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JBracegirdle

Video Astronomy for Beginners

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I'm new to astronomy, I got my first telescope in November (StarMax 90mm f/13), I was really happy with the view of the moon and double stars, but disappointed I could see but barely make out nebula (initially the ring nebula). I also tried to take a photo of the moon with my phone but trying to get a stable shot was too difficult, even with a basic smartphone adapter.

I did a bit of research, found about about Video Astronomy/Electronically Assisted Astronomy (EAA) and decided I needed a better mount and took the opportunity to get a faster telescope (StarTravel 102 f5/). I really like the Sky-Watcher -102 AZ GTe with the ZWO ASI 224MC. I've only used it for 4 nights as there is so much cloud about but it's allowed me to take images of things my eyeball wouldn't see. Although my setup is below the minimum specification most would consider for imaging and entry level for visual observations I think I've found a setup that seems to work for me. I like that with SharpCap I can get instant results and the day after when it's back to cloudy I can get a bit more out of the images with Deep Sky Stacker and Gimp. I have tried looking through the eyepiece at the Pleiades, that was a pleasure as well. I can see how observing with a big Dobsonian and amazing eyepieces would be great, but many objects seem better with a camera than eyeballs. The Horsehead nebula wasn't found until astrophotography came into being.

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The photo above was taken on my first night with the setup. The January 2019 issue of Sky at Night Magazine has a review of the Sky-Watcher StarTravel-102 AZ GTe and they give it 4.5 / 5. Combining it with an Explore Scientific UHC filter seems to reduce most of the chromatic aberration and increases contrast relative to the stars, and light pollution.

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Video Astronomy/EAA seems to offer a great window into both the visual and imaging worlds of astronomy. As First Light Optics say "Your first telescope is arguably the most important because if the views do not amaze and delight, your interest in astronomy will crash and burn on the runway!" I understand cost could be an issue, but if the beginner had a suitable camera Video Astronomy could be as accessible as a Go-To visual setup, and seems more likely to amaze (especially in the skies of a typical house).

My question is why is video astronomy not the first suggestion for beginners interested in both visual and imaging?

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Lovely captures!

I did some long exposure imaging with ST102 and similar camera - a bit wider FOV - ASI185. Also employed couple of tricks like aperture mask and yellow filter to control CA. It is interesting combination to play with.

26 minutes ago, JBracegirdle said:

My question is why is video astronomy not the first suggestion for beginners interested in both visual and imaging?

Probably because most beginners think of imaging as putting DSLR type of camera on the scope - usually most people who are interested in taking some pictures think of either that or holding compact camera / smartphone at the eyepiece.

Video astronomy is a bit more involved - one needs laptop computer (or even desktop, depending on their observing setup) and a dedicated camera for that - a bit higher costs than most people think of investing at the beginning. Not to mention software learning curve and there still is no dedicated software for EAA on the market - Sharpcap does the job but it is primarily capture application, rather than dedicated EAA suite.

Having said that, it is actually a wonder full idea - ST102 with low cost mount like AZ Gti, if it's capable of holding that scope, and guessing by your work - it can be done, and an astro camera like 178 / 224 or even 385 for more enthusiastic can be interesting combination to get them into both visual and video astronomy - and they can end up saving their VA sessions as proper images to share with friends and family.

I wonder how would Mak of let's say 102mm aperture fair in this role - no CA to fight, but long focal length requires big pixels (or heavy binning) to get to suitable resolution. Need to research that a bit more - suitable sensor and also corrected field of Mak and suitable reducers.

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Hi, I’m really glad that you are enjoying your EAA setup, it sounds like you are really appreciating its ability to reveal faint fuzzies. Your pics are great and that setup seems to be working really well. 

You ask why this kind of setup isn’t recommmended to those interested in both visual and imaging - I think that’s a really good question! I have found that EEA is like a ‘compressed’ version of imaging, which is less demanding on the person and the equipment. For example:

  • Tiny sensors mean less/no need to worry about elongated stars at edges even when really fast scopes are used - this can be a source of huge angst for full imagers.
  • Short exposure times means less accurate tracking is required, hence less expensive mounts are needed. Also altaz mounts are commonly used which are not acceptable for imaging. 
  • No need for guiding,  simplifying things considerably and reducing cost.
  • Seeing the images build up immediately is very educational in terms of understanding how capture and stacking works, and how tracking, hot pixels, darks, light pollution gradients, changing temperatures, etc can all affect the final image.
  • The ability to adjust the image quickly and easily in real time (depending on the software) is also a very good introduction to the basics of image processing. 

EAA in general is accepting of imperfect images because it has a different purpose. So blocky stars, noise, etc, are all perfectly acceptable. 

I would say that EAA is rarely recommended as you state for the following reasons (just my initial thoughts, I hope this won’t spark a massive debate!):

  • Many beginners want to skip visual observation entirely and start producing high quality images as fast as possible, so the benefits of EAA for real time views is not a requirement.
  • A low-cost EAA set up cannot easily be upgraded to produce high quality images, many or all of the components will need replacing should the imager wish to continue.
  • A starter setup for imaging is not THAT much more expensive than a low cost dedicated EAA setup, especially if DSLR is used which many people already have.

It was a good question though that made me think. I’d be interested to hear the views of others.

Keep posting your captures. ?

Edited by RobertI
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1 hour ago, vlaiv said:

Having said that, it is actually a wonder full idea - ST102 with low cost mount like AZ Gti, if it's capable of holding that scope, and guessing by your work - it can be done, and an astro camera like 178 / 224 or even 385 for more enthusiastic can be interesting combination to get them into both visual and video astronomy - and they can end up saving their VA sessions as proper images to share with friends and family.

 I wonder how would Mak of let's say 102mm aperture fair in this role - no CA to fight, but long focal length requires big pixels (or heavy binning) to get to suitable resolution. Need to research that a bit more - suitable sensor and also corrected field of Mak and suitable reducers.

Hi Vlaiv,

I have two setups for EAA, an RC6 reduced to F4.5 and a 72 semi-apo frac reduced to 3.7 ish. The RC6 sits on an CG5 mount and the 72mm sits on a simple SkyProdigy altaz mount. I do all EAA with a Lodestar mono camera, but the images obtained with the RC6 are just so much better, it’s like a different camera is being used. The images are sharper and more detailed and the stars are more pinpoint. I think they are even less noisy and ‘smoother’. I’m guessing it’s a combination of better mount and more different sampling (2.5”/pixel as opposed to 6.5”/pixel). Sampling is where my knowledge becomes, hazy, would be interested in your thoughts (apologies to th OP in advance for hijacking the thread!).

 

 

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3 minutes ago, RobertI said:

Hi Vlaiv,

I have two setups for EAA, an RC6 reduced to F4.5 and a 72 semi-apo frac reduced to 3.7 ish. The RC6 sits on an CG5 mount and the 72mm sits on a simple SkyProdigy altaz mount. I do all EAA with a Lodestar mono camera, but the images obtained with the RC6 are just so much better, it’s like a different camera is being used. The images are sharper and more detailed and the stars are more pinpoint. I think they are even less noisy and ‘smoother’. I’m guessing it’s a combination of better mount and more different sampling (2.5”/pixel as opposed to 6.5”/pixel). Sampling is where my knowledge becomes, hazy, would be interested in your thoughts (apologies in advance for hijacking the thread!).

 

 

There are many reasons why images are so much better with RC6, let's go with resolution / sharpness first.

2.5"/pixel is much more suitable sampling resolution than 6.5"/pixel. In general, under most circumstances, good sampling resolutions are between 1.3 and 2"/pixel. In order to go higher than that (meaning higher resolution - lower number of arc seconds per pixel) you really need large aperture, very steady seeing and excellent mount.

Mount will not play significant role for EAA if you keep your exposures really short, but once you start with exposure longer than say 5-6s, mount starts to be important. It is not just unguided performance that counts, mount stiffness (resistance to wind and vibration) and smoothness (does not produce vibrations due to drive mechanics on its own) also become a factor.

Things that go into sharpness of the image:

1. seeing - nothing you can do about that one, same for both scopes, and RC6 can be even more susceptible to seeing due to larger aperture (but tiny differences on these scales)

2. aperture - this is important thing - larger the scope - smaller the airy disk. Size of airy disk and it's blur contribute to overall star size and sharpness of the image. If we keep all other parameters the same - scope with larger aperture will have tighter stars. There is quite a bit of difference between the two - almost x2 airy disk diameter as it depends linearly with aperture.

3. Obviously the mount performance - if your single exposures are anywhere longer than few seconds - larger, more sturdy and smoother mount will have an edge.

4. Sampling pixel size and sampling resolution. I made distinction between the two, because they work in slightly different way. Let's go with sampling resolution first - this one determines details in the image. Obviously if 72mm frac is giving you 6.5"/pixel and RC is giving you 2.5"/pixel - image made with frac will simply be smaller and less detailed. If you "zoom in" by resampling that image - you will not recover details present in RC image. There is additional thing - sampling pixel size. Regular sampling implies getting values at points that are equally spaced - when I say point I mean like real point with no width and height - only position/coordinates. Pixels are not like that - they are little squares or rectangles, and when we sample signal with pixels we are integrating light over surface rather than getting value at a single point. This has consequence of creating additional blur (so called pixel blur). Larger the pixel - larger the blur.  In case of RC we can look at sky as function in arc seconds and each pixel is 2.5" wide and high (actually your camera has rectangular pixels rather than square, right? it does not change anything, so I'll stick with square pixels). On same function in arc seconds - 72mm frac will have 6.5" wide pixels - or simply put almost x3 larger pixel and that will create larger pixel blur (on top of coarser sampling).

One more thing to note - those GSO made RCs have pretty good optics, and RC design has quite good spot diagram so stars tend to be tight.

On the matter of better SNR, well only explanation that I can offer is that you are using mono camera and reflector system and you probably don't use UV/IR cut filter with that, and you do use it with 72mm frac.

As you noted RC system is at F/4.5 and frac is about F/3.7. Since you are using the same camera, faster system should get you better SNR. Part of F/ratio myth is that slow scope is always slower than fast scope. That is actually true if both scopes have equal light throughput and you are using the same camera - you will gain SNR in faster system at expense of resolution (not true in general because "slow" scope can be faster than "fast" scope if used with different pixel size and there is difference in aperture in favor of "slow" scope). Since you are using the same camera here F/3.7 should be faster than F/4.5 (how much faster depends on bunch of things, but faster in general - better SNR for same imaging time). Only way that RC produces better SNR images than frac in mono under such circumstances, that I can think of is if you are not using UV/IR cut filter with RC. That will not pose problem for mirror system and there is a lot of signal in IR part of spectrum from almost everything up there in the sky. Using IR/UV cut filter simply removes that and lowers signal part of SNR.

Btw, what sort of exposure lengths do you use? For shorter exposures you would certainly benefit from low read noise camera. Have you considered switching to CMOS based sensor for EAA?

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Thanks for the information Vlaiv. With the smaller setup I tend to do 10 second exposures and with the larger usually 30 second exposures. I also have a filter wheel attached on the larger setup and use a Baader luminance filter even if just doing mono - sounds like I shouldnt? Given what you have said I think the better mount on the larger setup might be helping, I guess The way to find out is to put the small scope on the larger mount and try the same comparison. (again apologies to OP for diverting thread).

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3 hours ago, RobertI said:

Thanks for the information Vlaiv. With the smaller setup I tend to do 10 second exposures and with the larger usually 30 second exposures. I also have a filter wheel attached on the larger setup and use a Baader luminance filter even if just doing mono - sounds like I shouldnt? Given what you have said I think the better mount on the larger setup might be helping, I guess The way to find out is to put the small scope on the larger mount and try the same comparison. (again apologies to OP for diverting thread).

Longer exposure explains the smoothness and less noise. Lodestar has about 10e read noise. That is quite a lot (not for CCD, although there are very "quite" CCD sensors out there - half that at around 5e).

Read noise in short exposures makes all the difference. In 3x10s you get about 17e of read noise (10 times square root of 3) while with larger setup you get only 10e in that amount of time (all other signals add up, only read noise is fixed per sub).

You should try to remove lum filter from RC. I don't know how much CA will be introduced by focal reducer at IR and UV part of spectrum, so you might get slightly bigger stars. I'm guessing that it will not have very large effect, so I think it's worth a try, after all it's a simple thing to remove it and try out.

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My most successful video work was done with a 12" SCT operating at 0.33, 0.63 with focal reducers and the native F10. The camera was a Stellacam 120n+ that stacked 512 images in around 10 seconds or extended to around 1 minute using the infinite integration facility. The monochrome images showed far more detail without further post processing than could be seen visually by much larger telescopes. For lunar and planetary imaging with the same 12" I used a Canon mini DV camcorder attached afocally via a 15mm Plossl, again the real time images were more detaied on the camera screen than those seen visually through the telescope. The cameras were simply connected to a TV monitor as well as a VCR if the recordings were to be saved.   ?

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Maybe its because EAA,IMO, tend not to be to OCD  ? ? (but I do admire/ like the images they produce ? ) on creating mega "Hubble" images but prefer to scan the sky - as they would using a visual eye piece - hence the EAA name. Having said that ultra fast EAA set up's can produce high quality images when post processed. 

In the UK we get small enough clear skies as it is and the idea of spending 254hrs of data on one subject would most likely wipe out my years "seeing".  

Why beginners are not pointed to EAA - dont know but guess we all start of with Bino's  which are the cheapest way of doing Star viewing and are probably enjoyed by all no matter what other kit they have/use now - because they are simple,quick and low Tech - nothing wrong with that either ?

And before people start moaning I "try" (and enjoy) to do all forms of Star Gazing . 

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All your setups sound interesting, reflectors, refractors, Maks. I agree binoculars are a fantastic way to start. I started with binoculars and they're still my favorite for visual use, as they're so quick and easy. The difference in light grasp between my eyes and binoculars are 51x more thanks to astronomy.tools. Observing the Andromeda galaxy through binoculars was fantastic.

I'd never thought of below 1 second images except for the sun, moon and planets. It may be interesting to test different settings one night. I tend to get excited when I can see an object and spend 5 minutes on one and go onto the next before the clouds roll in or my laptop stops working. I've not really worked out why that happens yet it's a Microsoft Surface (maybe dew).

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