Suitability of Canon 50mm f1.8 Lens for Astrophotography

[jgs001]

I have the f/1.4 50mm, and it's a big leap up in quality over the f/1.8 in general terms. However, for astro use, there isn't a great deal in it. You can get away with only stopping down to f/3.5 to remove the coma, but you get a fair amount of red CA across centre of the frame. At f/4.5 the result is very good, I've yet to test at f/4. I upgraded the f/1.8 to the f/1.4 for the faster focusing in low light, as I shoot a fair amount of AmDram, and the f/1.8 just wasn't fast enough or accurate enough for me.

[Knight of Clear Skies]

The 50mm f/1.8 is great, but you really do need to stop it down to at least f/4 if not lower to get the optics to work the best. Otherwise the coma is really dire. Yes at f/1.8 you let in some serious light, but you'll lost something like the outer 30-40% of the image. Even at f/3.5 you lose a fair amount to coma. The 50mm f/1.4 is much better with the coma, at f/3.5 there's none visible, and the red CA across the middle is dealable with. 

However, unless you're tracking, you're going to be really hard pushed to use it. On a crop sensor camera, you're looking at about 8 second exposures to avoid trailing... you may be able to get away with a bit longer... but as a rule of thumb. With tracking, it's short enough and light enough, that on any decent mount, you should be able to hit 5 minute exposures easily, and at that sort of exposure time, even my non modded Canon 450d is pulling in plenty of Ha. 

with the link wld be useful!! http://flic.kr/p/j66bKN

Thanks very much for the info and images, you've given me a much better idea of how the lens will perform. It sounds like it's going to be quite limited without tracking, although a nice dinky Orion nebula or Pleiades might be possible by taking lots of very short exposures.

I think for now I'll stick to playing with my kit lens and see if I can get more from it. Next time I'll shorten the tripod legs to try and limit the camera shake, and see if that helps with the stacking. I'll also play with laptop control. I may get a 50mm lens anyway as an addition to my general photography kit, but I won't make it a priority. The focus lock trick could be a good one for me, especially if I want to take darks in the middle of an imaging run. It's tricky to put the lens cap on without moving the focus ring.

It's a shame I can't see your images here at work as they're blocked. I'll have a look when I get home. I don't know what your budget might extend to, but if you're not interested in a scope, have you thought about an Astrotrac?

Maybe further down the line, but I can't justify the expense at the moment.

[Adamar98]

I started out doing fixed tripod astrophotography. I couldn't afford a mount to begin with so I built a barn door tracker. Cost me around £20 to make. I was getting about 60 second subs at 50mm with it. It maybe worth a thought?

Here's a link on how to make one.

http://astunit.com/atm.php?topic=handscotch

Hope this helps.