VERSION|0.5.1|SUBJECT|A Sunny Day in Southend|CONTENT|[url=http://antwrp.gsfc.nasa.gov/apod/ap130224.html][img=images/2013/02/pic130224.jpg popup=false float=right][/url]Given the leaden grey skies that we&#039;ve seen over the last few days, it&#039;s hard to remember that we had a beautiful sunny day earlier this week. I took the opportunity to try out the solar filter that I&#039;d cobbled together for my telescope.

I&#039;ve always followed the late Patrick Moore&#039;s advice, which was that you never point any optical instrument at the sun and look through it. In fact you never look directly at the sun at all without proper eye protection. For the 2004 transit of Venus I projected the image from the telescope onto a piece of white card.

[url=http://www.platitudes.org.uk/platblog/images/2013/02/Sunpics/transit.JPG][img=images/2013/02/Sunpics/transit_sml.JPG popup=false width=200 float=left][/url]The main advantage of this approach is safety, no one&#039;s eyesight is ever in any danger. The main disadvantage is that, with the sun moving across the sky, you have to keep moving the white card as well. There&#039;s also the theoretical problem of the eyepiece being damaged by the sun&#039;s heat but this can be mitigated by reducing the aperture of the telescope and I&#039;ve never found it to be a problem anyway.

This particular telescope came with any eyepiece solar filter, which I&#039;ve never been tempted to use. This attempts to filter the light from the sun [i]after[/i] it&#039;s been focused on the eyepiece - potentially very dangerous. If the heat cracks the filter then the focussed light from the sun will pour straight into the observer&#039;s eye, at least for the few milliseconds that the eye continues to exist.

Proper solar filters, that filter the sun&#039;s light [i]before[/i] it enters the telescope were always too expensive for me. So it was quite a surprise when a [url=http://www.bbc.co.uk/programmes/p014hpkh]recent Sky at Night episode[/url] showed you how to make a solar filter out of what looked like silver baking foil. It&#039;s not baking foil, it&#039;s [url=http://www.telescopehouse.com/acatalog/info_APM057.html]this stuff[/url], which goes by the catchy name of Baader Astrosolar Safety Film and costs about £20 for an A4 sheet.

[url=http://www.platitudes.org.uk/platblog/images/2013/02/Sunpics/telescope.jpg][img=images/2013/02/Sunpics/telescope_sml.jpg popup=false width=300 float=right][/url]The instructions that come with the safety film show you how to create a flat filter between two rings of cardboard and then suggest trimming the edges. The Sky at Night version is safer, as it doesn&#039;t trim the edges but folds the film over the ends of the telescope, cutting out any stray light. I decided to do both, to create a reasonably flat filter and also fold it over the edges. The result, a combination of filter, cardboard and lots of glue and sticky tape, looks like the picture on the right.

Although the film looks all wrinkly, this doesn&#039;t seem to have any effect on the optical properties of the filter. Don&#039;t ask me to explain why, I haven&#039;t a clue. 

One last safety check, I pointed it up at the sky and looked through to check for any pinholes - none.

So, with the filter in place, I lined up the telescope with the sun. Again, you don&#039;t use a sighting scope or even the red dot finder that I have on this scope. It&#039;s just a matter of minimising the scope&#039;s shadow against the background. I popped a low magnification eyepiece in and, with some trepidation I&#039;ll admit, looked through it to see something like this. (Click for a larger image.)

[url=http://www.platitudes.org.uk/platblog/images/2013/02/Sunpics/IMGP0879_sml.jpg][img=images/2013/02/Sunpics/IMGP0879_tiny.jpg popup=false][/url]

The image through the eyepiece is actually much sharper than this. I haven&#039;t quite figured out how to get rid of camera shake when I take a picture of it. The camera&#039;s got two timer modes. There&#039;s a 2s timer where the mirror lifts and then the camera waits 2s before taking an image. Trouble is, 2s isn&#039;t enough time for the all the vibrations to damp down. There&#039;s also a 12s timer, which is much better at getting rid of vibrations, but it only lifts the mirror just before it takes an image, thus reintroducing vibration all over again. Despite this, you can still zoom in on some of the sunspots.

[url=http://www.platitudes.org.uk/platblog/images/2013/02/Sunpics/sunspots.jpg][img=images/2013/02/Sunpics/sunspots_sml.jpg popup=false][/url]

Next sunny day, I might just try with a much lighter compact camera rather than the big old clunky SLR and see if I can&#039;t get some steadier pictures.|CATEGORIES|39,11|IP-ADDRESS|94.168.119.214|CREATEDBY|admin|DATE|1361688265