With a diameter of 120,000 kilometres and a bright reflective surface, Saturn is an unmissable object in the night sky right now. But at 1.3 billion kilometres away from us, it looks only a hundreth the size of the full moon. Which means the screen width of my Saturn video below represents one third of a lunar diameter across (for best view, click to full screen):
[jwplayer mediaid=”9786″]
I recorded the movie through my old but capable 1978-vintage 6″ Fullerscopes reflector – specially resurrected for Easter after 30 years in storage. (See my efforts with the moon and the smaller ETX-90 telescope in Armchair Astronomy.)
Getting the telescope up and running really required nothing more than (literally) brushing away some cobwebs and giving the mirrors a wash – something I’d be more hesitant of doing had I not just read a step-by-step ‘how to’ in Sky at Night magazine.
Although thick with dust and grime, I’d reason to believe the mirrors’ coatings beneath were o.k., as I remember having them vacuum re-aluminised and silica coated just before I abandoned the instrument and disappeared off to university. Some gentle soaking, swabbing, and rinsing down with distilled water, and all was shiny once again.
Fullerscopes’ german equatorial mountings were all built like tanks – this ‘Mark II’, rated to carry a 10″ reflector, is still in good order save for some rust on the exposed steel shafts.
The RA drive, that ordinarily would drive the telescope counter-rotational to the Earth’s axis, wasn’t operational for a variety of reasons; but the fine adjustment on the declination axis was working.
All of which goes to explain why on the clip Saturn appears to fly across the screen.
I’d forgotten how stunning to the eye Saturn is through this telescope. In better seeing conditions I’ve seen the gap in the rings – the Cassini Division – quite clearly. Now, Saturn’s moon Titan was unmistakable.
Filming what you see with your eye is a little more challenging, although the ‘live view’ on the Canon 7D makes life a lot easier. Rather than watch the live feed through a computer, on this occasion I used the camera’s LCD display directly to focus with the help of a magnifying glass. The clip was made by projecting the image onto the camera’s CCD sensor via a 12.5mm orthoscopic eyepiece; the main mirror’s focal length is about 1250mm. The scene could have stood higher magnification, but I was limited by the eyepiece focal length and size of the projection tube.
All in all, considering the state of the equipment at the start of the day, I’m happy with the end result. The gap between the disk of Saturn and the rings is clear enough; but no Cassini division – so still some work to do! All the same, a fun day messing around with telescopes and engineering – no better way to spend the Easter hols.
2. To be exact: the angular size of Saturn on 25/4/2011 was 19 seconds (“) of arc, approximately a third of a minute. There are 60 seconds in a minute, and the moon is typically 30 minutes across; so Saturn appears one ninetieth of the moons diameter.
It’s a good few years since I took a photograph through a telescope, so I thought I’d share my latest pics.
The moon’s been presenting itself as a nice late evening target in our Westerly outlook this week, so that’s where I’m starting. These two are the best of the bunch from the last couple of nights (click for bigger pictures):
And in this video clip taken by eyepiece projection, there’s quite a bit of detail visible in the Mare Criseum (Sea-of-Crises) at top left:
I’m particularly pleased with how the videos came out, capturing the fleeting moments of still air you need to look out for when observing live by eye.
The rig is built around an ultra-compact Meade ETX-90 telescope, picked up when I moved to London 10 years ago as a more suitable replacement for my 6 inch reflector. All I’ve added is a connecting tube and T-mount to get the camera hitched up.
Strictly speaking, you don’t need a telescope for astrophotography. Here’s the Plough (Big Dipper) taken with a tripod-mounted standard lens:
And these shots of an Earthlit Moon and Venus are two of my favourites:
I’ve also had some luck in the middle ground using telephoto lenses, where the results have been surprisingly good: like these pics of a lunar eclipse, the International Space Station (ISS), and Jupiter with its moons; all taken with a 400mm lens – in the case of the ISS, hand-held:
18 megapixels of digital zoom helps resolve the ISS into something other than an unrecognisable blob.
But to resolve surface detail in objects like Jupiter, a true astronomical telescope is called for.
I started by simply holding my smartphone to the eyepiece. Not a disaster, but I lost fine detail and the moon took on a weird pinkish bloom.
Attaching a digital SLR directly to the telescope gave better results, with the camera’s CCD (Charge Coupled Device) sensor at the prime focus. I also experimented with an old Logitech webcam with the lens removed, but the background noise was too high and the small sensor size made for a very narrow field of view.
The Canon 7D gives a much nicer image, and can be operated totally remotely via the computer. Live images are fed to the laptop screen for easy focus and exposure control.
With the still pictures, I want to get to grips with the various image processing techniques for stacking multiple images.
Of course, none of this competes with the Hubble Space Telescope, but amateur astrophotography for me is more about the satisfaction of seeing what a particular instrument can do, and learning along the way more about the various objects I’m photographing.
After the moon, my next target is Saturn, with the goal of resolving the Cassini division in the rings; and Jupiter, where I’ll be happy if I can resolve the Great Red Spot.
I’m also planning to take some guided wide-field photos of deep sky objects like the Orion Nebula. But that requires dark skys and the telescope’s drives being sufficiently accurate and strong enough to support a ‘piggy-backed’ camera and lens. All for another day.
The immediate issue, as the videos show, is just how bad the ‘seeing’ can be when observing at dusk from a building that’s been baking in the sun all day. I need to find more open skys.
But for now, with the telescope’s motors whirring away on the balcony, I literally am the armchair astrophotographer.
I’ve been amusing myself this evening scanning old black & white negatives and colour slides into the computer: strips of film that have languished in negative files on top of cupboards for years. It’s a boring process, but punctuated with the reward of finding something I thought was lost, or a negative that was never printed.
Some of the pictures go back to 1973, and are an unwelcome reminder of my antediluvian origins. But they’re also revealing of the state of technology at the time, and what I was doing with it. All the black and white pictures in this post are from the archive.
The photographic process itself is a prime example: the relative time and cost of developing and printing my own films being one reason many pictures haven’t been properly seen until now.
Things sure have moved on. I asked my 15 year old nephew if he’d ever used film, and after clarifying I didn’t mean video tape, he confirmed he’d never touched the stuff. Silly of me to ask really.
Regrettably, some of the more fun, not to say embarrassing, pictures from the archive are not suitable for public display. But I’m happy to inflict the sci-tech oriented discoveries – starting today with these pics of my first serious astronomical telescope.
The main components were bought in 1977, and this photo of the telescope in its observatory is probably from 1979. The instrument is a classic Newtonian reflector of a design that hasn’t changed in hundreds of years. It has a 6″ primary mirror, and was built by Fullerscopes of London, the same company that made Patrick Moore’s fork-mounted 15″. The mount is a Fullerscopes Mk III German Type equatorial. The ancillaries: motor drives, plinth, finder, camera attachments, and the observatory itself are home built.
To be accurate, this was my second telescope, the first being an entirely home-built open-tube reflector in an altazimuth type cradle. Constructed almost entirely from sturdy aluminium bar stock – largely because that’s what I had – it all proved a little unwieldy. No photos survive – probably for the best.
The 6″ was mainly used for visual observations. I later added an improved synchronous motor drive to the Right Ascension (RA) axis to make the instrument more suited to astrophotography, but as that happened in 1980, just before I left home for university and ever on, that feature was little used.
Warning – Telescope building aficionados, engineers, (and all other interested readers….!) only
Assembling, augmenting, or building a telescope from scratch is an excellent engineering, as well as scientific, training. To save money, I purchased only the RA axis worm drive from Fullerscopes, with a view to reverse engineering it and building a copy for the declination axis. Operations to do that included aluminium casting, worm screw cutting, and making my own integrated roller ball-bearings on the worm shaft (to remove any trace of play, and hence instrument movement). Thankfully, my brother was building a model steam engine at the time, so a good selection of machine tools were available around the home.
I realise now that some of these operations were quite sophisticated engineering tasks, particularly for a 15 year old – probably why things didn’t always turn out as planned. I struggled to reproduce the 4.5″ phosphor bronze worm wheel (although the trick for cutting a worm wheel, by winding a tool-post mounted wheel into a spinning tap mounted between lathe centres, I find fascinating and elegant), and instead adapted an ex-military gun-sight for the declination axis. That said, the worm unit I’d made was better than the original, and eventually replaced it.
The RA motor connected to the drive worm via a gearbox, also homemade using mecano gears mounted in a solid block of steel, the centre of which had been milled out on the lathe and fitted with individually turned and reamed phosphor-bronze bushes. The whole drive assembly was bolted to the plinth and linked to the final worm gear on a universal joint. This all worked fine, unless the telescope was incorrectly counter-balanced, when teeth would expensively shear off the little mecano gear wheels.
Despite these set-backs, or perhaps because of them, it’s my firm belief that this activity set me up well to tackle life’s later challenges: like building my own research equipment and mending the car.
The telescope’s plinth and observatory have their own stories. I’d read somewhere that telescopes need a rock-solid mount, and that plinths mounted in concrete are superior to tripods. In the photo, you can just see the top of a 5ft x 5″ x 1/4″ steel tube, 2 ft of which is buried in a 3ft square cube of concrete. The base of the observatory is covered in paving stones laid on sand, with a gap around the central concrete block to prevent footstep vibrations reaching the plinth. The plinth was capped by a 7″ square x 3/8″ thick oxy-acetylene welded plate. I remember this well, as the welder had to commission an unusually large nozzle for the job. This was of course total overkill for a 6″ reflector; but I suspect I harbored secret fantasies of some day owning a more substantial instrument.
The observatory was made from resin bonded plywood on a pine frame. Originally designed as a run-off shed, I switched to the fold-off roof idea when the weight of the structure dictated a need for major railroad-type work adjacent to the observing area – effectively doubling the project’s footprint. In practice, a south-facing aspect and relatively low observatory walls meant the compromise solution made little impact on sky visibility. A telescope mounted permanently out of doors is always ready for action – an important consideration with UK weather – with no need to wait for thermal stabilisation of the optics or to spend time aligning the equatorial mount. It goes without saying that, like all the world’s great observatories, it was painted white.
I keep saying ‘was’, because Mount Tim was decommissioned in the early nineties, such that you’d never know the paved area had ever been anything other than a regular garden patio. Amusingly, the plinth proved immovable, save for the use of explosives, so was instead ceremoniously tipped on its side in a shallow grave. I sometimes wonder what a future Tony Robinson might make of it.
Coming back to Fullerscopes. Buying a telescope in 1976 was not like popping down the road to Curry’s and carrying it home under your arm. When my father and I first visited Telescope House on the Farringdon Road, we were greeted by Dudley Fuller in person. He’d formed the company a few years earlier by buying out the historic but failing maker of optical instruments – Broadhurst & Clarkson Ltd.
We talked about my telescope-making efforts to date, and what I needed from Fullerscopes. He was wary of my plans to attach one of his diagonal mirrors to my homemade spider using glue (EvoStick No.2 – if I must!), but we agreed a package – including a Fullerscopes spider – and placed the order. (The spider sits in the top of the telescope tube and holds a diagonally placed mirror that diverts light into the eye-piece.) A month later, I returned to man-handle this tribute to Sir Isaac through the streets of London and back to Leicester – by train.
Telescope building was still being done in a traditional way. Fuller explained that all the brass tube-work on his telescopes was hand made using Broadhurst & Clarkson’s original equipment. That meant the brass sheet was rolled on an antique mill by hand, then soldered along the seam. On my telescope, the solder seam is visible on the brass focusing mount and Barlow lens adapter tube. The economics of this, particularly on parts destined for smaller instruments like my 6″, and at a time when Japan was starting to export mass-produced alternatives, must have been unsupportable. I’m guessing that’s the reason the Farringdon road shop closed down in 2005 and Telescope House moved out of town. It looks like they’re still trading though, with Patrick Moore’s endorsement into the bargain. (Telescope House website). But they don’t seem to be making their own instruments any more – please correct me if you know different.
There’s a related and slightly surreal twist to the story here, concerning my move to London in 2000. Needing a more portable telescope for out of city viewing, I visited Fullerscopes, now the UK agent for Meade Instruments Corp. of the USA, makers of the compact Cassegrain-Maksutov telescope I was after. The odd thing was, when I got chatting to the guy who handed over the box, it turned out he had personally been involved in making the brass-work for my 6 inch reflector 24 years earlier! It’s a nice story.
Anyhow, I hope that wasn’t completely boring and self-absorbed. If nothing else, it may have given you an insight into what I was getting up to in my formative years. You know, when I should have been out doing drugs, smashing up cars, and getting my underage girlfriend pregnant – like a normal teenager 🙂
Don’t forget to check back for the next exciting edition of Out Of The Archives……
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