Phil's Astronomy Amateur Page

The tunnel I'm talking about, being a tad metaphorical, is the camera lens and over the last couple of evenings I've been revisiting astro imaging with digital cameras. Having recently aquired an Olypus E1 I thought it was time I actually read the instruction book and took it through its paces! (I'm an 'engineer' - engineers don't read instruction books....)

Some years back, I've lost count...OK, about 8, I played around with a Olympus OM20 SLR film camera with which I experimented with direct viewing through telephoto lenses, screwing it onto variable telescope lenses and using it in prime focus mode. (Using the camera as the telescope eyepiece). To be honest my enthusiasm was cooled quite quickly due to the limitations - not seeing the results until the film had been developed mainly - and I regrettably let it slip.

With a digital camera able to recall the results immediately, my enthusiasm was reignited, motivated mainly by the Perseids meteors. Why I didn't seriously look into it earlier, I don't know - too lazy, too busy doing other stuff... I don't know. For goodness sake, I had access to my wife's Canon EOS 300 so there was no excuse really. To cut a long story short, I missed photographing the Perseids and was annoyed at that, given that over the course of three days I saw so many beautiful displays, so the next targets will be the Orionids in October... And I WILL have a camera ready.

So what are the main difficulties imaging the night sky? Well, cameras work by letting light fall onto a light-reactive sensor, be that a film or a semiconductor chip. The obvious difficulty with the night sky is that there isn't much light and what there is, you don't necessarily want to see (neighbours' bathroom lights, security lights, street lights etc.) . Consequently you may need to work around problems, gathering as much of the RIGHT light that you can. Of course, the best thing to do is get yourself out into the countryside if possible. But that's not always possible.

So here was I in my back garden with lights going on and off all around me, the sky glowing orange from the north west to the eastern horizons, trying to aquaint myself with the settings on two different cameras.

First, the Canon. I'll be honest, the trickiest thing is setting up the camera the way you want it. I couldn't find the instruction book...

First I found that the EOS won't do Manual mode unless the focuser is also set to manual - makes sense, I suppose, but an automatic override would be nice, instead of it just not working at all. I focussed on Jupiter - note that twisting the focus ring all the way round, takes it too far (can you go past infinity?? Obviously...) so rely on getting the sharpest image here, that you can, then don't touch the ring again!

I set the ISO to 1600 and the exposure to 10" (seconds) and aimed the 50mm lens at the Plough. (What was the aperture? I have no idea, I couldn't work it out.... I know that when the chipped adaptor ring is used, it defaults to F2 - I'll have to follow this question up...)

Anyway, I was moderately surprised by the result - a bit orange and grainy (noise) but at least I had the whole asterism in shot.
I then put the lens cap on and did another 10 second exposure. Why? Ah, the magic of digital photography. Read on, this is important.

When you take exposures of more than a second or so, you tend to get 'noise' building up on the image. It looks like little red dots scattered all over, sometimes you'll get a haze in one corner. Sometimes you'll see some blue dots and occasionally, some green too.
What you are doing with the cap on, is creating a blank image with the same imperfections. These imperfections should be for the most part, virtually identical to the imperfections on your picture. What you will then do when you get indoors after your session, is upload the pictures then edit them.
You'll probably open Paint Shop Pro or some photo editing software like that, then choose an image and a corresponding dark-field image. By a clever bit of manipulation using the Image/Arithmetic/Subtract function, you can effectively deduct the imperfections from your required picture, leaving a very much improved image. Simples :o)

Good question. The answer is probably a tentative 'yes', but not because there's necessarily any less to look at now than at other times in the year - it's probably because it gets dark so late in the summer, that people just can't afford to stay up that long to enjoy it. Given that in winter it gets dark really early, which is fab, it's so darned cold by comparison, that really only leaves spring and autumn for your 'average' viewer; Still handy for kids who need to get to bed at a sensible time and for older people whose blood freezes easily if they stand still too long.
And I'm slowly but inexorably sliding into that second category...

The reason it crossed my mind is that this afternoon I popped down to my 'local' astronomy shop, Astronomia in Dorking, for some Baader film for making a Solar filter. The plan, after so many years, is to do a little bit of Solar viewing and I can't afford a Coronado PST, as much as I'd like one. Making a blocking filter for my little Bushnell is the cheapest way I can accomplish this. (It still costs £18 for an A4 sheet, though, which they didn't have in stock...)

I have to say that Astronomia is a very nicely laid out shop with various 'scopes set up in the windows and on the floor - good job, very attractive, but I don't suppose at 16:30hrs on a Tuesday there's ever going to be a queue to get in the door.

Anyway, I was passing the time with the guy, Matt, who commented that things weren't very busy since the Solar Eclipse-followers had been in June/July for kit to take to China with them. (This was in response to my question on the subject, I have to say). Which is a shame really.

If he'd said that things were pretty good, I'd probably have inquired as to what people were actually buying (and I'll explain why, another day). Do they want reflectors, refractors, catadioptrics or just binoculars? The answer was going to be academic so the question was left unasked.

I spotted a flyer that had apparently been left this morning by a lady from the local WEA Astronomy Group (Workers Educational Association?) advertising astronomy meetings around midday, locally. I took a note of her number just out of interest - it may be worth popping down to see what it's all about... I'm always on the lookout for people who might benefit from information on my website, philanthropist that I am.

I gave Matt my contact details: webmaster@simpleamateurastronomy.com - well, I hadn't mentioned that I was publishing my own website as well as this blog and thought I'd let him work it out - so that he could contact me when the Baader film came in.

In the meantime I have plenty to do, including catching that elusive image of Jupiter with the Bushnell and a cheap webcam, just to prove it can be done, really! Trouble is the laptop charger has gone to meet its maker and I don't have a backup. I do however have a spare desktop PC but do I really want to cart it all outside right now, for a few minutes 'work'? Do I cocoa....

That's the trouble, you see. Sometimes the effort involved in getting your gear together, outweighs the impulse to go outside and observe, and that's bad. And that's also why big telescopes aren't always a good thing for beginners, or should I say those who don't have permanent observatories set up: With all that weight to hump around, it's too easy not to bother.

I know, being the owner of a 10" reflector on an HEQ5 mount... That's why it's nice to have a little 'scope around to drag out quickly if the urge grabs you.

So what's on telly, then?

It really was a lovely night last night, so I pulled the laptop out, hooked up the webcam and having first zeroed-in on Jupiter with a normal eyepiece, replaced it with the cam.

Anyone who's ever tried imaging with a webcam will know what a pig it can be to actually find the target on the screen. The trick is to set the camera source to 30 frames per second (far too slow for such a bright object but necessary to find it in the first place) with high brightness then move the 'scope ever so slightly, in a spiral. Hopefully you should then be able to pick up the bright blur that is the target (you can bet it won't be in focus!).

Another problem you may encounter when imaging with a webcam (or ordinary camera, even) is that the focuser may not have enough adjustment outwards, so a special spacer may be necessary.
Guess what? Once I'd found Jupiter, I couldn't get the focuser in far enough to get a sharp image.

I overcame that in a slightly unorthodox way, by removing the clamping ring from the top of the drawtube. That gave me the extra 5 mm or so that I needed and Voila!

Go back into Source, change the frame rate to 100fps, lower the brightness to halfway and I could now see distinct stripes on the planet.

The next step would normally be to set the camera recording for 10 seconds or so, to create a series of stills, the best of which would be 'stacked' using Registax, to compile a half-decent final .jpg image. As I say, that would normally be the next step but my laptop went dead. Flat battery. But I had the mains adaptor plugged in, right? (Light's on, it should be charging...)

So just as I was about to capture some images, my equipment let me down, not for the first time either. Pack it all up, off to bed.

Getting in the house again, I put the laptop on charge once more.
"POP!"
Then nothing. Oh, please give me a break - that's something else to fix now.

But not now - tomorrow, maybe....

One of the occasional jobs that befalls the owner of a reflecting telescope, is cleaning the lens when it gets dirty after years of use. Dusty atmosphere coupled with condensation (dew) can give the main mirror a thin coating of grime which can ruin image quality.

Cleaning the mirror on such a telescope isn't difficult at all (see details on my web site) - just take care not to scratch the aluminium surface (or if it's got a protective coating, don't scratch that). The trickiest bit is in reassembling it and getting the collimation right. (Collimation is the correct alignment of the mirror with the secondary and eyepiece and can be a bit of a 'black art').

If you've ever tried to collimate your optics, you'll understand what I mean. If you haven't, boy are you in for a treat!

Anyway, my little Bushnell was showing signs of mucky-mirror syndrome (it looked like brown staing on one patch of the surface) so it was time to take the bull by the horns. I removed the mirror from its cell - that took about 3 minutes - and ran it under tepid water from the tap.
With some Squezy washing-up liquid diluted in an egg-cup and a wadge of cotton wool, I carefully swabbed the surface of the mirror.

Aaaargh! What's happening? The aluminium was just washing off the glass like it was made of icing sugar! Bl***y great. Now I need a new mirror.

I don't understand to this day what happened but after the initial anguish, I decided to send the mirror off to a company called Galvoptics over in Essex county, to get re-aluminised. (Why did the Essex girl fail her driving test? Because she opened the door to let the clutch out...)

Interesting observation here: The word Aluminium is actually called Aluminum in America. Should the English expression for recoating not, therefore, be Aluminimised? Just a thought...)

Any way, back to the plot. The nice chap at Galvoptics said it could take up to 4 weeks to turn around the work, so I sent it off and waited patiently.
When it duly came back (£23 including DHL shipping) it was pristine. Yummy!

So after waiting a week or two whilst other work was completed, centred the mirror (put a dab of orange paint right slap bang in the middle to aid collimation) then returned it to its cell and reassembled it. That's another 20 minutes maximum. Then the fun bit...


I'm not a stranger to the 'black art' - indeed I also have a 10" reflector which gets collimated every time I bring it out of the shed, which isn't often these days, I regret to say. So I wasn't overly perturbed by the idea of collimating this little 'scope, even though the adjustments were horrible.
(A 'normal' reflector will normally have three spring-loaded adjusters which, with a little tweak here and there, will have you up and running in 2 minutes. This swining thing has 3 pairs of screws - one half of each pair to space the cell from the tube, the other half to lock the cell. OK once it's set because it shouldn't ever need doing again, but a pig nonetheless.)


Anyway, after 15 minutes messing about and resolving to convert the mechanism (watch this space!) asap, I had what I thought was pretty good collimation. Ready to test...

That evening was clear, like pretty much every alternate evening (until it clouded over) so far in August. Around 22:00hrs Jupiter was visible between my house and the one next door so there was my target. Sticking a Meade 12.4mm Plossl eyepiece in the focuser, (and having already set up the finderscope earlier) it was easy to get an image of the biggest planet in the Solar System, accompanied by its Galilean moons, but the image wasn't as sharp as I'd have liked.

Swinging across to Arcturus in the west I was rewarded with terrible coma. Or was it coma? It looked like a capital letter 'A' with extended crosspiece... Defocusing gave that clover-shaped blur again, instead of a disk divided by the three spider vanes.
Back to Jupiter and defocus it, looking a bit more carefully this time. There's that distinct clover leave shape emerging as I defocussed. Bizarre. So I started messing with the collimation, just in case my centre-spot on the mirror, on which the whole process rests, was slightly off. But I couldn't improve things, or indeed change them much at all. So I went to bed.

Next morning I pulled the mirror cell off. I checked the centre-spot. Yes, as near as possible to get it.
However, looking at the perimeter of the mirror, I could see what appeared to be little semicircular stress marks with the centres on the periphery. Had I perhaps mounted the mirror too tightly - I recall I'd left out some little plastic spacers because the mirror was actually loose in the cell?

So I remounted it, making sure it was snug but not tight, which included little pieces of paper around the mirror to stop lateral movement. Now it was possible to rotate the mirror in the cell without too much trouble, but it wouldn't rattle.

All back together again and collimated yet again and I was ready to test the next night.

Except the next night, Sunday, it was a bit cloudy so I watched TV. Anyway, opportunity offered itself and it was not without a little trepidation that I loaded up the 12.4mm eyepiece again and aimed at Arcturus. This time what it showed was a beautiful yellow point of light with 6 diffraction spikes. Lovely. Defocussing produced the required blurred disk. Swinging up to Vega showed its blue, again with diffraction spikes. Across to the double stars, Alcor/Mizar in the handle of the Big Dipper and they were beautifully split.

So what did I learn from this exercise?

Well, I didn't learn what caused the stripping of the aluminium from the original mirror.
However I did learn that it doesn't take nuch pressure at all to bend a 3/4"-thick piece of glass, because I believe this is what was causing the aberration after the first rebuild. It's all about trying to understand what you're doing, then if you get it wrong like I did(!), knowing how to diagnose it and provide the solution.

Next time out I'll probably hook the webcam up to it and post some images of Jupiter. Maybe even later tonight if the skies are clear! 'Til then, take care...

Labels: aluminising, collimating reflecting telescope, collimation, main mirror

What's been going on? Where have I been all this time? It's not at work, not in the conventional 9-to-5 sense anyway, though that does start in September so I'm looking forward to getting back into the 'rat-race'... unless I win the lottery first, of course!

It's been a while since I 'blogged' because all my efforts have been going into the web site. It became a bit of a labour of love (and more of a task than I originally envisaged) and it meant that this blog got ignored. So now it's time to change things!

This little ramble is going to be topical - it's about Meteor Showers and in particular the Perseids that half the world seems to have been following these last few days (which is great news for astronomy in general).
Of course, by the time you read this, it'll probably be too late to enjoy even the tail-end of the shower (it doesn't stop abruptly, it 'fades' in, reaches a peak (August 11th) then fades out again for another year). But there'll be other showers in October, November and December, so keep an eye on my 'What's on' articles on my web site.

As I say, much has been said about this particular shower in the press - well, it distracts from whatever devious or stupid things the governments are currently up to, doesn't it? - so what can I add that you may or may not know already?

Well, I could tell you that the Persids originate from the tail debris of Comet Swift-Tuttle which orbits the Sun once every 133 years or so and that even if it's cloudy, you can still 'watch' for meteors.
OK, you can't 'watch' for meteors in the normal sense but did you know that when a meteor breaks through the atmosphere and vapourises, it creates a RF (radio frequency) 'ping' which can be picked up on a FM radio or TV receiver? It sounds a little bit like a submarine's sonar echo! I've got to tell you though, that listening to that hiss for any length of time will likely drive you mad!

You can take this one step further (and preserve your sanity) by taking the audio output from your radio or TV and feeding it into the sound card on your PC where you will have installed a clever little piece of free software (BSTuner). Take it another step and another piece of software (Radio-Skypipe II) will filter out meteor occurrences based on their RF signature, and graph them for you so that you can actually see them. Magic! All you need is a PC with a Audio card and an internet connection.

Of course, in today's technologically advanced world, who on earth has a FM radio? Everyone listens to radio broadcasts on line, don't they? Well if that's you, you can also listen to the signals on-line and then feed them to your decoder if you like. See, it's made so easy.

So how do you do all of this? Well, I could explain it all again now but since I only just found out myself 2 days ago and have already committed it to the main website, I'm going to be lazy (!) and redirect you there for the details.
One of my pet projects in the near future, certainly before 20th-22nd October's Orionid shower, will be to get set up with a decent scanner and aerial just in case it's cloudy... Watch this space!

Meteor Watching

So what was I doing whilst God was emtying his Hoover bag into the upper atmosphere? Well, on Tuesday 11th, up to about midnight whilst the sky was clear, I was lying out in the garden with a notepad and pencil, gazing wistfully into the heavens in expectation. I'd seen lots of meteors before (they are one of my favourite sights as I've probably mentioned before) but the Perseids are the best of the year and to be honest I've really neglected my observing this year.

The key to pleasant observing, is to be warm and comfortable, and I was, thank you. Apart from the local midge population thinking I was a picnic.

From 22:40BST I started seeing really bright meteors. Not lots, maybe one every 10 minutes or so. With the exception of 3 sporadics travelling S>N across my zenith, all the rest were Perseids shooting out W, SW, S and SE. The best of 15 in total, went right overhead and lasted nearly 3 seconds in a gold/orange blaze more reminiscent of a November 5th rocket. It was the best I've ever seen. All the rest were impressive, all brighter than any of the stars in the sky, some brighter than Jupiter now rising in the Southern sky.

Wednesday 12th wasn't a great evening. It was 95% cloud most of the time. Having said that though, at about 23:20hrs a 'window' about 40 degrees square opened up above me (there IS a God!) and I could see the stars again. And just to make me happier, in the space of 15 minutes another 6 Perseids graced me with their brilliant displays. As the clouds closed in again just after midnight, one last brave Perseid streaked across the gap between cloudbanks as if to say 'goodnight'.

That evening should have been the 'peak' performance of the Perseid shower but it didn't stop many sky watchers braving it for a third night (and if it stays fine, I'll probably be out again tonight!)

So yesterday, Thursday 13th, as the shower was winding down, I was out there again, even pore 'comfortable' than the night before, covered in a waterproof picnic blanket to keep the damp off.
The skies were clear but the horizons from NW to E were very bright.

Results were about the same as Tuesday: A sporadic shot across from SE>NW and this heralded the arrival about half an hour later, of the Perseids. First one was really brightgoing straight overhead. The next was the faintest I'd seen in 3 days, again overhead. The following eight over the course of the next 80 minutes, were really bright, all shooting SW or S.

Throughout the three evenings I was keeping in touch with my new 'friends' on Twitter, particularly @NewburyAs, @Astronomer_Dave and @LouisS - this really is quite a good medium for sharing information.

I'd have liked to get some images of these meteors but I don't have a digital camera with a wide angle lens so that was a bit disappointing. Perhaps I'll be better prepared next time.