Photographing a partial eclipse
|A partial solar eclipse photographed by Paul Sutherland|
Most people know that the Sun is so bright that you can't look at it without risking your eyesight, but they may be less fussy about their cameras, or may risk viewing the event through the viewfinder of their camera. This guide tells you how to photograph the partial eclipse safely without risk to your eyesight or the camera!
The blinding Sun
The Sun is so bright that you need to cut down its light before it gets into the camera. Even if you can give a very short exposure time, the Sun’s light will be focused inside your camera while you are lining it up, and it could act in just the same way as using a magnifying glass in the sun to set fire to something.
|Below: How big the Sun will appear in the frame of a DSLR camera using different focal length lenses|
This means using a filter on the front of any lens you plan to use. The most readily available material is Baader AstroSolar, which you can get from several specialist suppliers in A4 sheets, costing about £20. It is thin multicoated polymer film, so it is tough but easy to cut with scissors. AstroSolar gives a neutral colour image (that is, white), but you can also use the material taken from approved eclipse viewers, which gives a redder colour, though this is usually only available in smaller sizes.
Probably the simplest way to use the material is to find a circular lid from something that will fit over the end of each lens you plan to use. You may want to use both wide-angle and telephoto lenses, for example. Cut a circular hole in the lid and tape a circle of your safe material on the inside, making sure that the hole is well-covered, with no chinks of bright light getting through, and there is no chance of the tape coming unstuck.
You don’t necessarily need to make the hole as large as the lens diameter if your lens is a large one. Even a hole only about 20 mm across will probably do.
With a compact camera there is often no fixed lens assembly, as the lens retracts into the camera when not in use, so you may need to choose your filter holder carefully.
What settings should I use?
Most people never need to worry about camera settings these days, because everything is done automatically. But cameras aren't expecting to be faced with an eclipse, so they probably won't give the best results and could well give you rotten ones! So find that instruction manual. which you ignored when you got the camera, or download another one from the web.
Experiment before the event to get the best pictures of the Sun’s disc. Usually you need a considerable telephoto setting because the Sun really is quite small in the sky. If you have a DSLR camera, at least a 200 mm lens is needed to get a reasonable image size, and you can go up to 600 mm or even 1000 mm.
Exposure times will depend on the brightness of the Sun at the time, and the density of your viewer. The great thing about digital cameras is that you can see what the results look like, so you can experiment as much as you want. But many people will find that the results are far too overexposed.
This is because cameras are designed to give an even balance of bright and dark in a picture. If the Sun is small in the field of view, the large area of black around it may fool the camera into giving more exposure. This is where you need to investigate the manual settings of your camera, starting with those little + and - symbols that you usually ignore. These will compensate for exposure differences, either making the picture brighter (+) or darker (-). So get to know your camera well in advance.
As the view is quite dim, an automatic camera will probably try to set off the flash. So work out how to switch off the flash. This will also stand you in good stead next time you want to take pictures in a museum or National Trust property! Look for a zigzag symbol. Pressing this usually cycles through auto flash and no flash, or maybe some other settings as well.
Tip: Most cameras have a P or Program setting and an A or Auto setting. Do all your experimentation with the P setting, then you can switch back to Auto for your everyday photography without all your pictures having the wrong exposure!
Photographing the total eclipse
If you're lucky enough to be in the path of totality, remember that when the total eclipse is in progress you won't need any filter at all, as the event is actually quite dark. But it must go back on as soon as totality ends.
Virtually any camera setting will get a result, but again overexposure can be a problem and with an automatic setting the camera will try to brighten up the whole scene. Not only will it overexpose the Sun, but it will probably operate the flash and may also try to give a very long exposure when it realises that the flash is having no effect -- maybe half a second or one second. This means that you will need to hold the camera steady for that time. A tripod is best, but if you don't have one try to steady the camera as much as possible. Even if your camera has no viewfinder other than the view screen it can help to hold it against your face to steady it, as we used to.
To record the inner corona and prominences an exposure time of just 1/250 second is needed at ISO 100, but you will probably need to control both the exposure and the focus manually to get this result.
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