M42 with just 27 mins total

[mikey2000]

I recently acquired a 200PDS scope and after barely a clear night, I got a clear patch in the vicinity of Orion.  I've not really tried M42 before....

I'd also read the sharpcap manual a bit closer and discovered it can produce sensor data for my camera by taking several test shots.  After that, it can take sky brightness readings to estimate the light pollution and recommend an exposure duration.  I was surprise to see a recommendation for 20s subs with my ASI1600MM so I compromised and rattled of some quick R G B Ha and Oiii subs (30s for RGB and 60s each for the narrowband).

 

I suppose the theory is that the read noise is low so short subs will allow the signal to sit above the read noise then shoot as many as possible to get smoother stacks.  

 

Enough background, here's the result....  ( 9 each of 30s R G and B,  6 each of 60s Ha and Oiii = 27 mins grand total).  Pixinsight processing.  I think the bright star it "Hatsya" - I find the Ha and Oiii haloes to be rather interesting!

[LightBucket]

 Very nice rendition, the core is excellent too, not blown out like many images you see...

[vlaiv]

Very nice capture in such short time!

Thing with short exposures is in diminishing returns.

Longer subs will always provide better data, but at some point there is not much difference, gains will be marginal. It's not about signal getting over read noise, it's about dominant component of the noise - in this case LP noise gets dominant after such time period and difference becomes too small.

BTW, Ha and OIII should have significantly longer exposure time for this to happen.

[mikey2000]

vlaiv, I see what you are saying.   I just used figures near to the sharpcap suggestions, to see what happens.   It seems the algorithm tries to get you in a place where you just meet the point of diminishing returns, noisewise.    I can see how many shorter subs has an advantage in plane trails, satellite trails etc, providing you stay beyond the marginal gain point.

 

It was just an experiment to see how I fared with 30s R/G/B and 60s NB in place of my usual 60s R/G/B and 300s NB.    

 

Of course the other side effect of shorter subs is the amount of extra data and processing time!  Ouch!

 

I read this article to try and understand it all a little more.  It's quite maths heavy  https://forums.sharpcap.co.uk/viewtopic.php?t=456

 

[gorann]

Obviously impressive for such a short exposure. How did you manage to produce that psychedelic star halo?