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Hello,
I did M31 recently and had to realize that APP totally screws up the galaxy core: Not only the luminance was flawed (totally burned out core), but also the colour around the core was not as expected (green cast instead of yellow/orange). From the rejection map you can see what APP did to the core. Same happened to a set of 1 minute exposures that was supposed to HDR the galaxy core.
Despite offering somewhat sharper structures and less noise, the result from Deep Sky Stacker looks a lot more what I desired - see attached stacking results below (no stretch on luminance, only on colour layer to make APP's mismatch colours obvious).
When you compare the stacking results, APP seems to alter the point spread function of the stars (PSF) in a way that makes this function look more like a stovepipe hat, rather than a bell-shaped curve. This apparantly has also occurred on the galaxy core, overexposing it with steep transitions to the surrounding area. Is this really what APP is supposed to do?
Anybody else experienced this on a galaxy with bright core?
Altering the point spread function of the stars also raises the question, if APP's stacking result is any use for a deconvolution operation. I would say no.
My data for this stack is as follows:
100x 5-minute exposures, ISO1600
Nikon D750 DSLR (unmodified)
Esprit 100/550
EQ6-R, MGEN-3
I stack TIFF insead of the NEF, because I do not like the result of APP's DDP.
So the enclosed pictures resemble unstreched stacking results of 100 TIFF files.
When using NEF for stacking and using DDP in APP, the stars get way too large for my taste. I also dislike the colour results APP creates from the Nikon NEF.
And I am still using APP version 1.079 (maybe that is an issue?).
Thanks for your advice!
Chris
PS: To get a decent processing on M31 I combined the APP 5-min. luminance stack with the core of my 1-min stack compiled by deep sky stacker. I aslo used the colour layer from the 5-minute DSS stack, not APP. Final result here: https://www.flickr.com/photos/147135308@N08/50356400121/
However, I would be happier if APP did this job alltogether...
