polar alignment

[eye in the sky]

Hi all

I have recently bought a few new items to further my imaging capabilities and one of these items being an ae mega wedge so i dont have to use drizzle with my dsi. The first question i would like answered in a list of many is as follows.

When polar aligning my scope which is a lx90 12" i centre polaris turn scope 180 degrees and polaris is still centred or there about. Now which way has polaris got to go left or right and by how much in the field of view. I know it depends on the eyepiece but the eyepieces i have are 6mm 9mm 12mm 15mm 20mm 26mm 32mm. The scope is at f10 with a focal length of 3048 and i will be using a diaganol.

Thanks

Dave

[roundycat]

You have a problem. with your focal length and a 32mm (Plossl) eyepiece what you will see is the smaller circle in the attached picture. I have laterally reversed it so it will appear the same as in your scope except that you cannot see anything in your scope because it is too long.

So, if you centre Polaris and then move the scope so the star goes off to the left you will be somewhere near right.

Dennis

[Aza]

I use this software to show me exactly where Polaris should be in my polar scope:

http://home.online.no/~arnholm/org/zip/polar202.zip

Then with a illumiated reticule eyepiece, I use this method to increase my alignment accuracy:

Tim Tasto Deep Space Imaging and Astrophotography

This gets me good enough for imaging with guiding.

[eye in the sky]

Hi again all

Would it be easier dennis if i used a 6.3 focal reducer would that allow enough fov with eyepieces stated. I have also got a digimaxt 40 eypiece (just remembered). I would be setting up as soon as it went dark about 9.30 so would polaris be on the left at that time in my fov as it rotates around the centre (polar).

thanks

dave

[eye in the sky]

Hi all

Ive just been reading up on that one star alignment procedure that arran has pointed me to. I think il give it a go tonight if clear (i doubt). Cheers arran.

Thanks again folks

dave w

[crovax]

Hi, sorry but I have a very noobish question. I don't get the whole point in the polar aligment. I have EQ2 where I set my latitude (50). Then I locate polaris (let's assume it's exactly at NCP) and then.....actually what? The dec circle is not movable as RA, right? I don't get why I need to locate polaris then.

[Psychobilly]

Accurate (the more accurate the better) polar alignment is needed to take long exposure astro photographs if you dont want to have any field rotation in the image...

Peter...

[crovax]

Yes, I understand. But what do I configure? Do I need to move the latitude circle?

[roundycat]

Dave, apologies for my original polar chart, I did it in the afternoon and it was not showing the right time. The new one below is for 9:30pm and your scope at f7 with a 40mm eyepiece which may have a different FOV to yours. Looks as if all you have to do is offset Polaris to the bottom edge at 21:30 hours and you are hot to trot.

Dennnis

[eye in the sky]

cheers dennis nice one mate only one question is that the way around it will look in my eyepiece using a diaganol

[roundycat]

Yes

Dennis