Using Lens Extenders

[mk_ultra]

Howdy,

Have been using the standard kit lens that came with my 40D for the past 12 months or so, and am now hankering for some new lenses... ordered a 50mm from Kerso (which is being delayed due to the adverse weather, dammit!)

Would like to get some sort of zoom lens, so have been looking at the 55-250mm f/4.5 - 6 IS or the 70-300mm f/4.5 - 6 IS (as much as I'd love to own some L lenses, I really can't justify the price and know deep down that my limited ability means that I'll never actually be able to get the maximum performance out of that level of lens anyway).

My plan was to also purchase one of the canon extenders, but having just had a quick search on here, I'm not sure that is viable... is it correct that adding an extender onto a non-L lens means that the auto focus no longer works?

I understand that there might be some loss of image quality, but to be honest, the images I take are purely for personal use anyway so I'm not overly concerned by that.

I think I've also read that adding an extender changes the aperture, e.g. an f/2.8 lens becomes f/4?

Is any / all of the above correct, and are there any other things to be aware of when using extenders?

 

[StewartR]

Basic facts about Canon Extenders.

(1) They only work with primes longer than 100mm and a few high-quality "L" series zooms (the various 70-200s and the 100-400). Other lenses can be damaged if you try to mount an Extender, because the Extenders have protruding front elements and most lenses don't have a recessed rear element to accommodate them.

(2) The 1.4x Extender multiplies focal length by 1.4 with a loss of one stop of aperture. So for example a 70-200mm f/4 becomes a 100-280mm f/5.6.

(3) The 2x Extender multiplies focal length by 2 with a loss of two stops of aperture. So for example a 70-200mm f/4 becomes a 140-400mm f/8.

(4) Most Canon DSLRs will only autofocus if the lens (or lens plus Extender) has a maximum aperture of f/5.6 or better. So in the examples above you would be able to AF with a 1.4x Extender but not with a 2x. However 1D-series bodies can AF with a maximum aperture of f/8.

(5) There is some loss of image quality with a 1.4x Extender and more with a 2x. Whether or not the results are acceptable depends on the lens and on your personal standards.

 

[mk_ultra]

Fantastic, thanks for the info... most useful

Found this place that has compatibility charts for the 1.4x and the 2x extenders...

Will have to put a few different lens options / combinations together and look at the prices

See you actually have them available too so may well get in touch to try them out in the New Year