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Stargazey Pie May 2007

Antony has managed to escape this month so the newsletter has been written by Pauline with a lot of help from Eric and John when it came to the technical bit comprising the Main Event. May was the inaugural meeting for John Gilmour as our new Chairman, who took to the job like a duck to water. Pat Williams, our Secretary, read out the notices:

  • Subscriptions are now due. Please send your completed form, which is found in your programme, and cheque to: Mrs. Pat Escott, 2 Muirfield Road, Inverness, IV2 4AY.

Full membership.................................£20.00
Family membership.............................£33.00
Junior membership (16 and under)..........£2.00
Unemployed/Student (aged 17 to 22)......£6.00
Non members (per meeting).................£ 2.00

If you do not wish to rejoin, please let Pat W. know.

  • The programme gives a date for the next Going Nova Science Festival. However, it appears this coincides with Easter next year so will probably change.
  • Gaelic TV observing night: The film makers sent HAS the following message. “We have now finished editing our sample tape and as of last week it is in the hands of the funding body. They will now decide whether or not they would like to fund a broadcast series. Here's hoping. I would like to thank you very much for all your help with our pilot tape and hope you can pass this on to all those involved in the astronomical society. Your help was hugely appreciated and I wish you well with all your forthcoming developments. We should know in the next month or so whether or not the programme is to go any further. If it does it may tie in with your building nearing completion. May be a possible feature in that.”
  • Stargazing events: There will be no more regular viewing evenings at Culloden for the moment. This is partly because the nights are now so light but also because the old observatory will have to be removed soon. We hope to have the new one up and running by November.
  • BAAVARSTAR. The BAA Variable Star Section Annual Meeting will take place at the Royal Observatory, Blackford Hill, Edinburgh on Saturday 5th May from 10am to 5.30pm. Further details from: Des Loughney Eclipsing Binary Secretary (BAA VSS) (Edinburgh) at "desloughney at blueyonder.co.uk".
  • Avanquest discount: Avanquest have offered HAS a discount on their Starry Night products. If you enter the special password(obtainable from Pat Williams)when purchasing any version of Starry Night from www.avanquest.co.uk you will receive a 15% discount. This offer will apply for a number of months.
  • Volunteer speakers needed. Our open night has been moved to January. Pat is looking for two members, who have never given a talk to HAS, but would like to do so to give a 20 minute astronomy talk. Your presentation skills will be honed by Bob Clark from the Inverness Speakers Club. He will give a twenty minute talk on presentation skills.
  • HAS Calendar: Eric will produce our own Astrocalendar for 2008 as we were very disappointed with the response from Liverpool AS. Anyone with images or production skills please contact him.
  • Observatory update given by John: We hope to open the observatory on Sat. 3rd November 2007. Planning permission was applied for the on 1st May 2007 after Rob had to put in a lot of extra work. You should note that the amount of funding required is liable to change until we obtain a final quotation for the building, which should happen in June. At the present time it would appear that we still need up to £7,800.00 but £2,500 of this is contingency and around £4,700 is for the waste disposal system which can be postponed until enough money can be raised. Further fundraising in the summer will include a car boot sale (watch this space) and possibly a car treasure hunt.
    Please note that there is still time to contribute £25.00 to have your name on the Observatory plaque. £100.00 was raised this way in April.

 

The Main Event

‘Imaging with the Canon EOS 20Da’ by Douglas Cooper.


Douglas hails from Doune near Stirling. He is a member of the Stirling Astronomical Society, the association of Falkirk Astronomers and is the Secretary of the Scottish Astronomers Group. A keen amateur astronomer for many years he has spent time recently researching solar magnetic fields at Glasgow University and has been asked to give a one day course there later this year. Douglas is married, with two children, and has a very supportive scientist wife who, fortunately, understands his 'need' for such an expensive hobby…

Digital imaging has revolutionised astronomy as well as photography because you can see immediately the results of your photography work and can adjust your camera settings accordingly to obtain the very best quality images. In the pre-digital past, you could spend hours taking photos then the film would have to be processed and often the results would turn out to be a disappointment. Douglas used the analogy of the Cadburys Smash advert in which aliens were looking down on Earth from space and wondering why humans were still peeling, cooking and then mashing potatoes when Smash was available. Photographic film is now looked upon in the same way by astrophotographers.

With photographic film, the exposure times required in astrophotography can be so long that the chemicals in the film can start to bleed or else too much light may fall on parts of the film. The same image can now be obtained using a digital camera in just two to three minutes instead of the ten minutes required when using film, with none of the aforementioned problems being encountered.

The Canon EOS 20Da was designed in June 2005 specifically for astrophotography. It is a combined digital and SLR camera with a chip in place of the film. It costs a cool £1600!

The EOS 20Da has a number of advantages over other digital SLR cameras. It was the first camera with a built in EF / EF-S lens mount. In addition to enabling the camera to use your existing SLR lens combinations it also permits the use of readily available telescope mount adapters so you can attach your favourite small APO to the camera body. This means that a small telescope can be used instead of the camera lens. With a polar aligned, guided mount, stars can be tracked without blurring. Being an SLR, it does mean that it is not possible to use the LCD screen when taking photos and the viewfinder has to be used instead.However, this camera has a unique mirror lock-up system which allows you you to look directly through the lens rather than reflected light off the mirror itself.Focus is paramount and this viewing system contributes significantly to the achievement of pin-point focus.

This camera has has two focus settings; fine focus and ultra-fine focus, which allow a zoom of either five or ten times.When the shutter is pressed, the mirror moves out of the way so that all pictures can remain in sharp focus during the zoom function.No other camera does this.

Using this camera, you can check for polar alignment, get the focus right, and then click away all night knowing you are going to get great images.

Early digital SLR cameras, and many ‘prosumer’ level digital cameras today, are subject to ‘noise’ and colour artefacts.They use a lo-pass hi-wavelength filter in front of the CCD sensor to minimise noise and enhance the visible red region of the light spectrum.They are very good for daytime photography but not ideal for astrophotography.The Canon EOS 20Da was designed with larger pixels and so is less ‘noisy’ and thus good at capturing light.It uses a CMOS chip which has been an improvement over the Canon EOS 20D.In addition, the filter was replaced with one which passes 2.5 times more light around the 656nm (H alpha or far red) wavelength allowing more details to be revealed in long exposures of emission nebulae such as M42 and the North American Nebula.

This camera also has a filter in front of the sensor. This has a high wavelength cut off to give a natural looking image without the reddish glow so often seen with many other cameras. This is important since a lot of interesting and bright emission nebulae emit in the H alpha (far red) wavelength but in this camera the filter used cuts off the higher wavelength but allows more IR radiation through and allows three times the amount of H alpha light to reach the sensor. This is very useful as it then becomes possible to pick up more red nebulosity in deep sky objects such as the Orion Nebula and North American Nebula.

It is possible to have the filter changed in a number of other digital SLR cameras – www.astronomiser.co.uk is a small UK based website who will offer this service for about £300. They will replace the original IR blocking and anti-aliasing filter with a Baader 245 9211 filter. This latter filter has a much sharper transition between passing visible light frequencies and blocking UV and IR giving a greater sensitivity to the Hydrogen alpha band and optimising this response for astro-imaging. Daylight photographs may look a little pinkish thereafter but this is worth it for the resulting nighttime astronomical images, if that is the primary use of the camera.

The Canon EOS 20Da, like other digital SLRs, doesn’t require a laptop when acquiring the images; all that is necessary is a remote control device to open the shutter in order to keep the camera absolutely steady. Images can then be downloaded to your PC or laptop later or alternatively printed straight from the camera card.

Unfortunately, the Canon EOS 20Da was made for only six months and is now discontinued as the niche market was just a bit too specialised. You can find them on internet auction sites but be prepared to pay a small fortune for this truly remarkable piece of imaging equipment!

Douglas then demonstrated the versatility of this camera by showing a series of photographs taken with his own Canon EOS 20Da using the small telescope attachment. He showed us quite stunning images of the North American Nebula, the Flame Nebula and the faint beginnings of the Horse Head Nebula with only a two to three minute exposure; the double cluster in Perseus, the Sombrero Galaxy, Andromeda galaxy, the Ring Nebula, M81 and M82, lunar and solar eclipses, noctilucent clouds, comets, double star size and colour differences and many others.

He also illustrated, using his good and ‘bad’ images, that a longer focal length can give greater magnification but errors / artefacts can show up.He showed by using a field flattener (focal reducer) that you can take stunning wide-field images – one image in the region of Cassiopeia-Perseus revealed 4-5 star clusters in the field of view.

The images taken by Douglas show what is possible with this camera – images that many of the audience would dearly love to strive for. I’m sure that more of us will now be inspired to take up astrophotography.

Highland Skies – May 2007

The nights are rapidly becoming shorter as summer approaches and in the north of Scotland, it is already twilight all through the night. This means it is never quite dark enough to view those faint fuzzies - they will have to wait until mid August.

However, all is not lost. Venus still shines brightly at magnitude –4 in the western sky as it follows the setting sun. Mercury makes an appearance this month but is difficult to spot until it rises higher in the sky. Look for this elusive planet at about 10pm BST towards the end of May, when it is setting a couple of hours after the Sun.

The crescent Moon inserts itself between the innermost planets on the 18th May making a pretty photo opportunity before setting at about 1am BST, closely followed by Venus.

Saturn is still visible nestling in the sickle of Leo the Lion but by the end of May it is observable for only about an hour. Jupiter can be seen around midnight shining at magnitude –2 and although bright it travels low in the sky at this time of year. If you wait until the early hours of the morning, Mars can be found on the Pisces/Cetus border, but at magnitude +1 is not particularly inspiring.

Around midnight on the eastern horizon the Summer Triangle makes its regular spring appearance. Vega, in Lyra, is the brightest of the stars followed by Altair in Aquila and Deneb in Cygnus. The summer triangle (a term coined by sir Patrick Moore)is so called because it is made up of the brightest and therefore the most noticeable stars, which appear during the light summer nights.

However, the brightest star in the night sky at the moment is Arcturus in Bootes. It is an orange giant about 27 times the diameter of our Sun and around 37 light years away. You will find it by looking directly south at midnight. Alternatively, the Plough can be used as a signpost by following the arc made by the handle in a downwards direction (arc to Arcturus) and you can’t miss it. Go further still and low on the horizon you’ll find Spica, in Virgo.

From the end of the month start to look for Noctilucent clouds. These are flimsy, diaphanous, and electric blue in colour, quite distinct from ordinary grey weather clouds. They are found on the northeast to northwest horizon a few hours after the sun has set and are usually best seen in the early hours of the morning. However they can produce spectacular displays in the late evening and are well worth looking out for. Especially interesting is that they may be becoming more frequent because of global warming – how many displays will you see this year?

Next time

Ken MacTaggart will be talking to us about the “Exploration and Discovery of the Moon”. The meeting will take place at 7.30pm on the 5th June at the Green House. So if you want to find out more about our only natural satellite, do come along.

 

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