how to add more image data from a later night

[iwols]

hi guys after my previous post with the grainy horses head i was wondering how to add more image data from a following night,mainly how to align the image in the same position as previous nights,im using sgp pro trial and pixinsight ,also does the exposure length have to be same as the previous nights for the lrg channels cheers guys

[cjdawson]

If I remember correctly from the demo at SGL 12.   SGP can hook up with AstroTortilla to do plate solving.  This will allow you to use the camera and scope to issue the goto commands, and do the plate solve.  What it will do is try to match your original image as close as possible.  Once done, you'll be able to carry on taking more subs.   Alternative to that, you can line up on the object as best you can, then correct any slight issues at the align and stacking time.

Ideally, when mounting your camera on your scope, you'll mount it in the same place as before, so there should not be any rotation issues to deal with.  If you haven't been, it will be something worth considering adding to how you setup, so as to minimise changes between sessions.

[Astrofriend]

Hi Iwols,

Normally you have the same exposurelength, but sometimes it could be a benifit to have at least two exposurelengths. That's is when your object have very high contrast, for some cameras it's even better to change the cameras gain or ISO. One problem I have when I have try to stack images from different nights is that they don't frame on each other. My optics have a slightly distorsion that makes the align process difficult. Nowadays I use AstroTortilla to frame the camera more exact on the object. The camera controll program I use, APT have some support for framing the object also, but havn't tried it.

 

APT:

http://www.ideiki.com/astro/Default.aspx

It's free so can do a test if you like it.

 

This is the software I use in my setup:

http://astrofriend.eu/astronomy/equipment/astronomy-equipment.html#part05

 

/Lars

[ollypenrice]

Make life easy for yourself and have the camera orthogonal with RA and Dec whenever you can. Take a quick sub while slewing and the star trail shows the camera angle.

There is no need to repeat an error in sub length if, indeed, you have an error. If you felt that your S/N ratio was disappointing first time, try longer. Experiment is everything in AP. You have to learn what works for you. I do many things in my imaging which the internet tells me not to do.  However, very few targets indeed need multiple sub lengths to cover the dynamic range. I can only name two in the last 1O years, personally.

Olly

 

[wimvb]

+1 for aligning the camera with RA and DEC. Even if you do plate solving, you still have to align the camera manually. If you don't / can't do plate solving, make sure your star alignment is spot on. Use a high power eyepiece (with reticule) while doing star alignment. This will give you better pointing accuracy, and better repeatablity.

Pixinsight has several tools to handle dynamic range. Even with "difficult" targets, you generally won't need to take multiple exposures.