setting circles

[leo82]

Hi all,

When looking for objects to view through the telescope, do you manually find the object using the finderscope or use the ra/dec coordinates on the mount. I'm new to telescopes and would like to learn the best way to use it and use the different features ie setting circles. I've had a look on youtube and on internet but it seems a bit of mixed opinions. Some say they are the best thing since sliced bread whilst others say they are just fancy decorations.

I'm confused.

[Uplooker]

Hi Leo82,

On all but the best mounts setting circles are all but useless for finding things in the night sky. Not sure what mount you are using / referring to but the setting circles are normally used by people to orientate their mount to achieve good polar alignment, when using a polar scope that is fitted to the mount.

The majority of people star hop to find stuff. This is done by ensuring that your finder is properly aligned to your scope. Centre a known star in the finderscope, then using a pocket star atlus or planetarium program like stellarium or Cart du Ceil hop from one star to the next to find your chosen object

Sent from my Fone

[Phil Fargaze]

A mount used for setting circles will be equatorial, so it will need to be polar aligned and the observers latitude set. Then set the RA circle according to the time or find a known object (using the finder scope) and then set the RA circle to the known objects RA. Then other objects should be able to be found by their RA and DEC. However whilst a lot of modern mounts have the RA and DEC scales on them they are not generally accurate enough for finding small objects. This is usually because of the small diameter of the circles. On my HEQ5 the circles are 75mm diameter and give a certain margin of error. A mount designed for setting circle use will have larger diameter circles such as 200mm.

A finder scope is quick and convenient to either find an object or get the scope in the general area of an object, being in dark skies will make a finder scope more useful. A decent aperture on the finder scope will make it more useful. 

I once managed to find The Eskimo Nebula with a mount using 200mm setting circles but it was quite a task and I would have found it quicker and easier by star hopping.

So I guess it depends on what type of mount you might have, and what method you might feel happy using. Of course, if you use a modern GOTO mount the use of setting circles is not required but a finder scope will come in handy to align the mount on target stars. 

[rockystar]

Here's a really good video on YouTube about them: https://youtu.be/geQszAVWMok

I've got an EQ5, thought exactly the same as you, that I should be able to use them to find stuff, but quickly realised that they aren't much use at this size. Takes some practice and trial & error, but I'm starting to get the hang of star hopping now; got a star atlas for Xmas, so just waiting for a clear might sky to put it into practice.

[laudropb]

I am afraid there is no short cut to finding targets, unless you use a go to scope. You have to learn your way around the night sky and how to star hop using a atlas or app. Still I find this great fun.

[Gazabone]

I find setting circles on both my EQ3-2 and NEW6 mounts work wonderfully well. I'm at least as accurate with those as either my GoTo mounts. In my view, I have to say that I would have less success on either an eq1 or eq2 mount (I keep a 102 frac permanently on an eq1 as a grab and go setup and haven't even bothered to try using setting circles on that one!)

Keep an eye on the Cornwall Astronomy Society website, we've just made a video for You Tube on how to use them (they are far easier than reading the instructions that come with the mounts would lead you to believe).

To some extent, you have to be mindful of how much of the sky you see in the ep but that's the same for any method of finding objects!

I use both GoTo and setting circles and find both those approaches far easier than star hopping but I know others will have the opposite view. As with most things in life, it's horses for courses. You won't know which method is best for you until you've given each a fair try. I do like using manual coordinates so much though that I modified my 10" dob to use altitude/azimuth coordinates to find faint objects.

[Jim78154]

I use setting circles extensively. On my 5" refractor I use electronic setting circles. On my smaller grab and go refractor I use manual setting circles, but not the ones that came with the mount. I made up a set. The Az. circle is 12" in diameter and marked off in one degree increments. The RA is 1/2 of an 8" circle and is also marked in one degree increments. Both scopes are on equatorial mounts. It is possible to put setting circles on an Alt/Az mount, but you will need something that will give you the coordinates in degrees. Stellarium will do that. I'm not too sure of Cartes du Ciel. I very carefully polar align my setup and slew to the correct coordinate. After that it is waving the scope around the sky using a lower power eyepiece to acquire the target. The more refined the polar alignment, the less waving around I need to do. I can very consistently slew to within a fraction of a degree of the coordinates and with an apparent field of view of close to 1 degree I can generally find my targets as quickly as the GOTO fellows busy pushing buttons and waiting for their scopes to electronically slew around to their targets.  I can push mine around much more quickly than they can slew theirs and my system costs about 98% less than theirs. A couple of my friends here use an electronic inclinometer  for the elevation and a digital compass for the azimuth and they swear by them. Either of these are available on E-Bay for very little, less than $20 U.S., and no need to polar align. Just point and shoot!

[leo82]

Thanks for the replies.

I have an eq mount albeit a basic entry level one.

As the clouds are a permanent fixture in the sky at the moment I think I will play around with the mount and see if the circles will point me in the general direction of where I want to be looking.

I wouldn't want to rely on it entirely(if it works), afterall starhopping is part of astronomy too.

[brantuk]

Find out how they work by all means - it's good to have curiosity and learn stuff. Just don't expect pinpoint accuracy from them for the reasons pointed out above. They'll get you in the rough area of your target but then it's down to star hopping using the finder to hone in on your object.

[Cosmic Geoff]

My frank opinion of setting circles is that they have been made obsolete by the electronic systems available nowadays under various trade names: Nextstar SLT etc.

I have found that a SLT will, most of the time, place an object within the field of a 25mm eyepiece in a scope of 1500mm focal length. That represents an accuracy of +- 20 minutes of arc or thereabouts. Not bad!

Compare this with the rather small circles on the popular EQ-5 mount. The circles do have a vernier which will resolve the difference between centre and edge of field with the above telescope setup. However, to make the circles effective, the polar axis has to be aligned to within a fraction of a degree, which is easier said than done. Without a polarscope (a £55 optional extra) and a good deal of faffing around, the best you can expect is to get the sought object within the field of the finder-scope, and hope it's bright enough to show up. There is also no guarantee that the optical axis of the telescope is perfectly aligned with the mechanical axes of the mounting.

On starter scopes and on mountings inferior to the EQ-5 the setting circles are almost certainly an mere ornament and marketing gimmick.  I had a Skylux 70X700 scope with an equatorial mount and never found the setting circles on it to be of the slightest use.

So if you want to blind-find dim objects, the most accurate and least time-consuming way to do it in the year 2016 is to use electronics.  I concede that circles can work, but are most likely to be practical in the context of a permanent observatory. And if you can afford that ...

127mm Celestron Nexstar SLT Maksutov,  102mm Sky-watcher Startravel, EQ5 mount, AZ-4 mount, Ross 70mm refractor.