Nikon F2 viewfinder - DP-3

Anyone can educate me on DP-3? Seems like it doesn't have metering?

and what's it's normally used for? Is this very rare or valuable?

It has a meter. Functionally, it's just like the DP-12 meter for the F2AS, except that it's made for non-AI lenses. (The F2/DP-3 combo is known as an F2SB) It's somewhat rare in that it was manufactured for about 1 year (a brief time compared to F2's manufacturing run of ~8 years?). For the right person (someone with an F2, a collection of pre-AI lenses, and a desire for the LED display and low light capable meter) it's a much sought-after item; having said that, they seem to sell for less than the DP-12. www.keh.com has a DP-3 right now in Bargain condition for $265. For more info, try this link:

http://www.mir.com.my/rb/photography/hardwares/classics/nikonf2/prisms/dp3/index.htm