Canon Extender EF 2x II >> no AF with 180 macro

[ymages]

I got today a new Canon Extender EF 2x II and the Auto Focus doesnt

work on the 180 L macro !, I have an old 180 does it work with the new

one ?

 

thank you

[jespdj]

That's normal.

 

The Canon 180mm macro is an f/3.5 lens. The 2x extender takes away 2 stops of light, so this makes it an f/6.3 lens.

 

What camera do you have? Non-1-series cameras can only AF upto f/5.6. If your lens is less bright than f/5.6, AF is automatically disabled. (1-series cameras AF upto f/8).

[mark u]

No. Look at the table on the right hand side here:

 

http://consumer.usa.canon.com/app/pdf/lens/EFLensChart.pdf

 

In any event, AF is often undesirable with macro work, since the chance of the point of the image that you wish to be sharpest lying under a focus point is small unless you are using a 45 point AF system (and even then there is plenty of room for the AF system to focus on the "wrong" thing), and any re-composing will throw focus off significantly.

[athinkle]

yeah, what everyone else says. Just thought I'd add that the EOS 3 can AF down to f8 as well. IT's the only non-1 series camera that can do so, to the best of my knowledge. However, as was said previously, at high magnification it's desirable (some would say necessary) to focus manually. Get a sturdy monopod if you have to be moving around, otherwise attach the whole setup to a sturdy tripod and take your time focusing.

[mark_chappell]

As others have said, AF will only work with the 180 macro on a recent or current 1-series

camera or an EOS-3, all of which can AF with a maximum aperture of f8. All other Canon

SLRs and DSLRs are limited to AF at maximum apertures of f5.6. I'm not sure what happens

to the aperture of the 180 as you focus closer; it has internal focus so it might not change

much (or at all).<P>

 

<I>The 2x extender takes away 2 stops of light, so this makes it an f/6.3 lens.</i><P>

 

Not quite: it's an f7 lens combination (2 X 3.5 =7)

[mark u]

I don't think the 180+2xTC will AF even on a 1 series body - unless you use a 3rd party TC. Canon specifically say it doesn't. The reason it is disabled is that the effective aperture for macro work is actually much smaller than the aperture at infinity focus. Another <=f/8 combination that doesn't work is the 2xTC on the 400mm f/4 DO.

[ymages]

I have a 5D and a 20D

 

thank you for your answers

[ymages]

and of course AF even for macro is usefull

[jack_rabin]

Erick. The 180 f/3.5L will not auto focus below 80cm with even the 1.4xTC with all Canon

bodies. It's in the 180L manual. Since I use this lens below 80cm most of the time, I am

manually focusing most of the time.

So, with a 2xTC, you probably do lose auto focus all together. It is related to the design of

the optics as much as the loss of light. I imagine Canon designs it that way to prevent the

camera body and lenses combo fro "trying" to focus, because the engineers know there

would be focus errors intolerable in macro work. It's a "feature," not a flaw.

 

The 180 f/3.5L is a little unique because it loses "only" 1 1/3 effective f/stops when at 1:1

close focus, instead of 2 f/stops like most macro lenses at 1:1. Thus, the amount of light

available for auto focus is the same as an f/2.8 lens at 1:1 close focus.

 

Jack

[mark_chappell]

<I>Another <=f/8 combination that doesn't work is the 2xTC on the 400mm f/4 DO.</i>

<P>

 

 

According to Art Morris, the 400/4 DO <B>does</b> autofocus accurately with the 2X

extender:<P>

http://www.birdsasart.com/bn86.htm<P>

(scroll down a bit to get to the section on the 400 DO). Here's a quote: <I>" Autofocus

with the 2X is very accurate, but predictably slower than with either the prime lens alone

or the 1.4X TC."</i>

[ymages]

Jack I was a 3 meters

 

and for exemple on the new 24-105 f/4 AF works perfectly

[jobo1]

Look in the left sidebar of

http://www.digiscoped.com/teleconverters.html

2c, /J