I have the Sola 600 and use it for a focus light as well as a night dive light. Its plenty bright enough as a focus light on the lowest power setting, even at night. Same with the red setting - plenty bright enough to focus at night or daylight shooting.
This is based on using a 25 yr old Nikon 105 micro, the 'Pre-D' version, which was the original auto focus version of this lens.
Camera is a Nikon D90.
Newer models should focus even easier.
If its my money, I would only buy the 800 if there were features I wanted - not the extra brightness. Unless you want to use it as a video light for shooting video.
