ASI294 2nd Light: Soul Nebula: Is this a waste of time..

[feilimb]

I might have been setting my sights a bit high, but I wanted to give the Soul Nebula a shot this evening.  I started shooting 180s exposures at gain 200, -10deg C on the ASI294MC Pro with *no filter* (as I don't have any yet).  I live in suburbs of a city, with moderate light pollution (I don't know what bortle scale number I am at).

The histogram of a single frame looks like this:

I initially tried 4 minute exposures, but the histogram peak was creeping to the right hand side of center so I brought it back to 180s.

When I do a very simple stretch on a single frame it looks like this (no debayering applied):

Am I wasting my time trying to capture this target without any filters?  Should I expect to see some diffuse nebula goodness in a single frame?

[Maxrayne]

With the Soul Nebula being an emission type nebula I would imagine it would be very difficult to get anything from a single image. If my memory serves right (and I'm sure others will correct me if I'm wrong), these types of nebula are best shot using an Ha filter or without an IR filter so as to capture that red easier.

That's probably a really poor way of putting it, but I think the gist of it is there. Either way, my personal opinion is that to expect anything from a single unfiltered frame is asking a lot, even at 3 minutes. Have you tried stacking them yet?

[Big Jim Slade]

Given the lower surface brightness, plus the high sky background, you may be better off with lots of short (60 secs) exposures. If you get 30 or so it may start to emerge. (Caveat - I'm a CCD guy, so someone with more CMOS knowledge may know better.)

[wimvb]

Cmos cameras have their highest dynamic range at low gain settings. This means that at lower gain, you can capture detail without stars becoming too bloated. In your case, I would lower gain a fair bit (maybe to half or a third of what you have now). The histogram that you have shows the effect of vignetting, more than any nebulosity. To stand a chance of actually capturing and showing the nebula, you will need to take lots of exposures at lower gain. Then take darks, flats and bias frames (or dark flats). Properly calibrate your data before trying to pull out the nebula.

Good luck, and clear skies.

[feilimb]

Thanks all for the replies, I ended up shooting about 40 exposures of 3 minutes each before I packed it in with heavy dew forming (I don't have any dew heaters yet).  The final few frames may be unusable due to dew which had formed, but I will stack what I have and see if there is any hint of nebula detail in there.

Thanks Jim for the suggestion on short exposures, I thought if I went as short as a minute I would not pick up anything but it is definitely worth a try and as you say even with 30 minutes stacked it would be interesting to see what comes out.

@wimvb thanks also, I'm new to this whole world of OSC so interesting to note that lowering the gain can work to an advantage in this way, so I have a few things to try and tinker about with on my next clear sky.

Ultimately I guess a HA filter or similar will greatly aid in cutting out the light pollution and allowing for much longer exposures without the sky background being washed out but it would be nice to see what one can achieve without the use of filters (but obviously that would be more achievable at a dark sky site).

 

[wimvb]

You can reduce the light from light pollution during post processing. But you'll be left with the associated noise. Your final stack will most likely be very noisy after stretching. There are only two solutions; either a filter or lots and lots more data.

[SteveNickolls]

You will be fighting local light pollution all the way with your colour camera I'm afraid. Some filter might help depending on the pollution and there's a number out there to try. A UHC type may well help.  Best to have a go stacking a number of exposures together with dark, flat and bias frames and see what you get as a starting point.

Cheers,
Steve

[Adam J]

On 15/11/2018 at 20:17, feilimb said:

I might have been setting my sights a bit high, but I wanted to give the Soul Nebula a shot this evening.  I started shooting 180s exposures at gain 200, -10deg C on the ASI294MC Pro with *no filter* (as I don't have any yet).  I live in suburbs of a city, with moderate light pollution (I don't know what bortle scale number I am at).

The histogram of a single frame looks like this:

I initially tried 4 minute exposures, but the histogram peak was creeping to the right hand side of center so I brought it back to 180s.

When I do a very simple stretch on a single frame it looks like this (no debayering applied):

Am I wasting my time trying to capture this target without any filters?  Should I expect to see some diffuse nebula goodness in a single frame?

Are you sure it was totally clear last night? This looks like bad transparency to me. At least when I see vignetting on my 130PDS its normally because of high level cloud. I can see from the stars you are correctly framed.  There are a couple of bright patches in the Soul nebula....I would expect those to have shown up at the very least irrespective of the filter you are using but I see nothing in the location they should be. Unless you are imaging from the Irish equivalent of central London.

[Adam J]

Hang on a min when I download that image and look at it in photoshop it comes up as mono 8 bit.....how are you converting it from a FITS to a TIFF / JPG?

You wont see anything in mono from a OSC camera or is this just the red channel?

Do you have the debayering set correctly?

Adam

[feilimb]

15 hours ago, Adam J said:

Hang on a min when I download that image and look at it in photoshop it comes up as mono 8 bit.....how are you converting it from a FITS to a TIFF / JPG?

You wont see anything in mono from a OSC camera or is this just the red channel?

Do you have the debayering set correctly?

Adam

The above image was *not debayered, the fits was captured in raw 16 bit mode, opened in PixInsight, stretched via Histogram Transformation and then saved as JPG from Pixinsight (after reducing its size). 

I have not had an opportunity yet to stack and process the subs I got on the night, but when I do I'll update the thread with what came out (though I don't expect much due to the light pollution). 

[feilimb]

16 hours ago, Adam J said:

Are you sure it was totally clear last night? This looks like bad transparency to me. At least when I see vignetting on my 130PDS its normally because of high level cloud. I can see from the stars you are correctly framed.  There are a couple of bright patches in the Soul nebula....I would expect those to have shown up at the very least irrespective of the filter you are using but I see nothing in the location they should be. Unless you are imaging from the Irish equivalent of central London.

The transparency was OK to begin with on the night, but as the night progressed it worsened (although the frame above was first of the night). There was no filter used, my light pollution is moderate certainly not on the scale of London

[Adam J]

6 hours ago, feilimb said:

The above image was *not debayered, the fits was captured in raw 16 bit mode, opened in PixInsight, stretched via Histogram Transformation and then saved as JPG from Pixinsight (after reducing its size). 

I have not had an opportunity yet to stack and process the subs I got on the night, but when I do I'll update the thread with what came out (though I don't expect much due to the light pollution). 

Yeah you wont see anything on a non debayered image.

[alacant]

Hi

Could you tell us what telescope you used and send a link to the fits file as it was directly from the camera?

Cheers

[PeterCPC]

If it help at all - this was 75mins total exposures with a Samyang 135mm on my Canon 1200d (modified). Heart and Soul.

Peter

[feilimb]

13 hours ago, alacant said:

Hi

Could you tell us what telescope you used and send a link to the fits file as it was directly from the camera?

Cheers

Hi alacant, I used a Skywatcher ED80 with the 0.85x focal reducer putting it at 510mm F/6.4.  I'll upload a FITS file to WeTransfer shortly, I tried stacking today and have not had any success in a very quick processing session, I fear the data is just not good enough due to (a) light pollution, and (b) a quarter moon and probably most importantly (c) no filter of any kind used ? It's all part of the learning curve !

I took some flats also, but I fear they may not assist in the integration due to dew which had built up on the objective by the time I took them.

I'll upload a single early light frame as FITS and deep sky stacker integration, the version without the flats (so lights only):

Single sub (180s at Gain 200) 22MB : https://we.tl/t-0p2PONXsyB

Deep Sky Stacker Stack (no calibration frames, around 38 lights) 67MB : https://we.tl/t-49TpDm7W57

@PeterCPC thanks that is beautiful! Can I ask did you use any filter at the time, or if light pollution was a factor?

[alacant]

8 hours ago, feilimb said:

Stack (no calibration

I can't find much nebulosity I'm afraid. Even StarTools' big hammer didn't work:( Still thinking...

If no one else comes up with a solution.... Do it again, but this time with dark and flat frames, unity gain and say, 90s snaps?

Cheers, good luck and clear skies.

[PeterCPC]

8 hours ago, feilimb said:

 

thanks that is beautiful! Can I ask did you use any filter at the time, or if light pollution was a factor?

No filter used at all. Light pollution here means that I would normally use an IDAS D2 when imaging with a scope but I can't use it with the Samyang obviously. I "processed" out as much LP as I could.

Peter

[feilimb]

2 hours ago, alacant said:

I can't find much nebulosity I'm afraid. Even StarTools' big hammer didn't work:( Still thinking...

If no one else comes up with a solution.... Do it again, but this time with dark and flat frames, unity gain and say, 90s snaps?

Cheers, good luck and clear skies.

 

Thanks for trying @alacant , it looks similar to what I was getting after a quick process but it's good to know it was not just down to my processing skills!  Thanks for the suggestion, unfortunately the moon is getting bigger again these days and it's probably going to be a few weeks again before the moon is not in the way but I will try your suggestion of dropping the expsosure time to 90s with unity gain.

I will probably get too tempted - and go straight for a filter (I might pick up a Ha in the near future).  It seems in the past 2 months like all the best clear nights for me are happening when the moon is getting bigger, and having a Ha filter would just give such a great edge on being able to image when the moon is out too.

I have a CLS LP filter for EOS clip in (for DSLR's) and as a stop-gap I might try blu-tacking it to cover front window on the ASI294 ... and see how that performs!