Having captured this
widefield shot of the NGC7000/IC1318 region last year with a 165mm focal length Pentax MF lens I wanted to try my hand at a four panel mosaic using my TEC 140. The 980mm focal length obviously meant a much narrower field of view and operating at f/7, as compared to f/2.8 with the Pentax lens, meant much more time spent capturing the subs. Here is a thumbnail of the final result at one eighth size:
Click here for the full-size version (6MB download)
Each panel required 16 x 1,000 second H-alpha subs and 5 x 200 second subs in each of red, green and blue for a total exposure time of a little over 21 hours. PixInsight was used to produce both an H-alpha and an RGB mosaic. The H-alpha image had the stars removed (in Photoshop) and was a blend of that "no stars" image together with processed versions using PixInsight's LocalHistogramEqalization and HDRMultiscaleTransform tools. The RGB image was split into "no stars" and "just stars" versions. The "no stars" image, while considerably less deep than the H-alpha image, was used to modify the colour of the brighter regions of the nebulosity while the fainter regions were coloured with my default "red plus a bit of blue". The RGB stars were then added to the colourised H-alpha data. Lots of tweaks along the way but those are the key steps used.
I think I've learned a lot while processing this image and I've come away with a huge respect for those who routinely do mosaics involving more than two panels. When I look at my own effort closely I see all sorts of defects and I rather doubt that I'll be jumping back into a similar four panel project for a while given the amount of telescope time required, time which has been particularly precious here in the UK this summer.