Pacman Nebula in Ha Atik 383L+ (NGC 281)

[tooth_dr]

Over two nights I gathered around 61 subs of 300s.  Out of these I ended up using 56 of them.  The Moon was about, and it was extremely windy during the first night of capture (it was the evening of Storm Ali and I believe the jet stream was unfavourable too) but this is still my best Pacman to date.  I did gather some nice RBG data after the Moon set, however I just cannot seem to be able to combine it without it looking washed out.

Here is my mono version so far, ED80/0.85x FF/Atik 383L+.

 

 

[LightBucket]

 Very nice, maybe you could get away with stretching a bit more..?. Just a thought...

[tooth_dr]

2 hours ago, LightBucket said:

 Very nice, maybe you could get away with stretching a bit more..?. Just a thought...

Thank you William. I think you may be right. I wasn’t too careful with my curves stretches and it got real noisy. In more capable hands I’m sure it would be better ?

[Allinthehead]

Nice. Snap on the choice of target. I've got 2 hrs Ha from last week and hopefully tonight stays clear for a proper run. Well worth grabbing plenty of rgb on this. I saw this beautiful image on astrobin which shows some nice dust in the background. 

https://www.astrobin.com/full/364083/B/

Hopefully you can find a way to combine your rgb.

[jjosefsen]

It is looking pretty good I think. What software do you use for processing?

[tooth_dr]

2 minutes ago, jjosefsen said:

It is looking pretty good I think. What software do you use for processing?

I used DSS to stack, and processing PS.  On my observatory PC which I am on now, it looks awful, but on my laptop and phone it looks ok!

[jjosefsen]

8 minutes ago, tooth_dr said:

I used DSS to stack, and processing PS.  On my observatory PC which I am on now, it looks awful, but on my laptop and phone it looks ok!

Yeah they difference from one monitor to another can really surprise you. I check on two pc monitors while processing and on a tablet before showing anyone else..

[toxic]

very nice image Tooth and field of view 

[tooth_dr]

Thanks Chris @toxic

I've been out imaging NGC7380 this evening, and went out to switch to NGC1499, but clouds have rolled in.  With a 16% chance of rain, I'm closing up shop for this evening.

[jjosefsen]

5 minutes ago, tooth_dr said:

Thanks Chris @toxic

I've been out imaging NGC7380 this evening, and went out to switch to NGC1499, but clouds have rolled in.  With a 16% chance of rain, I'm closing up shop for this evening.

Uuuh the Wizard.. Such a great object! I tried it with a stock DSLR last year and left defeated, so looking forward to seeing your, and having a go at it again some time myself.

[tooth_dr]

5 minutes ago, jjosefsen said:

Uuuh the Wizard.. Such a great object! I tried it with a stock DSLR last year and left defeated, so looking forward to seeing your, and having a go at it again some time myself.

Thanks. I tried it with a DSLR in the past too and it didn’t amount to much either ?

 

 

[jjosefsen]

I think I poured a little over twice as much data into it, and it looked pretty much the same. ?

It really needs a modified or dedicated Astro cam.

[tooth_dr]

6 hours ago, jjosefsen said:

I think I poured a little over twice as much data into it, and it looked pretty much the same. ?

It really needs a modified or dedicated Astro cam.

That was with a modded DSLR too

[tooth_dr]

@jjosefsen

here are 2 screenshots last night from my dual rig of ED80s. Modded 40d ISO800 300s with CLS filter (exif = 6oC) and Atik 383L+ 600s H-alpha filter (-15oC)! Both auto-stretched in APT using histogram function. 

 

[Xiga]

On ‎23‎/‎09‎/‎2018 at 16:08, tooth_dr said:

Over two nights I gathered around 61 subs of 300s.  Out of these I ended up using 56 of them.  The Moon was about, and it was extremely windy during the first night of capture (it was the evening of Storm Ali and I believe the jet stream was unfavourable too) but this is still my best Pacman to date.  I did gather some nice RBG data after the Moon set, however I just cannot seem to be able to combine it without it looking washed out.

Here is my mono version so far, ED80/0.85x FF/Atik 383L+.

 

 

Love the Pac-man nebula! And this looks great on my work monitor Adam. I thought about imaging on this night too, but without an obsy to shield me from the winds I didn't want to risk ending up with hardly any useable subs!

I saw you mentioning in another thread about the noise in your subs and how at 5 mins they probably aren't long enough. I definitely agree, you should aim for longer subs, you have the tracking capabilities to do it and you'd probably see a nice improvement.

If you want a little help in determining how long to expose for, here is a General Rule of Thumb:

You want your minimum Mean ADU to be no lower than   [Offset + (3 * r^2)/e] * (2^16)/(2^bits);          i.e for your 383L+       -> (203 + (3 * 49)/0.41) * 1 = 562

And likewise at the top end there's no need to go beyond [Offset + (10 * r^2)/e] * (2^16)/(2^bits);        i.e for your 383L+       -> (203 + (10 * 49)/0.41) * 1 = 1,398

The ideal level would be somewhere in between, and as close to the high-end as possible without clipping too many stars. Note, I had to Google the Offset value for the 383L+ so if I've got that (or anything else) wrong please someone let Adam know! Also, the formulae above aren't mine, they come from a very knowledgeable chap called Jon Rista over on CN.

If you have a program that reports the Mean ADU level of your subs then this is easy. I use SGP myself, and I've calculated that for my D5300 I need a minimum Mean ADU level of around 2,490. To achieve this I need to do 20 min long subs when shooting in NB, although I'm only just scraping it at the moment even with 20 mins, so I would probably see an improvement if I went to 25 mins.

If it's any help to you, you could post one of your raw subs and I could open it in SGP when I get home from work later and let you know what ADU it reports.

[jjosefsen]

What is r, e and bits on this equation?
I assume bits is the dac? (I.e. 12/14/16)

 

[tooth_dr]

4 minutes ago, Xiga said:

Love the Pac-man nebula! And this looks great on my work monitor Adam. I thought about imaging on this night too, but without an obsy to shield me from the winds I didn't want to risk ending up with hardly any useable subs!

I saw you mentioning in another thread about the noise in your subs and how at 5 mins they probably aren't long enough. I definitely agree, you should aim for longer subs, you have the tracking capabilities to do it and you'd probably see a nice improvement.

If you want a little help in determining how long to expose for, here is a General Rule of Thumb:

You want your minimum Mean ADU to be no lower than   [Offset + (3 * r^2)/e] * (2^16)/(2^bits);          i.e for your 383L+       -> (203 + (3 * 49)/0.41) * 1 = 562

And likewise at the top end there's no need to go beyond [Offset + (10 * r^2)/e] * (2^16)/(2^bits);        i.e for your 383L+       -> (203 + (10 * 49)/0.41) * 1 = 1,398

The ideal level would be somewhere in between, and as close to the high-end as possible without clipping too many stars. Note, I had to Google the Offset value for the 383L+ so if I've got that (or anything else) wrong please someone let Adam know! Also, the formulae above aren't mine, they come from a very knowledgeable chap called Jon Rista over on CN.

If you have a program that reports the Mean ADU level of your subs then this is easy. I use SGP myself, and I've calculated that for my D5300 I need a minimum Mean ADU level of around 2,490. To achieve this I need to do 20 min long subs when shooting in NB, although I'm only just scraping it at the moment even with 20 mins, so I would probably see an improvement if I went to 25 mins.

If it's any help to you, you could post one of your raw subs and I could open it in SGP when I get home from work later and let you know what ADU it reports.

Thats great Ciaran.  I had no idea how to go about working out what exposure times.  I think I chose 300s because it was so windy, and I didnt want to lose too many subs.  I've had a look at the APT manual and it looks like I can measure those values using that programme.

 

https://ideiki.com/astro/usersguide/pixel_aid.htm?ms=AAA%3D&st=MA%3D%3D&sct=MTE2MA%3D%3D&mw=MjQw

[Xiga]

11 minutes ago, jjosefsen said:

What is r, e and bits on this equation?
I assume bits is the dac? (I.e. 12/14/16)

 

r is the read noise of the camera, which I believe is 7e-

e is the Gain, which is 0.41e-/ ADU

and yes bits is just the dac of the camera, and the 383L+ is 16 bit. but if it was a 14 bit camera (such as mine is) then you would need to multiply by 4

[Xiga]

22 minutes ago, tooth_dr said:

Thats great Ciaran.  I had no idea how to go about working out what exposure times.  I think I chose 300s because it was so windy, and I didnt want to lose too many subs.  I've had a look at the APT manual and it looks like I can measure those values using that programme.

 

https://ideiki.com/astro/usersguide/pixel_aid.htm?ms=AAA%3D&st=MA%3D%3D&sct=MTE2MA%3D%3D&mw=MjQw

Perfect, then you're in business ?

It's been so long since I used APT I forgot it could do that

[tooth_dr]

@Xiga

Here is an image I took last night, analysed in APT. 600s exposure.

Some folks reckon the read noise is 8 or 9 e- so I need to aim for minimum 671 or 795.

10 minutes seems minimum time I need to use in Ha? I guess the big moon last night influenced this result though?

Thanks for your help again. 

Adam. 

[Xiga]

2 hours ago, tooth_dr said:

@Xiga

Here is an image I took last night, analysed in APT. 600s exposure.

Some folks reckon the read noise is 8 or 9 e- so I need to aim for minimum 671 or 795.

10 minutes seems minimum time I need to use in Ha? I guess the big moon last night influenced this result though?

Thanks for your help again. 

Adam. 

Whether we take the read noise to be 7e, 8e, or 9e, at a little over 700 ADU you're still in and around the minimum level of signal needed to significantly bury the read noise. The big bright moon would definitely have pushed it up some too, but as Ha is pretty moon-resistant it might not have made that much of a difference. 

So I'd say you're definitely looking at 10 mins absolute minimum for Ha, with 20 mins being the likely sweet spot. 

Once calibrated, Atik produces really nice clean, deep images. But it still needs long exposures to get there (in NB). 

Hope that helps some. Do you have an OIII filter yet Adam? If so i look forward to seeing the colour version of this. 

[tooth_dr]

10 minutes ago, Xiga said:

Whether we take the read noise to be 7e, 8e, or 9e, at a little over 700 ADU you're still in and around the minimum level of signal needed to significantly bury the read noise. The big bright moon would definitely have pushed it up some too, but as Ha is pretty moon-resistant it might not have made that much of a difference. 

So I'd say you're definitely looking at 10 mins absolute minimum for Ha, with 20 mins being the likely sweet spot. 

Once calibrated, Atik produces really nice clean, deep images. But it still needs long exposures to get there (in NB). 

Hope that helps some. Do you have an OIII filter yet Adam? If so i look forward to seeing the colour version of this. 

Thanks Ciaran.  I did try 900s last night intermittent cloud messed up the guiding.

I do have an Oiii filter, and after I did the image above in H-alpha, I did switch the FW over the it.  However it does not appear to be parafocal (which is a bit of a disappointment if I'm honest), so rather than spend time refocusing, I just switched back to the H-alpha and grabbed a few 600s subs.