« on: April 20, 2014, 06:03:54 AM »
All the data on the internet is an interesting thing. Stare at it too long and you'll lose perspective and go blind. It allows you to evaluate subtle differences in lenses beyond the point that you would actually be able to perceive. Also, much of the available data is based upon a single copy of a lens when it is well established that there is significant copy variation. I am not saying you don't learn something and that it isn't valuable, but I think you need to evaluate charts with some perspective.
My recommendation is that you start to think in broader terms such as "unacceptable," "acceptable," "good," "very good," "extremely good," and "elite." Each of these is in the eye of the beholder, but I want to emphasize that evaluating internet data tends to push everyone to the "elite" lenses when many amateurs would be very happy once you get past good (some with acceptable).
I do this because earlier you dismissed what is likely the perfect lens for you. You say that you want a landscape lens and are on a budget....the EF 25-105 f/4 is absolutely the best bargain "L" lens right now. But it in your kit when you get your 6D and wait for a deal that pops up and you can get it for $400-$600. That is a steal. Practically speaking, the lens is good at f/4 (all this talk of it being "soft" is highly overrated IMO), but it is very good to extremely good from f/5.6-f/8. It is about as good as any lens once diffraction kits in (which is still very good to extremely good) from f/8-f/16. It is a great landscape lens for the budget. Are there better out there, yes, absolutely. The charts show it and several lenses are even perceivably better. But it is good enough for most amateurs.
So, my recommendation would be to pick up the EF 24-105 in a kit, or maybe the EF 24-70 f/4 IS in a kit (depending on price) and then pick up a prime such as the Sigma 35A, or one of Canon's trilogy of 24 f/2.8, 28 f/2.8, or 35 f/2 for lower light photography. If you want astrophotography, that does change things. The value lens you can get is the Samyang/Rokinon 14 f/2.8 UMC. You can get by with f/2.8 at 24 mm (I've seen great shots even at f/4), but typically need f/2, by 21 mm or 14 mm, you can increase your shutter speed enough that you can get great shots with f/2.8.