Why couldn't I go faster than 1/250?

I was at an outdoor ceremony on flag day. It was sunny, mid-day. I had my 30d set to "P." Was using my 17-85 f/4-5.6 lens. My 580 EX II flash was turned on to prevent harsh shadows from the sun. ISO 100. Exposure compensation was +1/3 (I shouldn't have done this as many pictures were too bright.) I had the high speed sync turned on.

Turning on the high speed sync on the flash I assumed I could get faster flash speeds than 1/250. However, I noticed that it would not exceed 1/250. Instead the aperture would increase.

I did not want to use "manual" outside as I didn't have time to adjust for each shot. Would using "Tv" or "Av" work to get faster shutter speeds?

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John E wrote in post #5736906
Would using "Tv" or "Av" work to get faster shutter speeds?

Yes. In auto, the camera is always going to try to adjust exposure at the standard sync speed, but by using Tv, or Av would be preferred in your situation, the camera will use the appropriate shutter speed and HS sync will result.

BTW, it is relatively easy to do some quick tests around the house to prove that it works.

"P"? What is that?

+1/3 on a bright sunny day? The results would be obvious.

No.
Av would have given images overexposed by ambient if "Safety shift (a CFn) is not enabled.
Tv would not have allowed a shutterspeed faster then sync speed either.

The only way to get higher shutterspeeds would have been to use HSS, or turn off the flash.

edit: Okay, and then use Av or Tv instead of P.
I missed the part that you already had enabled HSS...

Outdoors using flash as fill = Av mode. You select the aperture and ISO, camera will select shutter speed to get a nice ambient exposure. Flash will output enough power to fill in shadows. Use EC to adjust ambient exposure (which would adjust SS), and FEC to adjust the flash exposure (how much fill you want). The trick is balancing the two exposures (as it always is using flash)

P mode, never used it.

To answer the question, It is a technical reason why you cant go faster than 250. At some point where the second shutter starts to close, before the first one is all the way open you get sync problems. High speed sync makes a flash for as long as the shutter is open. Because the flash went off but part of the sensor was covered and did not get exposed the same. So it flashes again. High speed sync makes the flash fire several times, to the eye it is still one flash. Light has to travel to the subject and back. So if you go too fast there is not time for it to make the trip.

This may show you a bit better....The first row is a slow shutter. The second is a faster shutter. As you can see slow shutters have a point where they are fully open. Perfect for flash. The high speed shutter is never fully open. Bad for flash.

Mark1 wrote in post #5737384
To answer the question, You cant go faster than 250 because the flash is not that fast. High speed sync makes the flash fire several times, to the eye it is still one flash. It basically runs the capacitor out of power. At some point where the second shutter starts to close, before the first one is all the way open you get sync problems. Because the flash went off but part of the sensor was covered and did not get exposed the same. High speed sync makes a flash for as long as the shutter is open. Technical and physical limitations are what is limiting it to 250

This may show you a bit better....The first row is a slow shutter. The second is a faster shutter. As you can see slow shutters have a point where they are fully open. Perfect for flash. The high speed shutter is never fully open. Bad for flash.

As technology improves I'm sure sync speed will increase.

actually, no

the original 1d has a sync speed of 1/500, yet the 1dmkii had only 1/250, and 1dmkiii has 1/320. kind of sad isn't it?

if you want fast sync speeds, get yourself a leaf shutter type camera

Every camera is different. The 250 is for the OP's camera. I didnt think I needed to make a list of every camera and their sync speed. As he didnt ask for that. However my explination is accurate.

WIth HSS enabled on your flash, it can synch faster than 1/250th, but in P mode the camera assumes the flash is the primary source of light. I haven't checked the EOS Flash Bible, but I suspect because of this the camera thus limits the the flash to the max synch speed regardless of whether HSS is enabled or not.

Had you chose AV or TV, then the flash would have properly acted as fill and your shutter speeds above 1/250th would have been enabled.

basroil wrote in post #5737439
the original 1d has a sync speed of 1/500,

Actually, the shutter had nothing to do with that: The shutterspeeds faster then 1/125s (IIRC) were taken care of by switching the CCD on and off. Apparently, this cannot be done with a CMOS sensor...

I don't think flash sync will get much higher then that: That woud require shutter blades to travel a lot faster, giving a much shorter life span.

ISTR reading somewhere that stopping a shutter blade at the end of it's travel is like crashing your bike into a brick wall

Mark1 wrote in post #5737384
To answer the question, It is a technical reason why you cant go faster than 250. At some point where the second shutter starts to close, before the first one is all the way open you get sync problems. High speed sync makes a flash for as long as the shutter is open. Because the flash went off but part of the sensor was covered and did not get exposed the same. So it flashes again. High speed sync makes the flash fire several times, to the eye it is still one flash. Light has to travel to the subject and back. So if you go too fast there is not time for it to make the trip.

the bolded text threw me off...light travels at approx. 300million meters/second. if, for example, the subject is 2 meters away, light would be able to make nearly 10,000 round trips even with a 1/8000 second shutter speed. maybe you meant to phrase this differently?

Mark1 wrote in post #5737621
Every camera is different. The 250 is for the OP's camera. I didnt think I needed to make a list of every camera and their sync speed. As he didnt ask for that. However my explination is accurate.

i didn't mean that your thing was wrong, it's perfectly accurate. however, sync speeds aren't going to get much better, as rene said

René Damkot wrote in post #5738587
Actually, the shutter had nothing to do with that: The shutterspeeds faster then 1/125s (IIRC) were taken care of by switching the CCD on and off. Apparently, this cannot be done with a CMOS sensor...

I don't think flash sync will get much higher then that: That woud require shutter blades to travel a lot faster, giving a much shorter life span.

ISTR reading somewhere that stopping a shutter blade at the end of it's travel is like crashing your bike into a brick wall

sync speed is sync speed regardless of how it's done isn't it

P&S cameras can have ridiculous sync speeds due to that. though few manufacturers actually take advantage of that..

edit:

Technophile wrote in post #5739224
the bolded text threw me off...light travels at approx. 300million meters/second. if, for example, the subject is 2 meters away, light would be able to make nearly 10,000 round trips even with a 1/8000 second shutter speed. maybe you meant to phrase this differently?

you mean 3 million meters/s in vacuum, slower in the atmosphere (in the center of the sun going outwards, fractions of an inch a second)

Never say never. Im sure sooner then we think flashes will be able to be used at every speed. I have no doubt they are already working on it.

Mark1 wrote in post #5740575
Never say never. Im sure sooner then we think flashes will be able to be used at every speed. I have no doubt they are already working on it.

They did already, its called HSS or ccd sensors =D That might change for CMOS but not with current CMOS technology. A leaf shutter wont get you much faster either, you rarely see shutter speeds above 1/500. SO there are options, just that none of them are quite ideal yet.

Thanks guys! You're obviously a whole lot smarter than I am. I'll try "Av" or "Tv" next time I need fill flash outdoors with high speed sync.