2X Tele Extender and auto exposure control

[ron31664876659]

<p>I shoot mostly land scape and wildlife photos with my 40D and a 70-200 F4 L IS lens. There has been much discussion about the lose of auto focus with the 2X extender, but no mention of the auto exposure feature with this set up. I can live with out the auto focus feature but exposure control could be a bit of a problem. Before I spend my money I need to know the facts on this set up.</p>

[craig_meddaugh]

<p>Auto exposure will work just fine. </p>

[JDMvW]

<p>Aperture priority works best, although all-manual is fine too. P sometimes works, sometimes overexposes, je ne sais pas pourquoi. Of course this is with manual stop-down of the lens or using it wide open--it will not stop-down automatically unless this is built in, in which case the AF would work too, most likely.</p>

[eric merrill]

<p>Your body will retain autoexposure with the teleconverter.</p>

<p>The teleconverter does not cause the loss of autofocus. What happens is that you lose light equivalent to 2 f-stops.</p>

<p>If you were using a f/2.8 lens, it would now be an effective f/5.6 lens in terms of exposure, and that would autofocus on the 40D. Your f/4 lens is treated like an f/8 lens. Only the 1 series can autofocus with a maximum aperture of f/8.</p>

<p>Before you spend your money on that setup, I would see if I could rent both the 1.4x and 2x. I have both. When used on the 300/4, the 2x produced results that were similiar to using the 1.4x and uprezzing in Photoshop. With the 300/2.8, the 2x is sharper than using the 1.4x and uprezzing. So I stuck with the 1.4x with the 300/4. I saw no need to lose autofocus if I were going to end up with the same image quality.</p>

<p>Eric</p>

[dcstep]

<p>The 7D will AF with a 2xTC on an f/4 lens, but not with a f/5.6, where even the 1.4x won't work with enough speed to shoot anything moving.</p>