May be a stupid question...

Mr. Fish

Mr. Fish

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Rob
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Yes
..but..ive never used a teleconverter before, and have just bought one to go along with my 300 2.8. (canon 1.4x II). i hear people say that youll loose a stop of light with the converter so itll make it a 420mm f4 etc. When on my camera the body still displays f/2.8. So im guessing it doesnt stop the lens going down to 2.8, its the light the sensor is getting is just effectively what it would be at f/4 without the converter if you follow me haha? is that correct?

Cheers!
 
Your camera is cleverer than you give it credit for :) The camera will show that the lowest aperture available will become F/4. That's certainly how it works on mine anyway.
 
Mine works the same as Graham's, when I've got the TC on with my 70-200 2.8 I can only dial it to f4 on the camera. With any of my lenses I can only get to 1 stop from maximum ie. f5.6 on 24-105 f4 or f8 on 100-400 at 400.
 
Hmm yea that's what I thought would happen..will have to try different lens and body combo to see what happens.. This was on a 1dmk3 and 300 2.8L + 1.4xII ...anyone else had this with a 1D?
 
Yea was secondhand so will check that later thanks!

Why would it be done? Apart from the obvious..is it bad/possibly damage anything?
 
You can conceal the presence of the TC from the camera by covering three of the pins with a bit of sticky tape. That way the camera has no knowledge that you've lost a stop on the aperture. This means that with an f/5.6 lens, plus TC, which should give you f/8, the camera just sees an f/5.6 lens and will allow AF to be attempted on all bodies and all AF points. It's the kind of thing people will try when using something like the 100-400 or 400/5.6L and trying to get a bit more reach for wildlife etc.. Sometimes it's successful and sometimes futile.

As you have an f/2.8 lens I would definitely remove the tape so that you get accurate EXIF data and the AF system continues to operate to spec as intended.

Picture of tape over pins here - http://forums.dpreview.com/forums/read.asp?forum=1029&message=16094506
 
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I thought of that just after I made the earlier post. I've had a 2x and 1.4x TC and both have only been 8 pin versions (which I don't think you can tape) but the 11 pin versions can be, but it slows AF a lot. Glad you've got it sorted.
 
With an f/2.8 lens (or faster) the camera will take advantage of that to use high precision focus sensors. If the camera thinks it is getting an f/2.8 quality of image data, but the addition of the TC reduces the data quality to only f/4 I would imagine that could throw off the AF performance. Better to let the camera know it has an f/4 lens/TC combination attached and to work within its intended design parameters rather than beyond them.

There's also the consideration that the addition of a TC can alter the AF calibration accuracy. If you have a camera with AF microadjustment it might be worth a double check that the focusing is accurate, if you have any doubts.
 
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