Many zoom lenses curve the field the opposite way when zoomed all the way in. Most lenses have barrel distortion when zoomed out and pincushion distortion when zoomed in. There'll probably be somewhere between where the field is flat. A few experimental shots of a grid will quickly find this out. Here's some examples from SLR lens reviews: http://www.photozone.de/canon_eos_ff/426-canon_28300_3556is_5d?start=1 http://www.photozone.de/canon-eos/295-tamron-af-24-135mm-f35-56-ad-aspherical-if-sp-lab-test-report--review?start=1 (there's many more on that site) Smaller compact cameras lenses often show hugely higher field distortion than decent SLR lenses.

You jest but the UK used to have a mobile tax - at least for business accounts. It was introduced in 1991 by the then Conservative Chancellor of the exchequer Norman Lamont. This tax was repealed in 1999 by then Labour Chancellor (and now of course prime minister) Gordon Brown. One of his better decisions to cut taxes on an enabling technology.

One of the great features of netem is that it isn't restricted to being used on a router. If you bridge two network interfaces together you can essentially use netem to make a device which looks like a faulty link. This can be plugged and unplugged [or routed using a VLAN infrastructure] into anywhere in your network without reconfiguration of any IP details on the machines under test.

Unfortunately, NISTnet can only delay IP traffic, netem works at the ethernet layer and can delay everything. One of the great things about netem is that it can be set up to act as a bridge. Think of it as an ethernet cable with 100ms delay. NISTnet is great but it can't do that.