adding more zoom

I have a Canon 40D 17-85 IS + Canon 70-300 1:4-5.6 IS USM lens and want to get more zoom.
Can i get a canon Extension tube or ring that will fit the above equipment.

Cheers.
Eyesociety

Extension tubes effectively decrease the minimum focus distance and allow you to get closer to an object (for macro type work). You lose the ability to focus at distant objects.

I'm assuming that you want reach and not zoom range.

A teleconverter will multiply the focal length of the lens, effectively increasing the reach. However, they decrease the maximum aperture and generally degrade IQ and focus speed. If you use a teleconverter on the 70-300, you will lose the ability to AF, because your camera can't autofocus at f/8. I'm not sure if the 70-300 is officially supported by the Canon t-cons.

Your best is probably to look into a longer lens, but pretty much anything above 300mm isn't cheap.

It does look like i will have to spend some penny's then o well.

Thanks for the reply,

Eyesociety

You can use a cheaper Kenko 1.4x (1.5x) extension tube, but you will likely be using manual focus and need lots of light for a good shot.

Yes, "cheap" and "high image quality" go their separate ways once you're past 300mm!

tkbslc wrote in post #7666916
You can use a cheaper Kenko 1.4x (1.5x) extension tube, but you will likely be using manual focus and need lots of light for a good shot.

Your talking about teleconverters not extension tubes...there is a big difference. Teleconverters have optics in them, extension tubes do not.

bacchanal wrote in post #7666764
, because your camera can't autofocus at f/8.

? HUH ?

No auto focus at F8 on what camera?

BigAlz1 wrote in post #7667688
? HUH ?

No auto focus at F8 on what camera?

All except the 1D series. The f/8 limitation is when f/8 (or slower) is the MAXIMUM aperture, not just when you choose to set f/8 on an f/5.6 or faster lens.

Think this is what he ment, so for the new guy this should explain it a bit better.

Most Canon EOS bodies require that the final aperture of the lens be f5.6 or faster in order for autofocus to operate. Since a 1.4x TC cost you 1 stop of aperture and a 2x costs you 2, this means that for a lens to AF with a 1.4x TC it must start out at f4 or faster, and for it to AF with a 2x it must start out at f2.8 or faster.

add the fact that the autofocus is hapenning before the camera moves the lens' aperture blades for the picture. If the starting point is too dim, the body can not focus the image.

I believe if you are really desperate, you can use teleconverters and just tape the pins so that the body doesn't "see" it. It will focus slowly, but it still may focus. Obviously this isn't anywhere close to the intended function, so you would want to do a bit of reading and research before attempting this.

I imagine the quality of the images that would come out of that lens with TC would be pretty poor.