100-400L/70-300L Decision

[ahab1372]

As far as I know, IS is the same, 4 stops with or without TC.
At 200mm w/o IS, recommended shutter speed is 1/200s, with 4 stop IS that comes down to 1/13s
At 280mm w/o IS, recommended shutter speed is 1/280s, with 4 stop IS that comes down to 1/18s

[clemmb]

Do you think it drops progressively with length?
Actually I have never seen an article or a discussion if a tele convertor affects IS.

I didn't know we were talking IS for subject movement, just low light situations.

While ahab1372 answered my questions in a logical manor, and he may be 100% right, I have to think the IS mechanism in the 70-200 lens is not designed to dampen out the shake at 280mm or 400mm as well. It would have to be over designed for that.
I was confusing this thread with a similar thread where the subject was going to be animals in Africa at dusk.

[HDNitehawk]

How do you know it is not designed for that, it is designed to be used with both tele convertors.

I just haven't seen anything that says otherwise, I would think someone would have tested this.

[ahab1372]

I'm actually almost sure I read it in one of Bryan's reviews - 4 stops is 4 stops, with or without TC. I haven't tested myself ...

[ahab1372]

from the Canon 2x TC review:
"

For example, a 2x extender (also commonly referred to as a teleconverter) makes a

Canon EF 70-200mm f/2.8 L IS II USM Lens

into a 140-400mm f/5.6 IS lens (yes, IS still functions normally on all compatible IS lenses)."