mpgxsvcd: Since when is an "aperture of F2.9-5.6 " considered "Fast"? If it was F2.0 all the way through that would be fast.
The difference between f/6.5 and f/5.6 is 26% less area - just a bit more than 1/3 of a stop (which would be 20%). The difference is also 14% less optical resolution, since any 16MP 1/2.3" sensor will be diffraction limited with any lens slower than ~f/2.4 (source: the calculator at http://www.cambridgeincolour.com/tutorials/diffraction-photography.htm)
qwertyasdf: DPreview, does the ball head give a tight lock, for lets say a 5DII plus a 16-35mm?!?
I do not think this is pointless. For travelers that go out for a whole day and only look forward to use a tripod at night, this makes absolutely perfect sense. It's simply not worth it to carry a tripod for 8 hours to take a few shots at the end of the day.For safety, I won't worry much, will the legs just snap and the camera crash to the ground?! Not a chance.Wind?! Might be a problem, it's so thin and probably very aerodynamic anyways.Needs a 10-sec timer to be steady? so be it.
I have one of these and occasionally use it with a Canon 40D /w Tamron 18-270 (original, non-PZD) while hiking. It works, marginally.
The legs won't snap, don't worry about that at all. However, you'll find that getting the ball head snug enough so that the camera doesn't repoint itself after you let go quite frustrating. This is especially true if you need to point it up or down, so the camera+lens's CG is out from under the ball head. For me, while hiking, the benefit of a lighter, smaller tripod outweighs this frustration.
I also wouldn't try to use it for multi-second exposures at night (or time lapse work) if there's much wind. It's stable, but it's not particularly rigid.
Ashley Pomeroy: I've always wondered if something could be done to beat the odd bokeh by replacing the secondary mirror with a partially-reflective lens of some description, and using software to do something clever with the results. Presumably it's nonsense - someone would have tried it already otherwise - but it does seem a shame that we can't all tote around pocket-sized 600mm lenses.
If you're OK with a crazy-slow lens, just put a lens cap on it with a circular cutout between the secondary lens and the edge.
There are some more exotic designs that offset the secondary mirror from the light path of the primary. Most of them are very slow designs (i.e. f/20) since they are used for telescopes and the aperture size is more critical to performance than focal length. Look up "schiefspiegler" and "yolo". This page claims that such a design can be made as fast as f/5.6: http://www.amsky.com/atm/telescopes/spscopes/spt.html
It'd be great if someone could bring one to market, especially if it could be made with autofocus and image stabilization. It'd sure be a weird looking lens though.