Night sky photography

Stuarty

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21 Jul 2005 - 5:40 AM

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I've got a Canon S1 IS, 10X zoom but no bulb setting, so I know my night sky pgotographing is going to be limited. Shooting the moon is no problem - well, it can be when it's really bright - got a shot last night where it looked like the setting sun, but I would like to photograph planets if possible. Last night I got two shots of, I think, Jupiter, both perfectly round images, surprise, surprise, but with very different colours. 15 secs is my slowest speed and at 1 sec, 10X + digital = 32X, 'Jupiter' looks green/yellow. At .5 sec, same zoom setting, it looks blue/purple. I would like to capture a 'realistic' colouring.

Any thoughts?

dougv (e2 Member)

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21 Jul 2005 - 10:35 AM

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Possibly a bit of chromatic abberation.
The differing colours would probably be caused by moving air currents shifting the frequency of the light being gathered.

You will also have a problem with long exposures unless you use a specialist camera with a cooled CCD to counter the heat generated by the amplifier circuit of the CCD.

But don't let that put you off!

Doug ;o)

dougv (e2 Member)

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21 Jul 2005 - 12:34 PM

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That is probably correct Terry.

Hubble wouldn't be much good if it used film though.

Astrophotography is realy rather specialised, and the advent of digital has brought it to a much wider section of the astronomy community.

Doug ;o)

dougv (e2 Member)

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21 Jul 2005 - 1:38 PM

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Quote: That was a magazine from the 1980s I guess?

Perhaps not Phil.
There have been some great advances in digital astocams in the last few years.
It wasn't that long ago that they were all sub-mega pixel as is my Starlight Xpress MX5C.

As a coincidence, my subscription renewal for S&T arrived today!

Doug ;o)

chriswebb

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22 Jul 2005 - 1:11 AM

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Stuart, reciprocity failure is caused when films are exposed for long exposure times, the effects being:

(1) an effective decrease in film speed, so for example if a correct exposure is 1/15sec at f1.4, you would expect 16sec at f22 to give the same exposure, but you would actually need a longer exposure time.

(2) and this is the bit relevant here, the colour balance also falls to pieces, I believe because the sensitivity loss mentioned above does not occur evenly across all colours.

As I mentioned, I've no idea whether this applies to digital and there are obviously plenty of astrophotography experts here to help you out.