How to use the r.a setting circle

[Unicronicus]

Can someone please, please, please guide me step by step on how to use the r.a setting circle to find an object in the night sky?

We know how to polar align the scope on the declination axis, and having the r.a axis so it is perpendicular to the declination axis. We done this using a method of putting a spirit level on the counter balance bar when it is horizontal, then using the r.a setting circle to measure 90 degrees so we can get it perfectly vertical.

So with the mount now polar aligned, we choose a star close to the celestial equator, such as Spica, and set it so it is perfectly centred in the eyepiece. We then set the r.a setting circle to read its coordinates. Now when we move to another bright, know object we should just align the r.a setting circle to the new coordinates and it should be lined up right? Wrong. It's miles off, and it should be roughly within a couple of degrees of dec at worst if it was working correctly.

Our r.a setting circle moves with the r.a axis, I.e. It's locked as it rotates. I would have thought the setting circle should stay stationary as the r.a axis rotates and the marker on it does the moving. You would then adjust the setting circle to what you are currently looking at before moving off again to keep it in time with the earths rotation.

There are two markers on our mount (eq2), one that moves with the axis (metal one) and the other is static (white line between the 'r' and 'a'. The one on the r.a axis moves with the setting circle when it is locked in place. But if you loosen the setting circle, it doesn't move with the r.a axis but it does sometimes bind which isn't good. So by that basis the marker on the r.a is pretty useless. So how can I use the static marker when the setting circle moves? Do I set the r.a to a known star, then move the r.a axis to + or - the difference in time to the next object I want to look at, instead of its actual r.a coordinate?

[Bizibilder]

To be honest I would ignore the setting circles completely - they are next to useless.  The easiest way to find a target is to "star hop" using a wide field finder or scope.  To do this find a nearby bright object and centre it in the field of view, using an atlas (either paper or computer) slowly move across to your target noting the patterns of stars as you pass them.  it is a tricky technique to start with but with practice you will become quite proficient at it.

The setting circles on your mount are tiny and only read to a couple of degrees at best - as your field of view is half a degree or less you can see why they are generally considered as not much use.  Before the days of computer controlled goto mounts when you had to use setting circles, it was normal for them to be at least 6" (150mm) or 8" (200mm) in diameter, very finely engraved, and used with an eyeglass and vernier scale.  Even then you had to be pretty good to get your target spot on at the first attempt!

[Unicronicus]

To be honest I would ignore the setting circles completely - they are next to useless.  The easiest way to find a target is to "star hop" using a wide field finder or scope.  To do this find a nearby bright object and centre it in the field of view, using an atlas (either paper or computer) slowly move across to your target noting the patterns of stars as you pass them.  it is a tricky technique to start with but with practice you will become quite proficient at it.

The setting circles on your mount are tiny and only read to a couple of degrees at best - as your field of view is half a degree or less you can see why they are generally considered as not much use.  Before the days of computer controlled goto mounts when you had to use setting circles, it was normal for them to be at least 6" (150mm) or 8" (200mm) in diameter, very finely engraved, and used with an eyeglass and vernier scale.  Even then you had to be pretty good to get your target spot on at the first attempt!

We have been using the star hopping technique recently and I think we have been successful with some targets, but it's hard to tell if what we are looking is indeed what is on the stellarium app because the object is either faint or a little bit blurry (nebula in Hercules, bodes etc...). That is why I wanted to get a rough idea of where to point our scope by using the setting circles. I understand that they aren't bob on accurate but to be 6 or so hours out too far isn't it? Hence why I think we are missing a trick...

[cotterless45]

Never used a setting circle. If you use a polarscope, just find Polaris, note the angle to Kochab and put Polaris on the outer circle in that direction and angle.

You'll find Kochab as the brighter pair of stars in Ursa Minor. This is in effect the Kochab clock. Very handy for setting up in darkness and under

Clear skies,

Nick.

[Unicronicus]

Never used a setting circle. If you use a polarscope, just find Polaris, note the angle to Kochab and put Polaris on the outer circle in that direction and angle.

You'll find Kochab as the brighter pair of stars in Ursa Minor. This is in effect the Kochab clock. Very handy for setting up in darkness and under

Clear skies,

Nick.

I think I understand that method, but as our polar alignment is pretty spot on anyway how does this affect the use of our r.a setting circles? I know everyone says the setting circles are next to useless for accurately locating a dim object in the sky, but surely with a wide fov eyepiece the r.a circle should get me somewhere in that region.

[Bizibilder]

If your PA is out by say, one degree, then the setting circles will also be out by a similar amount - they can only be as accurate as the polar alignment and cannot compensate, unlike a goto where the computer can compensate after you have done a three star alignment even if the polar alignment is a little bit out.  Obviously it is better if you have the minimum of "errors" in your overall alignment.

[Unicronicus]

I think we finally fathomed this conundrum out today! Basically there are two manuals for this mount that comes with the skywatcher 130p telescope, the skywatcher one and the Orion eq2 manual. The Orion one says to ignore the top metal pointer and to use the bottom pointer and lower set of numbers in r.a for the northern hemisphere, whereas the skywatcher manual says the opposite.

If you stand in front of the mount with it polar aligned and use the Orion manual method, the setting circle moves with the mount which doesn't make sense. You're moving the coordinates of right ascension instead of moving TO the coordinates if you follow?

But if you use the skywatcher manual, it says to use the top set of r.a numbers for right ascension in the northern hemisphere and use the top metal pointer. This would work IF the right ascension dial stays still whilst you rotate the r.a axis! because it is now the pointer that moves.

The fix. Possibly something as simple as a bit of blu tac. We actually taped a bit of rubber to the plastic cup that sits beneath the r.a setting circle so it touches the edge of the ring, thus creating a small amount of friction. But it is enough to keep the ring in place as you move the telescope through r.a. There is no need to tighten the locking screw unless you are tracking a known object with its r.a coordinates aligned. You just have to loosen the locking screw on the setting circle before moving to another coordinate. Ideally Skywatcher ( or Orion) should have put another locking screw on the lower half of the r.a axis to lock the setting circle to the bit that DOESN'T move!

I guess that's why some people have luck with these mounts with r.a and others don't. Some you can just loosen the r.a setting circle and it won't bind with the mount as it rotates. Others are not so unfortunate. And with the two r.a alignment marks! No wonder people like me have been baffled by the whole setup! I think a recall was in order years ago when these were put on the open market years ago...

Anyways, at least it will somewhat get us in a ball park region of where we should be pointing the scope, in conjunction with a bit of star hopping of course. ;-)