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I'm looking to buy a wide-angle lens for astrophotography, specifically on a Canon 450D (Rebel XSi). Which characteristics should I be looking for in a lens?

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    \$\begingroup\$ I've made an edit to your question which tries to stop it being a straight product recommendation question, which is off-topic here. You're obviously free to revert this change if you want to, but I strongly suspect the original question would just be closed. \$\endgroup\$
    – Philip Kendall
    Commented Jun 19, 2015 at 9:17

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1) The faster aperture the better. You probably want 1.4 if possible, especially on a crop camera. However, the widest 1.4 I know of is a 24, which isn't all that wide on a crop. 2.8 can work, but not as well.

2) It should have low coma. Distant bright spots should remain that - spots. Most lenses add a bit of a "tail" to them.

3) Ideally it should have a hard focusing stop at infinity. Usually you have to use live view to focus stars. I'm not absolutely certain but think some Zeiss and Rokinon lenses have this. (I have the rokinon 24 f/1.4 and 14 f/2.8 but haven't had a chance to use them for astrophotography yet. They are supposed to be good though.)

Really though this is one aspect where full frame will get you a real advantage. Then you can use a 24 f/1.4 with appropriate wideness, plus the high ISO shooting will be infinitely better than on the Rebel.

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  • \$\begingroup\$ Unfortunately I’m stuck on this 7 year old Canon 450D on a tight budget I really wish I could afford those lenses and also a full frame camera. Perhaps I can afford canon EF 50mm F1.4 or a 14mm lens. \$\endgroup\$
    – user40661
    Commented Jun 20, 2015 at 11:44
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    \$\begingroup\$ Due to the wide range of temperature variations possible when doing astrophotography, a hard stop at infinity might not be as big an advantage as would seem at first glance. Exactly where infinity focus is will change with differences in temperature. With most subjects this is not a big issue, but with point sources of light such as stars, the focus has to be precise or even a slight miss caused by very warm or (more often) very cold temperatures can leave stars just a little fuzzy. \$\endgroup\$
    – Michael C
    Commented Jun 21, 2015 at 5:18
  • \$\begingroup\$ I think the Rokinon 14 f/2.8 might be the best you can do on a budget. It's $300 and is still pretty wide on a crop camera. And yeah I believe Michael is correct.\ \$\endgroup\$ Commented Jun 22, 2015 at 13:04

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