Deep Sky Stacker Mosaic for larger DSOs

[Tommohawk]

Hi All

I've had some modest success imaging DSOs, and now find I want to image some which are larger than my camera sensor, eg M31 Andromeda.

I realise that I can get a field reducer, or indeed use just camera only - but I dont have any lenses for it.

I wonder can I simply image it in 2 sections and use the mosaic setting in DSS to effectively stitch them? Obviously I would need to ensure some overlap - not sure how much - but would this work?

I think I sort of did this inadvertently when doing M27 - after meridian flip my centring was a bit off, but DSS happily rotated the image and realigned. The only problem was that the border on one side was lighter - presumable had few exposures. No problem - just cropped it.

So I'm guessing for this to work I would need to ensure a larger number of expossures to avoid any differences on the 2 panels.

Any thoughts please?

[Tommohawk]

Well... I tried this and in principle it works fine. I dont know how much overlap is required - I allowed about 20% and it seemed to register just fine. the problem is that the overlapped area looks diffferent, presumably because it has twice the number of exposures.

Does anyone know how many exposures it would take to even things up? And is it likley that doing more shorter exposres would make this easier? This is M31 so pretty bright.

thanks

[Gib007]

Normally when you image a mosaic in segments, the background in both segments will have a slight difference in brightness and this leads to a discontinuity where the segments are joined. However, software can remove this seam and PixInsight does a wonderful job of it. A free alternative that seems to be very popular is Microsoft ICE. Have a look for it.

The way I would sort this is I would calibrate and stack both mosaic segments individually in DeepSkyStacker. Once I have two calibrated and stacked images that need joining, I'd stick them in Microsoft ICE and let that join them up. Then once joined, you can carry out the rest of your post-processing. 

[Tommohawk]

Normally when you image a mosaic in segments, the background in both segments will have a slight difference in brightness and this leads to a discontinuity where the segments are joined. However, software can remove this seam and PixInsight does a wonderful job of it. A free alternative that seems to be very popular is Microsoft ICE. Have a look for it.

The way I would sort this is I would calibrate and stack both mosaic segments individually in DeepSkyStacker. Once I have two calibrated and stacked images that need joining, I'd stick them in Microsoft ICE and let that join them up. Then once joined, you can carry out the rest of your post-processing. 

Hey thats great - never heard of ICE before. I'll give it a whirl - always keen for a freebie! I wonder about colour depth and format - had a quick look and I think ICE can handle 16 bit depth. So keep with 16bit .tiff I guess?

Thanks

[Gib007]

Hey thats great - never heard of ICE before. I'll give it a whirl - always keen for a freebie! I wonder about colour depth and format - had a quick look and I think ICE can handle 16 bit depth. So keep with 16bit .tiff I guess?

Thanks

No worries at all. I admit I have never tried it myself, but I've heard a good number of astrophotographers who have used it with great success. Indeed, I would stick to 16-Bit TIFF. 

[Tommohawk]

OK. Now all I need is some clear sky.... hmmmm. Could be in for a long wait!

I'll come back to this thread and post my best effort.