Tele Converters?

[ChrisBland]

I was looking at sigma zoom lenses, i require a focal length of about 400mm. What would be the best option for picture quality?
using a sigma 70 - 200mm 2.8 with a 2x tele converter
or
something like the sigma 150 - 500mm

i am aware that the teleconverter will also affect the aperture, other than that i have no idea how they affect the picture quality

thanks

 

[artyman]

Using a lens without a TC is always a better option, however top quality lenses can also perform well with a TC. If you wan't 400mm then I would go for a lens of that focal length, the Sigma 150-500 is an excellent lens, I used it for three years. Now replaced with a Sigma 120-300 f2.8 OS which I use with TC's, it is however a top quality lens and performs well with a TC. I changed to gain an extra 100mm over the 150-500, by using a 2X. LOng is never cheap, but the 150-500 offers the best value for money out there in my opinion.

 

[FatalSaviour]

As you've correctly stated the TC will affect the aperture, multiplying it by whichever mag factor you buy. So the 2.8 that you mention will become a f/5.6.
It'll also show up any flaws in the lens that much more, but if you're using it on a good lens to start off with, then this shouldn't be so much of an issue.

I guess it depends what kind of flexibility you require too - with the first option, you have the ability to shoot at 70-200 at f/2.8 (I've never used the Sigma I'm afraid so couldn't tell you what sharpness is like wide open but the option is there!). From there on, you can shoot 200-400 at 5.6.
I'm not sure at which point the aperture changes on the 150-500, but looking at the ISO charts on thedigitalpicture, it would appear to go from f/5.6 to f/6.3 between 250-300mm.
Don't know how much that will actually affect the AF, but it's something to consider.
If you're wanting the best IQ, then of course a 400mm prime will give you the best performance, but will depend on your budget and needs .