Drift Align vs. ASPA

[Kirscovitch]

I am starting to get the hang of PA with the VX and All Star Polar Alignment. The way I have been doing it is a little time consuming but am getting good results. Exposures of 120 are common now and on a good night was managing 190. But been doing some reading and watching some videos about drift alignment and how accurate it is vs. other alignment methods.

I was just wondering how much more accurate would DA be versus the ASPA? 3 minute unguided subs are pretty good and only takes me on average about 20 min of alignment to get there. From what I have been reading and seeing on the web, DA seems like it is a little more time consuming. That's all fine and dandy if it is that much better. 

What kind of subs would I be able to get if I used drift align? If 3 minutes would be about tops I would probably stick to ASPA. But if I could really turn up the length of the subs to around 5 min or so it might be worth the extra time and effort.

Any input would be appreciated.

[ollypenrice]

i like drift alignment because it is a software free measurement and software is fine when it works, as sometimes it does. Frequently, though, it doesn't, as everyone except software engineeers knows!!!

Olly

[Kirscovitch]

But how accurate can it be? What kind of subs are possible with DA? 5 minute? 10?

[Martin-Devon]

If you are getting nice round stars after 3 minutes, and if this is unguided, then that's reasonable - it's not just all about the accuracy of the PA though since many other factors also come into play to get optimal subs. Assuming your 3 minutes is non-guided, then I would strongly encourage you to guide as well since that will probably comfortably take you up to 10 minutes for subs delivering good round stars. 

Drift alignment is usually the most accurate method to PA, and for permanent observatory based set-ups it's definitely worth the effort. PemPro is a great software package which takes a lot of the pain out of the drift alignment process, it's a bit fiddly initially but once done it a few times you can normally get PA spot-on within 10-15 minutes everytime. If you have a portable set-up, then the quicker ASPA process you describe (especially if guided afterwards) may be absolutely fine for you.

Martin

[ollypenrice]

Drift alignement has the potential to be perfectly accurate, though you won't acheive that. It isn't even necessarily ideal if you're autoguiding. (Being slightly off and only guiding one way in Dec can be an advantage in defeating backlash.)

How long your subs can be depends on polar alignment, yes, but also on the periodic error of your mount and that is down to mount quality. it can be a couple of arcseconds for the big boys or 30 arcseconds for the budget mounts. Also relavant, big time, is your sampling rate. Fewer arcseconds per pixel has to be more accurate than more arcseconds per pixel.

I like drift alignment because it gets rid of software errors. These sometimes exist and sometimes don't. I prefer not to give them the opportunity to waste my time...

Olly

[Kirscovitch]

Eventually down the line I would like to start guiding. Hopefully by the end of the year. I might play around with drift alignment next time out. Since the moon is getting pretty bright right now I could try DA and not feel like I am wasting imaging time. Would be interested to see what kind of results I get.

[RAC]

The faster you start autoguiding the less imaging time you will be wasting. It doesn't take a lot to setup and is well worth it. I drift align with PHD using the guide camera.

[wuthton]

The faster you start autoguiding the less imaging time you will be wasting.

^nobody would disagree with that statement.

[Landy Dave]

I am using ASPA and getting 120 second subs with a CG5-GT  but only until I get the budget together to start guiding as it just takes some of the unknown away