If you have xtightvncviewer installed, you can use the command tightvncviewer -via observer@131.217.62.74 ops8:1 to automatically set up the appropriate SSH tunnel. Otherwise you will need to explicitly set up a tunnel with ssh observer@131.217.62.74 -L5901:ops8:5901. Once connected, you should be able to reach the ops8 VNC session by setting the destination to 127.0.0.1:1.

First, you will need to download a copy of puTTY. Once installed and started, you should first go to the SSH tab and then selecting the Tunnels tab. I've attached a screenshot of the configuration to add in. After pressing add, go back to the session tab, add in the destination as 131.217.62.74 and save the configuration as something like ops8tunnel. Once you open the SSH connection to ares, you'll be prompted to accept the SSH key and then enter the username and password (observer & the usual). Once you have a terminal on ares open, you should be able to connect to the ops8 VNC session by setting the destination in the VNC client to 127.0.0.1:1 (the localhost address with the port being forwarded to ops8).

Assuming the command lime provides an SSH client, you should be able to first set up the tunnel with ssh observer@131.217.62.74 -L5901:ops8:5901. Once connected, you should be able to reach the ops8 VNC session by setting the destination to 127.0.0.1:1.