I get bored with the never ending bigger megapixels vs. more megapixels war.
So, I thought I'd ask a new question that could start up a different battle for a change. Seriously though, I would like hear some informed opinions on this.
In practice, is there a diminishing return on focal length and if so, at what focal length would most people consider that diminishing return to occur?
Let me explain: As a user who is not an engineer, my experience has been that there are big gains in reach at the mid-range of telephotos. (Going from a 135mm to a 200mm feels like a big jump and going from 200mm to 300 also feels like a big jump. Going from 200 to 400 is huge.)
But, it seems like at some point, the gain in reach from a longer lens doesn't really offset the downsides of size, weight, speed, cost, etc.
I'm not talking about professional sports or wildlife shooters, but rather, for us mere mortals who have to pay for the equipment ourselves and can't charge it off to a client base.
Of course, ISO speed enters into this as well. Shoot with a shorter lens at a lower ISO and crop, or use a longer lens and a higher ISO?
Telephotos are often described by angle of view and the gains in angle of view get incrementally smaller as the lens gets longer. Is it really worth shaving a couple of degrees off the angle of view? What's that really mean in practice?
And, of course, there is the whole issue of APS-C crops. Since a 200mm feels like a 320mm and a 300 feels like a 480mm on a 1.6 crop sensor, how does that affect the trade off at the long end.
I got the idea for the question while reading the discussion board on the Sigma 50-500 and wondering, with my 7D the Canon 100-400 scales out to 640mm, while the "Bigma" scales out to 800mm. But really, what does that mean in practical terms? Would that extra 160mm really be noticeable at those lengths?
Just offering this up as new point of discussion while we all wait for news from Japan.