rthompson10 wrote:
...If one was "shorter" than the other does that limit my range. From what I've seen/read focusing to infinity(if I'm shooting sports shooting at 200) no difference
Thanks!
RT
That's right. Out in the real world, you would likely never notice the difference unless you happened put the lenses alongside each other, photograph a brick wall and then count the bricks.
It would be kind of a pain if they labelled lenses "73-196mm f2.965", or whatever "actual" numbers they delivered, wouldn't it?
If you look at the patents for lenses, where they exact focal length is listed, you'll find they are almost never exactly as labelled. Some websites that test lenses for in-depth reviews also give more exact numbers, that you might be able to find with a Google search.
JCII and other certification and testing institutes makes some allowance for this... so that designations can be rounded off to a sensible and relatively standardized number... tolerances of something like 5 or 10%, + or -. With some things it used to be much greater tolerances back in the days of mechanical cameras.... I don't know about focal lengths, but it was 25% + or - was considered acceptable for apertures, shutter speeds, metering. Today's electronically controlled cameras are held to much tighter standards. Maybe the lenses are, too. (Certainly, today's zooms are far, far better than the early ones in the 1960s and 70s.)
But, a lot of it doesn't really matter in the "real world".
I haven't used the particular lenses you ask about, so can't really compare them with each other from personal experience, or against the Tamron 70-200mm that you're using now, for that matter. I suspect you'll have a hard time finding anyone who has actually used all three.
I don't know if they have much commentary about these specific lenses, but Lensrentals.com is a source I like to check. Besides their brief notes in the rentals listings, they sometimes go into much greater detail in their blog. Not only do they have all the different lenses in stock, they also usually have multiple copies of any given lens, so might comment about variations from copy-to-copy if they see a lot of them. They test every lens when it's returned from a rental customer, to see if any service is needed, and have opportunity to see how the lenses hold up to hard use and frequency of repair. Plus they enjoy taking things apart, just to see what's inside!
dpreview.com is another good site, IMO, with in-depth analysis of and sample photos taken with many lenses.
The-digital-picture.com is yet another, with a lot of lab testing and sample shots of lens test targets at various apertures and focal lengths, that you can compare side-by-side with other lenses (if they have tested the particular lenses you want to compare... and they do appear to have all the 70-200s). A couple things concern me slightly about the comparisons on this site. First, they probably only test a single copy of any given lens, so are unlikely to address possible copy-to-copy variation. Also, the lenses are tested on various camera bodies.... an older lens might not have been re-tested on a newer camera... And, of course, Nikon lenses have to be tested on Nikon cameras.... Canon on Canon, etc. So, take these factors into account, when comparing lenses on the-digital-picture.com
70-200s are such important and widely popular lenses that there are a lot of very good ones. Virtually every camera and lens manufacturer makes one or more. Heck, Canon makes four different versions. Nikon has two. So does Tokina. And everyone has "refreshed and updated" their 70-200s a number of times, to really perfect them. The differences between them are pretty slight.
The difference really aren't all that significant, but the-digital-picture.com seems to show the Tamron 70-200/2.8 VC USD giving great contrast and sharpness wide open at 70mm... a little less so at 200mm. The Nikon 70-200/2.8 VR II appears to be the opposite, at it's wide open best at 200mm. The Canon 70-200/2.8 IS II appears to be the best of the bunch, at least matching the best of the others at both ends of the range, also with its aperture is wide open. Some reviewers have called it the best 70-200mm from anyone, ever. But, again, the differences between these lenses appear are pretty slight! (Note: I only quickly looked at the lenses at f2.8, and at 70mm and 200mm setting, because these extremes are likely where any of them would be at their "worst". You will probably want to compare at a lot more focal lengths and apertures.)
And there is a lot more to a lens, than just image quality. Ergonomics, autofocus speed and accuracy, durability and resistance to dust/moisture, size/weight/price and many other factors can make one or another stand out.
Likely one reason its images stand out a bit, might be because Canon's zoom is the only one of this group using a fluorite element in their 70-200. In fact, three of the four Canon 70-200s now being offered use FL elements, as do quite a few other Canon telephoto lenses. Fluorite helps minimize chromatic aberrations in telephotos. But naturally occurring fluorite crystals large enough for use in lenses are rare... and it can be fragile, difficult to shape into an optical element. So, some years ago Canon developed a means of "growing" fluorite themselves, for use in their lenses. As a result, more and more of their telephotos have used FL over the years and they are now able to use it relatively affordably. You can find FL in a $650 Canon 70-200/4 (non-IS), $1100 70-200/4 IS, $2000 70-200/2.8 IS II, or either of the 100-400mm versions ($1700 to $2100).... as well as in their $6000 to $12,000 super teles.
The other manufacturers simply don't (can't?) use FL as much. They use other specialty glass types, with more or less success trying to achieve the same results. In fact, to get a Nikon lens with a FL element, you have to spend at least $10,000 for a 500/4 super tele. They also use FL in premium priced 400/2.8, 600/4 and 800/5.6 primes. I don't know if any Tamron lenses use FL.