Blind polar alignment

[Terry Scope]

Hi all, just joined so thought I would burden you with my first problem. Polar alignment when you can't see polaris. Light polution and 30ft trees and buildings to the north mean I can't see Polaris. I know roughly where it should be and with a compass align my HEQ5 Pro. So I set Home position, switch on and start alignment procedure. I choose Arcturus first and of course the mount misses. Am I thinking along the correct lines now. I can use Dec & RA buttons to centre Arcturus and the next alignment star is closer. Eventually I can start viewing but anything I look at slowly drifts off presumably because it isn't truely polar aligned.

If it was perfectly polar aligned would the mount be able to centre on the first star? i.e. if not correctly aligned it would point to the position where it expects to find the first star in relation to where it started from. If that is the case would it not be better to centre the first alignment star using the Alt/Az controls? Is my thinking way off? Your comments would be welcome.

BTW I must appologise for the awful weather. It's been like that since I bought the mount.

[JamesM]

So its your fault is it Terry!

I maybe wrong here but I believe that polar aligning through the mount's scope and calculating polaris's precise position via time date etc is only really necessary when you are imaging as this potentially will effect tracking during exposures. For visual I don't see a problem in attempting to get the mount as closely aligned as possible be it using the alt/az bolts and of course the latitude scale which tips the whole mount back an forth (go steady with the latitude bolts - originals are on the soft side!)

First off I would do a three star alignment. The first one is always a little off and yes (even when I do a precise polar alignment) reposition mount via the handset to your chosen star in the middle of the eyepiece. Keep going till the third star but ensure that the three you choose (as your view is limited) are about the same height in the sky and that they are equally spaced apart which will normally mean that two of your choices will be in either the left or the right hand side of an imaginary line drawn from north to south (Meridian Line). I wold imagine that this will give you a good chance of objects searched will be on target but the ability to track for longer periods will depend on the accuracy of your 'rough' alignment. O f course I', talking here from an observing perspective and as you have a HEQ5 then there might be PC solution (EQMOD program) that could secure you better alignment if imaging is your goal.

Hope that helps.

James

[Terry Scope]

Thanks for the reply. I'm just wondering how the SynScan works. I have 30 odd years electronics so do know they must use Stepper motors. I'm not sure why it should need 3 star alignment to be accurate. Being a Stepper motor the designers should know how many steps per arc second the motor makes on RA and Dec so assuming perfect Polar alignment and perfect setting to Home before switch on it should be able to get pretty darn spot on to the first star. So the two variables that make it miss are incorrect Polar alignment and incorrect setting of Home position. Assuming you can set the Home position correctly then inaccurate Polar alignment should be correctable at the first star alignment using the Alt/Az controls. It's just a theory but when we next get clear skies I'll see if it works.

[lukebl]

Try Drift Alignment. I can't see Polaris from my scope's location, so I use Drift alignment, which is very accurate and pretty quick once you get the hang of it.

[chrisshillito]

I'm not sure why it should need 3 star alignment to be accurate. Being a Stepper motor the designers should know how many steps per arc second the motor makes on RA and Dec so assuming perfect Polar alignment and perfect setting to Home before switch on it should be able to get pretty darn spot on to the first star. So the two variables that make it miss are incorrect Polar alignment and incorrect setting of Home position. Assuming you can set the Home position correctly then inaccurate Polar alignment should be correctable at the first star alignment using the Alt/Az controls. It's just a theory but when we next get clear skies I'll see if it works.

There's a little more to it than just polar alignment and home position errors.

Only if you had perfect polar alignment, and the mount was in a perfect home position, and the mount was perfectly level, and the telescope is mounted perfectly orthogonally, and there is no flexure, and there are no optical distortions, and there are no atmospheric distortions, and your mount has precisely the right time, would the initial goto result in a perfectly centered object.

Chris.

[Macavity]

I empathise. Still working on this too - albeit Polaris being (semi) visible through the Syntrek polar-scope's "tomato soup"! I find a (full sized, 0.1 deg) digital level is helpful in many ways. <G> Tracking isn't too bad now. Thanks for the link, Luke... I am/was seriously contemplating getting to grips with drift alignment. The stiffness of (Skywatcher) polar altitude adjustment horrifies me though.

Using EQMod to perform the GoTo-ing, here. Intriguing how the "FIT" (genuinely!) improves as more stars are "synched" in. There's a wonderful (and lengthy!) exposé of how their 1, 2, N... star alignments function, on the EQMod pages. One for the enthusiast, maybe?

Not to sound churlish, but my (simply leveled, compass aligned) Ioptron Alt-Azimuth almost hits the first star and from first "synch" is good to go (sic)! Of course, it's not suitable for LONG exposures and doesn't have the load capacity of the HEQ5...