Canon 100-400L: can it be used with a Canon 2x extender?

If it can, please let me know, in your experience, the pro's and con's of its use.

Also, what about the extender's use with a 7D or a 5DIII?

Someone may correct me, but my understanding & use has found a 2X will have no AF with a lenses slower than f/2.8.

.....unless fitted to a 1 series, 5D3 or 7D2. With these, a 2x will focus on a suitable f4 lens. (but performance is hit)

tvphotog wrote in post #17352586
If it can, please let me know, in your experience, the pro's and con's of its use.

Also, what about the extender's use with a 7D or a 5DIII?

The pro is that you get your subject over more pixels, for better sampling of the subject.

The cons are that you get a darker viewfinder, and lose AF speed or accuracy, or lose AF completely. AF will work in live view, but will be very slow.

If you like proper sampling, and don't mind MF or slow live view AF, it's a plus. If you like the illusory benefit of sharp pixels at 100% pixel view, and need fast, reliable AF, then you're going to be very disappointed.

Is the soft focus an absolute, or can you cope by using smaller apertures?

tvphotog wrote in post #17353050
Is the soft focus an absolute, or can you cope by using smaller apertures?

I'm just saying that the original 100-400 isn't sharp enough that magnifying it 2x is going to give pixel-sharp results, at least not with small pixels. The "sweet spot" is the same physical aperture both with and without the TC, so if it is f/8 without the TC, it is f/16 with a 2x. If you are shooting an original 4MP 1D or a 3.1MP D30, then it still might be fairly pixel-sharp with the 2x.

It might be more info than you are asking for here, but it is my belief that pixels should be small enough or enough TC magnification is used so that sharp pixels are impossible, because it is impossible for a camera to record pixel-sharp without also recording unnatural artifacts and fake details.

The old 100-400mm never had outstanding performance with the 1.4X, I don't believe the 2X would work out well with this zoom.

I've got the 100-400 microadjusted. How will the extender read? Will the camera still see it as the 100-400, or as the extender and set up new parameters for it?

Passerby shot with 7D2 + 100-400 II + 2xTC III from about 60 meters away.

LV focus and gimbal head mounted.

tvphotog wrote in post #17355637
I've got the 100-400 microadjusted. How will the extender read? Will the camera still see it as the 100-400, or as the extender and set up new parameters for it?

The camera will see it as a separate entity, so you will need to give it new parameters.

I'm going to give it a try. I've had great success with my 100-400, and I'll play with the extender for a while. Thanks for all the input.

For anyone interested, here's the comparison. TOP IMAGE with 2x III extender; BOTTOM IMAGE without.

7D, 100-400L I (microadjusted at both extremes), 2x extender III, tripod, mirror up, cable release. Focus was AF without the 2x, manual with. I halved the distance when shooting without the extender. ISO 400. RAW files untouched, 100% crop, converted to JPEG to upload. No microadjustments made.

The images with the extender lack a little contrast and are soft, but the focus is on. I found I could increase the contrast in PS, but increasing sharpness increased noise. Wondering if I could do even better with microadjustment. I'm sure both images will be sharper with the new 100-400.

What I noticed was that the focus ring was pretty herky-jerky with double the magnification; It took me about 4-5 takes using MF to get the best one you see below, and 1-2 takes using AF without the extender. I wonder if focus with the new lens is smoother.

The bottom line for me is that this is a keeper. I'll use mainly for animals and birds, and hope that they're in the sun most of the time!

This is with a little Camera Raw and PS editing for brightness contrast. Can you tell which is with the 2X and which is without?

nightcat wrote in post #17353301
The old 100-400mm never had outstanding performance with the 1.4X, I don't believe the 2X would work out well with this zoom.

That was also my experience until I paired my old 100-400 with the 1.4 III TC and a 1Dx. That combo is working extremely well for me.