Help with manual Camera Rotation


#1

Hi Everybody,

I’ve been a visual astronomer most of my life, but am wanting to learn AP as well. I have an 18" starmaster f/4.5 with an alt-az tracking/goto drive system on it and an ASI294MC Pro cooled CMOS camera. Up to this point I’ve just been playing around with live stacking short exposures, but I would like to see what I can do with stacking large amounts of frames but am being told that field rotation will become a factor at some point. When I googled ways to counter it, SGP and it’s manual rotation feature showed up, So I became interested in purchasing it. I did look at the SGP manual and found the section on manual camera rotation. In the example it shows, it somehow determines how far of the camera was off and then generated the amount of degrees it needed to be rotated. Buy how do I know how much to turn the camera to match the number of degrees it shows? does a grid show up on the screen and to give me a point of reference to know that I’ve rotated the camera the required number of degrees? and secondly, since my scope is a newtonian, will I be able to accurately line up the diffraction spikes on the stars or will the stacking software handle that?

Thanks in advance for any and all help,

Patrick


#2

SGP doesn’t handle field rotation. It will allow you to rotate your camera but it doesn’t adjust for any type of field rotation. Your best bet is stacking lots of short exposures.

Thanks
Jared


#3

Hi Jared -

  Thanks for responding. I did realize that the program doesn't compensate for it, but it has a module within it to either work with an automatic field de-rotator automatically rotate the camera or you can  manually rotate the camera your self. Im interested in the manual camera rotation discussed in the SGP manual on pages 69 and 70 as shown below.

thanks

Patrick


#4

sorry, I left something out in my last reply - my question was how do I know how many degrees my camera is turning when I manually rotate it? is there a grid of sorts on the screen that when Im lined up with it I will know the camera has been rotated the correct number of degrees?

thanks again for replying Jared -


#5

A de-rotator and a rotator are somewhat different beasts…although similar in nature. Yes, you can use the manual rotator to rotate the image but you’ll have to figure out the amount of “derotation” that you’ll need for each image.

You will rotate the camera and then on the dialog click “ok” this will plate solve the image and calculate the rotation. You can set the allowance on how close is good enough.

Thanks,
Jared


#6

Thanks Jared!


#7

@Patrick1

Field rotation in an alt azimuth mounted scope is 15 arc seconds / second (360 degrees / day). Depending on focal length and FOV, you could start seeing star trails in just a couple of minutes. The stars at the center of the chip will show no rotation and the stars at the edge of the chip will show the maximum amount of rotation in any given period of time.

It might be possible to take a short exposure, stop, manually rotate the camera and take another exposure but the amount of manual rotation would have to be very precisely done or you would introduce more rotation error than the sky produced.

There is a not-too-expensive solution. Optec provides free de-rotation software that works with their line of rotators. The Optec Pyxis LE rotator is their smallest model; fits into a standard 2" focuser and is (probably) a good match for your camera. Also, it is reasonably affordable. The derotation software needs an ASCOM interface for your Starmaster DOB. Since the direction of rotation changes between east and west of the meridian, the derotation software needs to know where the scope is pointing.

Optec Pyxis LE

Charlie


#8

Very easy Patrick, just guess it, you will soon become quite a dab hand at it. If I found it easy, it must be!!


#9

www.mainsequencesoftware.com