TC & Sigma 120-400mm (Canon)

TheNissanMan

TheNissanMan

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Could someone please confirm my understanding of TC's and the ability to work with certain camera's lenses...

First one is a TC basically magnifies the current lens reach so a 1.4x TC on a 120-400 would give a maximum reach of 400x 1.4 (560mm) ?

Hoping thats right and I've got a basic grasp next set of Q's...

A 1.4TC will drop the F by 1 4=5.6 5.6-8????? This is where I'm really flaky (can you tell yet :D )

Certain cameras can only use AF up to a certain point so on different cameras (thinking about 450D and 500D here) at a certain zoom lenght the AF would stop working and you'ld be required to use manual focus???

If my thinking is right (albeit the explanations awful) and someone here understands what I'm trying to say on the 450D and 500D how far can you go with a 1.4x TC before losing AF ?

Many thanks for your patience reading this and hope your brains aren't hurting as much as mine this week :shrug:
 
TheNissanMan said:
First one is a TC basically magnifies the current lens reach so a 1.4x TC on a 120-400 would give a maximum reach of 400x 1.4 (560mm) ?

Hoping thats right and I've got a basic grasp next set of Q's...
Click to expand...

Correct, just multiply the focal length by the extender factor.

TheNissanMan said:
A 1.4TC will drop the F by 1 4=5.6 5.6-8????? This is where I'm really flaky (can you tell yet :D )
Click to expand...

Again, essentially correct. You lose 1 stop of light, so the f5.6 becomes effectively f8. It's still actually f5.6 but the light hitting the sensor is the equivalent of f8. In reality it means that you shutter speed will drop 1 stop, or you will need to double your ISO setting to get the same result.

TheNissanMan said:
If my thinking is right (albeit the explanations awful) and someone here understands what I'm trying to say on the 450D and 500D how far can you go with a 1.4x TC before losing AF ?
Click to expand...

Your two cameras stop AF with lenses having max apertures >f5.6, so AF will not work on the 450D or 500D with the 1.4tc on your Sigma 120-400mm at the longer end. I am not sure at what point this lens changes to f5.6, so you will find that AF functions, say, between 120-300mm and then stops after that.

Hope my explanations help
 
Helps a great deal and I'm glad someone could understand what I was trying to say :D

Thanks for confirming what I thought to be the case :D
 
Brachytron said:
Your two cameras stop AF with lenses having max apertures >f5.6, so AF will not work on the 450D or 500D with the 1.4tc on your Sigma 120-400mm at the longer end. I am not sure at what point this lens changes to f5.6, so you will find that AF functions, say, between 120-300mm and then stops after that.

Hope my explanations help
Click to expand...

Not correct, this lens will only manual focus with a 1.4x or 2x TC fitted to a non 1D series camera body....

The 120-400mm f4.5-5.6 will become a 168-560mm f5.6-f8 lens with the 1.4x TC fitted and a 240-800mm f8-f11 with a 2x TC fitted, but both combinations will only manual focus, but to achieve better results, you would need to close the aperture down an f-stop or 2 to improve the image, but then you hit problems of small apertures and longer shutter times and getting the light to achieve these settings.

What are you trying to photograph as this will bare a significantly outcome on whether you'll get an image. If its a wildlife shot, perhaps read up on field craft, I think if you do a TP search, someone mentioned that on a recent thread by get closer to the subject, for sports, forget about it, you won't obtain suitable shutter speeds to get the shot with that lens and manual focusing.
 
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