Teleconverters and Apertures - THE LINK

[sonny_jet]

Hi,

I am sorry if this question has been asked before. I have a Canon 20D

+ 70-200 f2.8 L IS and a 1.4x Canon TC. Is it true that I cannot use

AUTOFOCUS at apertures greater (in number) than f5.6 ? I.e. I cannot

use AUTOFOCUS with the TC + lens at f8,11,16,22... ?

 

Also, I read somewhere that I will have to use the CENTRE FOCUS POINT

if I use this combination?

 

IS THIS ALL TRUE? IS there anything else as important as the above

issues that you think I should know?

 

Thank you

 

ps. Alot of people on here have been very helpful and I hope to have

some pictures up to show you wonderful people. As a result of your

help - I reckon it's the best way to thank you guys and gals.

[marymac]

The rule about apertures and TCs is based on the largest aperture possible when using the TC. So, with a 1.4 TC the 70-200 f2.8 will be an f/4 so autofocus will work fine, regardless of what aperture you are using. Only the max aperture matters so if the AF works at the max aperture (5.6 or less) then it will work on all the other apertures on the lens (f/8, 11, 16 etc). With a 2x teleconverter the 2.8 becomes a 5.6 so autofocus will still work. I use the center focus point all the time so I'm not sure if having a TC on it affects which points are available.

[mendonphoto]

Even if you have your picture taking aperture set to something smaller than f/5.6, the aperture is kept wide open during focus. Only when you press the shutter button does the aperture stop down.

[mark_chappell]

<I>I have a Canon 20D + 70-200 f2.8 L IS and a 1.4x Canon TC. Is it true that I cannot use

AUTOFOCUS at apertures greater (in number) than f5.6 ? I.e. I cannot use AUTOFOCUS with

the TC + lens at f8,11,16,22... ?</i><P>

 

As the others have said, the only aperture that matters is the MAXIMUM aperture, which will

be f4 with the combination you mention. AF will work nicely with the 20D out to a maximum

aperture of f5.6 -- so you could put a 2X converter on your 70-200/2.8 and it would

continue to AF.

[dk.]

The others already answered your question but I thought your name was neat and wanted to share a picture of mine with you. :o)

 

DK.<div></div>

[sonny_jet]

Hey ,

 

Thanks for clearing that up for me. You guys and gals are invaluable!

 

I also found this REALLY helpful article by this gentleman called BOB ATKINS (whose name also seems to be everywhere on this forum site) and it cleared up many things for me. So, thank you BOB too.

 

One last thing, I did a bit of deep thinking (v. uncommon for me) and is the reason why the TC do not work in autofocus mode above f5.6 (i.e f8,11 etc.) because it is too dark ?

 

By the way, DAVID KOENS - brilliant stuff! I took a look at your portfolio and WOW! Thanks for that injection of inspiration. By the way, I agree with you when you said on your profile that you don't like to edit your pictures in PS. I hate it too, but I guess I should probably learn some of it as it seems to be part and parcel with d-photography these days.

[dk.]

Thanks Sonny Jet. About PS I do the basics like sharpening you have too or your pictures will not look to good and sometimes I darken or lighten the picture too and I know a bit about cloning but I don't use that to much unless I have to much sensor dirt showing up in the picture etc that's about as much as I know. I just don't like spending to much time on my pictures that's another reason why I take them in jpeg too as raw is more work also, and besides I like to get it right the first time when I press the shutter button. But I am still learning and this is a good place to do that. :o) Thanks again. Take care.