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back to article Hobbyist star-gazer cops amazing eyeful of Jupiter's space ball

An amateur astronomer has captured stunning images of Jupiter's moon Ganymede. Emmanuel Kardasis used computer kit, a "hobby" telescope, an off-the-shelf camera and his own observing skills to snap the heavenly body, and produce a rough-round-the-edges albedo map of it: Nothing amateurish about this majestic image. Pic credit: …

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Awesome

Just awesome.

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Here's his web page. http://kardasis.weebly.com/

That looks like a Celestron tube of some kind on a high-end SkyWatcher mount to me. Probably runs to a minimum of £3K worth of gear by the time you've got the extras, could be two or three times that without much trouble. Easy to spend a lot of money on astronomy kit, I'm discovering. I think you can still reasonably call his rig a 'hobby' scope though. Dedicated hobbiest, for sure, but not exactly crazy.

Certainly puts my wobbly, fuzzy and grainy pictures of Jupiter to shame.

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That prices is lower than keen amateur photographers will spend on a DSLR + lens. The priceless part is the clear sky in Greece - no hope here in south London. And patience. Lots of patience.

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Super-transparent skies are not really a benefit here, nor even is a lack of light pollution. Ganymede is fifth magnitude like the other Galilean moons - there's plenty of light to work with even at quite modest apertures. I don't know where abouts in Greece he is, but a certain amount of smog (as Athens is famous for) is actually a benefit for things like this - it helps to steady the skies and improve the seeing.

Really I don't see why so much attention is being paid to this: yes, it's high end stuff but not exceptionally so even by amateur standards. This kind of work doesn't even need particularly advanced equipment - a cheap webcam based imager, preferably a computerised or at least motor drive mount, and a copy of Registax to stack the images. Ultimately this is about time, patience and forward planning rather than fancy equipment.

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Given you can now blow £10k on a top end road bicycle (never mind the accessories or clothing), it's fair to say that hobby spending - any hobby - really knows no limits.

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fch
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... exactly.

... when my brother-in-law used to ask me "how much exactly again did you spend on that astroboffinry stuff ?" I only asked him back "how much exactly are you putting into your Harley-Davidson fund?".

I don't think for my astro-spending I could've gotten a Harley quite yet, nor an Audi TT instead of a VW Golf, or a luxury Mauritius holiday, or even, gasp, a pint a day for a decade. Still, had a lot of enjoyable nights out, of the other kind. Everyone to their own.

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There was a recent Sky at Night episode about amateur astronomers past and present who had built their own observatories. Archive footage of Patrick Moore visiting observatories in the 1950s, and a present-day tour by hos protégée around the UK comparing urban and rural amateurs. One bloke, a German fellow who had adopted Blighty as his home, even ground his own mirrors.

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Mirrors...

I think you will find that a large number of amateur astronomers grind their own mirrors. Apparently it is a fairly simple process (or so my brother says and he has done a few now) and makes it a lot cheaper than buying ready-ground.

In the main that means you can stretch your 8" budget to a 12" scope since the mirror(s) are a the bulk of the cost.

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LDS
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Re: Mirrors...

Depends on what kind of telescope you're going to build :) Ritchey-Chretien configuration is pretty hard to build due to its use of hyperbolic mirrors. The article doesn't state which kind of telescope he used, if it was a commercial high-end one, or a homemade one. From his word I can understand he used a good (and probably high-end) mount for stability, and other good tools to obtain those exceptional images. Sure, experience and dedication matter, but astronomy is one of the area you need exceptional skys and exceptional optics to get those kind of images.

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Boffin

Amazing!

Well done!

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It's an 11" Celestron Schmidt-Cassegrain

Even without the image on his website, the aperture of 11" tells you it is the Celestron C11, one of the only 11" scopes out there (and the big brother of my C8). Excellent planetary imaging scopes. You do not want a DSLR for this work, a decent webcam (CCD-based for preference) or a specialized planetary camera, which can maintain 30-60 FPS at VGA resolution is generally best.

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Re: It's an 11" Celestron Schmidt-Cassegrain

That's interesting. Why would you not use a DSLR?

I thought CCDs were used primarily because they were cheap.

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Re: It's an 11" Celestron Schmidt-Cassegrain

I don't think DSLR's can maintain the necessarily framerate, and given most of the image processing is done by the telescope, the SLR part is mostly overkill.

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Re: It's an 11" Celestron Schmidt-Cassegrain

Planets are tiny. Their image is only a few hundred pixels across even at the multi-meter focal length employed, and you'd be wasting most of the sensor's pixels. A 1/4-inch or 1/3-inch diameter sensor is best. Additionally, you want to capture thousands of frames and pick the best 500 or so, so a high frame rate camera is best for this high resolution work.

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DSLR for planetry imaging

I think something like the cropped movie mode on a modern (550D onwards?) Canon D-SLR would be excellent for this. That's what I'm going to use when the skies are clear enough for shots of Jupiter (and Saturn, when it comes back. ("Comes Back!? I didn't know it had been away - boom boom!")

Nikon probably have something similar too.

Shoot for several minutes and then let Registax (the "specialist software") go through the movie file, extract the decent frames, align and stack them.

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Facepalm

Re: DSLR for planetry imaging

Thumbs down?!? Why, FFS?

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Trollface

Re: DSLR for planetry imaging

Don't lose any sleep over it. I don't...

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WTF?

Re: DSLR for planetry imaging

I'm assuming the downvoters either:

1. Own Nikon and I mentioned Canon and they are aged 11.

2. Didn't understand the post.

3. There is a "webcam vs D-SLR" war in planetry astrophotography circles that I'd never heard of, to rival "Apple vs Andoid", "Canon Vs Nikon" and "Playstation VS Xbox".

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Boffin

Re: DSLR for planetry imaging

I was one of the thumbs down. I didn't comment at the time simply because I couldn't be bothered to go through the sums to show why.

DSLRs _are_ completely unsuited to planetary imaging. It isn't just the lack of movie mode on many models - sensor size is an equally important factor that is endemic to the format.

Since we're talking about the Canon 550D consider that it uses a 22.3mm sensor. This is a comparatively large sensor that is great for photographers since it reduces the cropping factor, but is a positive disadvantage in this application. The pixels are arranged on a 13.8µm pitch. A prime focus image of Ganymede at opposition (the most favourable time) is 25µm diameter even at the relatively generous 2400mm focal length of a Celestron C11. That makes a prime focus image area of less than 3 pixels. No amount of post processing can do anything with such limited information - even calculating the Strehl ratios (the first stage of the staking process) is more speculation than concrete mathematics.

Compare with one of the webcam derived imagers such as the NexImage 5 with a pixel pitch of 2.2µm. That gives you an image area of 101 pixels. That's enough for the stackers to begin working profitably with the data collected. The effective resolution can then be boosted by perhaps a factor of 10 or more as a side effect of the stacking process, depending on how many images you have to work with.

In practice however, you'd want to use eyepiece projection on both imagers rather than prime focus to get a decent resolution in the first place. Not a problem with the small sensors of the webcam imagers but if you extend the image over the much greater area of the DSLR sensors the curvature of the focal plane is magnified and completely takes over. The CCD sensor is flat, but the resulting focal "plane" is not. As a consequence only a portion of the image can be in focus at any given focus setting.

The OP's comments do not suggest a suggestion of appropriate tools based on knowledge and experience, but a case of techno-lust - looking around for relatively high-end equipment and assuming it must be exceptional regardless of the circumstances. I wouldn't knock that camera for wide field work, but it is a patently ridiculous suggestion for something like this.

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Re: It's an 11" Celestron Schmidt-Cassegrain

"I don't think DSLR's can maintain the necessarily framerate"

Shoot a video.

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Re: DSLR for planetry imaging

Um - crop movie mode. Look it up.

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Re: DSLR for planetry imaging

"The pixels are arranged on a 13.8µm pitch"

You might want to check that. Pixel pitch is 4.3µm

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Re: DSLR for planetry imaging

The CCD cells are on a 4.3µm pitch but they are binned for movie mode - you only get 1080p resolution. Have a nice time enjoying those three pixel images.

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Re: DSLR for planetry imaging

I'm with Fiona here. Pixel density is one thing, and as she correctly points out the effective resolution in video mode is generally far too low for planetary work. More important is the compression used. The key strength of the low resolution webcam-derived imagers is that you have access to raw pixel data even at video frame rates. Image stacking extrapolates information from incredibly subtle features of the base data, so subtle that you can't even see it (if you could there wouldn't be any point). It is also the kind of thing that gets approximated out of existence the instant you apply even the most conservative amount of compression to the images. Your Canon has to use that compression to get the data rate down to a manageable level - there is no escape from that.

This is not a matter of debate or conjecture. It doesn't work, period.

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Anonymous Coward

Re: DSLR for planetry imaging

Not in the 550D and 600d's crop video mode. 640x480 (for the 550D) and 1080p on the 600d, with no pixel binning going on.

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Trollface

Am I the only cynic

Who wondered if his special software was the Photoshop clone tool and a copy of the professional image ;)

In all seriousness - fair play to the man.

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IT - the great leveller ?

Good to see enthusiastic amateurs still have a place in science.

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Clever little bastard

Anyone can use a computer. But it takes a little dash of genius to come up with something like that.

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Bravo

Excellent work.

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Coat

Is this...

.. a Kardassian observation given his name is Emmanuel Kardasis .

I know, I'm just going.

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Well done that man

Chinese Skywatcher EQ6 equatorial mount = £840

Celestron 11 inch Schmidt-Cassegrain telescope = $1575

DMK 21-618 Mono high frame rate CCD camera = £385

Filter wheel and filters = £300-£400

Greek clear and steady skies = priceless

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