Ha, ha. I think you missed the bit where I said I paid £550 for the system (new).
The focal length is approx 60mm. I see the advantage in increasing this but due to the bed depth, my options are limited. Something to look at anyway.
My air pressure is 0.02MP (3 psi) and does a good job of keeping smoke away from the lens but probably not a lot else. Increasing the airflow is an option but I think the air exit nozzle needs improving as well.