Difference between 70-200mm F2.8L with extender and 100-400mm f4.5-5.6L

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bombfrog

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As the title says really. I'm a beginner and don't really understand the difference.

I'm hiring a Canon 70-200mm F2.8L lens next week and am planning to hire the 100-400mm lens soon to compare the difference, but I wondered what's just stopping me from using the 70-200mm with a 2x extender?

That would give me up to 400mm reach and I know the aperture would decrease when adding the extender but only down to the same as the 100-400mm has by default anyway, right?

So... um... there must be a downside?
 
Generally a lens designed to be 100-400 will be of a better quality than a 70-200 and a converter. Even a very good 70-200...
Converters are a compromise - you sacrifice a stop or two of light and some (and in some cases quite a lot) of the image-quality in exchance for convenience, lightness and portability.
 
I knew that there was an aperture compromise when using a converter but seeing as the F4 has a smaller maximum aperture anyway I thought it might balance out.
 
Arkady said:
Generally a lens designed to be 100-400 will be of a better quality than a 70-200 and a converter. Even a very good 70-200...
Converters are a compromise - you sacrifice a stop or two of light and some (and in some cases quite a lot) of the image-quality in exchance for convenience, lightness and portability.
Click to expand...

That's true. Adding an extender/teleconverter always reduces quality (and light) but if the mother lens is very sharp to start with, it's either acceptable or even unnoticeable. Rule of thumb is if you have a longish L grade lens, then it will generally take a 1.4x without too much loss, but a 2x is asking too much and also the loss of two stops of light is too much in practical terms.

However, one or two lenses break this rule and the new 70-200L 2.8 IS MkII is one. It's so sharp, and since it also starts at f/2.8 it will take a 2x telecon really quite well.

The 70-200 MkII might be expensive, but it is a sensationally good lens and has considerably higher resolution than the Mk1 (fluorite glass is the clue). In normal use you might not notice too much difference as the Mk1 is pretty damn good, but stick a 1.4x or 2x telecon on the MkII and it can almost match the 100-400L. There's really not much in it. If you look at the MkII lens and telecons as a 70-400mm f/2.8-5.6 zoom, it suddenly becomes a bargain (and it has 4-stops IS).

Have a look here. Load up whatever permuations you want and toggle on the arrow at the top/middle :) http://www.the-digital-picture.com/...meraComp=453&SampleComp=0&FLIComp=7&APIComp=0
 
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