Live Stacking of DSOs with SharpCap

[pmrid]

I read a small article urging a new approach to DSO imaging using 30 second subs and ZWO cameras. It looks quite interesting in that it puts a much lower priority on guiding and precise PA. Might be a good technique for usenwhen travelling. Anyone given it a whirl yet?

[Tinderboxsky]

I have just started experimenting with the technique to see what is possible.

The attached are my early results for M20 and M22 based on the following:

Four second exposures stacked in SharpCap for total of ten minutes exposure. All processing done in SharpCap on the fly including dark frame subtraction, histogram management and some stretching and colour balancing. No post SharpCap processing.
ZWO ASI385 camera with Vixen ED103S doublet refractor (with focal reducer to give 530mm focal length) on an Ioptron MiniTower Pro ALT-AZ goto mount. So, no accurate polar alignment and no guiding. SharpCap takes care of field rotation for ALT_AZ mounts within the stacking process.

These images are my first attempts. I can see there is plenty of room to improve on these within SharpCap. I am potentially more interested in using this technique for EAA (electronically assisted astronomy) observing rather than using this technique to produce images that are then further enhanced with extensive post processing.

It is definitely worth a go and yes, relatively simple travel rigs can give excellent results.

[Dave882]

Yes there’s huge potential for this short exposure live stacking. I think it lends itself well to alt-az mounts, and high sensitivity cameras but really will work for almost any setup. Don’t expect to get the same results as some of the top quality shots in this forum- but certainly good enough to be proud of and share with family and friends.

I found about 10-30sec subs are best with 20-30min integration- and with a UHC or dual band filter can get good definition on most targets even from the suburbs. When I shift to the next target I fiddle with the levels in PSexpress on my iPad and get a pretty decent result.

I use the ASIAIR pro live stacking but sharp cap will work the same with auto correction for field rotation and some degree of adjusting of contrast and white balance. The histogram slider can be used on the fly to focus on different areas of the target.

If using for strictly EAA then you can play with even more options. I’ve double and triple stacked reducers on my sct to get faster images, used different combinations of filters and sub lengths. It’s lots of fun when you’re not worrying too much about the star shapes!

One recommendation is that you want to be about f4-f7 on your scope to get the most out of 10sec!!

I’ve attached a couple of shots (Southern Pinwheel & Tarantula) with my cpc800 & asi294mc stacking 10sec subs for 30min integration. F4 with double stacked 0.63x reducers. No filters in these ones...but spent a few minutes to give a boost with PSexpress.

[pmrid]

Well done, David. Those are very encouraging results.

[Hemi]

Hey Peter,

I’ve been doing EAA for a few years now, and it’s a really interesting way to observe. There is a dedicated sub forum on Cloudy. There’s are also virtual star parties where you can join in and observe other people’s streams live or be an active participant. The videos are also available offline, and you can learn a lot about using sharpcap and other setups.

I mainly use a c11 at f10,6.3 or F2. My subs are usually between 4s-15s. And it’s very rare that total integration time would be more than 5m for me.
I’m currently in AZ, but prefer EQ for EAA. I mainly observe visually (especially in the dry season) hence the azeq6 is in AZ mode.

Some people do it for the aesthetic, others to observe. I’m in the latter, and it’s amazing what can be seen and learned.

I’ll edit this thread a bit later and add some pics from last nights session although I have posted some images in the beginners imaging section in the past…all of them EAA.

[Dave882]

Thanks Peter- as I said, you’re not going to get the cleanest results from this kind of imaging with such short integration times, but when it comes to bang for your buck it’s not bad at all! I’ve been playing with GEM mounts and a couple different OTA combinations lately and there is no doubt you can get much more out of longer subs and integration times so it just depends on what you want to do.

If you let me know your setup I’m happy to give you a few tips you could try

[pmrid]

Thanks David.
I oscillate between mounts, scopes and cameras to suit time of year etc. I generally keep my EQ6 and RC8 with a SBIG STF8300M intact for NB imaging nebula and for the rest, mess about with my HEQ5 with either a 127mm f7.5 refractor at 952fl or an 80mm f6 at 600 fl refractor. I image using an older SXVR H16 CCD. I’m in an urban location so imaging in LRGB has been problematic but I’m going to try some OSC to see what is possible with my ZWO ASI 290MC. That’s what made me take a second look at SharpCap and live stacking.

[Dave882]

Hi Peter. Asi290 has good QE but the issue you will face will be FOV. If you jump on to astronomy.tools you will notice that the targets you can image will be limited. However- there’s still plenty you can do, and with either the 80mm or 127mm refractors , but would strongly suggest adding a reducer in the order of 0.5-0.7x. You will want to be sitting at f4ish with that size scope for short exposures and will also increase fov. It will kill your star field but the target probably will still be ok.

Also, with smaller aperture scopes You might struggle to get much data (even for eaa) with under 20sec. I found with a 4se I was playing with I needed to get 30sec subs to show good detail even in something bright like Orion Nebula (irrespective of integration time). Since you are on (I presume) the heq5 if you do an ok PA you shouldn’t have a problem. Just a note on using EQ mounts for EAA- you still need to do a half decent PA otherwise the tracking is actively working against you unless you limit to 5sec or under subs. Most Alt-Az mounts I’ve used handle up to 10-30sec subs fine.

Try a broadband LPF such as Astronomik UHC-e or similar. A narrow band filter such as l-extreme will be far to aggressive for your setup.

Hope some of that is helpful
Cheers
Dave

[pmrid]

Hi again David.
I managed a bit of semi clear sky last night and ran up the F7.5 80mm refractor with the ASI290MC just for fun.

It is apparent that, as you seemed to say, aperture rules here. I did a 10minute stack of 30second subs in RAW16 mode and … well it was disappointing really. I was imaging M16 - a good strong Ha source. I registered only a faint green luminosity with very little contrast or definition. OK. seeing wasn’t great but …

Also an issue, I could not stack subs of unequal length in DSS or access the SharpCap stacks in Photoshop - format not recognised.

Not the best start.

[Dave882]

Sounds like could be a mix of issues. Here’s a few things to try:
- Green luminosity could be a white balance issue. You can adjust this in sharp cap during the livestacking without altering the saved subs. It could also be a function of light pollution or a filter if you are using one
- Try a couple different broadband filters (or no filter) and see if any difference
- 600mm fl on a 80mm aperture is f7.5. This is could be too slow for this 80mm setup if you want to get feint detail. Get a cheap 1.25” 0.5x-0.7x reducer and you will see a huge difference in 30sec subs.
- I’m convinced you will be able to get some eaa results, but don’t expect subs that will be worth your time to do quality post processing. Use your main setup for this.

I’m not sure about the dss issue as I haven’t got experience here. I usually do a screenshot or download the stacked version direct from ASIAIR which gives me a format I can play with. Maybe someone else knows about this...

Let us know how you go!

[Tinderboxsky]

Hi Peter,

SharpCap has a range of video format and still format outputs. Hopefully there is one available that Photoshop can read. You can find these output options at File>SharpCap Settings>General

[Camelopardalis]

Peter, I “play” with live stacking in SharpCap quite a bit these days and enjoy it :thumbsup: it’s less stressful than “proper” imaging, and the results aren’t quite the same, but it’s good fun.

One thing to try is to click the Histogram tab and click the lightening bolt to balance the colours out. OSC cameras are inherently green biased, not only because of 2 green pixels out of a cluster of every 4, but because peak QE of most cameras occurs in the green region.

[Dave882]

Hi Peter
My curiosity got the better of me last night and I thought I’d see what I could come up with while I was waiting for some other targets to get above the trees... trying to match your system as best I could on m16.
So with an older skywatcher ed80 @f7.5 and my asi290mm mini guide cam I did some 30sec subs unguided for about 13min (piggybacked on my sct so a bit overloaded on the cgem). Was able to get some pretty decent contrast (all be it in b/w) even though I was literally shooting directly into the almost full moon! No filters or any stretching, just the screenshot before post processing.

[pmrid]

Hi Dave. Thanks for going to the trouble to run this test. Makes me wonder what could be achieved by a little post-processing magic.

[Camelopardalis]

If you can forgive my dodgy coma correction, this bright target was shot about a month ago on a dark night with 15 second exposures on my QHY 183C and 8" newt.

IMO the data can be better than the quick live stack, where the stacking is time pressured using a limited number of stars. Processing with dedicated software after the event can make it pop a bit more.

Fwiw, I think I was between targets at the time, so let it rock and roll for about an hour... but with bright targets like this, they certainly don't need that level of exposure time to be pleasing. Usually 5-10 minutes can give a really interesting result.

Note: this has been hideously downsampled to fit in the file upload limit. PM me for a full resolution version if you're interested.

[Dave882]

Dunk that’s a fantastic result whether between targets or not and well processed too!
I agree with the timing too. If I’m home I’ve been doing 20-60min live stacks in the evening and then switch to an autorun function to do a few hours on a particular target while I go to bed. Best of both worlds I guess...

[Camelopardalis]

Thanks David :thumbsup:

Target was pretty much overhead at the time, but from sprawling suburbia. I was surprised at how well it came out :D

The 20MP camera is/was overkill for this, but it was what I had hooked up at the time :)

I think there's lots of fun to be had from this... regardless of scope/camera... (although fast scope helps of course)

[RichardJ]

Hi Guys,

I've been using Livestack with SharpCap Pro for nearly all the deep sky objects I image from Home (suburban Sydney) for a few years now. I have a 12-inch Dob on a Blandin equatorial platform.

I don't need to bother with EQ mounts, PHD, guidescopes etc etc. I can be setup from scratch and imaging within 20 minutes. I love seeing the image 'develop' in front of my eyes.

Sure, its not perfect but it has allowed me to take my astroimaging to a new level of detail and enjoyment I only dreamnt about.

RichardJ :)

[Tinderboxsky]

Fabulous results Richard.

I am just starting down the same path for observing faint objects after being a visual observer for a long time.

What sub lengths and exposure time have you been using. Interesting using an equatorial platform - is it driven or do you move manually.

[RichardJ]

Hi Steve,

The platform is driven. I turn the gain way up and my sub times vary but I only need 0.5 to 2 seconds max. I know it is very short, but it works! I stack images until I think I have a good enough image to process. You need to play with the histogram and colour balance.
Good luck.

Richard.

[DavidLJ]

Some years ago I tried my hand at traditional astrophotography using a cooled mono CCD camera, a range of filters and an autoguided 8 inch Newtonian. Typically it would take from 1 to 3 hours to image the brighter DSOs and from 4 to 6 hours for the fainter ones. And then, of course, there was the time taken to calibrate the individual subs, combine the separate colours and apply a range of post-processing procedures The end results were quite credible and personally very satisfying although they were never going to set the AP world on fire.

And then I discovered “video astronomy” (or EAA or EAV or whatever other acronym is now in vogue) which largely did away with most of the time and effort. And it was fun! Initially the results were pretty humdrum but over time the cameras and software got ever more sophisticated and the results started to close in on those of the earlier cooled CCD camera. Nowadays when using the same (but now unguided) 8 inch Newtonian and a cooled colour CMOS camera I invariably use SharpCap's livestacking feature to get fairly decent on-screen views of even quite faint DSOs and then go on to post process the saved results. In many cases the end result is almost as good as the earlier CCD camera work. But whereas with that earlier work it took some hours to produce a final image I can now produce its close equivalent in a matter of minutes. Let me be the first to admit that from a purist AP point of view the resulting images probably have many flaws but they are more than good enough to share with family and friends.

SharpCap offers many features and it is worthwhile taking the time to get really comfortable with using them. This includes, but is not limited to, determining which binning level is best suited to your camera and target; learning how to combine exposure and gain settings to best advantage; building a library of darks and flats that can be called on for most circumstances; and optimising the use of the livestack's histogram and other features. But thereafter using SharpCap is a breeze.

Some examples should suffice to illustrate where I have got to. None is of a particularly bright DSO. All use the camera's 2 x 2 binning mode which produces an image of 2,072 x 1,410 pixels resolution. All have been severely reduced here to conform to the 200 Kb limit for each file.

In the first case two images of the Gabriela Mistral Nebula and surrounds are attached. The first image is a screenshot of the displayed on-screen view. It is a livestack of 4 x 30 second exposures at 500 gain with the camera. The second is the saved livestack image after applying some mild post processing with a very old version of Photoshop.

The second case shows a further two equivalent images of the interesting region that is a camera frame or two away from the Lagoon Nebula. In this case the livestack was 15 x 60 seconds exposures at 400 gain.

The third case shows two final images, the Cat's Paw nebula ( 13 x 60 seconds exposures at 400 Gain) and the War and Peace (or Lobster) Nebula (7 X 120 seconds exposures at 300 gain).

[garymck]

Have a look at this excellent Sharpcap tutorial. It transformed my EAA results.

https://www.youtube.com/watch?v=0Fvm_DjOgaY

cheers
Gary