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M64 - 2400 x 1 second - 16"

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#1 MvZ

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Posted 13 April 2016 - 04:36 AM

Attached is a first test image with the 16" Dobosn on a new EQ platform I'm modifying. Conditions weren't good (not so good seeing, but especially it was very windy and the telescope was moving around quite a bit because of this), but this does make for a decent test case for the platform. The platform is quite simple - I bought a basic platform for about 300 euro - but I'm currently in the process of modifying it (a better tracking motor, that I control from the computer too - I'm using a tiny Arduino driven stepper motor and a worm drive I put together) , declination control (currently manual, but I want to motorize this too - still need to come up with something good), and I made it a bit more stable with some aluminium rails... Anyway, this is all quite a lot of work, and I'm not quite good at it either, so it takes time and failed attempts. I'm learning quite a bit, but I do fully understand why some good EQ platforms are rather expensive.... It can be quite frustrating and takes a lot of hours if you pretty much have to start from scratch.

I'm still not sure if I will succeed in making a robust platform, but having a test like this is hopeful of course.

 

I didn't pay much attention to anything outside of the core of M64, and the stars are a bit wooly (and not extremely round), but for a big Dob on a simple EQ platform I'm quite pleased. I think most of the non-roundness of the stars comes from  The short exposures help a lot of course to keep the stars small, both from seeing and wind smearing, but futher tests - under more favourable conditions - should give me a better indication of the cause. I'm actually also in the process of modifying the focuser position on the Dobsons, so there might be some colimation problems there too.

 

Imaged with the 16" Dobson using an ASI174MM in prime focus (2 meters) without any filters. In total I stacked about 2600 frames of 1 second exposure each. Stacking was done in sets of 400-800 frames in AS!2, and post-processing in Photoshop (paying most attention to the galaxy core).

 

20160410-11_M64_k.jpg

 

http://www.astrokraa...10-11_M64_k.jpg


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#2 Wford

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Posted 13 April 2016 - 05:23 AM

very nice



#3 happylimpet

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Posted 13 April 2016 - 06:00 AM

Emil - do you have any thoughts on how the asi1600mm will compare? I always had great success using my asi120mm for DSO imaging using 1-2 sec exposures, and much as I like my Atik460EX CCD, I miss the small tight stars that short exposures give you. So Im wondering about 'swapping' it for the 1600MM (or ideally another with larger pixels). The low noise is very attractive so under my urban skies I'll be sky noise limited in a second or two.

 

My main concern is whether other camera noise sources (FPN etc) will hinder my ability to go faint compared to a low noise CCD. What do you think? Do you have problems with FPN with the 174? I wondered if maybe this is why you stack in batches, as any field rotation complicates things.



#4 MvZ

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Posted 13 April 2016 - 06:31 AM

I haven't looked at the ASI1600MM, but hope that I can test it soon. It indeed has very low noise, but I'm not sure about the QE or any FPN or random banding issues it might have.

 

The 174 has some horizontal banding issues, but I let AS!2 fix this so this is not a problem (at least if the object I'm imaging doesn't take up more than about 2/3 of the image horizontally). There are still some gradients left in the stacks that I always fix using an artificial flat calibration (working from the image stacks), but I suspect these gradients are from outside the camera.

 

There was indeed also some field rotation still visible, but this was (I think) because I hadn't aligned the platform properly. It's a nice incentive to work on detecting and compensating field-rotation in AS!2. Now I manually rotated some stacks between 0.04 and 0.12 degrees left or right or so to get things right.

 

The main reason why I stacked in batches was because the object drifted a bit too much in the field of view (and I had to reset the platform at one point). I also used the opportunity to refocus occasionally.

 

I don't know the ASI1600MM, apart from the impressive read noise numbers (and a rough estimate of the QE). I will find out more when I get a chance to test the camera. If I had to guess, I think it would be (very) good at this kind of short exposure imaging.


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#5 happylimpet

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Posted 13 April 2016 - 07:19 AM

Cheers Emil, appreciate your thoughts. Of course the pixels are a little smaller too....

 

And I dont see why, approriately ROI'ed, it shouldnt make a good planetary camera.

 

I forgot AS!2 could remove banding etc.  I use the 'lines to equal values' in fitswork to get rid of it, so I get your point about needing a good amount of background in each row/column.

 

I think I might take the plunge with one of the CMOS cameras - it plays more to my strengths, and cheaper than one of the active optics guiders. And if I cant get super deep from my urban location, at least I can get hi-res and do some interesting gravitational lenses etc.



#6 tjugo

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Posted 13 April 2016 - 09:09 AM

Very nice! Those details are out of reach from long exposures!

 

Cheers,

 

Jose



#7 ivan11223

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Posted 14 April 2016 - 11:00 AM

Details in the center of the M64 is amazing!!!!



#8 calypsob

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Posted 15 April 2016 - 01:48 PM

Incredible! Does the atmospeheric dispersion corrector benefit this type imaging any?



#9 MvZ

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Posted 15 April 2016 - 02:23 PM

 

I suggest you look at my apod

 

The stars are oblong even at 1 sec?

 

 

Oh, I'm sure these details in this particular are possible with longer exposures (although perhaps not that common?), but as I explained, conditions were rather poor. The wind was constantly shaking the setup, and there was no way for me to place it anywhere with less wind. This made the stars look oblong, and yes, even at 1 second :) (I think I could have fixed it, perhaps using a more restrictive dataset to creater sharper star images - if I select the best 20% or so, most of the oblong stars might be gone. I can combine the stacks the stacks afterwards again. If I get bored, I might do just that this weekend!)

 

There is plenty of room for improvement, but for just a quick test-run - and with a rather simple (and cheap setup) - it's not too bad I guess. At least I was happy with this result given the circumstances. Sure, not APOD material, but I don't care much about that to be honest ;) I'm pretty sure that I can get better results under more favorable conditions. For me that is part of the fun to be honest, there is always room for improvement. In this case,  I know that already. 

A direct link to your image might be useful if you want to show it. I don't check APOD very often, and I don't keep track of who is getting one, so I'm completely lost if I want to find it..


Edited by MvZ, 15 April 2016 - 02:29 PM.

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#10 MvZ

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Posted 15 April 2016 - 02:26 PM

And thanks for the kind words, much appreciated!

 

>Does the atmospeheric dispersion corrector benefit this type imaging any?

Perhaps, yes, if the object is rather low. Dispersion wasn't too bad now I think. I tend to try and keep it as simple as possible, so this was without any extra glass in the way that might give me trouble trying to calibrate the images properly. This is image is not close to the resolution needed to have much dispersion effect I think, but it is good that you remind me. I'll try it some time, and, for a nice low object if I can't think of a target higher up in the sky..


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#11 DS INC

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Posted 15 April 2016 - 10:51 PM

This is very nice, great detail.  Nice contrast in B&W, really don't need the gawdy color of some APOD's at all.


Edited by DS INC, 15 April 2016 - 10:53 PM.

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#12 schmeah

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Posted 15 April 2016 - 11:29 PM

That's a remarkable image for one second exposures. This is a new kind of DSO imaging. Perhaps the wave of the future. I look forward to seeing more.

 

Derek



#13 calypsob

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Posted 16 April 2016 - 01:36 AM

Yea i must say im curious to try this with my asi120mm, Emil do you have a tutorial for processing dso instead of planetary? What is the aperture of the dobsonian? 



#14 korborh

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Posted 16 April 2016 - 08:02 AM

Excellent work Emil!!

That is some really good detail.

 

What post-processing did you do in Photoshop ? I am wondering how the stack looks without any processing just linear stretch. I mean, is the processing needed because of this lucky/stacking technique or is the same for something like a long exposure CCD image?

 

Oh and some of us have learnt to ignore pompous trolls here....so save you energy in future  ;)


Edited by korborh, 16 April 2016 - 08:06 AM.

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#15 hytham

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Posted 16 April 2016 - 09:17 AM

Fantastic job, Emil.

 

The detail is awesome and I love the contrast that B&W provides. Thanks again for providing something back to the community in a great way other than useless diatribes as displayed by one of our aging members that lacks any relevance.

 

You, along with Frank have put a significant amount of effort into your great software by providing it to all of us for free.


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#16 jgraham

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Posted 16 April 2016 - 10:48 AM

Wow, this thread has taken a surprising turn.

 

As someone who spent several wonderful years imaging with equipment from the bottom of the barrel I thought that this was powerfully cool!

 

My stuff still doesn't float to the top, but I'm having fun and enjoy learning and seeing new things.

 

Great stuff!


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#17 MvZ

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Posted 16 April 2016 - 10:52 AM

>Now add some color to it!

 

I might try that, but not before I do a better luminance of course, it would be a pitty to spend too much time on data I know can be done much better with the setup I have ;) But you know how it is in the Netherlands: far from ideal. The traveling is also a bit of a pita, so I'm often limited at imaging in the weekend 

 

Now.. time for another bag of popcorn. 

 

 

Nice image of M64 Mike, the colors are a bit weird though and noise reduction is a bit too much for my taste. The details shown in this rendition is what I hope to achieve sometime:  http://apod.nasa.gov...d/ap130404.html Of course, my location doesn't help, so it will be a big challenge.

Either way, there is plenty to learn. Always. On many different subjects actually....


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#18 coinboy1

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Posted 16 April 2016 - 10:59 AM

Hello Emil,

 

I have followed your webpage for many years now and I am always awe-inspired at the results you get for both planetary and deep sky! I also am very amazed how much you have contributed to the community with your program that many many people use. This is amazing, 1 sec exposures with a low noise, high QE CMOS camera. What is the SQM that you image from? 

 

-Tony



#19 Junior-CCD

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Posted 16 April 2016 - 11:03 AM

Hi!

 

Nice image, so the ASI cameras seem to do a good job.

 

So far I had no luck with using planetary stacking software for deepsky, but I have to try Autostakkert; seems to be a good alternative.

 

CS, Carsten



#20 MvZ

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Posted 16 April 2016 - 11:28 AM

Thanks Tony. 

 

>What is the SQM that you image from?

It should be around 20 I guess, I can see the milky way when conditions allow, but nearer the horizon it isn't very good. There are bunch of extremely bright streetlights in front of the house that are very annoying, and some towns within 10km radius. For Dutch conditions, I'm lucky though.

 

>So far I had no luck with using planetary stacking software for deepsky, but I have to try Autostakkert; seems to be a good alternative.

Be careful though, because it can be very tricky and is rather limited at the moment. Here are some tips I wrote down today; just a preliminary list, I might turn this into a small article for my website later on.

 

I'm assuming you are using planetary imaging camera's (where you can set brightness, gamma, gain, exposure, etc... )

 

- Make sure the camera it self is not operating in high speed mode.

- Always use a lot of 'brightness' when recording (I always maximize this actually, and get rid of the extra background brightness later on).

- Never use any gamma when recording (disable this, or set it to neutral - for ASI this is typically 50).

- Don't use gain above the point where read-noise is not getting lower anymore (about 25dB I think on the ASI1600, similarly for the ASI174 and Point Grey blackfly for example).
- There should be some (very limited) movement (dithering) in your images; I get this for free due to poor tracking. 

- I use FireCapture - free, good capturing software. I record in SER format. I find this very easy to use and process. Don't use AVI format preferably. 

- IF you use higher gain values, it typically doesn't matter at all if you use 16 (12) or 8-bit recordings, almost all of the extra bits are noise anyways. I pretty much always stick with 8-bit.

- Use the latest beta version of AS!2 (2.1 is terrible, 2.3 too, there are some bugs in the beta versions, but generally speaking they should work very well)

- Use a master dark at the very least (build it from a lot of dark frames inside AS!2, image calibration -> create master frame. The more darks you use, the better. But this is less critical if you have a bit of dithering in your light frames. Always try to use close to the same temperature and of course same exposure time and exact same other camera settings)
- Use column or row noise removal, but ONLY if the camera has that particular type of noise (and ONLY if the target is not too large, the image has to be rather 'flat' for it to work properly, no gradients, no object filling the entire FOV. You might tweak the settings a bit under advanced menu).

- Look at the light frames in AS!2 to see if calibration is done properly; you can increase the displaying brightness for example in the frame view in AS!2. This does NOT affect the image stack at all, it is just for inspection. Don't use the scaling option for this though, as this DOES mess with the actual data.
- Use surface alignment mode
- Place alignment anchor (to perform the coarse stabilization) onto a feature that is always visible (a bright star shoulw work, place it on top of the bright star, possibly you want to decrease the size of this alignment anchor - using numbers 1 to 9 on the keyboard, try with 3 or 4, but it depends on image scale, so simply try it out).
- (there should not be field rotation.. currently not handled properly. You CAN rotate frames - for example have it go from 0 degrees for the first frame to 0.2 degrees for the last frame, but near the edges it will introduce some artifacts. It does however work, so if you know what you are doing, and you know the actual field rotation, you can use this option)
- Choose expand for maximim image sizes (but less signal at the edges) or crop for minimum image size but with the same signal all over.
- Click analyze to run the image stabilization
- Always check after analyzing the images if the image stabilization worked. This is essential. Simply browse through the frames using the frame slider, there MUST be no jumps visible. If it does not look good, place the alignment anchor somewhere else and/or change the size.

- If coarse alignment is succesful, continue..
- Place an alignment point - on top of a NOT over-exposed part of the image, a not so bright star perhaps, or the deepsky feature itself.
- Use local quality estimator (default) to use the area of this particular AP to also judge the quality of the images (that is why this part should not be over-exposed)
- Decide how many frames you want to stack (typically a lot, but if many are blurred a lot, use  less). You could combine multiple stack-sizes later on. Just experiment a bit and see what happens.

 

Then post-processing; you're on your own for now. This takes most of the time; stretching the stacks is important, keeping track of all that you do also. Only at the very end think about some (selective) sharpening or noise reduction, never before. Perhaps artificial flats to get rid of any left-over gradients (I always do this), etc...  You can go crazy here, and it can really make or break the image. I typically work in Photoshop and just have some hours of fun with this. Occasionally I go back to the stack to see if messed up something or if - when I stack with some different parameters - I can get better results. There are many ways you deal with this, but essentially it comes down to:

- some kind of digital development to get both the brightest and darkest areas to still show details

- some further calibration (artificial flats - I often do this after some initial brightening so I can see what I do better.... )

- followed with perhaps some selective sharpening and at the very end perhaps some noise reduction

- sometimes I combine different stacks, which involves opening all stacks as layers in Photoshop, manually aligning them, and then changing the opacity of the stack layers in such a way that I get the lowest noise in the sky background. Typically I do this after the digital development stages.

 

Oh. And have fun of course. That is very important ;) 


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#21 Junior-CCD

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Posted 16 April 2016 - 11:46 AM

Hi Emil!

 

Many thanks for the instruction, I'll try it.

Actually I'm working with very short exposures for deepsky imaging for many years now, but long time there were only very few who used to do deepsky imaging this way. Now the method seems to become more popular.

 

CS, Carsten



#22 MvZ

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Posted 16 April 2016 - 11:50 AM

I started short exposure stuff back in 2007 or so, but that was 10 seconds, so quite long compare to this. The modified webcam just wasn't as good back then. 

 

I would love to get my hands on a decent photon-counting camera to be honest :)



#23 Junior-CCD

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Posted 16 April 2016 - 05:13 PM

Hi!

 

I would love to get my hands on a decent photon-counting camera to be honest :)

 

My experience with these camaras is that they do not replace clear sky. Thus:

 

I would love to get my hands on a decent CS weather machine to be honest :)

 

CS, Carsten


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#24 dr.who

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Posted 16 April 2016 - 08:53 PM

OK folks. That's enough. Keep it on topic, polite, respectful, and within the bounds of the Terms of Service or this thread will be removed. Thank you.

#25 Relativist

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Posted 16 April 2016 - 10:38 PM

Emil, glad to see you post on EAA! great example of what can be done with the right software. Just curious if you've ever used Astrotoaster/DSS? I've been wondering if it's possible to do something similar with faster captures for both DSOs and for lunar/planetary to clean up atmospheric effects.

 

P.S. if we could get pre-stacks from your software as subs into AT/DSS It would be a great workflow to allow us to digitally correct for some atmospherics.




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