View Full Version : Teleconverter question
I have Canon 7D camera
I have a 1.4 and 2 x Kenko Teleconverter and when i put them on the 70-200 f2.8 i loose 1 stop and 2 stops as i knew i would. (i've had them several years)
I put the 24-105 F4 with the converter on the other day (first time) (i'm going on a cruise next month and want to keep the weight down and am thinking of leaving the 70-200 behind)
but i didn't loose anything in f stops - i still get F4 with both converters - the focussing slows but i still get maximum aperture.
But i don't know why ?? any suggestions ?
Xenedis
02-01-2012, 2:32pm
I suspect that there isn't communication between the Kenko TC and the camera to indicate the actual f/stop.
The light reduction is a property of increasing the focal length, so even though your camera still reports f/4, you'll find that in reality you're at f/5.6.
As a simple experiment, take a photo with the lens natively at f/5.6, and then take an identical picture with the TC attached and the lens opened to f/4.
You should find that the exposures are more or less identical.
ameerat42
02-01-2012, 2:50pm
Even easier: meter a (uniformly illuminated) subject with and without the teleconverter both times while in Aperture priority mode (and obviously without changing ISO). Does the shutter speed increase/decrease 1 stop, ie, go from, say, 1/250s (without tc) to 1/125s(with tc)?
If it does, then the camera is not reporting the right f-stop.
etherial
02-01-2012, 4:03pm
I didn't think the 24-105 was compatible with teleconverters? Be careful you don't damage the lens!
Xenedis
02-01-2012, 4:08pm
I didn't think the 24-105 was compatible with teleconverters? Be careful you don't damage the lens!
It's certainly not compatible with Canon tele-converters.
I'm not familiar with the third-party offerings.
Bennymiata
02-01-2012, 5:28pm
I have the Kenko Pro 300 2X converter and it fits on my 24-105, but it won't autofocus, but it still works well with my 60D.
I mainly use the converter on my 100-400 to take shots of the moon and other far-away subjects, but it will even fit on my Tokina 11-16.
The Kenko doesn't have any glass sticking out the front of, in fact, the glass is recessed by around 5mm from the front face, so i think almost any lens will fit except for EF-S lenses which have elements sticking out behind the main body of the lens.
I haven't tried any other converters, but I'm very happy with the Kenko, and the price is pretty good too in comparison to others I've seen.
jeffde
03-01-2012, 12:34pm
Thanks guys for your replies - did the test as suggested and you are right shutter speed decreased - therefore aperture is NOT reporting correctly - so i think its best not to use the teleconverter...
Cheers and thanks
Jeff
(PS : such a simple solution - slapping myself for not trying that first ...) LOL
Xenedis
03-01-2012, 4:17pm
Thanks guys for your replies - did the test as suggested and you are right shutter speed decreased - therefore aperture is NOT reporting correctly - so i think its best not to use the teleconverter...
You can still use it if you need the reach; you just need to be mindful to add +1EV to your exposure to compensate for the light reduction.
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