Experimenting

Warm light, feathered friends, and a few accessories...

I read about using an extension tube with a long lens the other day.  (For example, here I used my 300mm with a 20mm ext. tube.)  It allows you to focus closer to your subject, therefore filling the frame with your small subject vs. having to crop.  (One of the downfalls of a long lens-telephoto lens can be min. focus distance.) Technically I did still have to crop, but that's more because I didn't get as close to the birds as I could have with this set-up... they were skittish over my fill-flash, so I backed up a tad.  But overall, I think it worked the way I was hoping it would.  
Just like it is when I use my teleconverter, I lost a stop of light.  However in this case, I wasn't shooting through more glass, so I felt like it maintained the sharpness of the lens a little better.  Not a bad option for close, well lit subjects I guess.
Made for a fun experiment anyway. :)  I alway enjoy trying something new.