Hey, I had a quick question...

For example, in cases such as ariel photography, waht is the lowest acceptable altitude for a something like a cessna to decend to.

If you're in the US: Sec. 91.119 Minimum safe altitudes:         
(a) Anywhere.  An altitude allowing, if power unit fails, an emergency landing without undue hazard to persons or property on the surface.

(b) Over congested areas. Over any congested area of a city, town, or settlement, or over any open air assembly of persons, an altitude of 1,000' above the highest obstacle within a horizontal radius of 2,000' of the aircraft.

(c) Over other than congested areas. An altitude of 500' above the surface, except over open water or sparsely populated areas. In those cases, the aircraft may not be operated closer than 500' to any person, vessel, vehicle, or structure.

If you're interested in taking a picture of you're house, for 
intance, just call the closest controlling facility(tower, ARTCC, FSS etc.). As long as it doesn't interfere with any TFR's or airspace they're usually pretty acomodating.
I used to fly out of KFLL(class C airspace) and tell them I had to take pictures downtown. I would then circle around my mom's house for 10 minutes, and wave hello!

LOL is that all. even for military:)
our poor jaguar pilots would get bored after 2 minutes of flying that high

Mil in Uk is 250ft in Low Flying Areas (LFAs) I believe

Charlie