Quote:
Originally Posted by gregbradley
..... then there is no point in getting F1.2 type lenses.
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Greg, I did a lot of testing with various lenses, and came to exactly
the opposite conclusion (the same follows from Christian Buil's test results).
For example, F1.2 lens, stopped down to f4.5 will perform better than F1.8, stopped down to F4.5.
Also, lens design for full frame (24x36mm) will perform better with smaller sensor, than equivalent lens, designed to be used on that smaller sensor (1.6x smaller, used in cheaper Canon camera models).
The reasons are, lower F-ratio and bigger sensor require much more careful design of the lens system.
That is why the older, manual and today way cheaper lenses will very often perform better than new, k$-range lenses (with IS, AF and what'snot, all that mostly useless in astrophotography anyway).
As for tilt, sometimes it is a matter of lens production and/or assembly quality - I found couple of Canon lenses with un-symmetrical distortions in corners - but all this is visible on star images only. For terrestrial photography, they are (almost) perfect from corner to corner.
Astrophotography is VERY demanding on lens performance, especially in corners.
From my experience, instead of searching for perfect wide field lens, it is better to concentrate on what we have and how to squeeze maximum from that
Mosaics done with more narrow field lenses take longer time to complete, but the results may be closer to perfection, compared to single frame wide field photo (Avandonks work is a very good example of this philosophy - his (relatively) ultra-wide fields with 300mm lens are really worth looking at)