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

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mmalik
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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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Starhawk
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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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Starhawk
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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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mmalik
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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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caseyfinn
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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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petemumbower
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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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mmalik
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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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petemumbower
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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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mmalik
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Re: Agile DSLR Astrophoto Imaging & Processing [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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Samir Kharusi
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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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Samir Kharusi
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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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N. Ham
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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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mmalik
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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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Tonk
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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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Samir Kharusi
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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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mmalik
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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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