strange results from widefield orion

[Andywilliams]

Hi all,

I took this data set 2 nights ago and have tried to stretch and process it with awful results. I thought would be noiseless and bursting with Barnards loop due to the exposure times.....but its as noisy as all hell and there is very little nebulosity....from a modded camera !! 

I have put the TIFF file up for anyone who feels interested in having a look (with my eternal gratitude !) .

canon 40d modified

Samyang 14mm @ f2.8

11X310 seconds lights

5X310 seconds darks

20Xflats

stacked in DSS

I just cant get a decent stretch and process out of this !

 

All advice is very welcomed.

Thanks guys.

Andy

 

 

barnards loop.TIF

[Rustang]

I think you have done what I've done recently and cooked the exposure time, I was struggling with 120 sec subs being a little washed out and hard to stretch so 310 could be even worse!? I've been told recently that more shorter exposure subs will give you the same results as the same period of time in longer subs, so x10 30sec subs will give you the same results as x5 1min subs and so on but you need an hour or two of the 30 sec subs but it shoundnt wash out. What's a single 310 sub look like? P. S I'm still very new so apologies if I'm learning wrong, someone will correct me if so. 

[Knight of Clear Skies]

What ISO setting did you use please, and how much light pollution is there in your sky? Have you tried looking at the individual subs? Barnard's Loop should show up clearly in a 5 minute exposure at f2.8.

One quick tip, stacking with just 5 dark frames will likely introduce more noise than it eliminates - it's not enough to frames to average out properly. Also, did you take dark bias frames? Personally I rarely bother with DSLR darks, unless the temperature profile is the same as the lights they won't reduce noise, but I do take bias frames.

58 minutes ago, Rustang said:

I think you have done what I've done recently and cooked the exposure time, I was struggling with 120 sec subs being a little washed out and hard to stretch so 310 could be even worse!? I've been told recently that more shorter exposure subs will give you the same results as the same period of time in longer subs, so x10 30sec subs will give you the same results as x5 1min subs and so on but you need an hour or two of the 30 sec subs but it shoundnt wash out.

This isn't quite right, as short subs will introduce more read noise to the stack. I don't know what the optimal sub time is for a DSLR, it will depend on the model of camera and sky brightness but 30 seconds is definity not ideal. On the other hand I've managed to image some fairly faint objects with 2 minute subs.

Like you, I also wonder if a 310 second sub at f2.8 might be over-exposed.

[Rustang]

The whole process of astrophotography keeps going round in confusing circles then! I assumed longer exposures where I live would help with deeper less bright sky objects but I was having difficulties with 2min subs, so questioned on another forum to get the response I posted above. As I say though I'm still very much learning. 

[Knight of Clear Skies]

Yes, it's certainly a learning curve. It's hard to give concrete advice on sub length as there are a number of factors at play. If your sky is bright you do need to reduce ISO (although you probably don't want to go below 400, at low ISO the camera starts discarding photons) and exposure time. Read noise differs from thermal noise. The camera introduces a certain amount of noise when reading the image out of the sensor, which is why longer subs give better results when it's possible to take them. 

[ollypenrice]

1 hour ago, Rustang said:

I think you have done what I've done recently and cooked the exposure time, I was struggling with 120 sec subs being a little washed out and hard to stretch so 310 could be even worse!? I've been told recently that more shorter exposure subs will give you the same results as the same period of time in longer subs, so x10 30sec subs will give you the same results as x5 1min subs and so on but you need an hour or two of the 30 sec subs but it shoundnt wash out. What's a single 310 sub look like? P. S I'm still very new so apologies if I'm learning wrong, someone will correct me if so. 

You've been misinformed about sub length although, with a CMOS chip with low read noise, it is possible to do well with a higher number of shorter subs. Using CCD at a dark site I used sub lengths of 15 minutes, 50 seconds and 11 seconds.

I'm downloading the file and will have a play with it if ever it manages to get through a rural French net connection!

Olly

[Andywilliams]

Hi guys....thanks for replying ?

iso 1600 and the skies are rural NZ .....so no light pollution at all.

having said that the ‘seeing’ wasn’t brilliant this particular night but the Milky Way and clouds of Magellan were easily visible. 

I am very interested in the length of subs conversation that’s going on.....I am learning here ??

[Andywilliams]

54 minutes ago, Knight of Clear Skies said:

What ISO setting did you use please, and how much light pollution is there in your sky? Have you tried looking at the individual subs? Barnard's Loop should show up clearly in a 5 minute exposure at f2.8.

One quick tip, stacking with just 5 dark frames will likely introduce more noise than it eliminates - it's not enough to frames to average out properly. Also, did you take dark bias frames? Personally I rarely bother with DSLR darks, unless the temperature profile is the same as the lights they won't reduce noise, but I do take bias frames.

This isn't quite right, as short subs will introduce more read noise to the stack. I don't know what the optimal sub time is for a DSLR, it will depend on the model of camera and sky brightness but 30 seconds is definity not ideal. On the other hand I've managed to image some fairly faint objects with 2 minute subs.

Like you, I also wonder if a 310 second sub at f2.8 might be over-exposed.

Thanks for replying.

iso 1600 ..... good clear skies but with some sky glow.

I’m interested in the darks advice and no, I didn’t take dark bias frames.

On individual subs I can see Barnards loop and the rosette.

Many thanks for your help thus far ?

I might stack without the darks and just keep the flats and see if that makes any difference.

Cheers, Andy 

 

[ollypenrice]

Here's my attempt. Not realizing that you were shooting from NZ I turned it upside down! Also, for a better reading in Levels, I cropped it. Sorry about the Pleiades! There seems to be a fair amount of uneven diffused glow. I'd have put it down to passing cloud but you say it was clear? You couldn't have a local and possibly intermittent source of extraneous light?

It was hard to persuade the colour to show itself. For anything Ha there's a simple trick in Ps. Go to Image, Adjustments, Selective Colour and, in the reds, move the top slider left to lower the cyans in red. Barnard's, the Meissa Nebula, the Rosette and the Cone do show but I'd have thought they should be stronger. I didn't fight with the top right hand corner because I wonder what's causing the broad green glow.

Olly

[Hallingskies]

12 minutes ago, ollypenrice said:

I wonder what's causing the broad green glow.

The only time I have ever seen Zodiacal light was in NZ.  Wonder if that natural sky glow is what’s showing up here?

[ollypenrice]

39 minutes ago, Hallingskies said:

The only time I have ever seen Zodiacal light was in NZ.  Wonder if that natural sky glow is what’s showing up here?

Won't Orion be a bit late at this time of year? I see it here in the Autumn but it's on the other side of the constellation and it's like an upward pointing wedge.

Olly

[Knight of Clear Skies]

Good to see Olly has found plenty of star colour there, so the subs aren't over-exposed. I'm also surprised there isn't a bit more Ha signal there.

Concerning the green haze, there is something of a wide ring at top right - just to the right of the Hyades - which makes me suspect it's an artifact caused by the flats. It's also possible there was some cirrus cloud about when you were shooting, did you stack with a kappa-sigma clip?

[Andywilliams]

8 hours ago, ollypenrice said:

Here's my attempt. Not realizing that you were shooting from NZ I turned it upside down! Also, for a better reading in Levels, I cropped it. Sorry about the Pleiades! There seems to be a fair amount of uneven diffused glow. I'd have put it down to passing cloud but you say it was clear? You couldn't have a local and possibly intermittent source of extraneous light?

It was hard to persuade the colour to show itself. For anything Ha there's a simple trick in Ps. Go to Image, Adjustments, Selective Colour and, in the reds, move the top slider left to lower the cyans in red. Barnard's, the Meissa Nebula, the Rosette and the Cone do show but I'd have thought they should be stronger. I didn't fight with the top right hand corner because I wonder what's causing the broad green glow.

Olly

WOW ! Olly....Thankyou so much !

That is much better than I had achieved.

I don't mind the green....we get a lot of sky glow here.

Also, thanks for the advice re PS for Ha imaging.

The seeing wasn't perfect this night but it wasn't enough to explain the diffuse glow....that said, and I don't want to brag, but the skies are so good here that this could be a mixture of sky glow and some milky way. I must concede that it could also be very high cloud ......the seeing was average despite a clear sky.

There could well be an artefact with the lights as there was an enormous dust bunny on the individual subs which I need to attend to.

What tips do you have concerning star colour?....you have brought them out beautifully !!

Once again, Many thanks

Andy

[Andywilliams]

7 hours ago, Knight of Clear Skies said:

Good to see Olly has found plenty of star colour there, so the subs aren't over-exposed. I'm also surprised there isn't a bit more Ha signal there.

Concerning the green haze, there is something of a wide ring at top right - just to the right of the Hyades - which makes me suspect it's an artifact caused by the flats. It's also possible there was some cirrus cloud about when you were shooting, did you stack with a kappa-sigma clip?

I have to admit that kappa-sigma clip is something I don't fully understand and therefore I tend to leave DSS on its default settings.

Ignorance is not always bliss !

[Knight of Clear Skies]

27 minutes ago, Andywilliams said:

I have to admit that kappa-sigma clip is something I don't fully understand and therefore I tend to leave DSS on its default settings.

Ignorance is not always bliss !

The Sigma clip option is great for removing artifacts such as clouds, satellite trails and airplanes. Basically it works by rejecting any data that is too far outside the average values. You'll find it under the DSS stacking options.

[Andywilliams]

2 hours ago, Knight of Clear Skies said:

The Sigma clip option is great for removing artifacts such as clouds, satellite trails and airplanes. Basically it works by rejecting any data that is too far outside the average values. You'll find it under the DSS stacking options.

brilliant.......I will use when needed from now on .....thankyou.

[Andywilliams]

On 28/02/2019 at 23:12, ollypenrice said:

Here's my attempt. Not realizing that you were shooting from NZ I turned it upside down! Also, for a better reading in Levels, I cropped it. Sorry about the Pleiades! There seems to be a fair amount of uneven diffused glow. I'd have put it down to passing cloud but you say it was clear? You couldn't have a local and possibly intermittent source of extraneous light?

It was hard to persuade the colour to show itself. For anything Ha there's a simple trick in Ps. Go to Image, Adjustments, Selective Colour and, in the reds, move the top slider left to lower the cyans in red. Barnard's, the Meissa Nebula, the Rosette and the Cone do show but I'd have thought they should be stronger. I didn't fight with the top right hand corner because I wonder what's causing the broad green glow.

Olly

Only, Could I please ask you for your workflow for your processing of my image?

With many thanks,

Andy