Star Trails

[KenMiller]

On longer exposures (5 mins.) I'm getting star trails - which I understand are due to inadequate polar alignment.

If I'm careful setting up my EM-400, what is the longest exposure I should expect to be able to take without doing additional alignment?

Is drift alignment my best option for refined alignment? I must set up and take down each evening.

Can I do drift alignment with the camera? I don't want to remove it after shooting my flats (I'm using the dusk sky at present).

[Spoonsize]

This works pretty good for drift allign with a toucam. I don't know if it will work with a DSLR or not.
The last step is hard to understand, IMHO.
http://wcs.ruthner.at/index-en.htm
Steve

[BT Technologies]

It really depends on the focal length and the precision of your polar alignment Ken. If you are using your E-180 and do a decent Polar alignment I would say 2-3 minutes should be very doable. For longer exposures you would probably need some kind of outboard guider to make minute adjustments.

A drift align would be the most precise way to assure the most accurate tracking without use of a outboard guider.

Originally Posted by KenMiller

On longer exposures (5 mins.) I'm getting star trails - which I understand are due to inadequate polar alignment.

If I'm careful setting up my EM-400, what is the longest exposure I should expect to be able to take without doing additional alignment?

Is drift alignment my best option for refined alignment? I must set up and take down each evening.

Can I do drift alignment with the camera? I don't want to remove it after shooting my flats (I'm using the dusk sky at present).

[KenMiller]

That looks just like what I need! Unfortunately, it appears to only work with webcams

I suppose I could mount a webcam, drift align the mount, and then mount the DSLR. I may give that a try.

[BT Technologies]

Ken, you have a brand new Phillips Toucam being delivered on Monday so you can always give that a shot!! The best part is that you can use the Toucam for guiding on nights when you want to shoot DSO's and on other nights when you want to capture some planetary shots, just use the Toucam!!

Originally Posted by KenMiller

That looks just like what I need! Unfortunately, it appears to only work with webcams

I suppose I could mount a webcam, drift align the mount, and then mount the DSLR. I may give that a try.

[neilfleming]

The illuminated reticle polar alignment scope on the EM-400 should be good to within 2 arc minutes of the pole. Then you can finish up with the approach I used when I used an NJP:
http://www.darkskyimages.com/gpolar.html

After that, you are then dealing with the periodic error in the mount. Depends on the pixel size in that camera. With an E-180 you should be good for 2-4 minutes. I'd actually suggest getting something like a used DSI-Pro, along with a copy of MaxIM. MaxIM will capture shots from your Canon, and allow you to guide with the DSI-Pro. You just need a light, inexpensive achromat to attach to the E-180. Your mount will not even notice the extra weight.

Focus will eventually be your next challenge. Either use the included MaxIM focus evaluation tools, or use a diffraction cross, like this:
http://astronomy.qteaser.com/diffspike.html

When I did it this way, I simply used two strips of duct tape!

...Neil

[KenMiller]

So I guess for only doing the polar scope alignment I'm doing OK. It's reassuring to know that. I thought I had a drastic problem.

I was thinking I could use a combination of the camera rotator on the E-180 and drawing a crosshair on the resultant image to emulate the illumiated crosshair reticle, but rotating the camera after shooting the flats would render the flats useless. I guess a light box would solve that as I could shoot the flats after the alignment. I guess I should move that up on my list of things to get done.

The STL11000 I have on order has a built-in guider and I'm planning on using that rather than a seperate guide scope. Am I likely to be successful going that route?

[neilfleming]

I wouldn't worry about the flats being useless after a camera rotation. Most of the flaws are associated with the CCD window and the dust on the filters. I notice that Richard Crisp is selling his custom focuser for the M-180. It was designed to work with the FLI PDF, and is kinda a beefed up version.

Autoguiding with the built-in chip on the 11K will be the best way to go, until and unless you start doing a lot of narrowband work.

...Neil

[KenMiller]

Originally Posted by Spoonsize

The last step is hard to understand, IMHO.
http://wcs.ruthner.at/index-en.htm
Steve

That's an understatement!

I tried using this application last night. Something was definately lost in the translation.

I couldn't figure out how it was supposed ot be used so I just used the tracking and did an iterative process of my own where I switched between a star in the East and one in the South and kept adjusting by my best guess until there was no more error.

I see a permanent pier in my future.

[Spoonsize]

I've got e-mail in to him for further clarificattion. If he sends it, I'll forward it.
Steve