I'm looking for a new fresnel lens with a focal length of 600mm.

I found this one so far:
http://www.bhlens.com/product_detail.aspx?pid=56

However this one is too small and the groove pitch is 0.3mm. My other fresnel has a groove pitch of 0.5mm, so I think I prefer another with .5mm .

Lumenlab perhaps?

The LumenLab Pro 650mm lens is actually about 600mm FL.

If it's 600, why do they say it's 650?

Wondered that myself. Maybe the bigger guys can tell

It's actually about 610mm.

Why is it called a 650mm ? Why is the sky blue. Who knows? Oh wait we do know, but we still don't know why it's called a 650mm fresnel

All seems very uncertain, too much of a risk. I really need a 600 (I'm not the only one). I'll keep searching!