This time to give an idea of the magnification abilities of tubes.
100-400mm L IS set at 300mm. f/11, ISO 100. Camera was not moved during these tests, so they show the magnification potential of each. I picked a random distance, which was 12'6".
To measure magnification I measured from the leftmost part of it's nose directly across to the rightmost edge of it's wing.
With 12mm tube. Shows a 10% magnification over the tubeless version.
With 20mm tube. Shows a 15% magnification over the tubeless version.
With 36mm tube. Shows a 27% magnification over the tubeless version.
From a previous post ( http://photography-on-the.net/forum/showthread.php?t=28017 ) testing the 100-400 @ 300mm, showing close-focus abilities:
With the 12mm tube. Minimum focus is 55" to sensor. Max focus is now limited to about 35 feet.
With the 20mm tube. Minimum focus is 51-1/4" to sensor. Max focus is now limited to about 21 feet.
With the 36mm tube. Minimum focus is 44-1/2" to sensor. Max focus is now limited to 11 feet.
I don't think that I'll ever leave the house without my tubes from now on.