1.4 Extenders. Sigma vs Tamron vs Canon

[quickben]

Does anyone have any opinions on which is the best in terms of price/performance ratio.

Does the Tamron allow AF on lenses slower than F4.0 ? I know the Canon doesn't and Sigma does.

Obviously, the Canon will have superior glass, but can you really tell the difference ?

All views welcome :D

Gary.

[Spargo]

From what I hear, with your Canon 100-400L you need the Canon 1.4x teleconverter. It's the only one that will work with it (I think).

[CyberDyneSystems]

Er.. No 1.4X will not allow you to AF on the 10D with the 100-400mm unless it has communication blocked.

On your L lens you would only want to use canon.. it will work with the 100-400mm fine.. but you will not get AF. But you can certainly use other brands as well and with some.. you may even get AF though only with "luck"

Please check the Sticky at the top of the EOS forum for more info.

Spargo.. before you answer a question on a forum.. do you think it may be advisable to know the correct answer? :)

[timmyquest]

I've always been baffled about the f/stops multiplication factor.

when you multiply 2.8*2=5.6 yes?

5.6*2=11.2 yes?

[Scottes]

Yes, Timmy, that's correct. It may be easier to think that the 1.4x is 1 stop, the 2x is 2 stops. The math still works out the same, just depends on which way is easier for you.

[timmyquest]

Yes, Timmy, that's correct. It may be easier to think that the 1.4x is 1 stop, the 2x is 2 stops. The math still works out the same, just depends on which way is easier for you.

I've done a quick search with no luck.

Is there a chart out there that gives me the "normal" "stops"

1.8-2.0-2.8-3.5-4-5.6-8

Are these all one stop?

[CyberDyneSystems]

Does 1.8 X 1.4 = 2.0?

Nope.

So it can't be a full stop difference can it? In Scotte's post above yours it says the 1.4X = one stop. Did you read that?

1.4, 2.0, 2.8, 4, 5.6, 8, 11, 16

[robertwgross]

1.4, 2.0, 2.8, 4, 5.6, 8, 11, 16

Those are correct for the full stops. It starts getting a little messy when you try to calculate the number of stops from f/3.5 to f/4.5 or fractional stops like that. Remembering the 1.4 factor between each whole stop is important, and you will remember the whole stop number after you have been shooting for a while.

---Bob Gross---

[Spargo]

Spargo.. before you answer a question on a forum.. do you think it may be advisable to know the correct answer? :)

Just trying to help. And that's why I said "I think".

[benjcox]

to remember the f-stop thingy just remember that every second number is the previous one doubled ie 1,2,4,8 and 1.4, 2.8, 5.6, 11 combine to 1,1.4, 2, 2.8, 4, 5.6, 8, 11.

anyway, back to the teleconverters. A 1.4x teleconverter 'magnifies' your lens by a factor of 1.4. So your 200mm lens will now be a 280mm lens! and likewise the 2x teleconverter magnifies your lens by a factor of two (ie 400mm!).

aditionally the 1.4x teleconverter loses you one stop of light (ie from, say, f/2.8 to f/4) while the 2x teleconverter loses you two stops of light (ie f/2.8 to f/5.6). Hence you have less aperture to play with when it gets dark or you want to stop action with a short shutter speed.

As with the autofocus: the camera body is the thing that controls autofocus (not the lens - the body works it out and then tells the lens what to do). For the camera body's autofocus mechanism to work it needs to have enough light let in through the lens to see what it's doing! This is why your camera struggles to focus in the dark

Anyway, Canon's cameras come in two ranges: the pro and non-pro. The pro-series (designated by the number 1, ie 1ds) can still autofocus even when the maximum aperture is only f/8. The non-pro bodies (ie everything else and probably what you own) can only autofocus when the maximum aperture is above f/5.6. So if you add a 2x teleconverter to, say, a 70-200mm f/4 L lens, you would effectively have a 140-400 f/8 lens. But because you have a maximum aperture of f/8 your non-pro body wouldn't be able to autofocus, which is a pain with such a long focus lens.

Other things to consider are the fact that a teleconverter magnifies the image your lens provides, complete with imperfections. So even with awesome L-series glass your image quality will degrade slightly with a 1.4x teleconverter. With the 2x teleconverter it can degrade quite a bit and many people fussy about image quality won't accept the results.

Another thing is that autofocus is slower, but in my experience not painfully so (i've got a 70-200mm f/4 with a 1.4x teleconverter)

Lastly, the Canon teleconverters will only work with some lenses. As a general rule, if your lens is big and white it'll work but check beforehand.

Oh, and i've no idea about the differences between the canon/tamron/sigma but from my experiences I can't really fault the canon products. They're built like rocks, have proper metal contacts, are weather-sealed and (I suspect) the best picture quality.