Elephant Nebula - Bicolour

[gnomus]

An attempt at the Elephant Nebula in bicolour.  I'd gathered the Ha data in October with a Tak 85.  The OIII was captured via my ED80 x 0.85.  These scopes gave different fields of view (450 mm for Tak vs 510 for the ED80).  I 'star aligned' these two sets of data using PixInsight.  At first I thought this had worked well.  However, on closer inspection, I noticed that whilst the stars in the centre were fine, those in the corners were not aligned well.  I was a bit confused by this.  Is it caused by the different field curvatures of the two scopes (according to CCD-I, the ED80x0.85 is flatter)?  In any event I cropped out the corners where the stars didn't align.  It made for a smaller FOV of course but I wasn't at all sure how else I could fix it.  I hope to get some SII soon (maybe even tonight).  Capture data in link below.  

Neither the Ha nor the OIII was captured at especially good times.  The moon was up and shining out brightly on all three nights.  But what was I supposed to do - watch Strictly?

[The_Sarge]

Looking good Gnomus.

Nice and contrasty.

Sarge

[michael.h.f.wilkinson]

Nice one!

[toxic]

very nice trunk Gnomus