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Old 01-04-2016, 04:30 PM
raymo
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Stunning DSLR images. How!

There are a few people out there that produce stunning images with DSLRs that are, to the uneducated eye at least, hard to separate from high quality CCD camera images.
Is how they do this the result of doing each step in the process of
capture and processing as close to perfectly as humanly possible? or
are there one or two discrete things that make these images possible, such as very dark sky sites, very long duration subs, huge total
exposure times etc: CCD cameras seem to be inherently sharper than any
DSLR, so how do these people produce images that rival CCD images?
Post capture sharpening?
raymo
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  #2  
Old 01-04-2016, 04:36 PM
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Somnium (Aidan)
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Check out this video by Tony Hallas , he does amazing dslr work and goes through some tips and tricks https://m.youtube.com/watch?v=PZoCJBLAYEs
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Old 01-04-2016, 04:44 PM
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blink138 (Pat)
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a cool climate does help a lot raymo with a dslr sensor!
pat
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Old 01-04-2016, 04:49 PM
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Atmos (Colin)
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If you over-sample quite a bit a DSLR can perform virtually to the same level as a mono CCD. The reason for the loss of sharpness is due to the bayer matrix. A 12mp DSLR has 3mp of red, 3mp of blue and 6mp of green. This does not just limit overall transition but also resolution. All of this you are probably quite aware of.

If you under-sample using a OSC on a short focal length scope you don't get the same resolution as it is lost in "missing pixels"... so to speak. If you over sample you have several RGGB "pixels" covering each star.
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Old 01-04-2016, 05:21 PM
raymo
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I'll have a better look at it later Aidan; I used to follow Tony's work back
in the days of film. He did the best film version of M31 that I have ever seen.
Yes I'm well aware of the benefit of coolth Pat.
Colin, being as I am an old gas emitter, I have no idea how to under or
over sample anything.[except maybe chocolate or ice cream].
As I get nearer and nearer to the great black abyss I seem to be
going from high school back to primary school, and finally back to
kindergarten and childcare.
raymo
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Old 01-04-2016, 05:44 PM
glend (Glen)
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You can create your own cold climate DSLR Raymo, just do a cold finger mod and shoot at 0C or below. If you want all those pixels working full-time get rid of the bayer matrix and run mono. Even if you don't want to do it yourself there are mod for hire businesses like CentralDS.
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Old 01-04-2016, 05:58 PM
raymo
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Hi Glen, Yes I am aware of that option; the only trouble is that I can't
decide whether it is worth selling my treasured Hartungs, and various
other possessions, in order to find the wherewithal.
raymo
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Old 01-04-2016, 07:14 PM
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Atmos (Colin)
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Over sampling and under sampling is just a matter of focal length. If you increase focal length you increase the number of pixels that each star (and therefore detail) covers. Working at an image scale of, let's say, 0.5"/pixel with a OSC could theoretically perform the same as a mono.
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Old 01-04-2016, 07:44 PM
raymo
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So following that reasoning, if I make my 1000mm scope effectively a
2000mm one by using a 2x barlow, I would get better resolution. I also
presume that you could keep going until the object becomes too dim to
image properly. That seems counter-intuitive, as we all know that the image quality drops away as the magnification increases, or is one supposed to use lower and lower power EPs to keep the target's apparent size unchanged.
Would that mean that a 2000mm scope using 20mm EP[100x mag]
would give a superior image to a 1000mm scope using a 10mm EP[100xmag]?
raymo
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Old 01-04-2016, 09:17 PM
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rmuhlack (Richard)
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from my experience with DSLR imaging, the key was to take all steps possible to increase signal to noise. For starters, I image from dark rural skies which helps considerably compared with an urban location. After various tests, I worked out an ISO and sub time that would give optimal signal to noise for my camera. This was about 3-4 minutes at ISO 1600 when I was using an uncooled DSLR, and then 8-10 minutes at ISO1600 when I used cold finger modded DSLRs. Making sure that darks and bias frames were temperature matched with lights was important, and then making sure collimation and focus were good during capture. I mainly used two telescopes - one with a focal length of 1278mm, and another at 650mm. I also had several images using Nikkor camera prime lenses which also worked well.

After that, my images made a huge leap forward when I started processing my images with Pixinsight - this allowed me to really pull all the data out of my images. From there it was then about extending total exposure to as long as possible - my maximum exposure was about 50 hours, with many images going for 15-20 hours or longer.

A lot of effort, but I think the resulting images hold their own, eg http://www.astrobin.com/users/rmuhla...blic=&sub=year

Moving to mono CCD has been a further learning curve - i haven't been nearly as productive with my imaging since I made the switch for various reasons (work-life balance being part of the equation, as well as other equipment issues which have held me up, like my obs computers both needing to be replaced). Hopefully those issues are now dealt with, and I can look forward to more imaging in 2016.
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Old 02-04-2016, 12:44 AM
raymo
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Thanks for taking the time to respond; all comments are carefully noted.
cheers raymo
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Old 02-04-2016, 11:46 AM
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kkk26 (Chit Ko Ko)
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Excellent images, Richard. All images were captured with DLSR? I am always interested to get cool modded DSLR
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Old 02-04-2016, 12:02 PM
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rmuhlack (Richard)
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The lunar images were taken with a qhy5l, however the other images linked there were all taken with a DSLR.
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