2,8/300+1,4T-con+25mm extension ring

[Image Stabilize]

Affording a 2,8 now, I learned that I can not get as close as with the 4/300.
When using the 25mm or the 36mm Kenko extension ring AND the 1,4 T-con,
I get confused what goes FIRST on the camera body for best optical quality:
the EXTENSION RING or the T-CON.?
(I'm not talking about widest magnification range , BEST OPTICAL QUALITY is my aim).
Thank you for an answer from someone, who did long-distance close-ups further than with the 180mm himself. (No problem putting two extension rings on at the same time, for more magnification. Of cause their sequence does not matter, that I know).
Have friendly sunshine over the week-end!
Simon-Peter

[DavidEB]

the longer the focal length of the lens, the less effect the tubes have. If the t-con is closer to the 300mm lens then the tubes will be acting on 420mm of focal length. If the tcon is closer to the camera, the tubes will be acting on 300mm focal length. So either way works, but you get closer with the tcon next to the camera and the tubes next to the lens. See this post (http://photography-on-the.net/forum/showthread.php?t=94471) for my experiment with the 300 f4 and tubes + tcon.