Using the Raytemp 8 without the probe, what distance can I be from the item whose temperature I am measuring?

There is no maximum distance. The area measured is indicated by a ring of laser dots. The further you are away from the target the larger the ring. The size of the ring of dots is a function of the Optics ratio, which is different for each model. Raytemp38 has a ratio of 30:1, Raytemp8 and Raytemp3 a ratio of 11:1, TN2  a ratio of 6:1 and TN1 a ratio of 1:1. For greater distances you would use the higher ratio units. Raytemp38 is a larger industrial unit good for relatvely large distances, TN1 would be used close to a measured surface.