Camera / OTA orientation?

[Larry 1969]

Hello all!

Since I've finally stepped up and got myself a decent imaging rig I think it's time to capture data and save it so I can add to it later. Then I started thinking about how to get repeatable images and now I'm struggling with orientation...
Is there a way to get my camera inserted into the focusser at EXACTLY the same orientation time after time? I think this might be important for stacking images taken over multiple sessions. Also, what's the best procedure for stacking these?
Let's say I have data collected from 3 different sessions and I want to combine it all into a single image. Would it be best to make three separate stacked images (one from each session) and then stack those three to make one image or
load all light frames from all 3 sessions and stack them into one image?

It's been awful cloudy here and this stuff is all I can seem to think about... :smile:

Thanks!

Larry

[Dragonsfire]

I used to use some red/white nailpolish and and place a Dot were they both met so I could realign each time.

[sdbodin]

I don't think you can make something accurate enough. I let software do the work, align by translation, rotation and scale. Nebulosity allows this and it is really slick, even different focal length setups, within reason. I have stacked 5 year old data with fresh stuff from overnight, no problem, just crop off the ragged edges.

Clear skies,
Steve

[bobharmony]

If you are using DSS for stacking, it is very forgiving of different angles between subs. On a night when I do a meridian flip, the images after the flip are rotated by 180 degrees from those before the flip, and it doesn't cause DSS any issue at all. I try to line up the camera with the top facing the front of the OTA every time out and only rotate the camera from that orientation if I have trouble fitting the target in the frame. M31 is an example of an object that just fits diagonally and needs a custom camera orientation for my image scale.

DSS also has methods to stack images of the same target from different nights in a single pass. Those can need to be stacked separately if temperatures require different darks or if orientation requires different flats. When you are ready to do that I can share more detail, or you can find information in the DSS documentation.

Bob

[yobbo89]

Programs like sequence generator pro has a manual camera rotation setting which should tell you how many pixels to rotate to.

Typically for most of my setups including dslr,s I alighn the camera to the declination axis on the mount with an aid of a cross hair in the live view with repeative panning left and right I am able to get it very accurate with minimal wastage.

I believe that if you randomly inserted the camera into the focuser at none parallel angle to the mounts mechanics then when you do a meridian flip there should be a large ammount of miss alighnment in pixels due to the mirroring of the target , you'll have to rotate each time to get the most usable space when doing meridian flip when imaging with such a camera rotation.

A simular effect is seen with cone error when a scope isn't alighned perfectly with the mounts mechanics/axis

[bladekeeper]

If you want an exact match, do not remove the camera from the focuser.

Another important thing to keep in mind are your flats. As long as you do not alter the imaging train, your flats can be used for the whole imaging session on multiple nights. The moment you pull the camera out of your focuser, etc., you'll need new flats to go with the next imaging run.

[Larry 1969]

Thanks for the replies!

I'm using DSS and I'm not opposed to some cropping.

Excellent point about the flats! I hadn't considered that. I just purchased a LED light panel to start shooting them. I suppose I could leave the camera in the focuser...
I always removed it in order to install the lens cap on that end of my coma corrector but I suppose as long as it is inside my OTA when stored dust and such may not be a concern.

I wonder if there is some sort of degree indicator that I could attach to the focuser and then mark my T-ring so I could note the preferred rotation for different targets?

Larry