Confusion regarding stacking order of Extension tube and Extender.

[amelo14]

I am currently trying to use a Canon 300 f4 IS to try to photograph some birds. I am also using as well a Canon 12mm extension tube and a Kenko Pro 300 1.4x extender. I understand that when you use a 1.4x extender you lose one stop of light. Generally my 300 f4 becomes an f5.6 when using it with my Xsi. However, I placed the 12mm extension tube in between the lens the 1.4x extender and the camera body continued reading an aperture of f4. Is this a real f4? Have I stacked them in the wrong order? What are your thoughts on using this smaller extension tube with the 1.4x extender so as to not deteriorate the image excessively? I mean, usually the tests on the web will stack  a 2x extender and a 1.4x extender and ...... so that the cost in image quality will be too high.

Thank you.

[Bob Atkins]

No, it's not a real f4. Why are you using the 12mm tube? If it's to get closer you might be better off with the order LENS - 1.4x TC - 12mm EXTENSION. The TC is optically designed to work best right next to the lens. In practice it probably doesn't matter much if yyou put the extension in fornt of the TC.

The reason for the f4 indication is probably that the extension tube doesn't have all the pins required to transmit all the lens and TC electronic information.

If you are not using the extension tube to get closer focus, you might as well not use it. It will not increase magnification. All it will do is prevent you from focusing to infinity.

[amelo14]

Thanks for your prompt reply. Very helpful as always.

The reason for using the extension tube is an article  in a Spanish photography magazine. In it, they set up a camouflaged blind and a system to attract the birds to their backyard. Since the birds were relatively closer, they recommended using the 12mm extension tube as well  to increase magnification of the 300mm lens even if it as just a little bit. I have already attracted the birds and going on to setting up the camouflaged blind for the camera.  It is quite a challenge!