I used to use extension tubes in my FSLR days, I still have the last ones
for my OM2 OLY.
You do lose a little light - but not as much as with a converter (with multiplying lens - eg 2xconverter). you convert your lens, effectively, to a macro only lens - so yes - infinity is out of range.
Just my 2p worth of input.
Geoff Chandler. UK/England/Surrey
NIKON D90 / D80. Nikon 16 - 85 VR, Tamron 28-200,
Sigma 70-300APO, Tokina 100 AT-X Pro D.
SB600 flash. Panasonic DMC-TZ25