Sorry if this seems like a noobish question, but how do star wars (starship) shields compare to shields seen in other sci-fi series such as 'Star Trek' or 'Stargate SG-1'  do they block a certain amount of shots and then fail, or do they only block some energy blasts? Also it seems they either don't block solid matter (fighters, missiles)  or they're enveloped around the ship rather then forming a "bubble" around it

to provide the not 100% canon answer but really darn close (at least my understanding, I don't want to get into reference hell)

SW shields fall into basically two different types

energy shields(deflector shields)  and particle shields (confusingly called ray shields)

energy shields are the standard shields that you think of, they essentially are planar projected fields that dissipate energy and spread it out to draw it away from the point of impact. They effectively splinter part of the energy and reflect the rest of it. These are powered directly from the main reactor and work in tandem with the armor. They can be expanded into a bubble or brought in closer to the ships surface. field generators are placed along the hull and link together to generate a hopefully continous shield. An individual segment of the shield can be overwhelmed with concentrated firepower or from continous fire that overheats it, this is the standard shield failure (this can also overload the generator subsystems as they have to generate enough field strength to deflect the energy) In WEG and WOTC Roleplaying stats this is the shield score. they essentially block a certian amount of incoming energy per second, so you either have to crush them or wear out the projectors (or concivably run the ship out of fuel to produce energy, but that is impractical) They also seem to be capable of blocking most if not all frequenies of EM radiation to some degree (and may have selectivity in this regard) they can also be windowed to let the ships own guns fire. the simple fact is that a small ship of energy output X could never penetrate the shields of large ship energy output X+10 because the large ship would be able to recover and dissipate faster than the small ship could output. think of it as a recharge rate with a reserve rather than a total hitpoints. Different recharge and max strengths can be dialed in depending on the desired protection (up to the maximum the equipment can deliver per second)

particle shielding is present as a similar projected field, it however stops projectiles and physical mass from penetrating the field. large masses or very energetic ones will cause the same overload problems as deflector shields. slow moving masses have the ability to go through shields so it seems to be some sort of inertial feedback going on. in the RP stats this is represented as either part of the hull score or as part of the Damage reduction of the ship. Particle shielding works in concert with the hull armor and may actuall be ntegrated with the inertial compensation and tensor fields holding the ship together. Missiles and other warheads may be partially slowed and absorbed but they still essentially impact the shield/hull directly

Hull Armor is hyperdense material that acts as a unitary heat sink to draw heat away from the target area and to reflect as much energy out into open space as possible. it also acts as a physical barrier that ablated when directly hit (Star Destroyer armor is up to 30m thick in places!)

one of the quandries of the ICS numbers is that the ship would heat space around it to millions if not billions of degrees during intense reactor , shield and weaponry usage, so I really don't know how this is handled.

usually under non-combat operations the deflector shields are dialed into whatever the ambient EM radiation flux of the area and the (ray)particle shields are on to protect against micrometeors and other debris

games are inconsistant on thier usage of missiles, EAW has missiles ignore shielding altogehter, whereas the Xwing games (fighter centric) have it absorbed by theshields first. My guess is inbetween, the shields and hull work together to attempt to mitigate damage as much as possible, but different weaponry poses different threats

again just my opinions, but rationalized as best as I can.

EJ, that explanation is niclely thought through

Nice and logical  As for slow moving objects, an example of penetration is in The Empire strikes back where an asteroid destroys the bridge of a Star destroyer.

Then how do we explain the star fighter flying right into the Executor's bridge?

How did the A-Wing fly into the bridge? I'll let Admiral Piett and the bridge crew answer that......

(A-wings launch concussion missiles, and destroy one of the shield generators/sensor domes on the bridge structure)

Crew Pit Officer: Sir! We've lost our bridge deflector shield!

Admiral Piett: Intensify the forward batteries! I don't want anything to get through!

(A-wing begins its final flight towards the bridge, and is spotted by Piett and other officer. Piett turns back to the crew pit)

Admiral Piett: INTESIFY FORWARD FIREPOWER!!!!!!!

(A-wing pilot yells as he loses control of his fighter)

Bridge Officer: TOO LATE!!!!! NOOOOOOOOOOOOOO!!!!!!!!

(A-Wing crashes through the bridge viewport

Simply put, Freek, the Executor had lost its bridge deflector shields and was then vunerable to physical impact. Had the shields been there, it wouldn't have happened. However.........

(At Komo val) - I don't think that asteroid nailed the Star Destroyer tower in ESB cos it was moving slowly. I think it destroyed it because it was the same size as the bridge. It wouldn't matter what speed it was moving at.

also remember that the bridge deflector shield projectors were mounted on the sensor dome, with both of them being out there was very poor coverage if anything at all. the resulting detonation of the sensor dome would have also hindered any other shielding from suplementing the bridge shields.

This is all in addition to the heavy bombardment ordered by Ackbar and well into the battle

(it was the imperials dumb fault to be standing on the flag bridge anyway)

The smartest thing would be to put the command crew in a heavily shielded room in the center of the ship, with viewscreens and computers to monitor the battle.

True, but then who ever accused the empire of being smart?

Looking at it, a Star Destroyer has two things going for it:

1) It looks really cool
2) It's design literally screams 'I HAVE HUNDREDS OF VUNERABLE POINTS!!! PLEASE EXPLOIT ME!!!!"

....well maybe not quite that bad but you get the point.

Didn't all Star Destroyers have a battle bridge though within the ship?
I think it was hubris more than anything else, the naval captain had to see with his own eyes what was going on around him.

It's called CINEMATOGRAPHY people. It's much easier to get large expansive views of battle and make awesome panoramic shots from bridges that have huge windows rather than a bunch of radar screens. Star Wars was really more about telling a story than it was about "let's analyze all the technical aspects and ensure that they all make sense to prevent overtly interested sci-fi nut-jobs from poking holes in our dramatic means of telling that story."

And the only reason I can call people sci-fi nut-jobs is because I AM a nut-job. 

We could take the Star Trek route and have all the actors look at a blue screen... wait.. they did that anyway..

heh what about BSG, the CIS on galactica actually makes sense and somehow it makes the drama better.

"My God Jim! I'm a Doctor, not some fictional character on Television!!!.........."

I love the way that message boards stray from their topic.

as i recall the Sensor globe's destruction was completely unrelated to the shield failure, it just occurred very quickly afterwards, and basically let the Imps know their shields were down (with such a huge imperial  fleet against such a small rebel fleet, the Imps figured why bother monitoring the Shields and focus more on other matters during the battle) it was instead the bombardment Ackbar ordered that took it's toll on the executor's shields

During the clone Wars many ships used Viewscreens and holographic projections instead of windows such as the Acclamator and the Lucrehulk, but this was largely abandoned due to vulnerability to jamming. The only Galactic Civil War era ship that uses this system to my knowledge is the Nebulon B. A Window can't be jammed unless you do it Lone Starr style. The Executor's loss of the bridge most likely caused no small amount of confusion and panic throughout the ship, which it never recovered from in time.

the globes are entirely sensor based, it's simply a VERY common misconception that they are related to shields (outside of being protected by the shields
themselves)