I agree with John, very well done and you certainly have it mastered. Just one little fault of which I am sure you are aware, do not pan in a circle at speed, it makes the viewer feel nauseous. :D The spot on the lens is unlikely to be on the front of the lens, something that small would be out of focus by the time it reached the sensor. It is more likely to be on the sensor.
There is a lot of controversy over the use of these things (I know yours is a 4 prop chopper) especially close to airfields or where there are lots of people. If in the event that you lost control and hit someone, do you have insurance? Four props could do a lot of damage to someone's face for instance.
I think the young lady you were stalking was known to you as she appeared too nonchalant to be a stranger. Getting a release from a stranger you photograph and publish is a requirement of copyright law in many countries.
All that said, you have done a great job, both in controlling the chopper and in using your Nex 5.
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