Of course if the decision to question or not was based on the type and cost of the equipment, then a terrorist could buy good expensive equipment and never be questioned.

Living in the NY area, and having traveled across all of the bridges, I know there are signs that say it is illegal. I remember seeing one several times on the Verazzano Bridge, and I'm pretty sure I've seen it on other bridges.
However, I did a Yahoo search on the question, "Is it legal to photograph bridges?" I got no definitive answer.
One of the sources suggested that it was a deterrent so that vehicles wouldn't stop on the bridge just to do so.
Several sources referred to the illegality of using other equipment (lighting and such) and especially prohibitting the use of tripods.

So, what does this mean? I have no idea. It appears to be legal but you can be stopped, or harassed by authorities, and photographers have won lawsuits for these actions.

Ok, I know this is lame but anyhow...

Few years back, down in Oklahoma, a guy had a little stand where he sold rabbit burgers. They were quite tasty and he had a good following. People would come from miles away to eat these rabbit burgers.

Then the economy got bad and things started to get a bit tight for everyone. People started to notice that the rabbit burgers were looking a little redder than normal. Someone complained to the local health dept and an investigation was soon started.

It was discovered the guy was mixing some horse meat (sorry horseart) in with the rabbit to stretch the expensive rabbit meat farther. He finds himself in court before the judge. Judge asks, how much horse meat are you actually using. The guy kind of beats around the bush and after more prodding by the judge, he finally admits that it is probably about 50/50.

Judge thinks well thats not so bad, and ask the guy to define his method of determining the 50/50 mix. Guy says, well, 1 rabbit to 1 horse...

We photographers refer to a focal length as relative to the film days. A negative was 24 X 36 mm and that size is now called
"Full Frame" for a DSLR sensor.

If you use a 50 mm lens on a FF sensor camera, the view you get through the viewfinder or with your bare eyes are essentially the same.

A cropped sensor camera ( which sensor is smaller by a third or so ) will narrow the view and make the pic 1.5 times smaller. That will equal to what a FF sensor camera would see as a 75 mm lens.

Therefore, with a cropped sensor camera, all lenses lengths are to be multiplied by 1.5 ( or 1.3 or 1.6 ) depending on the model, in order to be "equivalent' to the full frame camera.

There is no way to disable the preflash, apart from not using the onboard flash. The preflash takes care of the metering and sends the signal to the on board to fire. You can see the bottom of page 141 of the manual.]

The quote on page 141 is pertenant only to firing external Speedlites wirelessly (when the internal flash is disabled) and does not stipulate anything about the pre-flash. The preflash uses the onboard in low power stutter mode to aid focus when the button is half-pressed. It does not set off the synced flash for the actual photo. You can pre-flash a number of times before initiating a picture.

I have had no trouble with a 60D internal flash controlling external, wireless flash units that are designed to detect pre-flash events. External flashes such as the LumoPro LP160 Quad Sync are capable of being set to optionally accept the pre-flash event without tripping by selecting S1 on the slave selection switch. When selected the preflash does not set off the external flash units.

Of course, utilizing some wireless remote sync units to trigger the external flashes would increase the versatility of your equipment.