We have various examples of viewer settings. One in Achenar's book, one in Sirrus's, another on Atrus's desk in his bedroom, another on his work desk near the viewer,and one on Sirrus's desk near the viewer. They're all simple. Just transfer what you see to the viewer, and as long as we set the tower frequency to the number indicated in Atrus's journal, they're simple enough.

However, there's another one on Atrus's desk near the viewer. Due to Atrus's shoddy plumbing, a leak has damaged most of his viewer instructions for spying on Riven. But, we're armed with a note establishing various hard rules, a tower with a colour frequency range, and our own logic. Armed with the three, we're good to go.


Out of the gate, we have the following, with X's indicating missing information:

Lens - Colour - Iris - Position
1st - Orange - Open - X
2nd - Blue - X - 12
3rd - X - Midway - X
4th - X - X - 4

Ok, so going by the rules there cannot be more than 11 steps between the 1st and the 4th lenses, and we know 4th is at 4, and 3rd is at 12, meaning 1st is between 13 - 15. However, lenses physically must have two steps between them, which means 1st can only be set to 15.

Lens - Colour - Iris - Position
1st - Orange - Open - 15
2nd - Blue - X - 12
3rd - X - Midway - X
4th - X - X - 4

We also know that no two sequential lenses can have the same iris size. We know 1st is open, and 3rd is midway, so 2nd must be closed.

Lens - Colour - Iris - Position
1st - Orange - Open - 15
2nd - Blue - Closed - 12
3rd - X - Midway - X
4th - X - X - 4

We also know that while the colours can increase or decrease, they must do so in order. Using the colour frequency range from the tower, we know that from low to high, they go white, orange, purple, blue, cyan green.
We already have Orange and Blue, so we know they're ascending, which means 3rd and 4th have to be Cyan and Green respectively.

Lens - Colour - Iris - Position
1st - Orange - Open - 15
2nd - Blue - Closed - 12
3rd - Cyan - Midway - X
4th - Green - X - 4

We also know that the colour with the highest frequency (green in this case), must have the smallest Iris setting. So ...

Lens - Colour - Iris - Position
1st - Orange - Open - 15
2nd - Blue - Closed - 12
3rd - Cyan - Midway - X
4th - Green - Closed - 4

Lastly, we know that a lens between two small iris settings, which 3rd is, must be an equal distance away from the two adjacent lenses. They're at 12 and 4, so 3rd has to be at 8, giving us the full solution.

Lens - Colour - Iris - Position
1st - Orange - Open - 15
2nd - Blue - Closed - 12
3rd - Cyan - Midway - 8
4th - Green - Closed - 4

Cheers.