Setup and polar alignment tips?

Iancar29

Hi folks ,

So im still struggling to get a decent polar allignment with my CG-5 mount .
I can only seem to get 20 seconds , maybe 25 seconds the odd time without trailing .


Heres what i do currently.

i setup the mount at the back of the garden , with i facing roughly north. I try make sure its level with the bubble level. ( might take out spirit level to see if thats accurate ) . Then i try look through the polar scope ( which is very poor in the light pollution im in. ) I loosing the right left axis and try align it up as best i can and then tighten things once again and recheck.

I put on the scope and set check with the finder scope that its looking at polaris.

Turning things on then i usually just 2 star align with Betelgeuse and sirius .

Then i go from there.


Any tips or notes of how to improve on this would be greatly appreciated.

Thanks

Tzetze

The bubble level on the mount can't be trusted. Use a small spirit level instead.

I don't use a polarscope myself, I don't even own one. What I do is set up the mount facing North so that I can sight polaris through the hole in the mount where the polarscope goes and then do a drift align. I use DSI-WCS for aligning but there is a simple routine you can use to do it manually.

You need to take a long exposure to see how much drift is in your system.
First choose a star in the south close to the celestial equator. Start a 125s exposure. After 5 seconds start moving the mount East or West at rate 2. After 65 seconds reverse the direction and move back the way you came until the exposure ends. You will end up with an image like this...



You can see the start point clearly (Blob) and that there is a LOT of drift in this case. Make a correction using Azimuth bolts and repeat the exposure. Compare the two exposures to see if you have under or over adjusted.

When your exposure produces a straight line, you have perfect azimuth alignment.

Then you need to adjust altitude. Choose a star in the east or west, at about 20 degrees above the horizon and make a similar exposure again. This time you make adjustments with the altitude bolts only.

Once your image produces a straight line in the south and east/west you have perfect alignment.

Tzetze

I should add that the mount should be tracking at sidereal rate before you begin drift alignment. Enter time/date as usual into handset and when choosing goto alignment option select quick align.

Wailin

Good advice from Tzetze. I had similar issues when I first set up out the backgarden and found it all very confusing. Once you get the hang of it though you'll be flying. I don't do drift alignment, never tried it and think it can be a bit time consuming. I may have posted this guide here before http://www.astronomyshed.co.uk/forum/viewtopic.php?f=19&t=1893 but trust me, its excellent. It shows you how to set up from the beginning and explains everything down to the smallest detail. Its basically for the NEQ6 but any GEM is similar. Also with drift alignment you need clear views to the South and also East or West which isn't always possible. I now use the Right Ascension scale to do my alignment (see video) and can get 2 min exposure with little or no trails. Not sure if your mount has one but you can still get decent alignment without.

Keep at it and it will pay off

Iancar29

Thanks for the tips lads , ill have a go at tzetze's method if im able to get out to somewhere other than my small back garden lol !

Saw that video link you posted last time Wailin . Though i find the clock thing confusing as i don't see its use , my polar scope doesn't have any markings when i look through it too which is kinda crap also lol. AH sure , I'll give it another bash tonight and report my results!

endacl

Tzetze wrote: »

The bubble level on the mount can't be trusted. Use a small spirit level instead.

I don't use a polarscope myself, I don't even own one. What I do is set up the mount facing North so that I can sight polaris through the hole in the mount where the polarscope goes and then do a drift align. I use DSI-WCS for aligning but there is a simple routine you can use to do it manually.

You need to take a long exposure to see how much drift is in your system.
First choose a star in the south close to the celestial equator. Start a 125s exposure. After 5 seconds start moving the mount East or West at rate 2. After 65 seconds reverse the direction and move back the way you came until the exposure ends. You will end up with an image like this...



You can see the start point clearly (Blob) and that there is a LOT of drift in this case. Make a correction using Azimuth bolts and repeat the exposure. Compare the two exposures to see if you have under or over adjusted.

When your exposure produces a straight line, you have perfect azimuth alignment.

Then you need to adjust altitude. Choose a star in the east or west, at about 20 degrees above the horizon and make a similar exposure again. This time you make adjustments with the altitude bolts only.

Once your image produces a straight line in the south and east/west you have perfect alignment.

Elegant solution. And so bl**dy obvious! Just had a real 'why didn't I think of that' moment...

Tzetze

endacl wrote: »

Elegant solution. And so bl**dy obvious! Just had a real 'why didn't I think of that' moment...

All credit is due to Robert Vice who came up with the method.

ZeRoY

Iancar29 wrote: »

Thanks for the tips lads , ill have a go at tzetze's method if im able to get out to somewhere other than my small back garden lol !

I do have the same problem in my back garden where South is just not doable, I will however give the drift method another go soon, perhaps via APT Tool is the function is ever fixed!

Currently I use a compass to point mount head North roughtly then use Polar scope to find Polaris and center it in reticule of Polar scope using Alt + Az bolts, after this a 2 star align for the GOTO. Mind you I only been able to track 2 minutes once with this method - its usually ok up to 1 minute.

ThatDrGuy

ZeRoY wrote: »

I do have the same problem in my back garden where South is just not doable, I will however give the drift method another go soon, perhaps via APT Tool is the function is ever fixed!

Currently I use a compass to point mount head North roughtly then use Polar scope to find Polaris and center it in reticule of Polar scope using Alt + Az bolts, after this a 2 star align for the GOTO. Mind you I only been able to track 2 minutes once with this method - its usually ok up to 1 minute.

An astronomer who needs a compass to find polaris ? For shame

Popoutman

What focal length are you using to image?

I've an LXD75, and with a 600mm focal length refractor and a 600D dslr I cannot manage more than about 30-40 seconds unguided as the drift east-west due to the machining inaccuracies in the drive gears becomes too much. My polar alignment is pretty good, as I wasn't seeing any significant N/S drift in the images over a half hour or so. With 30s subs, I was getting 80% of them usable. With 1min subs I wasn't reaching 20% usable. I have decided not to sink the cash into an autoguiding setup as I simply don't have the spare time to devote to astrophotography, but I dabble every now and then I could probably rig up a half-decent autoguiding for ~€500 with an autoguider and a modified barlowed finderscope, and a convertor to allow the autoguider to control the Meade mount.

Just using the camera and an ordinary lens I can go maybe to 5 minutes (the time to saturation due to LP with my lens) without too much difficulty.

I don't think that the CG5 is much better without active autoguiding, based on what I've seen on other forums. With active guiding, it should work well enough.

ZeRoY

ThatDrGuy wrote: »

An astronomer who needs a compass to find polaris ? For shame

Not to find Polaris but to have a line to work with to align my tripod!

ZeRoY

Popoutman wrote: »

What focal length are you using to image?

752mm is the Focal length of my Newtonian. The 2 minutes exposure happened only an handful of time but I did do 1 minute a good few time with very little trailing.

I have a ST80 + SPC900NC Webcam for auto-guiding but not tried yet!

Nerro

Well I haven't seen any post how to use polar scope properly so here is my 2 cents...
basically when you look thru polar scope you should see this

Now note at the small circle with polaris marked beside.It should always be at specific angle.to know where it should be just download any app and it will show where it should be. when you will know where it should be adjust your mount and then USE ALT AND DEC screws to move polaris smack dead in that circle.when its done your mount will be perfectly polar aligned.With this methot one of my friends was getting 2.5min exposures on his HEQ5 and 8" newt.
Hope that makes sense....