extenders?


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#1
Hi all,

wanna check with you all about extenders?

i was looking at the canon 1.4x II extender, and i was thinking how does it work?

do i just attach it to the front of the lens and have my focal length extended by 1.4 times?

and if i'm using a dslr of 1.6 crop, does it mean that i will double my focal length???

and will using a extender decrease the lens IQ? or increase vigineting?

thanks alot guys!
 

lennyl

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Mar 27, 2008
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#2
do i just attach it to the front of the lens and have my focal length extended by 1.4 times?

and if i'm using a dslr of 1.6 crop, does it mean that i will double my focal length???

and will using a extender decrease the lens IQ? or increase vigineting?
It goes between your lens and camera body. It multiplies your focal length by 1.4x (or 2x for the 2x extender, obviously).

The 1.4x also reduces your light by 1 stop. If you have a f/5.6 aperture lens, that now becomes a f/8 lens, and you will not be able to auto-focus except with 1 series body. The 2x reduces light by 2 stops.

The extender is not compatible with all lenses. Check compatibility first. Kenko is supposed to have extenders that work with EF-S lenses.

You multiply the crop factor with the extender's multipler to give equivalent FOV, not add. So it's 2.24x.

Somewhat off topic :

1.6 crop cameras do not increase your focal length, the focal length remains unchanged - it gives you a FOV that appears to be equivalent from a lens with 1.6 times the focal length, but your DOF remains unchanged. But if you really want to think of it that way, with a 1.4x extender on a 1.6x crop body, your FOV will be similar to a lens 1.6 * 1.4 = 2.24x the focal length of same lens on a full frame camera.
 

GavinTing

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Oct 16, 2007
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#3
You multiply the crop factor with the extender's multipler to give equivalent FOV, not add. So it's 2.24x.

Somewhat off topic :

1.6 crop cameras do not increase your focal length, the focal length remains unchanged - it gives you a FOV that appears to be equivalent from a lens with 1.6 times the focal length, but your DOF remains unchanged. But if you really want to think of it that way, with a 1.4x extender on a 1.6x crop body, your FOV will be similar to a lens 1.6 * 1.4 = 2.24x the focal length of same lens on a full frame camera.
An easier way to see is for example, 50mm lens,

You will get 50 X 1.6 X 1.4 = 112mm
 

photobum

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Apr 17, 2005
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#6
ok...

so using a extender actually would give me 1 stop lesser huh?

so if i'm using a F4 constant?

what would happen?
1.4x = about 1.5 f-stops less.
2x = 2 f-stops less.

You do the calculations yourself.
 

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