Never been sure which lens to buy next for your 5D? Thanks to Gebbs for this very instructive guide. More after the break when there's also a low light comparison test between the 5D and the Sony F3.

So we've all been there before: you've recently purchased a DSLR, you're pleased as punch with your new acquisition, and although you've spent large, the outlay has only just begun.

Now it's time to enter into the magical and at times frighteningly expensive world of prime lenses. But which one do you choose? You do your initial research, look at Amazon, then specialist sites, go to the next level, check out the forums, talk to your friends who have one. Still not enough.

You want to see it in action. You think "lots of recommendations, but where's the real evidence". So next step, go to a store with your DSLR, check out the prime weapon of choice, fix to your body, and give it a test run. In the store, in the hurry. No, not the answer.

So when you discover that Gebbs has done the hard work for you, and explained it all so well with video evidence, you suddenly know exactly which lens is going to be your next purchase. Thanks Gebbs!

BTW the fcp.co editor swears by his 50mm 1.2, I think it's top of my list as well!

Another big question is do you go to the next level and purchase a Sony PMW-F3? Or stick with your 5D?

Take a look at what Matthew Allard did in testing the 5D against the F3 in low lights conditions.