polar alignment question

[stan26]

Hello there, Hope you guys can answer a question regarding pricise polar alignment. (bare with me on this im still trying to get my tiny brain around it all)

I want to be able to do some astropotography from my back garden when I get my scope in a week or so. The problem is beacause I live on a typical new build estate house cramed in eveywhere I have very limited views towards the horizon in all directions, and (from what I understand) the requirments for an effective star drift align is to have a good view of the southern/eastern horizon.

Now, would I beable to align the scope at a more suitable location (i.e a nice flat dark spot with good 360 views I located about a mile away) and take as accurate reading I can of the mounts position with a compass and realign it at home so that i don't have to leave home everytime I want to do some DSO Imaging....? Or am i being stupid..?

If I'am being stupid which I highly suspect I'am, Are there any other methods for accurate polar alignment with restricted views...?

Thanks

[carpman]

Unfortunatley i'm in a similar situation but i have a hill to my west , i use a polar scope Skywatcher - Skywatcher Polarscope for EQ3-2 & EQ5

Where are you gonna be doing your imaging from ?

The reason i ask it is when ever/where ever u take you scope outside you will have to re-align it every time

i'm hoping this is the info you require (i'm a newbie to)please guys if i've got this wrong excuse me ....

[stan26]

Hi Carpman, thanks for your reply.

I read somewhere that once the scope is polar aligned you can mark the ground where the tri-pod legs are and as long as you very careful with moving the mount/scope it can be re-setup quickly by putting it exactly on the marks next time its used, Although this could been a load of ol BS off course lol.

I want to image from home, Mainly so I don't have to be away from the kids/missus as much. My main hobby is sea fishing, and if I started spending more nights away taking pictures of the stars she'd go mental!!

[Merlin66]

Although handy, for drift alignment, you only need to be able to see a suitable star near the east or west horizon. In the south you want to look towards the celestial equator ( zero declination) which is about 30 degree altitude....

[SteveP]

Stan

Good idea! Unfortunately it's very unlikely that it will work. I doubt very much that you can take a sufficiently accurate compass bearing and then replicate it equally accurately when you get home to overcome your problem with polar alignment. If you can, then many thousands of astronomers have been wasting their time doing some form of drift alignment over the years!

On a more positive point, can you see towards the west rather than the east? If so, then you can still drift align but in that case, all the adjustments would need to be reversed

Steve

[Steve 1962]

Stan

You could get a rough polar alignment with a compass and then mark the position of your tripod legs so that you can repricate the position for every time you setup your kit.

While this may get you fairly close, I would drift align...and I find the quickest way to do this is to use PHD auto guiding program which is available for free at Stark-Labs.

Quoting from Polar Alignment;

The process begins as all the other drift alignments. To check the RA alignment chose a star at 0° elevation close to the meridian. To set the DEC alignment choose a star as close to the E or W horizon as possible.

1. Turn on the guiding program (PHD) , select the mount and camera and run thru your calibration a usually.
   
2. To Check the RA select a star near the Meridian at 0° elevation.
   
3. Start Guiding on the selected star.
   
4. Turn on the GRAPH and select DX/DY instead of RA/DEC.
   
5. Turn off the DEC guiding
   
6. If your mount is perfectly aligned the DY ( red line) should track across the graph near the center line. If it drift up or down you need to make a very small adjustment to your AZIMUTH screws to compensate for that. You will see the change immediately. No need to wait 5 or 10 minutes for the visual drift.
   
7. Now set up the elevation.
   
8. Stop the guiding and look for a star near the western or eastern horizon at whatever elevation allows you to clear any obstruction. The lower the better.
   
9. Recalibrate the guiding on the new star.
   
10. As in step 3,4 & 5 above start guiding and make sure that the DEC guiding is off.
    
11. Once again if your alignment is on then the DY trace should not drift from the horizontal graph line. If it does, carefully mar small adjusts to the ELEVATION screws to compensate. Again you should see an immediate change in the graph.
    

This process is simple enough to allow you to check you polar alignment whenever you feel it necessary. The only requirement is that you get a copy of PHD and have a camera that is supported by the program ( there are many).

Hope this helps

Steve

[stan26]

Thanks Steve,

I do have a "better" view to the west where the house's are further away but its very badly lit with street lamps. The only visible object in that direction lately has been jupiter, hardly any stars can be seen through the orange haze

[stan26]

thanks steve1962.

I have a Canon 500d, hopefuly its supported. I will definately look into that program cheers

[SteveP]

The only visible object in that direction lately has been jupiter, hardly any stars can be seen through the orange haze

Do you mean that no stars are visible through the scope or just with your eyes?

[PeterW]

The PHD method sounds like a good one as I have a building in the way of Polaris. Surely if you have PHD setup then there is no point in getting the polar alignment accurate as you are correcting out the errors?

Cheers

PEter

[stan26]

Do you mean that no stars are visible through the scope or just with your eyes?

With eyes, I haven't got the scope yet.

[Merlin66]

Peter,

PHD and other guide software just "locks on" to a nominated star and makes corrections to keep ONLY that star in a fixed position in the FOV. It will not correct for field rotation caused by polar misalignment.

[SteveP]

With eyes, I haven't got the scope yet.

Stan

When you get your scope, you'll be surprised how many stars you'll be able to see even through light pollution. However, heavy light pollution will make imaging more problematic

Steve

[PeterW]

....which will be a second order effect! The instructions with PHD soubd simple enough, so definitely worth a go. Of course the next question is what to do in the daytime for some quick solar observing, or are the errors from "plonk and play" such that they won't affect DMK imaging too much as you can just manually do the autoguiding.

Cheers

PEterW

[Merlin66]

When I solar image, I have the tripod position marked on the ground and just drop the tripod in the holes.

The exposures are generally so short no guiding is required, only tracking at solar rate. Registax will correct any minor Dec dift during the stacking process.

[PeterW]

Goodie. I do whole disk lunar imaging with a DMK and fixed mount... Avistack deals with the drift. Thanks for all the help! All I need now are some clear nights to practice this stuff!

Cheers

PEterW

[Steve 1962]

Peter,

PHD and other guide software just "locks on" to a nominated star and makes corrections to keep ONLY that star in a fixed position in the FOV. It will not correct for field rotation caused by polar misalignment.

Just to pick on Merlin's point - he's entirely correct but I think it's worth clarifying that you can also use PHD as described in my earlier post to relatively quickly identify polar alignment errors and manually adjust the polar alignment of an EQ mount....which, when correctly set, will avoid field rotation.

You'll only get noticable field rotation in long exposures so accurate polar alignment is less critical for short exposure lunar and planetary imaging.

Also, in answer to Peter's point - you may as well try to get the polar alignment "nearly right" before using PHD if you can because it'll speed up the process of making the final adjustments.

Steve

[Merlin66]

Steve,

My post was just to answer Peter's question about using PHD to "correct" during guiding for polar misalignment.

Using PHD as a tool/ aid for achieving alignment on the pole in the first place is a completely different story. I agree with your method.

[Steve 1962]

Cheers Merlin - I just wanted to make sure we're all singing from the same song sheet!

Regards

Steve