First Stacked Widefield

[Knight of Clear Skies]

Just had my first success with stacking images in DSS. I took a set of The Plough on Thursday when out hoping to spot the aurora, and here are the results:

It's 8x 20 second subs at ISO 1600, with 10 darks. (18mm lens at f3.5 on my Canon 1100D). I'm pretty pleased with it, but there is definitely plenty of scope for improvement. Does anyone have any tips please?

One issue is that the bright stars are very bloated - Alcor and Mizar appear to be sharing a common envelope(!). Stopping down the aperture a little might help, but they aren't nearly so large in the original subs. Is this something to do with the stacking, or have I stretched the curves too much? Would 15 second subs be better? Here's my reference frame:

Light pollution is a problem around here, my dark-sky site is about a mile out of town. Here's a single frame I took on the same evening (ISO 800 30 sec), with a touch of light-painting to bring out the nearest tree:

Given the conditions, does anyone have any guidance on how many subs I should be taking before I can expect to run into a signal-to-noise wall please?

The forecast is looking good tonight, so I'll have another go. Might put my 50mm lens on and try a load of short subs on Orion.

[Langy]

Some nice pics there. I'm sure the more experienced will give some better advice.

Looking at the images the best way I can put it is that if you look at your second image the plough is nicely defined and there are lots of faint stars around. Now compare that to the first image which has the bloated plough, you have far more stars brought through from the hidden areas and they have all been made much brighter. So the plough has also increased in size inline with the rest.

Now I'm sure someone will tell you how to get over this but I suspect that you may need to work between a couple of images and maybe do some masking of some sort. I also think you suffer the way I do in getting the sky as black as possible. Even with bins they sky isn't pitch black so try not to darken it off so much.

That's my thoughts but I'm new to all this too, may just offer something different to help you along the way.

[Knight of Clear Skies]

Thanks for the suggestions.

I've played a bit more this morning. I looked at my subs more closely and noticed odd star shapes in some of them - not trailing, more of a double image. It was a windless night, but perhaps my tripod wasn't tightened up properly or walking around it was enough to disturb it. I tried discarding the worst subs manually but the results are no better. Then I tried applying my darks to the best single sub, and still got very bloated stars which really confuses me.

If anyone could point me in the right direction that would be great, otherwise I'll have another search through the DSS guides and posts again.

[wxsatuser]

Double image may be the camera moved somehow, vibration of some sort.

How are you releasing the shutter?

Paul is right......the sky should'nt be pitch black, try and ease it off a bit.

[Russe]

Your polar alignment is slightly off and you are starting to get startrails (egg shaped stars).

The first image is overexposed, the second underexposed. For clusters/star asterisms the right exposure is difficult to determine - trial and error I'm afraid. I'd image at ISO400 or 800. Get your alignment up to scratch - then do 50 or more subs of 60 to 120s. Darks, bias, flats and stack in DSS. Think about an LP filter.

While postprocessing - do a separate star layer, change blending mode to "colour" (photoshop) and up "match colour" and "saturation".

Good luck and keep trying!!!

F

[Knight of Clear Skies]

Hi Russe, I'm just using a fixed tripod for the time being. The plan is to learn what I can up here in Hertfordshire so I can make best use of my time on my visits down to Cornwall. Further down the line I might invest in an astrotrac or something similar, and LP filter.

I've dumped the worst subs, here's a better one (20 sec):

There is some trailing apparent towards the top right, but it's a trade off between a little of this and getting usable data.

Here's my second attempt at stacking just the best subs, I'm not sure if it's an improvement really:

I followed Langy's advice of not making the background so dark, but I suspect it's just showing stretched noise.

What I find really strange is that even applying my darks to the single sub above I still get bloated stars. Would I be better off using something other than DSS if all I want to do is filter out the noise from a single exposure?

[Knight of Clear Skies]

Double image may be the camera moved somehow, vibration of some sort.

How are you releasing the shutter?

I'm using the camera's self timer in continuous mode, to take a group of ten shots at a time. I switch to live-view before taking the first one. I'm not sure if it's flipping the mirror each time or not - it sounds like it does.

Edit - just tried this with the camera in my hand, I can feel it flipping the mirror. Looks like I'll need to get software control working in order to lock the mirror. Can I do this with EOS Utility, or do I need something like ATP please?

[Russe]

One sub noise control is DIFFICULT... To say the least... In PS - you could stretch the image as far as it goes, then select all stars and make a star layer. I keep stretched layers inbetween to choose one in the end as my background.

Does that make some sense?

Cheers

F

[Mr TamiyaCowboy]

mirror flip. 

to combat this you can run the camera in mirror hold mode.

you focus up and hit shutter, the mirror flips up out of the way, a second trigger

activates the the shutter, then closes. the Mirror flips down. two clicks flip mirror up and then it takes shot

this stops Most internal vibrations and those seen on the cheapy EQ-1 mounts to.

takes time to get used to mirror lock mode but its an added bonus.

another problem people do not think about is the VIEWFINDER itself.

i always have a habit of popping on a viewfinder cover. any stray light entering the viewfinder can make its way to the sensor.

so i always tend to have the viewfinder cover clipped to my lanyard/neck band.

if you are manually triggering camera with hand you can induce a very slight wobble, stars will have a somewhat inverted V look to them.

camera slip, where the camera slips a tiny bit can give a crisp clear image but zoomed in faint rail lines appear.

Dark frames, if you have like 10 or 15 dark subs, get DSS to make them into a master dark image for you.

i have a little folder on the PC stacked with single master dark frames, each one has a little info like 20sx10@iso1600

20 second subs x 10 at iso1600, so if im shooting 20second subs at iso 1600 i know my master dark should be good to use.

its simple but effective.

Using gimp and or canon software i have noticed HIGHLIGHTS can cause bloating of stars.

i tend to shift contrast more than messing with highlighting.

[niccodeamus]

In live view you shouldn't have the mirror flipping.  the noise is probably the curtains making the exposure.  this has to happen, and has little effect on the camera.

I would like to offer a suggestion.  I have to confess that I haven't had an opportunity to try it, and I know I am in a forum of experts, which i certainly am not, but this is what I would try/will try.

I would either set the camera in live view or set the mirror lock up function.  you don't mention which model you have, but on my 5d mirror lock is in the camera functions CF3 Autofocus/drive menu.  also set auto noise reduction to on.  this creates and applies a dark to each frame.

apologies, you do mention the model and lens.  so, an 18mm lens on an APSC sensor is equivalent of 29mm on a 35mm sensor.  rule of thumb 600/29 give you a max exposure time of 20 seconds.  my recommendation would be to shorten this to 15 and up the ISO.  I know this seems to run contrary to other opinions, but here's the thing, noise is random and a lot of the other atmospheric stuff is random, so should be removed in the stack, so crank the ISO, shoot 15 seconds, and perhaps even shut the aperture a bit.  I suggest this because the 18-55 is a poor lens and a wide aperture will amplify its shortcomings which may include bloated highlights.

you mention DSS.  I have no knowledge of it.  but if you have access to PS import the images (maybe 5 frames to try) into a single file in layers to align them.  they will have rotated about the pole star, which is conveniently in the image.  the simple method of alignment is to remove all the top frames from view until you have the background and next layer visible, set the actual visible layer to difference mode.  If you are lucky the Pole star should be in the same place, i.e. not moved between frames, flip between difference mode and normal or move the whole layer to see it appear and disappear, so when you are happy that you have lined up polaris, edit/transform/rotate and move the point of rotation to polaris and the rotate the layer until the image goes black i.e. fully aligned.  some of the randomness will leave ghosts so you will be able to see roughly what you are doing.  repeat this step for each layer, takes a minute for each perhaps.  when they are all aligned, in the layers menu create a smart stack  and set the stack mode to mean or median.  At this point you should have quite a nice smooth image, but some simple editing will bring it forward, levels, curves, desaturate the orange channel (cuts the LP instantly) etc etc.

now this is quick and dirty but it is quite simple and bang for buck, i think it would be worth a go.

i will give it a go...there are a couple of stars out.  we will see if it works

:-)

[niccodeamus]

i rotated this about jupiter.  i struggled to line them up.  i will hope the north clears up.

this was shot at ISO3200, 15 seconds, auto NR and was 7 frames

[niccodeamus]

here are some more.  i am no longer convinced that it is simple to align a wide angle shot by hand.  distortion is a problem

the third is an unedited file for comparison

[niccodeamus]

another that wouldn't load.  this is a stack of 4 made from a series that included the unedited frame in the above post.

i may have unconvinced myself...perhasp stacking software is easier...if you have it

[Guy Wells]

Let someone proccess an image for you. We can then see if its a proccessing issue.

[Pete Presland]

i think your last image is excellent, worthy of a frame!

[Knight of Clear Skies]

Thanks for the suggestions. I like the images niccodeamus. Unfortunately, my 1100D doesn't have a mirror lockup function.

The weather looks good for another experiment tonight. I've just dug out an old and painfully slow netbook (so doesn't really matter if I drop it in a puddle) and will try and get APT working on it.

Let someone proccess an image for you. We can then see if its a proccessing issue.

If anyone would like a try they are welcome. I'd have to get the data to them somehow, but I'm sure that could be arranged.

i think your last image is excellent, worthy of a frame!

Thanks, glad you like it.

[Tinker1947]

Buy a remote control, there very handy i think you can start the first frame in liveview the rest will then stay in liveview, these remotes allow any length of timer (over 30 seconds) any time between imagines, any number of imagine, think the max number is 99 that on all 3 options..

http://www.ebay.co.uk/bhp/canon-1100d-remote

[Knight of Clear Skies]

Buy a remote control, there very handy i think you can start the first frame in liveview the rest will then stay in liveview, these remotes allow any length of timer (over 30 seconds) any time between imagines, any number of imagine, think the max number is 99 that on all 3 options..

http://www.ebay.co.uk/bhp/canon-1100d-remote

Thanks, I've been meaning to get one but hadn't got around to it. Would this one be suitable?

[Tinker1947]

Thanks, I've been meaning to get one but hadn't got around to it. Would this one be suitable?

Seems to tick all the boxes, and cheaper than my find..

[Langy]

I have that exact one for my 300D, bought originally for time synchronization as you can use the camera settings or bulb. Set the exposure time and the delay between shots which is handy to allow time for the save to the card.

Sent from my Windows Phone 8X by HTC using Tapatalk

[nameunknown]

your last image is brilliant - stars and sunset with the speckled night drawing down its curtain on a golden eve

P

[Knight of Clear Skies]

your last image is brilliant - stars and sunset with the speckled night drawing down its curtain on a golden eve

P

I'm happy with that one. It hadn't really occurred to me how much it looks like a sunset, it was taken about 5 hours after the Sun went down. The yellow is light pollution from the nearest town.

[Knight of Clear Skies]

I've solved my wobble problem by the way, there was another tightener on my tripod I didn't realise was there. I think my bloated star problem is due to having the aperture wide open, so the bright stars have a faint ring around them. This doesn't show up in the subs but becomes apparent when I try to stretch the curves. I'll experiment with stopping it down a little when I get the chance to see if this is the case. Think I'll also go for 15 second subs, as there is a little trailing at 20 seconds.