70-200mm VS 120-300mm

Overread · Dec 26, 2011

So I currently have a fantastic Canon 70-200mm f2.8 IS L MII which is a great lens that I have no problems with at all; its so good I can push it to 400mm (with a 2*TC) and still get very good quality results from it.

However I've recently been looking at the new Sigma 120-300mm f2.8 OS lens as a cheaper (under half the price) option to get a 300mm lens that is capable of pushing to 600mm (with a 2*TC) and still deliver good quality results. I was originally going to push for a 300mm f2.8 IS L for this slot, but with the MII and price rises its price is not only very high (and thus time consuming to reach) but also now nearer to the other long primes (eg 500mm f4 or 400mm f2.8). Therefore I'm now very tempted to go for the Sigma, get a good quality lens and then push toward saving for a higher quality long lens (whilst having up to 600mm reach for a longer period of time).

However 70-200mm and 120-300mm share very similar focal lengths and whilst I've no complaints about the Canon (and whilst I respect that this is likely to be a situation where personal preference is strong) I'm curious as to if any here use a similar setup or share experience of making the same choice. I'd hate to end up with two lenses, of which one is simply not going to get used ever (I also won't lie that the temptation of selling the Canon is getting me a big part of the cost of the Sigma already saved up).

Derrel · Dec 26, 2011

The loss of TWO f/stops' worth of light with the 2x converter is the fly in the ointment that you just do not seem to be weighing into the equation...the loss of two f/stops will impede somewhat, the AF cpabilities on most Canon bodies that are in yuor curent price range...f/5.6 is "marginal" in terms of AF performance, especially under low-contrast subject matter, or lower-light situations. But...lower light situations--pretty much a "no-go" with a lens that is f/5.6 wide-open, and compromised at every single focal length by the 2x converter...

With the 2x on, the 120-300 is a 240mm f/5.6 with bad corners--soft, low-contrast, and with fall-off... at 200 it is a 400mm f/5.6....again...compromised...

You'd have better image quality with a CHEAP Nikkor 400mm f/5.6 ED for $650...you'd probably get better image quality with a 400mm f/3.5 ED-IF Nikkor...

Long focal length GREATLY exacerbates mirror slap, camera shake, and the one thing that OS, IS, and VR can NOT correct for: subject motion blurring....set the lens to f/5.6 and head out tomorrow, and see what kind of shutter speeds you can get at 400 ISO...you'll be at ISO 1,000 quite soon in the afternoon, around 3:45 PM I would wager...

Basically, what it boils down to is than an f/5.6 lens arrived at via use of a 2x converter has several optical issues...and the critical one is the loss of effective aperture...which leads to elevated ISO, slow shutter speeds, and then the problems creep in...subject was moving, image is blurred, even with OS...

If you have a 70-200, the NEXT lens you want is a 300mm f/4 prime lens. Period. TO THAT 300mm f/4 prime LENS, then add a 1.4x TC unit, for a 420mm f/5.6 that has better image quality than any zoom will have. ANd the 300/4+TC 1.4x will be what? Five pounds lighter than a 120-300/2.8? Also, keep in mind, the Sigma 120-300/2.8's earlier incarnation was NOT 300mm...it was "short"...not sure how this new, re-designed optical formula and build is in terms of measured focal length at the long end...but I think it is a mistake to think of it as a very effective "penalty-free" long tele with the 2x added. You'd probably be better off using a 1.4x, and cropping to make up the difference. Just the extra shutter speed from a 1.4x instead of a 2x would be worthwhile on many subjects.

Overread · Dec 26, 2011

True AF will take a hit, I've got a 7D at present so whilst it does indeed take a hit I really can't improve on that without hitting the 1D line of bodies (a second hand 1DMIII might be better though I'm unsure, plus I'd rather not invest any more into bodies at this stage).
I would also have ended up with f5.6 even with the 300mm f2.8 prime lens - indeed at 600mm the prime itself is an f5.6 and one step below is the 500mm f4 - which with a 1.4TC again is hitting the f5.6 aperture. Far as I know the only way to beat that is with the 200-500mm f2.8 from sigma - and that only gains one stop.

The point on the focal length is something that is a consideration, though I think the sigma does hit a true 300mm, but only at long focus settings; when focused closer its focal length at the long end does appear to reduce compared to its stated length.

On the ED front if I head that way I lose all AF with a converted Nikon lens - whilst the optics would be superior there would be a problem with the total AF loss on the setup. I certainly don't view the 120-300mm as a lens that won't lose quality with a 2*TC, even the 70-200mm loses quality; but if the results are usable (100-400mm type usable) then its a hit I would be prepared to take whilst saving serious money for one of the longest options; whilst allowing me to have access to a longer reach much faster.

It is a tricky choice, and whilst I'm researching I'm not fully sold on the idea; though I honestly can't test out the lens options until I've at least the funds to make a purchase (no point testing much longer before in a shop and I don't know any locals with those lens options).