The Astro-Imaging Thread

[Green Baron]

@Epox75: less is more. Really. Try fewer but longer exposures and you get a better snr. Like 20*2min or so. The center may be overexposed, so you can combine like 10 * 30sec L only. PixInsight does it right then (hdr-wise). I did the same with my M42

I have done a better version in the meantime without those artifacts and satellite trails, but i don't find it. It's 10*4min LRGB plus 3*1min L (f/5.8). Darks and biases.

@munlander1: no. But for an f/4 it is very small.

Edited June 20, 2017 by Green Baron

[Epox75]

3 hours ago, Green Baron said:

@Epox75: less is more. Really. Try fewer but longer exposures and you get a better snr. Like 20*2min or so. The center may be overexposed, so you can combine like 10 * 30sec L only. PixInsight does it right then (hdr-wise). I did the same with my M42

I have done a better version in the meantime without those artifacts and satellite trails, but i don't find it. It's 10*4min LRGB plus 3*1min L (f/5.8). Darks and biases.

I know but it's not me.. it's the camera, Jon Rista from cloudynights forum:

"You are likely using exposures that are too long. This camera is a very low read noise camera. You don't need exposures that are very long unless you are imaging at a dark site. IF you are imaging at a dark site, and by that I mean a green bortle zone or darker, then you might be able to use 2-minute L subs and 4-5 minute RGB subs. However, if you are near or in the suburbs or the city, even at Gain 0 you will likely find that you can't use L exposures much longer than 30-60 seconds and RGB exposures much longer than 60-120 seconds.

I live at a red/white zone border, and a 60-second Gain 0 L exposure is actually WAY overexposed (I get a background sky level of 300e- to 500e-, which is swamping the read noise by 85-150x (and you only really need to swamp it by 20x!))"

As for the "optimal" setting. If you truly want to optimize, then you'll need to do some experimentation. You can take increasing exposures for each filter, over many nights, at several different gain settings, to determine, for a given telescope and set of filters, how long you can/should expose to get optimal results. What is truly optimal is going to depend on your seeing, your sky brightness, and your optical system (primarily, your f-ratio and aperture). These will differ for every imager. As a general rule of thumb, you can either aim to swamp the read noise by 20x, or swamp the read noise squared by 3x. So, if your read noise is 1.55e- at unity gain, you would either want to expose until your background sky in a calibrated sub was 31 ADU (20xRN rule) or 7-8 ADU (3xRN^2 rule). Some ASI1600 imagers these days are using something midway between those two, so 15-20 ADU @ Unity Gain, to find a balance of ideal read noise swamping vs. minimal clipping. 

That said, most ASI1600 imagers are using Gain 0 and/or Gain 76 (Offset 15) for LRGB, Gain 139 (unity) or Gain 200 (Offset 30-50) for NB, and are using exposures ranging from 30s to a few minutes for LRGB, and 90-300s or so for NB."

Let's find an agreement, 60 for L (Lumicon Deep Sky or UR/IR Cut Baader), 120 for RGB (Baader CCD) and let's say 180 for NB (have UHC and OIII but are for visual, in the future I will order the Baader set for the Hubble Palette)

Tonight I will probably have another go and I would like to ask some opinion: I may either try to tweak again the distance from the corrector and chose another target (Cocoon or Crescent) or keep the actualy imaging train, that still give some distortion, and do the first RGB session for the IRIS nebula. Another possibility is to tweak the imaging train, do more luminance on the Iris Nebula, see if it gets better and maybe also the pictures I've taken yesterday will benefit. 

Was just thinking of your picture, very nice btw, but how come stars have 2 diffraction spikes? I've never seen that.

Edited June 20, 2017 by Epox75

[Green Baron]

Thanks for sharing. So the guy says that because of the low read out noise of the camera and a high background lighting you should use short exposures. Hmmm ... *rubchin* i am only a beginner like you but that doesn't seem logical to me.

I would just try it out. Worst thing that can happen is that i will have learnt something new.

But wait ... 2min for the RGB at f/4 ? That is more or less the same as my 4min at ~5.8, even a little longer. And L should be at least as long as the colour channels because L defines the fine structures.

Be it as it my, i am going to put my stuff outside now for cooling.

 

[Epox75]

Nice! What are your plans? I may try the new imaging train (added a 5 mm extension since getting closer got things worse) on the Crescent Nebula, with lower gain and 60 sec exposures. I also flushed 20 lt of water under my tripod, soil was very hard, this way it should dampen vibrations more.

I really don't know what to say about the camera, I have no comparisons to make. I know thou that it has been defined like a sort of breakthrough in AP, expecially for those, like me, living under very light polluted skies. 

 

[Green Baron]

It condensates again. But i have hopes for the second half of the night.

Well, one of your suggestions, why not, Crescent or Northamerica nebula. The first has 18*12min and is rather small, i have the reducer mounted now. Also i haven't tried to run guider and framegrabber on the "new" old eee pc i got. I mean, they start and ask for the cameras, that's a good sign.

Will keep you informed :-)

Isn't that a famous last word, attributed to the captain of the submarine Thresher short before it sank ?

Edit: yes, it sadly is.

 

Edited June 20, 2017 by Green Baron

[Epox75]

I'm on the Crescent at the moment, There might be the chance of clouds here too thou. I'm doing 60 sec exposures (76 gain 15 offset) and i set 240 of them even if I won't be able to do all of them before the sky becomes too bright. I'm quite interested to see the result, this is the lowest I ever went with gain and offset.. and I wonder how the distance from the corrector works. 

I hope I don't have to buy a new extension. I hate ordering things and paying more of expedition costs than the piece price.... maybe I should add the Baader filter set or another scope in the order  This looks sexy to me for instance, I think I understood all the newtonian "features" now and If I got decent stuff out of an umbrella holder, a nice sturdy scope like this (it weights like my c11) with a secondary that is even smaller than the one I have on my 6'' makes me really want to try it out. Moreover that will mean a 6'' at f/4, an 8'' at f/5 and a 11'' at f6.3 or even f/10 for crazy stuff. 

 

Edited June 21, 2017 by Epox75

[RoadRunnerAerospace]

No objections to m57, as it goes right above me!

[munlander1]

Packed up for a short cloud band. Will try again tomorrow night hopefully.

[RoadRunnerAerospace]

okay, so i got some additional lenses for my telescope around a year ago, and the 2 times power doubling lens has been driving me mad, it goes between the main tube, and the mirror that sends light to the eye piece, but when I try it with my highest magnification lens (6mm), it gets really blurry, is it due to the power being too high? or some kind of "operator error"? I`ve been trying to figure this one out for a while.

[munlander1]

@FokkerAce did you attempt to refocus it?

[RoadRunnerAerospace]

Just now, munlander1 said:

@FokkerAce did you attempt to refocus it?

yes

many times

[munlander1]

Just now, FokkerAce said:

yes

many times

It could be that it's just pushed out too far then. Or the atmosphere is messing it up because you are magnifying it so muchg.

[RoadRunnerAerospace]

Just now, munlander1 said:

It could be that it's just pushed out too far then. Or the atmosphere is messing it up because you are magnifying it so muchg.

i`ll check soon (tomorrow), and see what happens if i push it in farther

[Epox75]

So it turns out that putting a 5 mm extension to the imaging train gives still strong distortion... yet a very different one compared to the distortion pattern i had before, I think that the exact distance is within this 5mm. I got so p..... off by this, that I invented the ultimate imaging train. This one is not only just 1 mm longer compared to the train that so far gave me the best result, but is also extendable for approx 2 mm or even more if I had a longer thread:

[kurja]

5 hours ago, FokkerAce said:

okay, so i got some additional lenses for my telescope around a year ago, and the 2 times power doubling lens has been driving me mad, it goes between the main tube, and the mirror that sends light to the eye piece, but when I try it with my highest magnification lens (6mm), it gets really blurry, is it due to the power being too high? or some kind of "operator error"? I`ve been trying to figure this one out for a while.

So it's a barlow lens? It's quite usual to see lowered image quality with those, especially with a short ocular lens. Also, what's your total magnification versus aperture size? Could be just too much.

[RoadRunnerAerospace]

18 hours ago, kurja said:

So it's a barlow lens? It's quite usual to see lowered image quality with those, especially with a short ocular lens. Also, what's your total magnification versus aperture size? Could be just too much.

it has a aperture of 70mm, the total magnification is around 3mm 

a lunar photo, with my dslr only:

I kept it small for a reason......

 :

 

Edited June 22, 2017 by FokkerAce

[kurja]

5 hours ago, FokkerAce said:

it has a aperture of 70mm, the total magnification is around 3mm 

a lunar photo, with my dslr only:

I kept it small for a reason......

 :

 

We seem to have a different use for "magnification", the usual formula would be telescope focal length divided by ocular lens focal length; so a 600mm long ota with a 3mm ocular would give 200x magnification. Typically, magnification of roughly twice the aperture of your scope in millimeters is the highest sensible magnification. More than that, and it gets blurry.

Adding a 2x barlow lens doubles your magnification. Poorest, cheapest barlows such as those that often come with 100$ all in one- telescopes touting "now with zillion-x magnification!" are always too blurry to be of use for photography.

Did you attach a dslr to your telescope+barlow for that moon photo (prime focus, without ocular)? What telescope do you have?

[RoadRunnerAerospace]

8 minutes ago, kurja said:

We seem to have a different use for "magnification", the usual formula would be telescope focal length divided by ocular lens focal length; so a 600mm long ota with a 3mm ocular would give 200x magnification. Typically, magnification of roughly twice the aperture of your scope in millimeters is the highest sensible magnification. More than that, and it gets blurry.

Adding a 2x barlow lens doubles your magnification. Poorest, cheapest barlows such as those that often come with 100$ all in one- telescopes touting "now with zillion-x magnification!" are always too blurry to be of use for photography.

Did you attach a dslr to your telescope+barlow for that moon photo (prime focus, without ocular)? What telescope do you have?

nope, no telescope in that picture, I have a Celestron astromaster 70mm refractor 

Edited June 22, 2017 by FokkerAce

[Epox75]

Crescent Nebula.. very starry. 3 hours of integration with Lumicon Deep sky filter. 180x60sec exposures at the lowest settings I've ever tried which is 76 gain / 15 offset. 

Easy to see how the stars annihilate the sky and nebulosity. And how the brightest stars are overexposed. There were also strong distortion due to the (again) wrong distance from the coma corrector, which I managed to mitigate with masks and deconvolution. Anyway looks like this type of filter is too light for this type of target, I need a narrowband for luminance. Would be also interesting to see what happens with the lowest possible gain settings.

After the Crescent 2 nights ago, tonight I had (incredibly) the 5th clear night in a row. I tested the train I created yesterday and guess what? Going even 1 mm farther, compared to the train that so far gave me the best results, increases the distortion so I gotta get closer. I did Iris nebula again 30sec exposures at same gain/offset of the crescent.. just to see how stars behave. 

Next time (tonight and the next days clouds for sure) I will try minimum gain/offset with longer exposures. 

[RoadRunnerAerospace]

5 minutes ago, Epox75 said:

Crescent Nebula.. very starry. 3 hours of integration with Lumicon Deep sky filter. 180x60sec exposures at the lowest settings I've ever tried which is 76 gain / 15 offset. 

Easy to see how the stars annihilate the sky and nebulosity. And how the brightest stars are overexposed. There were also strong distortion due to the (again) wrong distance from the coma corrector, which I managed to mitigate with masks and deconvolution. Anyway looks like this type of filter is too light for this type of target, I need a narrowband for luminance. Would be also interesting to see what happens with the lowest possible gain settings.

After the Crescent 2 nights ago, tonight I had (incredibly) the 5th clear night in a row. I tested the train I created yesterday and guess what? Going even 1 mm farther, compared to the train that so far gave me the best results, increases the distortion so I gotta get closer. I did Iris nebula again 30sec exposures at same gain/offset of the crescent.. just to see how stars behave. 

Next time (tonight and the next days clouds for sure) I will try minimum gain/offset with longer exposures. 

how long was the exposure? (just curiosity) 

[Epox75]

42 minutes ago, FokkerAce said:

how long was the exposure? (just curiosity) 

Read better

[RoadRunnerAerospace]

oh! its above the picture! (duh)

Edited June 22, 2017 by FokkerAce

[Epox75]

1 minute ago, FokkerAce said:

you said it was the iris nebula......

 2 hours, more or less, I will see how many frames I have to reject. 

[Green Baron]

@Epox75: it seems that there is less noise and the filaments are clearer than in the 30sec exposures, what do you think ? Now with 2min exposures the nebula might even be clearer. Yeah, stars are overexposed. There is nothing one can do i think ...

 

There was an open sky this morning, i saw the galaxy high in the sky. The next two days we'll have a phenomenon called Calima, that means high moisture and a lot of desert dust in the lower atmosphere. Thereafter we'll see :-)

Edited June 22, 2017 by Green Baron

[RoadRunnerAerospace]

I have a cruddy dslr... I may have to "commandeer" my dad's camera if i want to do astrophotgraphy.......

Before (cruddy dslr only)

 

 

After 45 minutes of photoshopping:

I miss you trees

Edited June 22, 2017 by FokkerAce