Canon 2x or 1.4x teleconverter on a 300mm f/4L

[denandannie]

I would like to add either a 2x or1.4x teleconverter to my 300mm f/4L lens. The info from B&H indicates I can add it, but it is not totally clear if the autofocus will work. Does anyone have any first hand knowledge on this issue they can offer?

 

[HughGuessWho]

Per Canon...only compatible with fixed focal length L-series lenses 135mm and
over, as well as the EF 70-200/2.8L, EF 70-200/2.8L IS, EF 70-200/4L, and EF
100-400/4.5-5.6L. Additionally, please see the lens and/or camera body manual
for full compatibility information with the Extender EF 2X III

 

[Overread]

Both teleconverters will fit the 300mm f4 IS L lens (as far as I know), however:

1.4 TC will make the lens into a 420 f5.6 IS L lens of good quality, retaining all normal lens functions including auto focus.

2TC will make the lens into a 300mm f8 IS L lens of questionable quality*, losing auto focusing on any DSLR camera body that isn't a 1D series body. Note that newer camera bodies with live view can retain auto focus in live view mode only, but that it will be significantly impaired (and live view AF is already slower than regular AF).



*wide open it is likely to look soft and closing down one stop from wide open will leave you with a very small aperture which, whilst sharper, is going to eat into your shutter speeds a lot even on a bright day. That will likely mean you'll have to take your ISO higher and suffer more image degradation from that (even on a good clean exposure). Note that personal opinion, standards and output use all factor into what is considered acceptable so there will be some variation in how people interpret the results, but in general its on the more negative side overall.


In general the 1.4TC is well worth purchasing and using, the 2*TC is generally reserve for lenses of f2.8 maximum apertures or wider

 

[Hardrock]

I use the 300 f4 on a 7D with a kenko 1.4tc and it works really well. For me its seems that as long as you dont have to crop the image much it is pretty darn sharp wide open and once you step down it gets a little better. The focus speed does take a big hit unless it is a bright day.