Short exposure images, showcase, tips and advice.

[Peco4321]

Hi all. 

Following on from a few previous threads, it was suggested to clump it all together. So, here's your chance to show off short exposure images, probably best to keep it DSO as planetary, solar and lunar are a little easier. 

Also, please add help, tips, techniques etc to get the most out of this. 

So here goes with my first offerings all at prime focus through 150p on non tracked eq3-2 mount:

M57 Ring Nebula approx 30 x 1.3 sec exposure ISO 6400, stacked in DSS, and tinkered with in Gimp. 

M13 in Hercules, single exposure of 1.6 seconds ISO 6400 cropped and lightened just in Windows. 

M31 Andromeda Galaxy, single exposure 2 seconds ISO 6400 cropped and lightened in Windows. 

And a very crude attempt at the Whirlpool Galaxy, single 2 seconds exposure messed about a bit to within an inch of its life to show any sort of detail, horrible, but all mine!

Please show me yours and techniques used greatly appreciated. I tried the other night at Dumbbell Nebula but focus was well off.  

[iapa]

Nice shorts.

What is the upper end of 'short' exposures?

[Peco4321]

Good question. Shall we say 5 or 10 seconds. Open to suggestions. 

[iapa]

10s seems to me to be short.

Maybe 20? no more certainly

[Peco4321]

Tried again with M57 last night 119 x lights 1.3 sec ISO 6400, 20 x darks , 20 x bias stacked in DSS and not much else done to it.  Result is ok but seems very blue and loads of blue specs that are not stars. Any advise welcomed. 

[Peco4321]

Well, here's my next instalment M31, 45 x 1 sec exposures 20 x dark 20 x bias ISO 6400 stacked in DSS and levels messed about with to nearly bring out some detail.  Focus was not bad compared to the same nights attempts at M57 and M27. Fairly pleased with this though as starting to eek out a bit of detail. Next time will go for more subs. 

[Gina]

Amazing!!

[sharkmelley]

Here's a single 20second exposure at ISO 2000.  H-alpha modified Sony A7S on Tak Epsilon 180ED.

The only problem with a single exposure on a colour sensor is that the smaller stars occupy less then 1 pixel and so they might appear red, green or blue depending on which pixel they hit.  These weird effects reduce when a few dithered exposures are stacked.

Most subs I take for deep sky images are 30 seconds so I had to root around on my hard drive to find this shorter exposure.

Mark

[ollypenrice]

This is largely about F ratio, I'd have thought. Mark's sub above is truly amazing but F2.8 didn't do any harm!

Olly

[sharkmelley]

5 hours ago, ollypenrice said:

This is largely about F ratio, I'd have thought. Mark's sub above is truly amazing but F2.8 didn't do any harm!

Olly

I definitely agree about the fast F-ratio for short exposures - it's an unfair advantage!  It means that the exposures are not dominated by read noise or thermal noise.  Sky quality then becomes the limiting factor.  That same image taken in darker skies would have pushed the noise level down further.  An F2.0 Hyperstar or Rowe-Ackermann would increase the signal to noise ratio even further. 

Mark

[happy-kat]

That was a motrorised mount?

[sharkmelley]

52 minutes ago, happy-kat said:

That was a motrorised mount?

Yes.  I think most of the above images are using motorised mounts.

Mark

[Martin Meredith]

Not mine, but I found this recent image on CN built from 0.5s subs with a relatively cheap camera (but 300mm scope) very impressive and shows what the potential is for short subs when combined with low read-noise cameras.

[in edit] of course, this is only short in terms of each sub; there were a mere 21000 of them ;-) But is this thread about short subs or short overall exposure? If the latter then I guess my example is irrelevant...

Martin

 

 

[happy-kat]

My take is this thread is about short exposures on a none motorised mount as I think the thread starter's mount may not be motorised by the sub lengths they used.

[iapa]

Interesting point about motorised or not, and number of exposures

OP uses short exposures but also multiple exposures.

not sure, but I think 21000 subs is maybe out side the criteria for this discussion?

[wimvb]

Nr of subs shouldn't be limited, imo. Only single sub exposure time should be the limit. But we should differentiate between dslr, ccd, and low noise cooled cmos.

Someone earlier stated 20 secs single sub exposure time as the limit. I got several at 30 secs per sub. 

[iapa]

I think it was me suggested 20s , probably as I have some pretty decent unstacked 30sec subs.

Agree re differentiating around rigs.

 

 

 

 

[laser_jock99]

Some interesting images posted so far. Proof perhaps that not all DSO images need take hours?

Here are a few of mine with a Lodestar X2 camera (technically my guide camera- but can used for stills).

 

M27 Dumbell Nebula, 10 seconds through a 10" F4 Newtonian

 

M81 Bodes Nebula, 4 seconds through a 10" F2.9 Newtonian

 

M51 Whirlpool, 5 seconds through a 10" F4 Newtonian (+ full moon according to my notes!)

[wimvb]

M44, imaged 11 march 2016

Skywatcher 150P on EQ3 Pro mount (no coma corrector)

Camera Pentax K20D with Baader UHC LP filter

66 x 15 second exposures @ ISO 1600, which is way underexposed for this target. The number of subs didn't help get the noise down much, so heavily processed.

 

 

[wimvb]

Stretched the living daylights out of this one (no pun intended), but here's a shot of the flame nebula (well, kind of at least).

Fixed tripod, Pentax K20D (not astromodded), 135 mm lens @ f/5.6, ISO 3200 (cameras max iso)

1.5 sec exposures, but 240 of those (6 minutes total integration time).

I took this image in the beginning of january, just to see what extremely short exposures would pick up, and test how much noise was reduced with stacking.

It did pick up M78 (upper left), the flame nebula (left of Alnitak), a few reflection nebulae, and possibly the poorest excuse for a horse nebula anyone has ever dared to mention (the very faint red stretch below Alnitak)

The image reminds me NOT to do short exposures.

Here's a single raw, converted to jpeg in RawTherapee

 

[Space Cowboy]

Few images I've taken over the past couple of years with alt/az tracking and short exposures.

This is m42 taken with 10" Dob and 1000D. 20 Sec exposures :

 

M31 with ST102 and 1000D again 20 sec exposures on alt/az mount :

Finally m27 with zwo asi224mc using 1 sec exposures with ST102 :

 

[Peco4321]

Single 1 sec exposre 6400 ISO of Orion Nebula last night. Was too late in the night to be taking loads of pictures and stacking etc. 

[Peco4321]

M42 last night, 7 x 5 sec exposures ISO 3200, 10x darks and 10 x flats stacked in DSS and processed in GIMP. Quite happy, I actually rotated the RA fine tune control during the 5 sec exposures, that's why only 7 used as the rest were no good. 

[happy-kat]

You are improving with your RA turning, is be so tempted to change to just a camera lens say the kit lens and see if your fine turning buys you 20+ seconds.

[Peco4321]

3 hours ago, happy-kat said:

You are improving with your RA turning, is be so tempted to change to just a camera lens say the kit lens and see if your fine turning buys you 20+ seconds.

No need soon, took delivery yesterday of RA and Dec motors. Wife won't let me fit till after xmas though?