Polar Scope and alignment issue, advice please?

[Chris81]

Good day all

When looking through my Polar Scope the display of the NCP and cross hairs are at an odd angle (the smaller circle is at about 5 O'Clock if it were in reference to a clock face) and the cross hairs are at the same angle. does this matter when polar aligning the mount? is there a way of calibrating so the cross hairs are exactly vertical/horizontal or does it not make any difference? I have attached a snap shot of what I see when looking through.

Any advice, as always, is appreciated

Thanks

Chris

[Oddsocks]

Hi Chris,

The geometric relationship of the cross hairs with reference to the Polaris indicator is purely arbitrary since at the point of polar rotation there is no "up" or "down" if that makes sense?

The only thing that is important is the angular separation (distance) of the centre of the cross hairs to the inner ring and the Polaris marker.

The orientation of the cross hairs is etched on to the the reticule together with the Polaris marker and the outer star markers all at the same time.

You can't change the orientation of the cross hairs with respect to the Polaris marker alone and it would have no effect to the precision of the polar alignment if you could.

The only important thing is to ensure that the centre of the cross hairs are aligned mechanically to the centre of mount RA rotation before carrying out polar alignment for the fist time in the dark.

Check this in the day time by moving the mount in azimuth and altitude and aligning the cross hairs to something small and far away like a church tower, mast, flag pole, TV ariel etc and then rotate the RA axis with the clutch released.

It's best to do this with no weights or OTA fitted, check that the cross hairs remain firmly pointing to the chosen object and do not drift away as you rotate the mount RA axis.

The following describes the routine for polar scope mechanical alignment, I expect you know this already and it is in the manual but if you don't know it I have repeated it here:

If the cross hairs do move away from the object then adjust the RA rotation until the point of maximum displacement from your chosen object is reached, lock the RA clutch and then adjust the polar scope adjustment screws to move the cross hairs back to a point exactly half way between the chosen object and the current position.

Now use the mount azimuth and altitude adjusters to move the cross hairs back to the chosen object and check the cross hairs stay on the object as you again rotate the RA axis.

You will probably still have some drift but not as much as before so just repeat the adjustment again and keep repeating until the cross hairs remain fixed on the chosen object as you rotate the RA axis.

As long as you don't knock the mount too much when packing up etc then the polar scope will remain pretty well centred but it will need checking from time to time.

Regards,

William.

[Chris81]

Thanks for the response and yes that does clear things up for me. I have been getting a little confused recently when watching various youtube tutorials and got to the point where I assumed my polar scope was not correctly aligned or something like. Truth is I have been observing and photographing for a little while now, and although it is far from perfect, it seemed to be relatively close, although anything more than 30 seconds I was getting some star trail, but I think that may be more down to the limitations of the EQ5 and lack of a guiding scope. Thank you for the advice.

[Oddsocks]

Glad that made some sense Chris,

You should be able to increase the unguided times by more accurate polar alignment even though you aren't guiding.

I use the drift method quite a bit when using my mobile setup, HEQ5 with 4" refractor and Nikon DSLR.

The drift method can be done easiest with a illuminated reticle eyepiece and barlow but also with DSLR.

There are many explanations of drift alignment on this forum and elsewhere but here is a link to a page at Ian King Imagine that I used to learn the method.

http://www.iankingim...ticle.php?id=11

If you can minimise the drift in Dec by accurate polar alignment then you will only have the periodic error of the RA drive left in the system so one or two minute exposures will become attainable.

William.

[StevieDvd]

Chris,

Have you seen that Synscan updates now have a polar alignment feature?

If you have a rough polar alignment (i.e no polarscope and pointed north at right att settings) then when you perform a 2 or 3 star alignment there is a post alignment procedure to correct any polar inaccuracy.

Basically after doing the alignment to say 2 stars you use one of them as a reference point, the handset will tell you to centre the star using the handset controls and then it will move the mount a little and ask you to re-centre the star using the mount adjustment bolts. You do this a few times and by doing so the mount axis is correctly aligned with Polaris.

if you start with a better alignment by using the polarscope the above can still be used to fine tune it. Some software such as Alignmaster can do the same sort of thing.

Hope that helps.

Steve

[Chris81]

• That's interesting, I shall get my firmware updated asap then. thank you both (Oddsocks & StevieDvd) for the great advice, I am confident my problems will be resolved!
  

Happy star gazing and clear skies!