70-200 f/4L IS + x2 extender vs 100-400/4.5-5.6L

DikkeryDok wrote:

I've had a lot of great moments captured with my trusty 70-300 DO, but recently got into bird (and occasionally wildlife) photography where 300 mm is barely enough and picture quality starts to deteriorate a bit. I had to crop almost every shot lately, and I don't really like it. Currently, I have two options:

1. Canon EF 100-400/4.5-5.6L IS USM (MkI)
2. Bundle of Canon EF 70-200 f/4 L IS USM (Also MkI) and Extender 2x II

Both choices are almost mint-condition with all respective accessories and equally priced. In theory, the first option is more universal, better available aperture selection, trombone zoom/focus which I adore and doesn't require spending additional money on tripod mount. Second option basically gives two lenses on a price of one, has better build and stabilizer, weather-proof but really lacks in available apertures. At a first glance, it's not that big of a problem, since for most wildlife photography the lens should be stepped down anyway. But in a long run... Who knows. Also, changing 2x for a more viable 1.4x is not an option. The other way it would be a no-brainer.

Thanks for advices in advance.

the native aperture wins every time! i wouldn't bother with a TC, especially a TC 2.0x on a 70-200 f4.0 IS, it is a beautiful lens and i'd leave it alone, IMO i owned one 70200 f4.0 IS in the past and it was my most favorite. it is alike a magic, never lets you down.

the 1st package, even the mk1 is a good lens and you can use TC 1.4 III very easily without noticing hit in IQ. for birding, i'd go easily with option #1.

good luck.