Unfortunately I was too slow and missed a Type 3 from the same source. I was familiar with later Sun keyboards but didn't know this one.The Sun Type 4 uses unbranded (as far as I could see) foam and foil switches with rubber sleeves for the tactile response. It feels quite pleasant to type on, much more than the later models (the Type 5 is not too bad for a rubber dome, and it went down from there). This being said by someone who has used almost exclusively buckling springs for the past 20 years.
This model introduced what came to be known as the "Sun keys" on the left side (Stop, Again, Props, etc). The keys were present on the previous model (Type 3) but were only labeled L1 to L10, the Type 4 is the first with the new labels. Unlike the Type 5 and later models it doesn't have a separate navigation cluster. The big Ctrl key is on the left of A where it belongs, and a small Caps Lock is relegated to the spacebar row. It has a Compose key (not present on the Type 3), a Line Feed key (not present on later models) and the right cluster sports an '=' key that morphed into Audio Mute on the Type 5 (they share the same scancode). Another uncommon feature is the ISO-shaped Enter on an otherwise purely US layout.
The caps themselves are double shot, the left and right cluster have additional markings on the front (L1 to L10 and R1 to R15, respectively).
Sorry about the picture quality, it's the best I can do at this time with low light and no camera stand.
