First light with an ASI 1600mm Pro

[JSeaman]

My 'new' (to me) camera arrived today and I am very pleased indeed! It looks to be in mint condition and was a bargain at £750 with a dew heater and next day delivery thrown in thanks to a very kind seller. 

Running at 27% the TEC sat at -10 degrees with ambient of around 5 so it is very capable of cooling

My guiding was only around 0.8 arc-seconds which is way above the 0.53" I think I need with the 1600. Even with that (and the clouds) I am bowled over by the performance. 

I am using unity gain (139) and an offset of 15 to get me started - if anyone has any thoughts on this please chime in!

I finally have stars that are dots not blobs! The Atik 314 I have been using was a great entry into narrowband but with my 1,500mm focal length on the 300PDS it really was pushing it. This is a much better match with an FOV I can actually use! I ran a quick sub of NGC281 (Pacman) in Ha just to compare old and new and I'm very pleased with the result. t will be a while before a proper pic can be done but this is a very positive start.

So here are the pictures, first a 2x2 binning 10 minute sub from the Atik (cropped heavily). You can see I have drift and blobby stars but a reasonable bok globule from a single sub

Next, a 5 minute sub with 1x1 binning (so effectively 1/4 duration) from the ZWO:

Obviously a bit more noise but blimey is that a step forward! I think I can seriously look at 5 minute 1x1 subs and certainly 10 minute 1x1

Here's a 5 and 10 minute sub in Ha (full field of view)

 

And this was the fov I was playing with before:

Lots to play with still but for some first light I am very very happy indeed!

[Adreneline]

1 hour ago, JSeaman said:

I am using unity gain (139) and an offset of 15 to get me started - if anyone has any thoughts on this please chime in!

As you say a promising start with your first light.

There are numerous views on what gain and offset to use on all the forums. I've used a 1600 for a couple of years now and always use gain 139. I use the 1600 with an ASIair and ZWO set the offset at 50 with no means to change it. On that basis alone you might say 50 was a good place to start. Sticking with one setting makes life easier with calibration frames too.

HTH

Adrian

[JSeaman]

Great stuff, many thanks for that input, appreciated

[JSeaman]

I can't get over how good this is, below is a single 5 minute sub crudely converted to red with 1 dark frame and some bias:

 

[Adreneline]

7 minutes ago, JSeaman said:

and some bias

The perceived wisdom is not to use bias frames - better to use flats, corresponding dark-flats and darks to calibrate.

Adrian

[JSeaman]

Oh really, I've always taken bias previously so didn't think twice. I have no idea what a dark-flat is but I guess I'll get searching now. The darks are definitely showing some glowing around the edges:

 

[Jamgood]

1 minute ago, JSeaman said:

Oh really, I've always taken bias previously so didn't think twice. I have no idea what a dark-flat is but I guess I'll get searching now. The darks are definitely showing some glowing around the edges:

Dark Flat is the same exposure as a Flat but with the cap on. 

[Adreneline]

1 minute ago, JSeaman said:

Oh really, I've always taken bias previously so didn't think twice. I have no idea what a dark-flat is but I guess I'll get searching now. The darks are definitely showing some glowing around the edges:

With the likes of the ASI1600 bias frames are likely to increase noise in the image. @Jamgood has provided the info on a dark-flat.

Adrian

[JSeaman]

Ah thank you, not sure what that adds beyond the darks and bias?

 

I just stretched the master bias and it's the cleanest I've ever had, I don't know what issues people have with them normally? Grey outline is pixinsight window and the grey square is the bias

Edited February 16, 2021 by JSeaman

[JSeaman]

Very interesting, I just re-ran that 1 minute sub through with the single dark but no bias and it has a dramatic effect for sure, the contrast is much worse without bias but there is a noticeable increase in noise, this is the pic with then without bias:

 

[JSeaman]

I couldn't get over the difference so I just double checked, I must have saved some PI processing in the old picture. There is almost no difference with/without bias frames, a very slight contrast improvement is all I see

[Adreneline]

 

@JSeaman there are numerous threads about this (like this one on CN - you don't really need to read past the second post) and the consensus seems to be that unless you are scaling darks there is no advantage in using bias as it may increase noise.

I take flats and dark-flats for each filter, and a small set of darks (180s, 120s, 60s and 30s) and that works well for me. I only use gain 139 and offset 50. There are enough variables in this hobby without adding more than are necessary.

 

[JSeaman]

OK great, thanks again for the insight, I'll continue to play around with bias but very carefully reviewing what effect it has. Again, appreciate the headstart in finding my feet with the new toy