Horsing Around In Orion

The Horsehead was a notoriously difficult deep sky object for film based astrophotographers.

It's an Icon of Astrophotography!

I decided to find out if it was possible to capture anything of it with a 2 minute exposure using the Orion 100mm Refractor.

The Orion is on an Equatorial Mount with an RA drive attached to follow the stars.

I've found 2 minutes is the window guaranteed to give you a well tracked exposure.

After that its astro-roullette! You really need a guider for longer exposures.

Stage 1

A lot of images were trailed due to vibration, wind and drifting. I had about 4 good frames to use for stacking. A couple of these were around a minute and didn't show much, so I ended up using just two frames of 115 and 120 Seconds at ISO 1600.

This is the first frame straight off the camera

and unprocessed.

Stage 2

Frames 1 and 2 had a Dark Frame

(an exposure of similar duration with the lens cap on to capture just camera noise) subtracted using Photoshop, and were stacked together. Stacking reduces noise by increasing Signal to Noise Ratio.

Stage 3

Finally the image was adjusted for colour, brightness and contrast in Photoshop and passed through 'Neat Image' to reduce noise. The image was not adjusted to look 'red'. The red colour came out when brightness and contrast were greatly boosted.

Update from 2009

This horsehead image is much closer to the exposure times required and is a stack of 7 frames

taken at 2 minutes each with an Antares 8" Newtonian on equatorial mount.

Conclusions

The Horsehead is faintly visible. The noise levels limit how far you can process. Looking at the results, I'd like to capture three frames at lower ISO (200) with longer exposure times (4 minutes) to greatly reduce noise. I will need an off-axis guider to stop the scope from drifting during this time.

Next time out!