LBN 534 - first light of the season

[gorann]

Finally a clear night last Wednesday that had enough astrodarkness to be worthwhile!

I aimed my dual RASA8-rig at the rather seldom imaged LBN 534 in the constellation of Andromeda. It includes the blue reflection nebula vdB 158. There is also a small planetary nebula near i (PK110-12.1). I used starless processing to bring out as much nebulosity as the data allowed, and remarkably the Star XTerminator filter did recognize the planetary nebula and left it in while removing virtually all stars. Apparently, in her catalogue Beverly Turner Lynds missed the patch of brightish nebulosity to the left of LDN 534 (but then she did not have a RASA😁) so it may have no designation.

I include the annotated image from Astrobin.

Two RASA8 with ASI2600MC (no filter) on a Mesu 200 mount. 124 x 3 minutes, so 6.2 hours. Processed in PS and PI.

Cheers, Göran

 

 

Edited August 29, 2022 by gorann

[Dan_Paris]

I have never heard of this nebula, it was for sure a difficult capture, well done Göran

[gorann]

34 minutes ago, Dan_Paris said:

I have never heard of this nebula, it was for sure a difficult capture, well done Göran

Thanks a lot Dan! I like chasing those less well known objects out there.

[peter shah]

Not one we see very often.....another super image Goran

[gorann]

8 hours ago, peter shah said:

Not one we see very often.....another super image Goran

Thanks a lot Peter, much appreciated!  Being a natural scientist (although not in astronomy) I am set to go for the relatively unknowns, so sometimes picking out the objects takes as much time as imaging them.

[symmetal]

Another great image Göran. I've just enabled the LBN catalogue in Stellarium and loads of new targets arrived for RGB imaging. 😊

Might I asked what made you choose 3m exposures. I found that with the RASA 8 and ASI2600MC and no filter, the sky background noise will swamp the read noise by a factor of 5 in Bortle 3 skies in around 30s. I've been using 60s exposures just to avoid too many subs and hopefully not saturate too many stars so the colours can be resolved.

At gain 100 and offset 50 the sky background ADU is 717 to swamp the read noise by 5. 🙂

Alan

[gorann]

3 hours ago, symmetal said:

Another great image Göran. I've just enabled the LBN catalogue in Stellarium and loads of new targets arrived for RGB imaging. 😊

Might I asked what made you choose 3m exposures. I found that with the RASA 8 and ASI2600MC and no filter, the sky background noise will swamp the read noise by a factor of 5 in Bortle 3 skies in around 30s. I've been using 60s exposures just to avoid too many subs and hopefully not saturate too many stars so the colours can be resolved.

At gain 100 and offset 50 the sky background ADU is 717 to swamp the read noise by 5. 🙂

Alan

Thanks Alan,

so do you say I should go for 60 s subs or less? In the winter I can get 20 hours with my dual rig in a night so then I would spend days stacking 1200 subs (not to mention the harddrive space needed). Or should I run it at gain 0? I do not feel I have much problem with the stars and I do have to stretch the data a lot sometimes to get to the faintest stuff. But I never made any calculations like you have.

CS, Göran

[symmetal]

4 hours ago, gorann said:

Thanks Alan,

so do you say I should go for 60 s subs or less? In the winter I can get 20 hours with my dual rig in a night so then I would spend days stacking 1200 subs (not to mention the harddrive space needed). Or should I run it at gain 0? I do not feel I have much problem with the stars and I do have to stretch the data a lot sometimes to get to the faintest stuff. But I never made any calculations like you have.

CS, Göran

As vlaiv has mentioned in other topics, swamping the read noise value by a factor of 5, by the sky background noise value, makes the read noise contribution to the image insignificant. If the ASI2600 RN is 1.5 e- (electrons) and you expose long enough so that the noise from the sky background is 5 x 1.5 e- = 7.5 e- then the combination of read noise plus sky background noise is 7.64 e- which is no different in reality to just the sky background noise alone.

At this point you may as well start another exposure as the stacked S/N of 10 x 3min subs is then the same as 30 x 1 min subs. The shorter subs of course will have less star bloating.

The sky background ADU for 5 x RN swamping is (RN * 5)^2 / gain + camera_bias for a 16 bit camera

= 230 + camera bias average value

The gain here is the e-/ADU gain taken from the supplied camera graphs which is 0.245 e-/ADU at Zwo gain value 100

The bias value includes the default offset value of 50, which for me is 503 ADU so 230 + 503 = 733 ADU sky background value required.

The sky background value is the median value of the image for an image not dominated by nebula, or hover your mouse over the image background and read off the ADU value.

The downside of course is more storage, and time needed to stack the subs as you mentioned. 🙂

Take a 60s test sub in the middle of the night with no moon and see what the sky background value is. If it's over 733 ADU then 60s is a good exposure to use. You can use 90s or 120s if you don't want so many subs, but I think less than your current 180s  would be beneficial.

I would stay at gain 100 as that is where the HCG (high conversion gain) mode is enabled which greatly reduces the read noise, for little loss in dynamic range.

These exposures are for no filter imaging with the ASI2600. With an IDAS NBZ the 733 ADU target value is the same, but much longer exposures will be needed to achieve this value.

Hope that helps Göran. 😊

Edited August 30, 2022 by symmetal

[The Admiral]

As always, Göran, a beautiful image of a little known object. Refreshing to see targets different to the oft imaged favourites.

It crossed my mind though, at what point do you draw the line? Could you go deeper on a target with more time, and if so, why do you decide to stop where you have?

Ian

[gorann]

28 minutes ago, The Admiral said:

As always, Göran, a beautiful image of a little known object. Refreshing to see targets different to the oft imaged favourites.

It crossed my mind though, at what point do you draw the line? Could you go deeper on a target with more time, and if so, why do you decide to stop where you have?

Ian

Thanks a lot Ian!

My lines are somewhat arbitrary, and usually I go for one object per night, so on long dark nights in the winter I may get up to 20 hours or more (since I have a dual rig). For this one the night only gave me 2 x 3 = 6 hours. For relatively bright objects like this one I found that 5-7 hours or so is enough and I would probably need more than the double to see a very small difference in S/R. For very faint stuff like IFN and SNRs I usually aim for at least 10 hours. It is all at f/2 of course so I soon get very deep and 10 hours of RASA data correspond to several days at f/7

[The Admiral]

28 minutes ago, gorann said:

at f/2 of course so I soon get very deep

Not to mention your pristine skies .

Ian

[MartinB]

And he's back.  Glad you are getting back into darkness Goran.  The summer hasn't dulled your edge.  Wonderful image.

[gorann]

4 hours ago, MartinB said:

And he's back.  Glad you are getting back into darkness Goran.  The summer hasn't dulled your edge.  Wonderful image.

Thanks a lot Martin, much appreciated! Yes, I am back and working hard and late to collect data for a fourth image of the season😁. It would have been the fifth if not a nap unintendently on Sunday turned into a full night sleep🥴