100-400L with TC 2x

Just got a Canon TC 2x for use with 100-400 L IS USM, mainly for Moon shots. AF is gone with this combination. I can live with manual focus but was wondering is there any way around this?

Here's a shot I took last night with my 100-400 and Kenko 1.4X teleconverter. With that combination you can tape over some pins to hide the teleconverter from the camera so that it will continue to (try) to autofocus, but with a 2X teleconverter you may as well forget it. At f/5.6 plus a 2X teleconverter you will effectively be at f/11 and the AF will be hopeless, even if you could get it to try to function.

This was shot with my 40D using manual focus and 10X Live View. This is a crop, reproduced at 50% size.

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Thanks for that Tim. I had figured AF was not an option, so will adapt to MF for these shots. Am looking forward to trying lunar shot when it next appears!

Pixels wrote in post #6340776
Thanks for that Tim. I had figured AF was not an option, so will adapt to MF for these shots. Am looking forward to trying lunar shot when it next appears!

is AF important for a shot like this?

ed rader

In my limited experience, no.

I taped the pins on my Kenko 2x and snapped off some shots with AF, there are some samples in this archive.

https://photography-on-the.net/forum/showthre​ad.php?t=529692

ed rader wrote in post #6340863
is AF important for a shot like this?

ed rader

No. My query was relating to use of TC generally.

The pro bodies (1 series) are designed to work with lenses having apertures of f/8 or faster, but I think f/8 is only OK on some AF points (not certain about that). The non-pro bodies are only designed to work with lenses having apertures of f/5.6 or faster.

If you stick a 1.4X teleconverter onto a lens you lose 1 stop on the aperture...

- f/4 becomes f/5.6
- f/5.6 becomes f/8
- f/8 becomes f/11

If you stick a 2X converter onto a lens you lose 2 stops on the aperture....

- f/4 becomes f/8
- f/5.6 becomes f/11
- f/8 becomes f/16

The cameras are designed to cease AF function if they think a lens has been mounted that exceeds the AF design limits. You can fool the camera by taping certain pins so it is unaware of the teleconverter and blindly continues to attempt AF function. It may work. It may not. But you can be sure that AF performance will be reduced. Pushing your luck 2 stops beyond the design parameters, I would guess, is simply not going to deliver results you can use, even if you tell lies to the camera about the effective aperture in use.

You might get an f/5.6 lens + 2X teleconverter to work on a 1 series body, if you tape the pins, but never (I imagine) on a 5 or 350D.

curious - whats the difference between a 5.6 lens in low light, and an f8 lens in bright light? Is there a reason there is a particular limit to the max. aperture for focusing and not simply an available light limit?

It's not about the brightness of the light. It's about the angles from which the light hits the focus points and the phase differences that result when things are not focused correctly. The larger the aperture the broader the spread of angles from which the light is focused onto the AF points. While good light is important, and good contrast, you still need enough phase differential for the AF to calculate where things need to be moved to. The smaller you make the aperture the smaller the phase difference becomes and the less data the AF has to work with.

Canon has decided that rather than give you crappy AF performance, and have people complaining that the AF was poor, they have set a specification threshold to ensure good performance under a wide ange of lighting conditions, and would rather give you no AF at all if you exceed that threshold. As annoying as that may be for some of us, some of the time, it makes things a lot simpler for Canon and avoids pointless support calls when people expect more from their camera than they were designed to deliver.

been thinking of this combo, with this in mind:

using a 100-400L + any T/C, means that your best shots would be of those that are stationary? I imagine that if i wanted extra reach for birding/sports photography, i'm better off buying a longer prime lens? (i.e. 500mm, 600mm?)

The 100-400 with the 2x TC will give you pretty lousy results - irrespective of the AF (which won;t work of course). I use my 100-400 with a 1.4 and the result is OK, but with the 2x TC the quality is just too bad.

5Dmaniac wrote in post #6692069
The 100-400 with the 2x TC will give you pretty lousy results - irrespective of the AF (which won;t work of course). I use my 100-400 with a 1.4 and the result is OK, but with the 2x TC the quality is just too bad.

Completely depends on your body, and the quality of both the 100-400, the TC, and how well adjusted this combo is to the body. The blanket statement here is not always the case. And again, regarding the working AF, depends on the TC and body.

5Dmaniac wrote in post #6692069
The 100-400 with the 2x TC will give you pretty lousy results - irrespective of the AF (which won;t work of course). I use my 100-400 with a 1.4 and the result is OK, but with the 2x TC the quality is just too bad.

i've never tried the 2x TC on my 100-400L but i have tried the 1.4 combo and it's not something i will use.

ed rader

ed rader wrote in post #6340863
is AF important for a shot like this?

ed rader

Well, the moon is moving very quickly....

Thats sarcasm for people who missed it.