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Astrophotography and Sketching >> DSLR & Digital Camera Astro Imaging & Processing

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mmalik
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Agile DSLR Astrophoto Imaging & Processing
      #5357638 - 08/08/12 08:09 AM

I would like to start a discussion around "Agile DSLR Astrophoto Imaging & Processing"; a term I am just coining.

With the advent of newer DSLR cameras (for example, Canon 60Da, and I don't mean to make the case for it, just using it as a good example), I am feeling rapid imaging/processing is becoming possible without overly long integration times, and without overly exhaustive & complicated processing techniques.

What are your thoughts about this changing dynamics of DSLR imaging? And I don't mean to devaluate long integration times and extensive post-processing in anyway; I am just wondering given the right mix (the camera, the scope, sky conditions, etc.), it may be possible to reach "relatively close to the perfect image quality that once took hour upon hours of imaging/post-processing?

When it comes to agility, DSLRs are already a step ahead of monochrome CCDs where they cut down individual channel times. I am just thinking why not make DSLR astrophotography even faster, with the newer technology we have at our disposal.

All schools of thought are welcome, for or against this concept; if you happen to be for it, we could expand it later into imaging/processing techniques that may help achieve this goal. Your thoughts?


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Maverick199
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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: mmalik]
      #5357946 - 08/08/12 12:19 PM

That is a definite possibility. Already there are widefield images strewn around taken with a camera without even a tripod and 10 secs exposures from a dark site. I know a saw a couple.

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D_talley
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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: Maverick199]
      #5358069 - 08/08/12 01:41 PM

Newer DSLR cameras does not mean they are Faster. The Canon 60Da, a nice camera, lets in less Ha light than my older modified 350D and T2i. So no increase in imaging speed.

We are still regulated to long intergration times to get every bit of starlight we can to make a noise free image after you process all of the sub frames, darks, flats and such. Software had automated some of this and has made this easier but you still have to pay your dues getting the images.

The right mix of equipment is something we all strive for. The perfect scope, sky and camera is something most people never obtain.

I live on the East coast. I suffer from humid summers, light pollution and the jetstream. So I will never have the best sky.

The perfect scope is out of my budget so I work with what I have. Swaping out different cameras does not make my imaging time shorter. I then have to take the hard drive full of images and process them.

You will need to define the term "faster".


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Alex McConahay
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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: D_talley]
      #5358173 - 08/08/12 02:28 PM

If we are satisfied with the quality of film images of twenty years ago, we are already there with DSLR's. (In general). The problem is that the goalposts have moved.

Alex


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mmalik
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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: Alex McConahay]
      #5358542 - 08/08/12 06:08 PM

My experience with 60Da has been that one is going to capture almost 95% of the features of most DOSs in about 30 min combined exposure. It is the rest of 5% features in my opinion that will require hours upon hours of exposure time. Inversely, if an object is too dim to show up on 30min combined exposure, then chances are one will need to spend night after night of exposing to get decent result. Just my experience.

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Astro Boy
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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: mmalik]
      #5362175 - 08/10/12 05:57 PM Attachment (52 downloads)

I would have to agree about with you keeping things simple but I've taken it to the extream of shooting single exposures of 3 mins with a modded 5DII and an FSQED at F3.6 no flats just auto dark and although the guys that shoot one object all night then process it all day get a better result for show piece stuff I don't think its worth it , the realy faint stuff is another matter.

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mmalik
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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: Astro Boy]
      #5362195 - 08/10/12 06:17 PM

Quote:

I would have to agree about with you keeping things simple but I've taken it to the extreme of shooting single exposures of 3 mins with a modded 5DII and an FSQED at F3.6 no flats just auto dark and although the guys that shoot one object all night then process it all day get a better result for show piece stuff I don't think its worth it, the really faint stuff is another matter.




You got it; this IS the kind of concept I had in mind for this discussion knowing techniques will vary depending upon the kind of scope/camera one has. Since I don't tend to expose too many frames, I mostly end up taking auto darks. Your image looks great for 3mins.


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zerro1
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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: mmalik]
      #5362743 - 08/11/12 12:37 AM

It really has more to do with the targets, than it does anything else. That 60Da or My modified 1000D or the 5DMk2 that took that image above(Nice one) will only get you so much. When you put your sights on fainter objects you'll get highly frustrated. example = M1.

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Astro Boy
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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: mmalik]
      #5362840 - 08/11/12 03:42 AM Attachment (49 downloads)

I agree with you Robert , I supose I'ts because Ive been down the slipery slope of CCDs and all the trauma involved an the endless hours at a computer ( not my idea of a good time ) that I've gone back to basics.
The other night I shot a lot of the objects in Robert Reeves and Verinbergs books and ACTUALY HAD FUN IMAGING ! remember when this hoby was fun and not just for the computer boffins .
If any thing my 3 min shots were better than they did with thier Schmidt cameras.
I think I'm becoming some sort of a ludite but isn't having fun the reason were in this hobby ?
More power to people that can spend hour after hour on one object but for now I enjoy doing my " one shot wonders "
this one an 8min shot of the Key Hole with 12" RC


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D_talley
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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: Astro Boy]
      #5362950 - 08/11/12 07:47 AM

Nice images but it is clear you are in a nice area for imaging. I would have to image for hours to get what you did in minutes because of light pollution, humid night and seeing. So some people shot all night to ensure that they have enough data to make a good image.

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Alnitak2009
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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: mmalik]
      #5363081 - 08/11/12 10:02 AM

In terms of "faster capturing" the newer camera's do allow for higher ISO settings which increases the gain as in a webcam. But the real items that would allow for faster recording of faint light with lower noise levels would be larger aperture telescopes with fast f/ratios. The larger the scope/F/ratio, the faster ability to go deep in short order. I sometimes image through a Meade 16" F/10 system but I incorporate a focal reducer to speed up imaging by 4x with a much larger field. I took a single image at this setup of a comet at ISO 3200 and I did have to use some noise reduction applications to get it comparable to a multi-stacked image. For a single one minute exposure it came out very good.

Don


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Alnitak2009
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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: mmalik]
      #5363082 - 08/11/12 10:06 AM

A good example is the Witch head nebula. I can't even make it out on the back of the camera LCD. I have to take many imaging and stack and then enhance with photo programs. I often can bring out the nebulousity but at a cost of increased noise. I think a larger aperture scope and darker sky may increase the contrast of this nebula and background sky.

Don


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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: Alnitak2009]
      #5363263 - 08/11/12 12:21 PM

Quote:

In terms of "faster capturing" the newer camera's do allow for higher ISO settings which increases the gain as in a webcam. But the real items that would allow for faster recording of faint light with lower noise levels would be larger aperture telescopes with fast f/ratios. The larger the scope/F/ratio, the faster ability to go deep in short order. I sometimes image through a Meade 16" F/10 system but I incorporate a focal reducer to speed up imaging by 4x with a much larger field. I took a single image at this setup of a comet at ISO 3200 and I did have to use some noise reduction applications to get it comparable to a multi-stacked image. For a single one minute exposure it came out very good.

Don




I think it is photographically fast optical systems combining aperture with ever lower noise DSLR's, in good sky conditions that is the core of the principle here. However, I do not think the term "agile" describes the process at all. (The OP may be deriving it from a software development methodology emphasizing iteration and collaboration of which fast turn around is only a component) I would suggest a cut-off, that if it takes more than 60 seconds to generate a good quality image it is taking too long. In my view, there should be no or little post-processing and no agility in techniques required. I think what we are aiming for is "express" or even "instant" astrophotography, and it should be one-shot, fast, and deliver heavy doses of fun and instant gratification straight out of the camera such as my 15 second exposures in an earlier thread.

http://www.cloudynights.com/ubbthreads/showflat.php/Cat/0/Board/DSLR/Number/5333184/page/3/view/collapsed/sb/5/o/o/fpart/all

Of course this works for bright eye-candy objects in dark skies. As soon as you are chasing faint objects and going deep, exposure times will increase again but thats not the point. The point is to have fun in generating great results of those objects that do lie within the exposure time threshold - straight out of the camera.

One other aspect of cameras like the Canon 60Da is that it in terms of apparent resolution (for a given telescope/camera combination) it only has 4nm pixels. Its bayer quadruplet has equivalent resolution to most mono CCD cameras in the 7nm to 9nm pixel range such as my SBIG STL 6303e CCD camera. (If not in QE or depth etc)

Chris


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Maverick199
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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: Aquatone]
      #5363275 - 08/11/12 12:30 PM

Chris, your 15 seconds images are outstanding to say the least, but another point which needs to be factored in is the amount of equipment to gel with being an instant astrophotographer. For me, obtaining an image with minimal equipment in the fastest possible times is what I would describe as instant gratification. I have seen some images with just 10 seconds exposures wide field which baffles me still. I wish I had those type of skies, another thing to be factored in.

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Aquatone
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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: Maverick199]
      #5363285 - 08/11/12 12:38 PM

Quote:

Chris, your 15 seconds images are outstanding to say the least, but another point which needs to be factored in is the amount of equipment to gel with being an instant astrophotographer. For me, obtaining an image with minimal equipment in the fastest possible times is what I would describe as instant gratification. I have seen some images with just 10 seconds exposures wide field which baffles me still. I wish I had those type of skies, another thing to be factored in.




I would agree that minimal/simple equipment or at least easy portability is a requirement. Most of don't live in very dark skies (I certainly don't) In my situation I am going to argue that a simple 24" reflector is minimal equipment! (I can transport, setup, and align it, much more quickly than a standard astrophotography rig with scope, equatorial mount, counterweights, pier, camera, guider, computer, laptop, cables, power, yawn...)

Chris


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mmalik
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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: Aquatone]
      #5363496 - 08/11/12 03:28 PM

Quote:

I would suggest a cut-off, that if it takes more than 60 seconds to generate a good quality image it is taking too long. In my view, there should be no or little post-processing and no agility in techniques required.




What I am intending from "Agile DSLR Astrophoto Imaging & Processing" is NOT necessarily one-shot imaging. Since imaging agility will vary given the scope/camera/sky conditions, the idea is to produce decent images in less time. That less time, for example, may be 10 min (combined) for 24 scope, 30 min (combined) for 10 scope, and may be 45 min (combined) for 5 scope, etc. Note: These times are just examples, not actual recommendations. So time scale will vary a little given the variables, but concept remains the same, NOT having to do hours upon hours of exposing and everyone finding their own imaging agility parameter (shorter the better).

And yes, for processing agility, I am suggesting little/quick post processing (basic stacking, basic processing, etc.) but WITHOUT major/time consuming post processing techniques.

Keep your ideas coming...


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CA Stargazer
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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: mmalik]
      #5363508 - 08/11/12 03:35 PM

How about DeepSkyStacker Live? It watches your target directory and stacks as the images download from your camera.
http://deepskystacker.free.fr/english/live.htm

Is that what you have in mind?


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mmalik
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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: CA Stargazer]
      #5363557 - 08/11/12 04:16 PM

Quote:

How about DeepSkyStacker Live?... Is that what you have in mind?




Thanks for your input; concept again I have in mind is everyone using tools they like/prefer but doing little post-processing, not just to save time but to avoid time consuming tweaking/altering of the original/combined image (I see some folks doing processing to the point image starts looking synthetic). I, for example, use ImagesPlus, but use it to quickly combine, do basic stretching/smoothing and get done in few minutes.


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Eric Gage
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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: mmalik]
      #5363666 - 08/11/12 05:44 PM

This might be more lazy than agile, but my general strategy is 60-90 minutes of images, equal darks, quick flats, color balance and stretch. I spend less than 10 minutes on post-processing and I always finish my image(s) before going to bed. I usually toss the subs as soon as I stack to save space on my laptop.

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mmalik
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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: Eric Gage]
      #5363713 - 08/11/12 06:11 PM

Quote:

I spend less than 10 minutes on post-processing and I always finish my image(s) before going to bed. I usually toss the subs as soon as I stack to save space on my laptop.




I would call it quite 'Agile' post-processing; that's partly the idea.


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Astro Boy
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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: mmalik]
      #5363987 - 08/11/12 10:16 PM Attachment (31 downloads)

Chris nice images with your 24" I have a similar Dob and a camera adapter on the way for the Paracorr 2 on it will be good to see what the 5D II will do I hope I can get good tracking out of the Servo Cat.
I find the tracking on the mount is the limiting factor ( unguided ) 3mins on the AP600E , if I have to resort to autoguiding the camera noise is the limit which I thought was 10 min but will have to experiment.
Maybe if we call it Minimalist or Fast Track imaging would cover what we are trying to do.
As some have pointed out I have the advantage of dark skies down here , but like most things in life , Its what you do with what you've got .
Number one thing is to have Fun !
This shot M83 10min exposure and about 10min post processing.

Zane


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mmalik
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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: Astro Boy]
      #5364226 - 08/12/12 02:10 AM

Quote:

Maybe if we call it Minimalist or Fast Track imaging would cover what we are trying to do.




Or we could include what you are suggesting into the definition.

Great looking image of M83; I presume it is single 10 min exposure?


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Starhawk
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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: mmalik]
      #5364249 - 08/12/12 03:05 AM Attachment (25 downloads)

The DSLR has a little to do with this. But the big one is available optics to go to lower f/#s.

I took this photo with a Pentax K-5 (which doesn't have the aggressive IR filter Canon and Nikon are in love with), and a C11 using hyperstar.

The frames are 30 second subs, and you can see a lot of the dim hydrogen clouds are coming through. For this fall, I still want to go to longer exposures to get cleaner data on the really deep exposure portion.

Because of that, I have to disagree with part of the supposition of short exposures being a 90% solution. The longer exposures still have less fixed pattern noise, and the cameras really only reward low f/# imaging trains.

-Rich


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mmalik
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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: Starhawk]
      #5364324 - 08/12/12 06:00 AM

Quote:

But the big one is available optics to go to lower f/#s.

...I have to disagree with part of the supposition of short exposures being a 90% solution. The longer exposures still have less fixed pattern noise, and the cameras really only reward low f/# imaging trains.




Welcome to the discussion Rich; I don't think anyone is suggesting short exposures (< 1min) per se if I understood you correctly; although folks with really large apertures (e.g., 24) have tried sub-1min exposures and I think rightly so.

Partly the idea is to reduce overall integration time, regardless of individual exposures which are going to vary given the equipment and type of the object. So yes, longer exposures with shorter overall integration time are part of the Agile equation just as shorter exposures with shorter overall integration time are.

Lower f# is a good point you mention; I'll let folks chime in on that.


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austin.grant
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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: mmalik]
      #5364473 - 08/12/12 09:39 AM

Don't we already have an entire collection of threads based on this "style" of imaging? It's called Beginning and Intermediate Imaging.

What you are proposing fits that existing model precisely: short subs, low total integration times, minimal processing and a "natural" look.

Whatever the purpose of this thread, I think you should revise one of the opening statements. The idea that, "one is going to capture almost 95% of the features of most DOSs [sic] in about 30 min combined exposure" is simply absurd.


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Starhawk
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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: austin.grant]
      #5364706 - 08/12/12 01:10 PM

The point is, the K-5 has the most sensitive detector (ISO 51200) thusfar deployed in a DSLR, and while the noise is quite low, it is still the signal you see in an image.

Where the DSLRs do well is high signal. I've been using something I invented called the brightness factor to compare setups:

Br=1000/(f/#)^2

So, here are a few to give an idea how it works. It puts the brightness of the image on the focal plane on a common footing where a brightness factor twice as big means the image really is twice as bright.

AP130 EDFGT, f/6.3:

Br=1000/6.3^2= 25.2

AP130 EDFGT with 0.75 reducer, f/4.725:

Br=1000/4.725^2= 44.8

Note, a magnitude change in brightness reached on the camera in a given interval requires a 2.512 improvement in the brightness ratio. So, the focal reducer isn't even giving 1 magnitude improvement as there was only a 1.78x improvement in image brightness.

Here's another:

C11, f/10:

Br=1000/10^2= 10

C11 with f/6.3 reducer, f/6.3

Br=1000/6.3^2= 25.2

Note, all identical focal ratios give identical image brightness. Also note the 2.52x improvement in the brightness ratio means this is getting a full magnitude in performance improvement. Compared to the AP130 EDFGT, this has less than half the field of view, though.

C11 with hyperstar, f/2:

Br=1000/4^2= 250

This is the configuration DSLR cameras made possible. The 25x in brightness improvement means an exposure gets close to 3.6 magnitudes of improvement over an f/10 image.

But this comes at a cost- the very low back focus leaves no room for filter wheels, and the fact it's in the middle of a glass plate means the camera has to be light. But the DSLR has built in filters and a compact light form factor, so this is possible.

As for other magic, going wheels up without a PC following the telescope around is awesome.

-Rich

Edited by Starhawk (08/12/12 02:58 PM)


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mmalik
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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: Starhawk]
      #5365830 - 08/13/12 02:34 AM

Quote:

Where the DSLRs do well is high signal.

But this comes at a cost- the very low back focus.../-/...DSLR has built in filters and a compact light form factor, so this is possible.

...going wheels up without a PC following the telescope around is awesome.




You bring up some important points. And thanks for your brightness factor details; I presume the 'factor' is in support of the premise of this discussion?


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mmalik
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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: austin.grant]
      #5365839 - 08/13/12 02:46 AM

Quote:

I think you should revise one of the opening statements.




You may have taken some of the statements out of the context; there was a follow up statement "Since imaging agility will vary given the scope/camera/sky conditions, the idea is to produce decent images in less time. That less time, for example, may be 10 min (combined) for 24 scope, 30 min (combined) for 10 scope, and may be 45 min (combined) for 5 scope, etc. Note: These times are just examples, not actual recommendations."

This is a discussion/work in progress, not a conclusion per se. I'll try summarizing along the way as evidence accumulates.


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mmalik
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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: mmalik]
      #5365870 - 08/13/12 03:45 AM

Following are few samples of ~30 min integration with a 254mm APO and Canon 60Da of larger brighter objects:

Note: All images are cropped.

NGC 7635 - Bubble Nebula in Cassiopeia
M51, NGC 5194 - Whirlpool Galaxy


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mmalik
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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: mmalik]
      #5365871 - 08/13/12 03:47 AM

Following are few samples of 45 min and 15 min integrations, respectively, with a 254mm APO and Canon 60Da of smaller dimmer objects:

Note: All images are cropped.

NGC 7048 (Planetary Nebula in Cygnus)
Minkowski 4-11 (Planetary Nebula in Scutum)


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Astro Boy
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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: Astro Boy]
      #5368792 - 08/14/12 05:59 PM

I take it you didn't use any noise reduction software , the images show a lot of promise but a bit noisy for my taste .
The only way I can get images I'm happy with is using Topaze Denoise and Adjust , I find them both quick and easy to use .

Zane


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Eric Gage
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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: Astro Boy]
      #5368903 - 08/14/12 07:15 PM

I just read the fine print...254mm APO? Wow! Congrats!

I think most imagers would notice an increase in agility with that kit under dark Aussie skies.


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mmalik
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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: Astro Boy]
      #5369381 - 08/15/12 12:57 AM

Quote:

I take it you didn't use any noise reduction software , the images show a lot of promise but a bit noisy for my taste . The only way I can get images I'm happy with is using Topaze Denoise and Adjust , I find them both quick and easy to use.




I would agree, some smaller/dimmer ones are bit noisy; planning to redo those. Given short integrations, I have been using in-camera noise reduction.


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mmalik
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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: Eric Gage]
      #5369386 - 08/15/12 01:01 AM

Quote:

I just read the fine print...254mm APO




Actually, those image samples are from a suburban/red zone; not a perfect spot but still worth the try.


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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: mmalik]
      #5369867 - 08/15/12 10:38 AM

Partly- the DSLR format isn't going to have an infinite horizon for sensitivity improvement. The quantum efficiency of the professional cameras is not going to appear in DSLRs without a technology breakthrough. Because of this, they really need fast optics (previous post tells how much energy you get on the detector versus f/# of the optical system).

The conventional photographers are the driving reason for the cameras, and their needs are driving development. The internal automated routines are often impossible to turn off. So, there is a lot of hidden effort with DSLRs to bypass behaviors which affect the data.

So, I kind of feel the DSLRs are operating in a niche. If they are going to completely supplant other cameras, they are have to grow in ways their main user base is not strongly interested in. For example, the up and coming application in the mainstream world is HD video. While it's nice to see Canon throwing a bone to the astrophotography crowd now and then, the cameras they are doing it with aren't even as sensitive as the 3rd party mods.

So, I like the sentiment of the OP, but it seems to rely on something we haven't seen, yet.

-Rich

Quote:

Quote:

Where the DSLRs do well is high signal.

But this comes at a cost- the very low back focus.../-/...DSLR has built in filters and a compact light form factor, so this is possible.

...going wheels up without a PC following the telescope around is awesome.




You bring up some important points. And thanks for your brightness factor details; I presume the 'factor' is in support of the premise of this discussion?




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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: Starhawk]
      #5370559 - 08/15/12 06:56 PM

Quote:

Partly- the DSLR format isn't going to have an infinite horizon for sensitivity improvement. The quantum efficiency of the professional cameras is not going to appear in DSLRs without a technology breakthrough.




Understandable. That would mean CCD is in the same boat as well, correct (horizon for sensitivity improvement I mean)?


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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: Starhawk]
      #5370571 - 08/15/12 07:06 PM

Quote:

So, I kind of feel the DSLRs are operating in a niche. If they are going to completely supplant other cameras, they are have to grow in ways their main user base is not strongly interested in. For example, the up and coming application in the mainstream world is HD video. While it's nice to see Canon throwing a bone to the astrophotography crowd now and then, the cameras they are doing it with aren't even as sensitive as the 3rd party mods.




Very well said; I have asked this before in other threads, what are your thoughts on, hypothetically speaking, Canon offering an 'a' version of 5D Mark III? I wonder if that would be any closer to 3rd party mods.

Other thought I have is why would Canon leave 60Da hanging in terms of sensitivity compared to mods? Why not go all the way and meet or beat the mods if you (Canon) are going to do it anyway? Daytime argument...I don't get it; I never use mine for daytime; if I did, there are better choices.


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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: Aquatone]
      #5370577 - 08/15/12 07:12 PM

Quote:

Link...




I recall you did amazing single 15 min exposures through your 24"; wondering would you like to may be try stacking/combining a few samples of both, larger/brighter and smaller/dimmer DSOs to take the 'Agile' discussion further? I am thinking may be doing ~5 minutes of integrations for each object and posting results here? That's if you are up to it.


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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: mmalik]
      #5370620 - 08/15/12 07:46 PM

I don't know if you would call this "agile" or not, but here's a shot of the Milky Way and Summer Triangle shot on a fixed tripod:

http://www.astropix.com/HTML/SHOW_DIG/Summer_Triangle_Fixed_Tripod.HTM

18 x 8 second exposures at ISO 6400 at f/2.8.

Jerry


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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: Jerry Lodriguss]
      #5370841 - 08/15/12 10:46 PM

Quote:

18 x 8 second exposures at ISO 6400 at f/2.8




Definitely agile... 2.4min integration. Very nice wide FOV.


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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: Starhawk]
      #5371171 - 08/16/12 07:40 AM

Quote:

...Where the DSLRs do well is high signal...

...C11 with HyperStar... This is the configuration DSLR cameras made possible

...they really need fast optics... how much energy you get on the detector versus f/# of the optical system




I agree with most of what you said. Only part I am bit leery about is your example regarding C11 with HyperStar; my concern being added obstruction with the camera in an SC. Plus such a setup may be more suited to video. I am for unobstructed APO instead when it comes to DSLR agility.


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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: mmalik]
      #5371331 - 08/16/12 10:01 AM

Hyperstar works beautifully. The f/2 focal length of a C11 is only 560mm. So, stars are pinpoints even with the central obstruction at that focal length. This is why this is the configuration used in giant scale for the Catalina Sky Survey's 60" asteroid finding telescope on top of Mount Lemmon. The only peculiar part is what happens with cables- they cause diffraction spikes, so you can pick your spikes by moving them around.

-Rich

Edited by Starhawk (08/16/12 10:14 AM)


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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: mmalik]
      #5371344 - 08/16/12 10:08 AM

I don't know if the Canon cameras are the end-all. That's why I'm using a Pentax K-5.

Far less aggressive native IR filter inside. Very large dynamic range. Bigger detector than Canon's APS sized offerings. Last, but not least, ISO 51,200.

And at the end of the day, if I was using the same camera as everyone else, I'd be doomed to produce equivalent results.

-Rich


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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: Starhawk]
      #5371704 - 08/16/12 02:45 PM

Quote:

I don't know if the Canon cameras are the end-all. That's why I'm using a Pentax K-5.

Far less aggressive native IR filter inside. Very large dynamic range. Bigger detector than Canon's APS sized offerings. Last, but not least, ISO 51,200.




Could you post some 'Agile' pics you may have taken with your Pentax with specs (duration, ISOs, etc.)

On a side note, you keep mentioning ISO 51,200; who shoots at that, except may be for framing, and stuff? Wouldn't you get a ton of noise? I hardly go over ISO 400-800; same is the case for most pics posted on DSLR forum.


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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: mmalik]
      #5388480 - 08/26/12 06:38 PM

Hi all. First post. I am new and have been reading for months now. My plan has evolved like so many peoples have. I copied the idea from a web search. There are some folks in the Middle East with 5 huge Cannon lenses (300mm f2.8 I think) connected straight to some really high speed ccd cameras. My guess would be they had each camera with its own filter.
Now I plan on mounting my 8"lx90 on my Atlas GEM with two Canon dslr's (one is a t3i-still shopping for the second camera) on-top. One gets a combo of a Canon 70-200 f2.8 L + 1.4x teleconverter and the other a Canon 300mm f4 L IS + 2x teleconverter . The guiding is still being worked on but currently a Meade DSI looking through the LX90. My idea is to be able to have two good lenses and one telescope trained at the same object thus reducing exposure time. How this is going to work is still not know. It sure is fun trying.
Casey


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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: caseyfinn]
      #5421128 - 09/14/12 03:24 PM

Ok, I am now lost on the purpose of this thread or the concept. Is it about avoiding dedicating multiple nights to a single object to go deep or overcome LP? My takeaway is for a minimalist approach to time/processing. To me this approach is more about getting more objects a night than for a better result. Granted I find it tough to stick with a single object for multiple nights, the end result is always more satisfying to me when I put in the hard work. Now my processing at this point is very minimum since I am still learning that part of this hobby.

Again, correct me if I am wrong, but I am not seeing the concept here very well.


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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: petemumbower]
      #5421178 - 09/14/12 04:02 PM

Quote:

Is it about avoiding dedicating multiple nights to a single object to go deep or overcome LP




Idea is to produce good quality astro photos with less time and effort, both imaging and post-processing. I am not saying we should cut down on sub-exposure length necessarily (although, that may be part of the equation), but mainly cutting down on total integration time. This may be possible with better technology (e.g., 60Da and other newer modified/optimized cameras). As I stated in my first post, goal is to use new and evolving technology in faster/better manner.

There are variables to this equation and agile imaging/processing will vary from person to person and equipment to equipment. For example, a half hour integration time for a DSO on a 254mm APO could be one hour integration time on a 130mm APO; a half hour integration time for an a modified/optimized camera could be one hour integration time on an unmodified one and so on I am also suggesting reducing processing time/effort and NOT going out of the way to make images look pretty to the point they start looking synthetic. Some amount of processing is always needed, but over processing can be avoided.

@Falcon said in another post there is an "ideal" exposure length for sub exposures. Go shorter than that and you are losing out on faint detail, go longer and you gain very little even after adding a lot more exposure time. Agile effort in my opinion is partly about finding that minimum optimal time for a sub as well as finding minimum total integration time (of all subs combined).

Hope this helps. I am looking for ideas and would like to develop some kind of consensus that this is something worth pursuing and that it could be a worthy goal. In short, idea is to use newer technology in creative ways which results in reducing time and effort it takes to take images and process them. Ill post some example images in coming posts and processing methods used.


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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: mmalik]
      #5421471 - 09/14/12 07:43 PM

Thanks mmalik, I understand what is being presented here. More of a best practices via equipment/technique that will produce good results with minimum effort.

Which I am all for, but unfortunately does become a issue of throwing money at the various pieces of equipment. Like the latest camera, mounts, fast optics, filters, etc... But it does give a good reference point to what state of the art can produce.


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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: petemumbower]
      #6272373 - 12/25/13 03:21 PM

Thought I'll chime in on the subject of "diminishing returns" being discussed in the other... thread. I am also of the view, as I have discussed above, that there is a way to maximize your return with "logically" optimal effort, and that effort has to take into account both acquisition and processing related happy medians; cross those thresholds and you'll find yourself struggling and spending countless hours acquiring as well as processing. Regards

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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: mmalik]
      #6273181 - 12/26/13 07:32 AM

Cutting down on the length of subs, use:

1. OTA with a very fast focal ratio to yank the Skyfog Peak well away from the Read Noise.
2. Camera with very low Read Noise, to guarantee good Stacking Efficiency (i.e. so that the Skyfog Signal is overwhelmingly larger than the Read Noise)
3. Camera with large pixels so more photons fall on each pixel and the signal generated by the Skyfog (and of course the target object) is huge.
4. A mono astroCCD if you are willing to settle for a B&W final image.

To minimise integration time:
Use 1., 3. and 4. above.
Settle for a small final image. An HDTV screen is only 2 megapixels (1080x1920) and even the larger monitors we use today on our PCs do not have more pixels. So anything over 2 MP is perhaps redundant. But "retina" displays may well be coming down the line tomorrow (4k TV anyone?).

How do the above work out? Using a current Canon crop DSLR and an OTA at f2 (Hyperstar) will require half-minute subs for satisfactory Stacking Efficiency at any site on Earth. If you use a Canon with larger, but (current technology) pixels, you can of course cut down the length of subs substantially.

Integration time depends on the eye of the beholder. If all you want is an image no larger than 900 pixels x 600 pixels and you are shooting from a dark site then you might well be very happy with less than an hour's worth of integration time. Of course if you are looking for large prints, then no integration time is ever going to be "enough".

How can we speed up everything further? Use a mono camera (also include the IR, so only mirror scopes need apply) and cut both the length of subs and integration time by a factor 5x. That ought to be quite "agile"! 6 second subs and 12 minutes integration time.

Even more agile? Find/fabricate a camera that fully utilizes the image circle of a Hyperstar (27mm diameter) but has only 2 megapixels (recall that is the best that can be displayed by an HDTV or most of today's PC monitors). Each pixel would be about 14 microns square (or about 10x the area of a pixel in a Canon crop DSLR). If it has a Bayer Array (for agile color imaging) then each sub can be as short as 3 seconds) but if you are ready to settle for mono then each sub can be only half a second! Again, integration time can also be shortened 10x (6 minutes for Bayered RGB, or ONE minute for mono). That would be awesomely "agile"

In brief, with existing cameras and OTAs: 30sec subs and one hour integration time using a current model Canon crop DSLR is about as "agile" as it gets. Cut down the size of the final image to 600x400 pixels and you can cut down the integration time to half and still be very happy with the apparent SNR. Use an f2.8 OTA and you need to double up. Use a slow OTA, say, f6 or slower, and you are no longer in agile territory.

Is there another way that does not require a Hyperstar? Almost certainly do-able with items available in the market. Steps to find such equipment:
Find an astroCCD that has around 2 megapixels of recent technology. It will be quite small and I expect that it will be sufficient to use it with C-mount cine or video lenses. These lenses have small image circles and are consequently very compact compared to 35mm camera lenses. These C-mount lenses also tend to be very high quality and have very fast focal ratios. I have come across some with f1.0 but of course they cost a lot. This route really makes sense only to those with access to such lenses in their other line of work. Secret to "agile" imaging is always to start with very fast focal ratios at a dark site. An f6 is 9x slower than an f2 OTA. Suburbia requires 15x to 40x as much integration time as a dark site. Specs like Quantum Efficiency, etc have trivially small variations in comparison.


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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: Samir Kharusi]
      #6273195 - 12/26/13 07:44 AM

Methinks this is quite agile. Single 5-minute exposure in an unmodded camera (Canon 1Ds) at f4:


Covers most of the sky in one go


I was not chasing agility, but a large print, otherwise I could have shot it at f2.8


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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: mmalik]
      #6275652 - 12/27/13 04:08 PM

My view of agile imaging is this. canon 60da with images saved to a card. I amusing an SBIG stand alone guider and am using the Canon remote controller for exposure time settings, so no computer is involved with capturing.

I was totally visual before except for shots of Hale Bopp and Panstars.

Lots of fun so far though the weather has been challenging here in mid GA the last six weeks.


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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: Samir Kharusi]
      #6275752 - 12/27/13 05:02 PM

Quote:

with existing cameras and OTAs: 30sec subs and one hour integration time using a current model Canon crop DSLR is about as "agile" as it gets. Cut down the size of the final image to 600x400 pixels and you can cut down the integration time to half and still be very happy with the apparent SNR. Use an f2.8 OTA and you need to double up. Use a slow OTA, say, f6 or slower, and you are no longer in agile territory.




Being a "lenser" (lens imager I mean) you have quite a unique perspective on 'Agile DSLR Astrophoto Imaging & Processing'; I had typical astrophotography in mind in terms of agility, the one done with a scope (which mostly is an f/9 or higher). Regardless, you bring some interesting perspective to the table. Regards


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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: mmalik]
      #6275846 - 12/27/13 06:15 PM

As alluded to above the most obvious way to cut down on imaging time is this principle ...

http://en.wikipedia.org/wiki/SuperWASP

Note all 8 cameras have F/1.8 lenses ...

Some amatuers (such as Prof Greg Parker in the UK) are now emulating the WASP configuration. Yup 4 or more scopes on same mount all imaging the same field simultaneously .... oh how I wish!!!

Parker's mini-WASP .... go and drool

http://www.newforestobservatory.com/wordpress/wp-content/gallery/projects/con...


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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: mmalik]
      #6276474 - 12/28/13 01:01 AM

I think the traditional refractors have just about had their day as astrographs. They have a number of shortcomings that are almost unacceptable in 2013 given their prices:

Imaging chips are now quite large, at least APS-C and one has to pay a LOT to get a decently flat, large enough, image circle.

Slow focal ratios. f9 is even slower than what I was thinking of!

Star FWHM that are rather large given current pixel sizes. 15 micron FWHM require premium APOs with premium prices. We are talking Tak FSQ territory. Yet Canon DSLRs already have 4.3 micron pixels that would be well matched to 9 micron stars.

Compare the above to a Hyperstar set-up:

Absurdly fast focal ratio, f2

Star FWHM of around 7 microns

Dead flat image field over an APS-C chip size.

You can see why agility and convenience really steer us to Hyperstars. Almost all mirror OTAs designed as astrographs are much faster than typical astro APOs, cost less, and have tighter stars. New purchasers: choose your tools carefully. These days the available options are really far more convenient than the tools available even a decade back. Film has been superceded by CCDs, APOs are getting overtaken by mirror scopes. Both Astrophysics and Tak have excellent mirror astrographs in their stables. For mere mortals Celestron+Hyperstar are already affordable.


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garret
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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: Samir Kharusi]
      #6276633 - 12/28/13 05:01 AM

Quote:

I think the traditional refractors have just about had their day as astrographs.




If you are Imaging @F1.9 with the C14 Hyperstar the focal-lenght is only 675mm.
If the pixels of a CCD camera are 5,5 micron wide, the smallest details you can capture is just 3,36 arc/ seconds wide (including 2x Nyquist criterion) with a color ccd camera it is even worse: 4.5 arc/ seconds (2,7x Nyquist).
You gain is short exposure, you lose possible resolution.

If the seeing is about 2 arc/ seconds, and the CCD camera has 5,5 micron black and white pixels the focal-lenght should be 1120mm to capture every detail.
( 206265* (0,0055/X)= 1 arc/second )*2 X=1120mm.
The TEC APO 160 F7.0 is just what you need: 1120mm focal-lenght.
F 7.0 is slow, if you want speed take a 16 inch Newton Astrograph fit a 0.73 reducer and you have a (optical) ideal F2.8/ 1110mm imaging telescope.
With 9 micron black/white pixels the focal-lenght is 1850mm: a very large APO or a small RC telescope.

But never forget: ' There is no such thing as a perfect telescope'

Garret van der veen


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mmalik
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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: garret]
      #6276649 - 12/28/13 05:53 AM

Quote:

If you are Imaging @F1.9 with the C14 Hyperstar the focal-lenght is only 675mm.

... You gain short exposure, you lose possible resolution.




I tend to agree; this point was discussed at length in this... thread. Regards


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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: Samir Kharusi]
      #6276654 - 12/28/13 06:05 AM

Quote:

APOs are getting overtaken by mirror scopes.




Not to go on a tangent here, I feel this... discussion may have reached a different conclusion?


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garret
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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: mmalik]
      #6276747 - 12/28/13 08:24 AM

Quote:

I feel this... discussion may have reached a different conclusion?




23 pages! if I read all pages, the day is over


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Cotts
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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: garret]
      #6277021 - 12/28/13 11:31 AM

I like this concept of 'agility'. My take on it extends beyond the actual taking of astrophotos and their processing to the 'agility' involved in portability.

I will be travelling to Chile in March for 11 nights, during which time I need to capture as many objects as possible, leaving a few nights for visual observing as well.

My portable set-up: Canon60Da, AstroTech 65EDQ (420mm f/6) or Nikkor 105mm f/3.5 piggybacked, Orion SSAG, iOptron ZEQ25 mount, PC laptop. The AT has a field about 3d x 2d while the 105mm is about 12d x 8d.

My 'agile' image acquisition would involve taking about 6 subs of about 3 min, ISO 1600, with auto dark subtract*. Take the bias and flats during the day so as not to waste time at night. I would be shooting in raw + jpeg and saving them on the camera chipcard.

"Agile processing" at this time is a mystery to me. What I would like to find is a processing program into which I place the subs, flats, darks and bias, press a button and the program does the rest - perhaps using certain 'tried and true' processing routines... I have a nice big iMac and a decent enough PC laptop so programs for either program would be nice. I do not have Photoshop and have no intention of forking out that kind of dosh for it. Suggestions?

* about auto dark subtract. I know the importance of darks. I also know that they must be the same length as the subs and taken at pretty much the same time as the subs in order for the temperatures to match. It takes time to do these and, as far as I can see, this time is taken from your 'under the stars' imaging time. So whether I take a bunch of darks immediately followed by my subs or use the auto-dark subtract while doing the subs the same amount of time will be 'lost'. So auto-darks seem to be more 'agile' for my purposes...

Of course, I could have everything wrong....

Dave


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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: Cotts]
      #6277208 - 12/28/13 01:12 PM

there's no such thing as agile processing, unless you want cruddy astrophotos. the closest you will get is to capture high-quality data from a dark site (which is what you are going to do) and then the processing becomes MUCH easier.

as for the darks you don't have to take them on-site unless you think you can't replicate the temperature when you get back home. there is always the refrigerator

rob


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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: pfile]
      #6277272 - 12/28/13 01:52 PM

Yes - I would shoot the darks while you are packing up. Why waste 50% of your expensive dark sky time?

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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: Tonk]
      #6277357 - 12/28/13 02:30 PM

Putting my camera in a box on the back porch gets the darks done while I sleep. The box keeps the critters out and the temps are often in the range well below the refrigerator.

Agile AP interests me, especially in the view of it being strictly a fun hobby and not an all-consuming retirement activity. The capture phase is definitely more interesting and holds infinite possibilities of gear combinations and targets. Targets can dictate the gear to a large degree and results can depend largely upon one's tolerance for imperfection. While we all strive for the ideal I know that I settle for mediocrity more often than not. I just want to feel some level of satisfaction from the results. Everyone's mileage will vary.

How agile is enough?


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Cotts
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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: Ranger Tim]
      #6277579 - 12/28/13 04:56 PM

I understand the idea of getting a dark 'library'. I could do this before I leave and save a lot of shooting time as you all suggest... How accurate must the temperature of the dark match the shooting temperature? Or, putting it another way, assuming a given ISO and sub length, what temperatures should I use? The nighttime temps at atacama will range from freezing to about 10C. So, 10 darks each @ 0C, 2C, 4C etc.? Or at 0C, 1C, 2C etc.?

Thanks,
Dave

Edited by Cotts (12/28/13 04:58 PM)


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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: Cotts]
      #6277584 - 12/28/13 04:58 PM

Quote:

I understand the idea of getting a flat 'library'




You mean dark-library?? - flats must be taken with your specific camera orientation on the OTA on the day (+ dust motes etc)


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Cotts
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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: Tonk]
      #6277870 - 12/28/13 07:25 PM

Yes, dark library. I have corrected my post.

The question remains: If it is 4C when a set of subs is taken how close to 4C must the dark frame be? +/- 1C? +/- 2C?

THX

Dave

Edited by Cotts (12/28/13 07:34 PM)


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pfile
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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: Cotts]
      #6278045 - 12/28/13 09:11 PM

no more than 5C is what i strive for, but it's probably better to get as close as you can.

the 60Da will write a field called "camera temperature" into the EXIF data; if you are using backyardeos at least, you can put this EXIF value into the generated filename. that makes it a heck of a lot easier to sort. APT might support this as well, i am not sure.

there is also a windows script/application running around that was written by someone here on CN. i think it directly looks at the EXIF of the CR2 and helps you sort darks and create a library per temperature. it's called "dark library" if i remember properly. i think this is the latest but i am not sure:

http://www.cloudynights.com/ubbthreads/showthreaded.php/Cat/0/Number/4710249/...

note that the temperature reported in the EXIF, while from a sensor inside the camera, is not necessarily the sensor temperature. however, it's a reasonable proxy for the sensor temperature. once the camera has been running for a while, you can see what the rise from ambient temperature is like for your camera.

finally some people advocate a cooling-down period between frames. while this will certainly drop your sensor temperature a bit, i think the effects are exaggerated because, thru experimentation, i found that the camera samples the temperature at the beginning of the exposure. it's not clear how fast the sensor heats up again but after a 10 min exposure it will definitely exceed the temperature at the start of the exposure.

rob


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Samir Kharusi
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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: Cotts]
      #6278234 - 12/28/13 11:25 PM

Quote:

Yes, dark library. I have corrected my post.

The question remains: If it is 4C when a set of subs is taken how close to 4C must the dark frame be? +/- 1C? +/- 2C?

THX

Dave




Two things work in our favor:

Short subs and modern CMOS have very low Dark Signal, hence the hot pixels that we need to treat are much fewer than 10 years back.

With the use of Bias Frames (a library at each ISO you use is good enough), it is possible to "scale" the Darks in a lot of astro software, so +-10 deg (C or F) is probably good enough. While 10 deg C may be pushing things, recall that the first para above is already in your favor.

Finally since we all dither the frames anyway, whether intended or not, in a large stack that also smears out the hot pixels.


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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: garret]
      #6278277 - 12/28/13 11:48 PM

Quote:

Quote:

I think the traditional refractors have just about had their day as astrographs.




If you are Imaging @F1.9 with the C14 Hyperstar the focal-lenght is only 675mm.
If the pixels of a CCD camera are 5,5 micron wide, the smallest details you can capture is just 3,36 arc/ seconds wide (including 2x Nyquist criterion) with a color ccd camera it is even worse: 4.5 arc/ seconds (2,7x Nyquist).
You gain is short exposure, you lose possible resolution.

If the seeing is about 2 arc/ seconds, and the CCD camera has 5,5 micron black and white pixels the focal-lenght should be 1120mm to capture every detail.
( 206265* (0,0055/X)= 1 arc/second )*2 X=1120mm.
The TEC APO 160 F7.0 is just what you need: 1120mm focal-lenght.
F 7.0 is slow, if you want speed take a 16 inch Newton Astrograph fit a 0.73 reducer and you have a (optical) ideal F2.8/ 1110mm imaging telescope.
With 9 micron black/white pixels the focal-lenght is 1850mm: a very large APO or a small RC telescope.

But never forget: ' There is no such thing as a perfect telescope'

Garret van der veen



Quite right that the Hyperstar is not quite ideal as yet. With a C14 Hyperstar I dream of a camera with 3.3 micron pixels (one arc-sec per pixel). While there is at least one astroCCD with pixels smaller than 4 microns, the chip's overall size is on the small side. Hence I thought of why not increase the focal length by using tele-extenders? Unfortunately the gain in focal length deterorates the star images. Nevertheless, with existing cameras the trend is definitely towards fast mirror scopes, rather than fast refractors. Camera lenses are the only affordable way to fast, large aperture refractors. Even Astrophysics has launched a Riccardi-Honders 305mm/3.8 superb mirror astrograph (at an astronomical price, of course, and a long wait list!). But any of the Celestron Edge HD SCTs can also be used at f7, even though that is as slow as APOs and the focal length is often too long for modern chips. The C8 Edge HD ends up at 1400mm focal length, perfect for yesterday's 7 micron chips, but too long for the circa 4 micron chips currently. There ain't any perfect scope, but mirrors are the way forward. The professionals realized that some time back


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Cotts
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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: Samir Kharusi]
      #6278286 - 12/28/13 11:54 PM

Thanks, Rob, Samir. It won't be hard at all to do a dozen darks at 0C, 5C and 10C each then and I will be covered, it seems.

As for 'dithering' is this a post-processing routine that will be in Nebulosity or Deep Sky stacker?

thanks,

Dave

Edited by Cotts (12/28/13 11:58 PM)


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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: Cotts]
      #6278299 - 12/29/13 12:05 AM

no - dithering is a capture-time technique, and is (usually) a cooperation between your autoguider, the mount, and the camera control program.

basically you are asking the mount to move a few pixels between each sub so that the fixed pattern artifacts of the chip (hot pixels, banding, bad columns) do not lie on top of one another in the stacked image. if you have enough frames, your stacking software can identify the hot pixels as outliers and simply omit them from the pixel stacks. even if you don't reject hot pixels, with enough frames the hot pixels will get averaged with a bunch of 'good' pixels and not stand out as much.

if you are using an astrotrac or any mount not being controlled by a computer it's kind of impossible to do automatically. of course you can still do it by hand.

recently tony hallas used a 6d for some widefields and he recommended 'extreme' dithering (10s of pixels?) to try to cut down on the color noise you see in DSLR raw frames. usually autoguiding programs are set up to only dither a few pixels so you if you want to do that you may have to do it by hand anyway.

rob


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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: pfile]
      #6278754 - 12/29/13 09:37 AM

Quote:

if you are using an astrotrac




My astrotrac has an autoguider port - I don't know when this feature appeared but I got mine in Jan this year if that helps. Its a "AstroTrac TT320X-AG" - the "AG" is for autoguider

So yeh some Astrotracs can be dithered!


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Re: Agile DSLR Astrophoto Imaging & Processing new [Re: Tonk]
      #6279135 - 12/29/13 12:54 PM

wow! i had no idea about that... that's awesome. i have been in the market for a small eq tracker like that for some time and that changes things a bit.

rob


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