Sigma 2x Tele Converter

[shortclaws]

Hello. I thought I'd ask my question here, as it seems a natural extension of the topic.

I often hear that a 1.4 TC is a better choice than a 2.0. However, I have a 2.0 (got it before reading the advice!) and even with that there are plenty of times when it's hard to fill the frame with a wild subject. "Just get closer" doesn't really work with otters, for instance! ; )

So, if the choice is between:

- use a 2.0 TC and get a full framed image
- use a 1.4 TC and then crop the image down to fill the frame

...which is going to give me a better quality end product?

[glsammy]

The biggest problem with 2X TC's is the aperture you end up having to use, often making it nigh on impossible to get a half decent shot in anything other than the brightest of days unless your subject is very still.
I've got one I've used with a Canon 300mm F4, it worked quite well. On my Sigma 50-500mm, it wasn't worth the effort. F13.0 was the fastest possible aperture, and the images were hopelessly soft. I was better off cropping an image taken without the TC.
No harm in trying though, you go out and prove us wrong!

[grey:squirrel]

I'm extremely interested in getting a 1.4x converter for a Sigma 70-300 F4:5.6 APO HSM, for use my D40 but I'm worred the stop I would lose would make this combo impossible to use. Is there a chance I may be able to keep the autofocus and/or would the added stop make this useless for any sort of wildlife photography?

[wizzo]

John, is that the combination you use for you fantastic close ups of the birds. What camera do you use? Wizzo