pixNW
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astrolucida wrote:
PetKal wrote:
pixNW wrote:
How much difference is there in IQ between a 300 f4 IS with a 1.4x and the 400 5.6?
I have owned/tested two 400 f/5.6 and three 300 f/4 IS lenses. In that sample, the 400 f/5.6 was decidedly a sharper lens. Once you mount a TC on the 300 f/4 IS, the "sharpness distance" between the two increases even further.
A lot of people say that the 400f5.6L is clearly sharper than the 300f4L IS + 1.4x TC. However, photozone.de has actually measured that the 300+TC is sharper in the center (1796.5 lines per picture height) already wide open at f5.6 (vs the 1657 of the 400). Though losing in the corners about the same amount as winning in the center. And considering that the 300+TC is 420mm, that adds 5% more to the resolution, bringing it to an effective 1886 (with a fixed camera position)!
Thanks astrolucidia, very helpful post.
My own experience also support this, having tried a friend's 400f5.6L and owning a 300f4L IS + 1.4xTC myself. In fact, I don't ever hesitate to use my 300f4L IS with the 1.4x TC when the need arises. True, it does not take the TC as gracefully as the Sigma 300f2.8 EX DG or the 400f2.8L II, but still well enough for it not to be a real issue.
Though, as others have said, AF is clearly slower - although that has not prevented me from taking successful BIF images with the combination. In fact, with the 40D, more than 90% of blurred images are because I was not able to keep the focus point on the bird. When you follow a bird, AF only needs perform small adjustments all the time, so AF speed is actually not that big an issue. Only when you see a bird and quickly try to grab it, then AF speed really matters. Or when you lose the bird and need to recatch the focus.
The only place where the 400f5.6L clearly wins in image quality is astrophotography. Aberrations are almost unnoticeable throughout the image area (1.6x crop at least) while even the plain 300f4L IS shows oddly-shaped bright stars even in the center.
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