Quote:
Originally Posted by jimmyh1555
Thanks for that. Very interesting tests, Bojan! So it seems that using a fast lens (ie f1.4) and faster speed is not really any good! I might as well put on my regular DA* Pentax and take the shots at F5.6 or so and risk a longer exposure. The lower the f stop, it seems the more purple fringing around the stars!
Calculation.... 10 sec at f1.4 = 20 sec at f2 =40 sec at f4 =80 sec at f5.6 Sounds feasible! I willl try tonight 
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Fast lenses are good, but they still need to be stopped down (for most lenses). Generally a fast lens stopped down will outperform a slower lens at the same f-stop until you get up to like f8, as seen in the 50mm tests in the link below. so if you have a f2.0 lens and a f2.8 lens both stopped down to f4, the f2.0 lens will generally be sharper.