condor981
Topic Author
Posts: 9
Joined: Sun Mar 14, 2010 4:20 am

Confused With Key Technical Concept.

Mon Apr 19, 2010 1:56 am

Hello, I am having difficulty understanding some key technical concepts regarding lenses and apertures. I own a Canon lens EF- S 18-200mm f/3.5-5.6 IS. I was trying to understand if the autofocus will work on this lens if I attach a 2x II Canon extender magnifying accesory. On the Canon site it says it will provide autofocus if:

"With the EF 2x II, AF is possible with any EOS body if the lens has an f/2.8 or faster maximum aperture, and compatible Image Stabilization lenses maintain the IS feature when used with any current EOS camera. "

Can someone tell me if AF will work on my lens at all focal lengths if I get the 2x extender?

Thanks for the advice.
 
dlowwa
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RE: Confused With Key Technical Concept.

Mon Apr 19, 2010 3:41 am

I think you've answered your own question:

Quoting condor981 (Thread starter):
I own a Canon lens EF- S 18-200mm f/3.5-5.6 IS
Quoting condor981 (Thread starter):
With the EF 2x II, AF is possible with any EOS body if the lens has an f/2.8 or faster maximum aperture

You need f/2.8, you have f/3.5+ = no you can't use AF at any focal length, nor should you try a TC with that lens, you'd lose way too much light, and the quality would be terrible.
 
sovietjet
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RE: Confused With Key Technical Concept.

Mon Apr 19, 2010 6:26 am

So then how were these photos taken? It says 600mm + 2X and the 600mm is an F4 lens.


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Silver1SWA
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RE: Confused With Key Technical Concept.

Mon Apr 19, 2010 6:28 am

Quoting sovietjet (Reply 2):
So then how were these photos taken? It says 600mm + 2X and the 600mm is an F4 lens.

Manual focus?
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ua935
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RE: Confused With Key Technical Concept.

Mon Apr 19, 2010 6:31 am

"So then how were these photos taken? It says 600mm + 2X and the 600mm is an F4 lens."

I believe both phtogs concerned have EOS 1 Series bodies, you get AF to F8 with a 1 Series.

[Edited 2010-04-18 23:32:22]
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JRadier
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RE: Confused With Key Technical Concept.

Mon Apr 19, 2010 6:43 am

Besides the autofocus point, as far as I know the extender doesn't even fit on that lens. Another point is that you really don't want a marginal lens such as the 18-200 on a marginal extender like the 2x.....
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aviopic
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RE: Confused With Key Technical Concept.

Mon Apr 19, 2010 7:55 am

All Canon bodies apart from the 1D series require at least F5.6 for AF to work(F7.1 for a 1D) thus to retain AF with a 2.0 TC a F2.8 lens is needed or a F4.0 for a 1.4 TC.
This is not a technical limitation though but just decided by Canon for you who burned this limitation into the bodies operating software.
Tape the outer 2 contacts and you'll be fine although I personally wouldn't put a 2.0 TC inbetween body and a 18-200.
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JohnKrist
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RE: Confused With Key Technical Concept.

Mon Apr 19, 2010 8:44 am

Quoting JRadier (Reply 5):
Besides the autofocus point, as far as I know the extender doesn't even fit on that lens

That's correct, it will noy physically fit as part of the extender actually goes inside the lens. You can use a 3rd party extender on many lenses that can't take the Canon extender but then you will lose even more in quality. You'd be better off getting a 70-300IS which is not that much more money wise than an extender, and it has IS.
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condor981
Topic Author
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RE: Confused With Key Technical Concept.

Mon Apr 19, 2010 7:24 pm

Thanks a lot guys who responded. I will definetely not get the extender. I will most probably invest in a new lens, most probably the EF 100-400mm f/4.5-5.6 L IS USM. I have read great reviews about it. I am still trying to have my first picture accepted in this site, and I have to admit, its not easy at all!

Once again, thanks and keep shooting  
 
JakTrax
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RE: Confused With Key Technical Concept.

Mon Apr 19, 2010 8:57 pm

Quoting condor981 (Reply 8):
Thanks a lot guys who responded. I will definetely not get the extender. I will most probably invest in a new lens, most probably the EF 100-400mm f/4.5-5.6 L IS USM. I have read great reviews about it. I am still trying to have my first picture accepted in this site, and I have to admit, its not easy at all

Just remember, buying great lenses won't suddenly make your pictures ten times better. In fact, with a complex lens such as the 100-400L you may actually get disappointing results initially until you learn how to handle a long zoom. I recently bought Sigma's 100-300 F4 EX IF lens and although optically fantastic it took a few shoots to learn its strong and weak points. I still haven't quite mastered it yet and I have over 20 years experience behind me!

As for extenders, the general concensus is that you should steer clear of the 2x completely, as the drop in quality is just too steep. There are conflicting reports concerning the 1.4x - most agree however that the loss in quality is hardly noticeable unless you 'pixel-peep'. I guess it depends on how sharp your copy of the lens is and indeed how good a copy of the extender you've ended up with.

It's perhaps irrelevant anyway as I'm fairly sure neither extender is compatible with your lens. On a final note, I don't really know what the big deal is with losing AF - it's not like anyone is forcing you to use an extender. With the new manual focus modes available on the newer bodies manual can actually be more accurate!

Karl

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