Longer reach.

I am trying to decide weather to go with a 100-400L or add a keno 1.4x dgx TC for my 70-300. I do not need the extra reach to often, just on occasion when I am plane spotting at some of the vantage points at jfk. Any opinions or other ideas. Do not need a fast lens, only spot with good light.

You'd lose AF at the long end with the TC and 70-300, unless shooting with a 1d series body...don't know if that breaks the tie or not.

I tried it out, in very good light, it will AF at 5.6 at 300mm.

I have a 70-300L and bought the Kenko pro300 DGX 1.4x to use at a mid-power rocket launch. With the Kenko against a medium target (for example, a two stage 25' long rocket @ 2/5 of a mile from the pad) I had trouble with autofocus -- I'm shooting a 40D, perhaps your 60D would do better, and maybe a 7D even moreso -- my problem may have also been technique for this type of target with a lens combo that probably shouldn't allow autofocus to work (@300mm+TC = f8 wide open) -- I found myself switching to manual focusing on several of the launches. This was especially true as the rocket climbed to 10,000 feet and started deploying payloads. I shot some stunning photos this weekend using that combo -- I also had the IS on mode 2 settings -- the IQ of the "L" is outstanding and the TC didn't knock off too much sharpness -- I intend to "play" more with focus settings and techniques to avoid the focus searches when focus was lost -- I'm certain this combo can do better -- the results were worth it.

shoturtle wrote in post #12865557
I tried it out, in very good light, it will AF at 5.6 at 300mm.

If you have a TC that works that way, I'm surprised; but I'd go that route if you don't use it very often. But, I much prefer 'native' lenses, myself, to TCs; at least when discussing zoom lenses. There's too much variation across the zoom range for me to be comfortable with getting consistent results from a TC.

They're great for pairing with high quality primes, but I'm not overly sold on them for zooms.

shoturtle wrote in post #12865462
I am trying to decide weather to go with a 100-400L or add a keno 1.4x dgx TC for my 70-300. I do not need the extra reach to often, just on occasion when I am plane spotting at some of the vantage points at jfk. Any opinions or other ideas. Do not need a fast lens, only spot with good light.

the 100-400 would certainly give better image quality and better AF

if you don't use it very often, and light isn't a factor you could look at some of the sigma telephoto zoom offerings...the old bigma did well if you can get by without OS...and it's cheap for 500mm...there's also the sigma 150-500OS...which is also quite cheaper than the 100-400L...

i don't know if your 70-300 is the L or just the IS version...if it's just the IS then the sigma will offer better image quality than the canon

the-digital-picture.com discusses this in many of his reviews.

From what I understand, The best 400mm IQ and AF performance comes from the 400mm f/5.6 L (assuming we are only talking about lenses in this price range). But you don't need 400mm very often so it would be kind of silly to buy a 400mm prime. The 100-400 comes next followed by the 300 f/4L IS +1.4x tc. The 300 is faster and has better IQ at 300mm, but sgain, since you don't need the longer reach very often, the zoom makes more since.

I think Sigma used to make a 100-300 f/4 that is supposed to have pretty good IQ. If you paired that with a tc you could get to 400mm and retain AF (I think). This might be a more affordable alternative to the 100-400.

Having said all of that, the 100-400 seems like your best bet. I was in love with this lens for awhile and then fell out, kind of waited for its replacement, and am staring to lust for it again. They pop up here used pretty frequently. Buy one, try it, and if you don't like it, sell it.

another thought is that if you know you're not going to use the longer range that often is to look at a 70-200f2.8 to replace your 70-300mm, and then get a TC for when you need the extra length...