1.4x or 2x Converter Which Is Best For Me?
 

I want to buy an extender for my 100/400 mm lens and I am not sure whether to go for a 1.4 times or a 2 times. I am aware of the 1 and 2 stops light loss respectively and that this will affect the ease of focusing. Due to a complete lack of experience I have no idea just how much more difficult focusing will be.
I would try it using AV mode and preview but I understand that one should not refocus when in preview. My inclination is to go for 1.4 times, but I think I will need all the extension I can get. I am mainly interested in kingfishers and herons which are usually on the far side of the river at about 150 m. Hopefully someone with experience of both converters will come up with an answer.

I have both 1.4 and 2x converters. With the 1.4 on a 'L' lens the image quality hardly suffers at all but with the 2x you can see a definite drop in quality.

Thank you Roy. Is the drop in quality with the 2x more than the drop due the extra enlargement that you would need when usiing a 1.4x? If you answer yes, then that is enough to sway me.

Kind regards,
JOhn

Many auto-focus systems do not perform when the effective maximum aperture is beyond f5.6. I do not recommend the use of a teleconverter on a lens with maximum aperture already at f5.6 such as Canon 100-400 f4-f5.6.

If a lens has maximum aperture f2.8 then both 1.4X (1 stop) and 2X (2 stops) can be used but many find acceptable or imperceivable degradation of quality using 1.4X but 2X it becomes more marked and its a debate within itself.

A teleconverter will exaggerate lens imperfections and should only be used on the front of the finest glass, there is no substitute for a 500 or 600mm lens.

How about a Sigma 50-500mm 'bigma' for greater reach only a little more cost than the best teleconvertors I am sure quality should be as good if not better and 100/400 with TC.

Thank you very much Stephen for your comprehensive reply. I would be prepared to put up with the manual focus because the particular subjects I wish to photograph are fairly static on the far side of the river. I refer to herons, kingfishers (not that static) and a little owl which displays its self all day, every day, at the front of a hole in a tree. Once, I owned a Sigma 50/500 and I never got a sharp shot from it even though I always used a tripod. I did read, most of these lenses are extremely good, but there were one or two duds in the basket. I think I had one of the duds. Could a camera on my spotting scope be the answer? I have an IXUS400 which has an infinity setting on it. I may be able to find an adaptor. Incidently, this is a cracking camera I can produce extremely sharp A4s from it.

I have no experience of digiscoping but if you are happy with manual focus then 1.4X will give 560mm at full reach from 100-400L, with little loss of quality (depending on TC). I suggest the lens is stopped down one stop to maintain quality but, is there enough light on your subject to allow low ISO, f8 and decent shutter to avoid blur/shake at 560mm?

I asked that question on this forum not so long ago and received some very helpful replies from Andy Bright and others. Apparently the image quality is not exactly steller even with a top end scope.

Leif

Thank you,
John.

Stephen, in short, no there is not enough light for f8(f11 as it beomes) and low ISO, I will need to use ISO 800. Neat Image should clean up the noise which isnt too bad at 800 on the 20D.

Thank you all for your replies. After reading all of them I have decided on the Canon 1.4x.