John I have been using the 2x with the 100-400 today.Unfortunately I had no tripod and had to stand to hold the cam and use manual focus.I was using 400ISO.They were very acceptable.Would have been fine if using a tripod.Without the converter the shots were sharp,but did not have the magnification,it was a situation where digiscoping would have been ideal.It perhaps depends what you are wanting to shoot.In my case it was Curlews in a field,therefore I needed the greater magnification to show a larger bird.The ideal lens to use with a converter,esp the 1x4 is the Canon 300F4 IS.This lens takes superb shots with a 1x4 and still retains auto focus.

Thank you Christine. Any chance of you emailing a hi-res shot to me. Thank you.
John

Hi Christine,

i've seen you mention the 1x4 before but was unsure. Is this a 4x or a 1.4x convertor?

Rob.

Rob it is a 1x4 which changes a 400 to 650 or threabouts.

Thanks . I always thought it was called a 1.4x convertor. It looks like a common misconception.

Cheers, Rob.