Perigee

Camera	Sony DSC-F828
Exposure Mode	auto
Focal Length	51.0mm
Aperture	f/8.0
Exposure	1/250 sec.
ISO Speed	64
Flash	off

I misspoke last week; I'd completely forgotten that I'd played with the camera and taken some interesting photos of perigee which I could have blogged about. So guess what... this weeks blog is about perigee and the reason you might want to use the white balance button if your camera has one. Let's start with a little bit of science before we get to the photo.

I'm sure that by now you will have all worked out that perigee is related in some way to the moon but for those of you who have never heard the word before, I thought I'd give a little astronomy lesson. Whilst we may often draw the orbits of planets around the sun (or moons around planets) as circles they are actually elliptical in shape. This means that as the moon moves through it's orbit there is a point at which it is closest to the earth and a point at which it is further away. These are known as perigee and apogee and the diagram probably does a better job of explaining this than my words on their own. Perigee occurred on the 29th of January and it coincided with a full moon giving us a good opportunity to photograph it. And so with the astronomy lesson out of the way let's move onto the photo.

Even though the moon was larger than normal I still decided to use the telephoto adaptor I bought for the camera and so I'm working at a zoom level of x30. Before I even tried to take a photo I knew that the auto settings would be of no use what so ever. They tend to do average metering across the scene to work out exposure settings and given the vast difference in light levels between the sky and the moon that was never going to work. So I switched to shutter priority mode, and spot metering. I experimented a bit but found that an exposure time of 1/250 second gave a pretty good picture and didn't require a tripod to get a crisp image. The photo on the left shows this first attempt. Whilst the photo is okay there are a few problems with it. First there is quite a lot of noise in the sky but more importantly the moon is yellow. Even if some of you happen to believe that the moon is made of cheese I can tell you that on the night in question it was white rather than yellow. Now I could have corrected this on the computer but I decided I'd try and work out how to get the right colour from the camera instead. Fortunately my camera has an option for setting the white balance which is just what I needed to ensure the moon didn't look like cheese. I cycled through all the white balance modes on the camera (other than fully manual -- I'm not quite ready for that yet) and found that choosing fluorescent gave the best match. According to the manual the fluorescent mode gives a colour temperature of 4000K and is used (not surprisingly) for shooting under fluorescent light!

The added advantage of setting the white balance properly is that the sky is now much blacker and the distracting noise is reduced. Whilst I could have accomplished that on the computer it would probably have taken quite some time and I'd prefer, where possible, to do as little post processing as necessary to retain as much quality in the image as possible. I wouldn't say I've now mastered the white balance but I'll certainly remember to use it in future.

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