enable you to aspire to observe fainter, more difficult objects.  To give yourself a chance at seeing these in the finder, the finder has to collect more light -  So, naturally, larger telescopes require larger finders.  As a rough guide, your finder should be a minimum of one fifth (20%) of your telescope diameter. (But never smaller than 25mm!)

The reason for this recommendation is that if you're hoping to line your telescope up on Neptune, or the fainter Messier Objects, you have to bear in mind that the object is somewhere around magnitude eight to nine and to find it easily in the finder, the finder has to gather a good deal of light too!  The 70mm Refractor in the picture (above) had a finder of just 15mm diameter when bought - I couldn't see much of anything fainter than magnitude +4.  This made it impossible to find even Uranus, at magnitude +6.  You should be able to see objects of at least magnitude nine in your finder to be able to reliably locate many of the objects you want to see.
The Flagpole on the Imperial Hotel in Crosshairs.
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The Flagpole on the Imperial Hotel in Crosshairs.

Lining Up Your Finder.


Lining up a finder is done in the daytime, using a distant object.  I used to use the golden ball on the top of the flag-pole on top of the Imperial Hotel in Blackpool as my finder target object as it was visible from my dining-room window (Yes, you can even line up your finder from the comfort of the indoors - We're not interested in viewing quality, just accuracy.).
Find the object in your telescope using a low power and then lock the axes.  Change to a medium power of 50 - 80x, making sure you still have the object centered in the eyepiece, and then look through the finder.
If you're really lucky the object will still be on the crosshairs.  If not, then a little adjustment is necessary. 
Start by loosening one of the adjusting screws and then tighten the oposite screw a little...  See what difference this has made. 
Adjustment screws.
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Adjustment screws.



The next step is to continue to make fine adjustments until the crosshairs of the finder are exactly on the object while the object is in the very center of the telescope view.  Then, gently tighten all adjusting screws making sure the alignment doesn't go off.
The reason you do this in the day, using an Earthboud object, of course, is because all astronomical objects move and you would be fighting a losing battle trying to make sure your object was in the center of both views, as the world turns for its amusement! 
A finder with two adjustment rings.
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A finder with two adjustment rings.



Some finders have two rings with adjustment screws.  This is for fine adjustments.  In normal use you would center the tube in the front rings and then make all adjustments to the alignment using the rear screws.
These types are prevalent on older designs and photographic models mainly.  Most finder mounts have a front ring that fits snugly to the tube and the adjustment screws are in the back of the housing or second ring only (As seen on the 6x30 finder above).

Saturn on the Crosshairs.
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Saturn on the Crosshairs.

Using the Finder to Locate an Object.


When you want to find an astronomical object first you point the telescope in the approximate direction squinting along the tube of the telescope. 
Then you transfer your eye to the eyepiece of the finder and make small adjustments (With slow motion knobs) until the object is sitting right at the intersection of the crosshairs.
Then you can transfer your eye to the main telescope eyepiece and focus. 
You then follow the object using the slow motion controls, or motor drive if you have them.
The Good, The Bad and The Ugly!
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The Good, The Bad and The Ugly!

So - Which is the best?


It really depends on what you want to look at to be completely honest.  There are many beginners who want to look at galaxies and nebulae and for them, the best is the light gathering magnifying finder because the things they want to see are faint and the eye needs help to locate them.

The planetary observer can manage with the Red-Dot type to observe Mercury, Venus, Mars, Jupiter and Saturn and our dear Moon, and lots of bright stars! 

However, if you want to observe Uranus, Neptune and the Asteroids (approximately 10 visible in a small telescope) then, once again, you need the light gathering magnifying finder. 

Here's a telescope with an 80mm Finder!
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Here's a telescope with an 80mm Finder!

Conclusion.


So, I think, on balance, that the light-gathering magnifying finder would be useful for many, many more objects than the Red-Dot finder.  And it is the traditional light-gathering magnifying finder that I would recommend.
If you buy, or already have, a telescope with a red-dot finder you can use it to look at bright objects while saving up for a replacement light-gathering magnifying finder, should you think you need one to locate those faint objects.  Not too expensive at around £25.

Most telescope types that come with Red-Dot type finders have a replacement light-gathering magnifying finder available as an optional extra.  
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IF IN DOUBT - PLEASE ASK!


IF I CAN BE OF ANY HELP I AM MOST WILLING TO ANSWER QUESTIONS ON TELESCOPES BY E-BAY MESSAGE.






I will answer as soon as I can and it's no bother – Honestly!
I have nothing to do with SkyWatcher telescopes, neither do I sell telescopes professionally (I do sell on eBay from time to time as I upgrade). 
The information in this guide is my own opinion and can be taken as my best honest advice. I have over forty years experience in astronomical observation.
SuperCooper

Clear skies and good seeing... I hope this guide has been useful. :o)

More information? Google "supercooper telescope help".

All text and images © Barry Cooper 2008-16 unless otherwise credited.
Paul Money's website is called Astrospace.

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