First attempt at dithering and IC1396

[alan4908]

My first attempt at IC1396 over the summer turned out also to be my first attempt at dithering and multiple night exposure.  I was motivated to try dithering since I'd previously noticed the presence of hot pixels on my images, particularly after they had been stacked and streached.

When I switched on dithering, I was surprised to discover that the guide scope needed about 20s to recover between sub frames (each dithered by 2pxls).  On examining my first nights output, I also discovered that IC1396 is a very faint object which drove which me to try stacking sub frames over multiple nights in order to increase my overall exposure time.  I subsequently discovered the pointing limitations of my telescope mount (basically I was pointing at slightly different parts of IC1396 each night  ) and consequently the limitations of automatic stacking algorithms  - when you try to you try stack subframes that have large misalignment between them it doesn't work well. Fortunately, the main item of interest,  the so called "Elephants Trunk" feature had been captured over all the 4 nights. So, to overcome the problems of stacking, I decided to go for a SD Clip stack over each night (thereby hopefully minimizing the hot pixels) which gave me 4 stacked images.  Having reduced the hot pixels with the SD Clip stack,  I then decide to maximise my signal to noise ratio by stacking each night with a SUM stack.  I presume I could have done this via a manual 2 star stacking but I didn't fancy manually aligning 53 sub frames. (As a matter of interest, I also tried an astrometric stack where I plate solved each sub frame prior to stacking - this almost worked but I noticed that some of the stars did not appear to be precisely aligned).  

Anyway, after all that the resulting image is below - I'm not sure if I can see an Elephant's trunk but I can see a horse.  LIGHTS: 53 x 600s at -20C; BIAS:100; DARKS: 40; FLATS: 40 per night.  

Equipment: SW 80ED with 0.85 F/R and Trius SX-26C,  Startravel 80 guide scope with X2lodestar, NEQ6 mount, EQMOD mount control, MAXIM DL image capture, Photoshop CC post processing. 

Alan