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Something New to Argue About

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unfocused:
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.

neuroanatomist:
At least in the Canon lineup, the logical break-point would seem to be 400mm (or 420 mm if you want to count the 300/4 + 1.4x).  You can get 'affordable' (a relative term, I know), primes and even a zoom out to 400mm, with very good IQ, as long as you're ok with an f/5.6 aperture at that length.  Once you get over 400mm (or faster than f/5.6, but the topic is focal length), the cost goes up dramatically - not many amateurs/hobbiests can afford >$7K for a lens.  There are some exceptions to this, one being people who don't mind (or even prefer) manual focus and can use longer, manual primes that are in the $2K range (used), like the Minolta MD 600mm f/6.3.

Lawliet:
About the practical terms: At longer focal lengths the resolution of the lens , the quality of the support and the clarity of the air are more important then 20-30% more fl. The more MP you have, the sooner the effect kicks in. :)

I wouldn't be surprised to get more details from an upsized crop of a picture taken with a 70-300L then from one taken with a Sigma50-500 non OS, at least with the shooting techniques usually used.

Regarding the numbers: don't think in mm, but in factors. Going from 85 to 135 to 200mm are 50% increases, from 400 to 500 only 25%, like zooming from 40 to 50mm. Sound less impressive then the additional apparent 160mm of the Sigma on a crop camera. ;)

unfocused:

--- Quote ---like zooming from 40 to 50mm
--- End quote ---

Great point. I hadn't thought about that comparison. Puts it into perspective.

Anyone disagree?

neuroanatomist:

--- Quote from: unfocused on April 01, 2011, 01:34:46 PM ---
--- Quote ---like zooming from 40 to 50mm
--- End quote ---

Great point. I hadn't thought about that comparison. Puts it into perspective.

Anyone disagree?

--- End quote ---

I disagree.  For a given subject, the perspective at 40-50mm is going to be very different from the perspective at 400-500mm... 
 :P

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