Been pondering my long tele options over the last few months... A 100-400mm is looking very likely, but I'm left pondering, why would anyone but the 400mm f5.6 prime ?
Serious question, what does it offer other than being very slightly cheaper and lighter ?
Just another list of pro's for the 5.6/400 for ME:
* IQ (sharpness, contrast) because I want to use it with my 2x TC (mark 1)
* contralight flare rejection (assumed to be better due to the low number of lens elements)
* sturdy construction
* fast reliable AF
* built in lens hood
* I like the idea of a 24mm - 40/50mm - 100mm - 200mm - 400mm prime set since I startet photographing
The prime won against the 100-400 zoom because I really like shooting "perfect" primes. The 70-200 4.0 is an exception because it delivers excellent IQ (except direct contralight situations).
Sometimes I missed the flexibility of a 100-400 zoom because I like to walk with ONE lens / body.
Another point about sharpness/resolution: Under real world conditions the excellent IQ of the prime goes down to roughly 1 MPix when you do landscape photography - due to shimmering atmosphere.
If I were NOW in the situation to decide between the 5.6 400 and the 100-400 I would perhaps wait - if possible - for the mark ii version of the zoom. If it has similar IQ like the prime, a 4x IS system and sells for 2.5 kEuro it would be my choice.
Just my 2ct - Michael
PS: An example of 5.6/400 with 2x TC (mark i) from an HD video with 3x zoom (EOS 600D, 1 sensor pixel = 1 image pixel), effective focal lenght is roughly 4000 mm.
Very nice video still of the moon! At 4000mm, I can certainly see why atmospherics are a factor, and why many astro photographers use video rather than shooting a lot of stills. The shutter vibration would definitely also be a factor at 4000mm...not to mention you get to choose the best shot from hundreds or thousands of frames of video. Nice job! I personally would have sifted out some of the deep aqua sky saturation, whether you think you remember it looking like that to your eye, or not...Also the moon has some subtle yet rich browns and olive green hues if you push its saturation...