How To: DIY Solar Filter

NEVER LOOK DIRECTLY AT THE SUN, ESPECIALLY THROUGH A TELESCOPE, BINOCULARS OR A CAMERA WITHOUT PROTECTION. 
THIS CAN RESULT IN INSTANT AND IRREVERSIBLE BLINDNESS.

If you want to view the sun through a telescope, or photograph it using a DSLR camera, it is neccessary to either buy or make a solar filter. You can buy them in many places online, but they can be a bit pricey. I have previously made a filter for my telescope using Baader AstroSolar film, and it has worked perfectly (see here and here), but for this DSLR filter, I decided to try out Thousand Oaks Optical polymer film.

I purchased a 4"x4" sheet, as it was all I needed to cover the lens, but if you are making a filter for a telescope, you should definitely go for a bigger size. I ordered mine from amazon.co.uk, and it arrived really quickly, despite coming from Israel!

So to make the filter, I decided to use the end of an empty Pringles can, as it was the perfect size to fit over my lens. I cut the end off to about 4 inches. 

I then cut a hole in the base. I wasn't concerned about vignetting, as everything outside of the sun is going to be dark anyway, so I left a good cm edge around it, to hold the film in. 

At this point, you can sand down the edges if they are sharp, to prevent damage to your filter paper. I opted to cover mine in electrical tape. You then need to cut your filter paper to fit inside the Pringles can. This must be done carefully in order to avoid damage to the paper. The oils on your fingers can damage it, as can any tiny nicks or scratches, making it dangerous to use. Try to handle the paper as little as possible.

I then covered the outside and the base of the can with electrical tape.

The filter paper is then placed inside the Pringles can, and held in place using a circular piece of plastic (cut from a spare Pringles lid) and 4 pieces of strong card folded into an L-shape and then taped to the inside of the can. 

I'm using the Pringles lid as a pseudo lens cover.

In order to attach the filter to my camera, I taped some thick cardboard to the inside of the can, so that it fits tightly around my lens. I also punched two holes in the can, through which I tied some elastic bands, which will hold it very securely to my camera body. You *really* do not want this to fall off while you have the camera pointed at the sun, so it is very important to make sure everything is securely fastened together. 

I tried mine out this morning and it worked an absolute charm. 

Fingers (and toes) crossed for (relatively) clear skies!

How To: Safely observe a Solar Eclipse

NEVER LOOK DIRECTLY AT THE SUN, ESPECIALLY THROUGH A TELESCOPE, BINOCULARS OR A CAMERA WITHOUT PROTECTION. 
THIS CAN RESULT IN INSTANT BLINDNESS.

On Friday, March the 20th, 2015, there will be a solar eclipse visible in Ireland. More than 90% of the sun will be obscured by the moon making it is easily the best eclipse visible in Ireland since 1999, and the next decent one wont be until 2080! So this is a very exciting, and pretty much a once-in-a-lifetime, event! 

The eclipse will begin at 08.20, maximum will be at 09.24, and it will end at 10.32,* which makes it ideal for school groups wishing to observe this event. It might be nice to make pinhole projectors together in class on the Thursday, talk about what happens during an eclipse and make sure the students understand the safety aspects, then take the class outside together to view the eclipse on the Friday.

*Note: the above times are for Cork - you can check times for your location here. 

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There are a number of ways to view this eclipse safely:

1) Projection

This is the easiest way to view a solar eclipse, and is an ideal way for school groups to all watch together.

The simplest projection that you can do is to poke a pinhole in a piece of card using a thumb tack or sewing needle, making sure the hole is as round and smooth as possible. Then hold it at arms length in front of a piece of paper. It will project a tiny image of the sun, which you can use to view the eclipse. The further away you hold the pinhole, the larger the image will be.

Pinhole projection of the sun.

You can also cut out a square in your card and tape a piece of tin foil to it, then poke a hole in that.

Tin foil taped to a piece of card, with a pinhole through which the sun is projected.

Another variation is to get a large cardboard box, put a pin hole in one end, and a piece of white paper on the inside. This is then held over your head, with the pinhole facing the sun in order to project an image onto the paper.

Eclipse projection box.

2) Eclipse Glasses

If you absolutely must look at the sun, the safest option is to get yourself a pair of eclipse viewing glasses. They are available online in many places, including First Light Optics, eclipseglasses.co.uk, and amazon.co.uk. These will unfortunately probably sell out quickly.

Through a pair of eclipse glasses, the sun is visible as an orange disc.

The current issue of BBC Sky at Night Magazine also comes with a free pair of eclipse glasses, and is available at all good newsagents. They are the glasses that I will be using.

BBC Sky at Night Magazine eclipse glasses.

3) Filters

Anyone wishing to view the eclipse through a telescope or binoculars, or wanting to photograph it, will need to either buy or make a solar filter. First Light Optics have filters and filter paper for sale here.

Buying a ready made filter can be pricey though, so this year I've decided to make a filter for my camera using a Thousand Oaks solar filter sheet. I will hopefully be posting a tutorial for making a filter later in the week.

Thousand Oaks solar filter sheet - soon to be a solar filter for my camera.

I have a filter for my telescope that I made using Baader AstroSolar safety film, and I've taken some nice shots with that (check them out here and here), but unfortunately I wont be able to drag my telescope out to my eclipse viewing spot, so some binos and the camera will have to do the job.

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The most important thing with this eclipse however, is to get out and enjoy it!

We live in a time when the angular size of the moon is the same as that of the sun, despite the distance between them, and this is what makes total solar eclipses possible. However, at present the moon is pulling away from the earth at a rate of about 3cm a year, and there will come a time in the future when total solar eclipses are an impossibility, so enjoy it while you can!

A solar eclipse is something that many people never get to see, and to have one on our home turf is very exciting!

Now if you could all cross your fingers for clear skies, that would be great!!