Buying an extender but not sure what to get?

I am wanting to try out an extender. My issue is I'm not sure if the extra reach of the 2x is worth losing more light to the lens?

I am also wondering, since I probably won't use it much, if there is much difference between version 2 and version 3?

I will be using this mainly on my 70-200 2.8 but will also give it a go on the 100-400.

why wouldn't you just use your 100-400L instead of putting an extender on your 70-200mm to make it a 140-400mm?

I have a 100-400 and rented a 1.4x III converter. My 5DIII maintained autofocus for the center point only but your 6D will lose AF completely. The 1.4x TC costs sharpness. The 2.0x would be even worse. In fact, shots without the TC looked better after cropping than shots with the TC.

DreDaze wrote in post #17080252
why wouldn't you just use your 100-400L instead of putting an extender on your 70-200mm to make it a 140-400mm?

That is a very good question......

For one, I like the 70-200mm for a general carry around.
Two.. I had a Sigma 50-150mm and like the range on my crop body (240mm equiv.)for my nephews soccer games. I'm sure the 200mm would work but if I added the 1.4X to it, then I would be back a little better than what I had as far as reach and it would only be an f4 with the 1.4x on it.
If I jump into the 2X extender then yes, I guess it's pointless to use on the 70-200 when its about the same as the 100-400. BUT, I would like to have the 800mm for moon shots so that's why I'm torn.

I just need to buy the 4200mm f1.2 IS L lens and be done..

I wouldn't do it. I use extenders quite a bit, but I don't have a 100-400. I rarely use the 2X on my 70-200, mostly when I don't want to bring my 500 I'll have the 2X to use on the 70-200.
While the 2X III performs well on my 70-200 I doubt you would see a noticeable benefit compared to your 100-400.

I had the 1.4XII and 2XIII for the 70-200II. Both were fine, but AF and IQ took a hit and the combo is huge. I ended up buying a 100-400 to use instead of the 70-200 with extender. IMO, keep what you have as it covers 70-400 very well. If you want to do moon shots, crop at 400mm.

Tapeman wrote in post #17080464
I wouldn't do it. I use extenders quite a bit, but I don't have a 100-400. I rarely use the 2X on my 70-200, mostly when I don't want to bring my 500 I'll have the 2X to use on the 70-200.
While the 2X III performs well on my 70-200 I doubt you would see a noticeable benefit compared to your 100-400.

I appreciate both replies! Maybe I will step back and rethink this...

For the relative costs of new extenders, why not pick up a used 7D instead? It's essentially a 1.6x extender that isn't going to lose a stop or two of light or slow down the AF at all for a fairly similar price.

Frankly, your best bet would be to buy a crop sensor camera and use your 100-400mm on it. That would give you better image quality and better performance than any available teleconverter combined with either of your lenses.

Using one of the cropper cameras is like having a "free" 1.6X TC on your lens... no loss of light slowing or defeating autofocus (your 100-400mm with any 2X added becomes and effective 800mm f11 lens that will not autofocus on your 6D). Your 100-400mm on a 70D or 60D or 7D would perform like a 160-640mm f4-5-5.6 lens would on your 6D.

I also agree it makes little sense to use a 2X on a 70-200/2.8 II, when you already have a 100-400mm lens. You'll end up at exactly the same place, but with lower image quality.

70-200/2.8 Mark II reportedly works pretty well with Canon 2X Mark III. Some people are happy with it, others are not. I wouldn't expect as good image quality with 2X Mark II TC on that lens... And I won't use a 2X at all on 70-200/2.8 Mark I, due to too much loss of IQ.

EDIT: great minds think alike... I just saw Lloydd's response.

Well...I just sold my 60D. Then I bought the 100-400.
Probably going to just work with it for now.

Please post some shots with the new 100-400
Like everyone said above, stay away from the teles for now and work with the glass you got.

reefvilla wrote in post #17080652
Well...I just sold my 60D. Then I bought the 100-400.
Probably going to just work with it for now.

It's easy to pick up a crop body for little money -- get a used one, or get the 100D/SL1 new for $500 -- 18 megapixels gives great pixel density which is what you want to increase your reach. Used 7D bodies are also going for cheap now.