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Lunar and Astro Photography (7)

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mikey2000 View Drop Down
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Post Options Post Options   Quote mikey2000 Quote  Post ReplyReply Direct Link To This Post Posted: 05 February 2020 at 09:31
My christmas present was an Sii filter for my astro camera, to complement my Ha and Oiii filters. So I can now capture narrowband light from excited sulphur as well as hydrogen and oxygen. Which is a fancy way of saying Deep Red, Red and bluey-green. These are the three commonest light spectra from deep space nebulae, so now I'm sorted for some proper hubbling!

Here's my first sketch, combining this year's new Sii data with the Oiii and Ha I caught this time last year on the Crab Nebula (a supernova remnant, occupying a patch of sky 1/5 the size of the moon). It's a proper colour explosion!

M1 Crab Nebula SHO
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Post Options Post Options   Quote Jozioau Quote  Post ReplyReply Direct Link To This Post Posted: 05 February 2020 at 09:42
Amazing image.
Look forward to more please.
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Post Options Post Options   Quote Tricky01 Quote  Post ReplyReply Direct Link To This Post Posted: 05 February 2020 at 11:02
Wow, stunning mike! Whereabouts do you take these from, Does it need to be away from light pollution or does the narrow field of view mean those considerations aren’t a worry?
A7iii, 14f1.8, 16-35f4, 24-70f4, 24-105G, 35f1.8, 85f1.8, 135f1.8GM, 100-400GM // A mount: Sig180 3.5 Macro, Gitzo Traveller, Flashes+PixelKings website
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Post Options Post Options   Quote mikey2000 Quote  Post ReplyReply Direct Link To This Post Posted: 05 February 2020 at 11:13
I’m lucky to live at the edge of a small town so light pollution is mostly on one side of the sky. However, my roof and some trees obscure a decent chunk of the space for me. As targets then set in the “good side” of my skies, they sink into the light pollution mush from Milton Keynes (big town, about 5 miles away) and then all the details get swamped by sky glow.

It means I need to wait for a few months for a target to sit in the right part of the sky and then it’s often cloudy! Still, there’s always next year... Astrophotography is not for those of an impatient nature :-)
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Post Options Post Options   Quote Dopol Quote  Post ReplyReply Direct Link To This Post Posted: 05 February 2020 at 11:23
Beautiful Mike.
Much looking forward to more 'starry' night shots.
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Post Options Post Options   Quote Fred_S Quote  Post ReplyReply Direct Link To This Post Posted: 05 February 2020 at 20:32
Originally posted by Dopol Dopol wrote:

Beautiful Mike.
Much looking forward to more 'starry' night shots.

+1. Impressive work!
 



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Post Options Post Options   Quote WestCoastCannuck Quote  Post ReplyReply Direct Link To This Post Posted: 06 February 2020 at 04:01
Originally posted by mikey2000 mikey2000 wrote:

The 100ED is working very nicely for those moon shots...


Have you ever visited Astronomy Tools Astro Calculators? (put it in Imaging Mode then choose your kit)

I tried finding your 100ED and camera and it says the resolution would be

0.55arcsec per pixel. It then says the Dawes Diffraction Limit is 1.16 arcsecs. Hence the pixels are smaller than the scope's theoretical max resolution. In theory, this means you are 'wasting' camera resolution by photographing at a higher res than the scope can provide.

Interestingly, with a 6 inch newt (150mm aperture) the figures become 0.66arcsec per pixel and Dawes Limit of 0.77 arcsecs.

It would be interesting to compare shots from either scope on the ASI183 camera to see which comes out best as , in theory, the 6" newt should provide more resolution than the 100ED...

It's all about Aperture when it comes to scope resoltion...


Thanks Mike!! I use that site all the time! Its awesome - though mostly I use it to find field of views. lol

I have a mentor in this hobby who I have been trying to learn from - he is a friend now... and frankly one of the smartest people I know. It was with his help I chose my camera and scopes. Contrary to what Dawes Limit suggests my camera is very nearly exactly matched to my scope for potential resolution. I will quote some of what he said on the matter.... Hope you can make some sense of it. (probably more than me)

Originally posted by Marty Marty wrote:

] DSO imaging has nothing in common relative to resolution when talking about angular resolution and sampling. DSO imagers are trying to match their image scales to FWHM seeing conditions, if attempting higher resolution DSO image scales, or its ignored, and simply go for as much subs as possible to get high signal to noise ratio, with bigger pixels and way under-sampled data. This is most common. What this person is doing is simply looking at Dawe's limit and looking at the image scale. But none of it is considering how to record information with the airy disc involved.

Dawe's limit is the max potential resolution, angular resolution of wavelength in arc-seconds, that the aperture itself can potentially achieve. Diffraction limits come into play because there's a field stop to the source, ie, the actual aperture's physical shape and field stop which effects angles of light entering and literally defines diffraction. If you can record angular resolution at the same level as the Dawe's limit, it's diffraction limited (ie, aperture limited). In perfect (circular) image trains, the smallest feature you can record at diffraction limited size (aperture limited, not seeing limited) is the airy disc. As you decrease aperture, diffraction increases (less resolution, less space between the airy discs), this is why camera lenses stopped down to wee apertures that result in focal-ratios like F22, F32, etc, are all diffraction limited, as the aperture is the limit, not the seeing, and it goes soft (losing data, losing resolution).

But we cannot image anything to a single point (ie, one pixel). That's not possible. It's due to wave nature of radiation (light!), diffraction occurs due to the limiting edges of the aperture stop (ie the circle of the aperture. That's why we cannot image at Dawe's limit. The image point is always a blur, due to the aperture stop, no matter how well corrected. That is the diffraction (blur) of the airy disc itself. Size of blur is proportional to the wavelength, so the diffraction effect becomes the limiting factor, quickly, in systems focused on long wavelength. This forces a trend to use smaller and smaller pixel sizes to increase the system resolution, to separate airy discs so that the energy overall is spread out from center to the rings of the airy disc where they start to overlap with each other. This leads us to the next principle.

The Rayleigh limit is when the center of the airy disc is in the first minima of the other. So, to make more sense of this, instead of using Dawe's limit, we use the Rayleigh limit, because its the minimal real world result of being able to separate two light sources based on the airy disc's overlap of each other (less theory, more reality). This leads us into image scales.

When it comes to sampling, under-sampling always leads to potential loss in resolution, whereas over-sampling, you do not lose resolution, you lose integration time, or basically for us in solar system imaging, require more exposure (ie, more light due to stretching of light over surface area, but you're not losing data or resolution). So when imaging this way, its better to oversample in the system in general (the limit becomes seeing). So how to do we sample?

To approach sampling, we assume perfect seeing so that the airy disc is the limit to resolution. For lucky imaging, that's what we assume, as we luckily capture moments where seeing is excellent as best as possible and we are closer to airy disc limited resolution (ie, aperture limited, or diffraction limited). We do not use FWHM seeing limits as a guide. Because of needing to separate airy discs to discretely result in more than one light source on the pixel, we need space between each airy disc. This will relate to Nyquist sampling theory. But basically to scale the airy disc, the pixel spacing needs to be greater (higher resolution) than the angular resolution of the radiation (light). This is why we use smaller, higher resolution potential pixels, than the actual limit of the angular resolution (the aperture). So when we calculate critical sampling, we basically triple the pixel spacing to be able to have room to see a difference between the airy disc overlapping, when we image at the limit of the airy disc (seeing being perfect or great, lucky imaging, and the limit being the airy disc, or diffraction limited, aperture limited). Due to this, the resolution potential of the sensor itself will always be higher than what the optical system gives it. We must be able to outresolve the airy disc potential of the optical system, or how do you differentiate the airy disc blur? So that's where sampling theory comes from. That's where the calculation comes from, to take the aperture (angular resolution limit, defines airy disc, diffraction limit, aperture limit) relative to the pixel size at a specific wavelength to determine the best sampling ratio, the focal-ratio needed, to achieve that, with enough space to notice a clear separation of each airy disc of a light source (ie, the detail). And this why we calculate 656nm wavelength at 2.4um pixels to be F9. F9 is exactly the focal-ratio of your system. Thus, you are sampling at the critical level and not under-sampling, but not grossly over-sampling. Your resolution is maximized to the limits of the total system under current sampling of frequency theory.

If you were to increase the pixel size, to achieve an angular resolution or image scale to match the dawe's limit (or diffraction limit, aperture limit, airy disc limit) of your actual aperture, it would require a larger pixel, which would then decrease the ability to differentiate difference between each airy disc overlapping, severely undersample, which means losing data, inability to notice a difference between light sources, and it becomes lower resolution.

Proof is in the pudding. Your 100mm aperture (same as found in any 600mm F6.3 camera lens, etc) murders any "dslr + camera" image anyone can post in the threads. You were critical sampling. They were not. Despite the numbers on a calc website saying you were not at the resolution potential of your camera sensor, but in reality, you were. They just don't understand frequency sampling and the need to be able to differentiate airy disc. Your sensor needs to be higher resolution to approach the resolution of the angular resolution from the aperture.

Hope that is clear as mud!


My friend is a wizard. lol. Generally, I just take what he suggests and GO with it!   



Basically, the consensus on my shot seems to be that I achieved maximum resolution for the 100ED at 610nm wavelength. (quote marty: 656nm 100mm aperture 2.4um pixels = F9 ideal critical sampling - 610 = F9.7, very close )
(I was using a 610nm long pass filter). The image is sharp at 1:1 pixel level.

Next, for me resolution wise is to achieve the same with my 6 inch newt. (its F5, so to critically sample I will use a 2X barlow, bringing me to F10 - again matching my camera's 2.4 um pixels)... and then, if the seeing ever supports, my C8!! (also F10)

And WOW what an image you made! That is magic to me.... I don't expect I will ever go that way for my imaging. Lunar, and maybe some planetary one day for me. lol

Very best regards!!

Mike

Edited by WestCoastCannuck - 06 February 2020 at 04:14
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mikey2000 View Drop Down
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Post Options Post Options   Quote mikey2000 Quote  Post ReplyReply Direct Link To This Post Posted: 10 February 2020 at 14:15
I had to read that about 3 times to even begin understanding it!

I think that's what I love about the astrophotography... Every time you think you start to understand something, someone better trained comes along and teaches you something new!

I'll have to go and work out the numbers for my own camera/scope setup now and just hope I've got lucky. That said, I'm "into" DSO instead of planetary so it looks like different criteria maybe. Pixel level sharpness is less important than overall light gathering ability.

Still, I think you'd should have a go at Jupiter and see how it goes :-)
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Post Options Post Options   Quote WestCoastCannuck Quote  Post ReplyReply Direct Link To This Post Posted: 11 February 2020 at 03:48
Well... that you begin to understand it tells me you have a better handle than I do. I just do as Marty suggests and always check with him when I get some hairbrained idea! I will learn the math one day though.

I fully intend on trying Planetary one day soon!

Cheers

Mike
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Post Options Post Options   Quote mikey2000 Quote  Post ReplyReply Direct Link To This Post Posted: 13 February 2020 at 11:00
HorseHead Nebula 22min each R,G and B + 100minHa

ASI1600MM Camera, Skywatcher200PDS
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Post Options Post Options   Quote clk230 Quote  Post ReplyReply Direct Link To This Post Posted: 13 February 2020 at 20:22
Originally posted by mikey2000 mikey2000 wrote:

HorseHead Nebula
Really impressive Mike. Fascinating to the see the structure in the nebulosity.
C & C always welcome
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Post Options Post Options   Quote Mark Twain Quote  Post ReplyReply Direct Link To This Post Posted: 14 February 2020 at 13:13
Fantastic shot! It is always a pleasure to visit this thread.
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Post Options Post Options   Quote WestCoastCannuck Quote  Post ReplyReply Direct Link To This Post Posted: 28 February 2020 at 04:43
WOW!! Absolutely stunning work Mike!!!!!   

Here is my tonight's effort in poor seeing. But... beggars can't be choosers.

Click for full size.

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Post Options Post Options   Quote WestCoastCannuck Quote  Post ReplyReply Direct Link To This Post Posted: 01 March 2020 at 22:32
Caught another window last night... had to do some fast work! (sucker holes)

Full disc with Skywatcher 100ED click for larger, though still downsized file.


Managed one high rez with C8 - Click for 100% resolution.


Here is the latest set-up - from last nights shoot in my driveway here... though I am geared for portability. I am planning to replace the 100ED with a larger 120mm/F7.5 refractor soon (about as big as I can comfortably go for this mount.)






Thanks for looking!

Mike
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