Manual flash in Av or P

I was testing my 580EX that I just got back from Canon today and it seemed weird. I sent it in because it would only fire at full power in Manual flash mode (Av on camera). Don't ask "how do you know... etc." It did, I know. They fixed it and replaced some other things on it and now it works. I did have a question though about how manual flash works on the camera because it was acting weird (my other 580EX was doing the same thing, so I'm guessing it's correct, I just don't understand WHY it was doing it...).

30D, 50mm 1.8, 580EX on camera
Metered the dining room without flash in Av mode... 1/25, f/1.8, ISO 100
Turn the flash on, set to Manual flash, 1/128th power... and it changed the shutter speed to 1/250th (x-sync). It didn't matter what the ISO was or what the f-stop was... always 1/250th.

Then I tried setting it to Program and still Manual flash, 1/128th power. Now pointing it at the same thing in the dining room it was saying 1/250th, f/22 blinking. Definitely not right.

Like I said before, both of my 580EXs were doing this so it must be normal, or something wrong with the camera (I'll try my other 30D tomorrow). What do you think?

How does it function with the camera in full manual mode?

Edit: Oh sorry. I'm an idiot. It's late for me :P

gtrag94 wrote in post #13105391
It didn't matter what the ISO was or what the f-stop was... always 1/250th.

There's a menu option that tells the camera to lock shutter at 1/250 when it detects that a flash is attached, but I think it only applies to Av.

Yeah, I know about that custom function, it's set to Auto.. and you're right, only Av, not P.

Don't know about M on the camera, didn't try it. I'll let you know tomorrow. Any other ideas?

I always use manual mode, and for sure start with the lowest denominator when trying to figure out an issue (try manual and add things from there).

I should have tried that, but I wasn't sure what it "should" show up as... still ambient readings right?

It's called Flash Sync Speed in Av Mode.
C.Fn. 03-1 on the 30D.
But I don't think that's your problem.

It's a "feature" of the way Canon designed things. With a dedicated flash in manual mode and the camera in one of the auto modes, it does really stupid things. Just switch to M and be done with it.

As for behavior of camera in P, flash on M, I just experimented with my 40D...

• Ambient light and no flash turned on, camera in P, ISO 100: 1/20 f/2.8
  
• Flash on ETTL, camera in P, ISO 100: 1/60 f/4.5
  
• Flash on M full power, camera in P, ISO 100: 1/60 f/4.5
  
• Flash on M 1/128 power, camera in P, ISO 100: 1/60 f/4.5
  

It's been a while since I tested this, but from what I recall, P mode is not so problematic. Av and Tv modes are.

Curtis N wrote in post #13108895
It's been a while since I tested this, but from what I recall, P mode is not so problematic. Av and Tv modes are.

OP commented on the P mode..."Then I tried setting it to Program and still Manual flash, 1/128th power. Now pointing it at the same thing in the dining room it was saying 1/250th, f/22 blinking. Definitely not right."

I countered with what seems to make P mode seem reasonable in its actions with flash: the same in ETTL and M/1 and M/128

gtrag94 wrote in post #13105391
Then I tried setting it to Program and still Manual flash, 1/128th power. Now pointing it at the same thing in the dining room it was saying 1/250th, f/22 blinking. Definitely not right.

What do you think?

I think your camera is busted. If your camera is in P and ISO 100, 1/250, f/22, means it thinks it is metering a VERY bright scene. Even if a flash is attached, or if it is in manual flash mode, it should not meter like that indoors.