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-   -   Overriding 300Ds Flash Shutter Speed.? (

mf_blues Jan 29, 2005 12:19 PM

I want to use my on board flash to trigger studio flashes but I can only set the shutter speed to 1/200th of a second when the on board flash is up.

I know this is the cameras max sync speed for the on board flash but I need to set 1/1000th of a second, is it possible to override the cameras default flash setting.?



pauloffrance Jan 29, 2005 9:11 PM

Hi Mart

I don't think you will be able to set the shutter to 1000th with on board flash. I am puzzled/curious as to why this would be necessary.

In a studio setting for example, you could reduce ambient light to practically nothing and let the flash freeze the action. This would have a better effect than trying to sync at 1000th. Even if you could find a way to trigger the flash at 1000th of a second the pictureis likely to be only partially illuminated. Here is a brief description of the problem:

Good luck


mrkryz Jan 29, 2005 9:40 PM

You can use a flash with an x-sync higher then 250. I *think* the Sigma Super DG will allow a 1/500 sync in high speed sync mode.

pauloffrance Jan 30, 2005 4:20 AM

The problem is not with the speed of the flash itself. The curtain of the shutter must be fully open when the flash fires and this only happens on the 300D at speeds up to 1/200th of a second. At shutter speeds faster than 200th of a second the shuttercurtain starts to close before it is fully open. This effectively means that just a slit is moved across the focal plain, the size of this slit reduces with increases in shutter speed, so if the flash fires at any point in this process only that part of the picture will be exposed.

Some cameras use different methods to make exposure and allow higher flash sync speeds. Only a change of camera willfacilitate flash sync at 1000th of a second.

Happy shooting.


NHL Jan 30, 2005 7:15 AM

IMO I can only guess what mf_blues is trying to achieve - synchronizing the studio strobes to the camera's flash using a photoslave ;)
Could it be that 1/1000th was to minimize the effect of the built-in flash?... in which case it won't work (@ any shutter speed!) because the preflash will cause the studio strobes to trigger prematurely, hence one only get the effect from the built-in flash when the shutter truly open (and not before when the shutter was still close for the pre-flash/studio strobes!) :(

A better approach is to use an AS-15, or similar device and to set the camera on manual, in which case you can choose any shutter/speed combination (since the DRebel does not have a PC-sync terminal): :cool:

BTW any cheap small manual flash mounted off the DRebel hot-shoe will also work (ie they don't preflash) to trigger the studio strobes... unlike the camera's built-in flash :evil:

mf_blues Jan 30, 2005 12:13 PM

Thanks for the replies guys.

The reason I need 1/1000th sec shutter speed is that the studio flashes fire at this speed, the 300D will go upto 1/2000th of a second with a dedicated canon ex flash gun but they're not cheap. The 1/200th of a second limit only applies to the onboard flash. The manual doesn't tell you this info. That's what I have heard anyway.

But if the camera can't be overridden then I can't use it with these studio flashes which seems a bit bad for a SLR. IMHO



NHL Jan 30, 2005 2:57 PM


You do not need 1/1000th of a second like pauloffrance has explained! The camera will sync just fine even at 1/60s...

If you go with 'high-speed' sync -> you'll get a partial picture: the EX pulses rapidly at high-speed to follow the shutter slit :?

mf_blues Jan 30, 2005 3:37 PM


I understand what pauloffrance says but the fact remains according to what I have read, that the 300d is capable of higher sync speeds with the ex guns. The other issue is that the studio flashes at the college I am attending fire at 1/1000th of a second. Our tutor told us that we need to set the cameras shutter to this speed and just meter for the aperture to give the correct exposure.

My problem is that the 300d with built in flash only allows 1/200th of a second shutter speed so won't be able to sync with the studio flashes. knowing that the 300d is capable of higher sync speeds I was just seeing if it was possible to override the built in flashes shutter speed setting to enable correct sync with the studio flashes.

It seems to me that without an external ex flash I will not be able to do what I want.



NHL Jan 30, 2005 5:10 PM


Tell your tutor to read this forum! :idea:
The DRebel (and most dSLRs) do not sync at 'high-speed', but they fake it out which the flash stroboscopic 'trick' ;)

IMO you are confusing the flash duration with the flash sync speed... :?
Most flash duration are much shorter than 1/1000s (or several magnitudes faster), there's nothing wrong with synching at a lower speed than 1/200s! :-)

pauloffrance Jan 30, 2005 6:02 PM

Ok.. in the simplest terms possible. Keep the ambient light low. Set the camera to desired aperture, and set shutter speed to 1/200th of a second. Press the shutter release button and then the shutter curtain opens. When the shutter curtain is fully open the flash fires and the picture is exposed. The shutter closes. If the ambient light is kept low then this will not affect the exposure, as exposure is controlled by thepower of the flashand camera aperture settings. Use a slower shutter speed if you want to include more of the ambient light in your picture.

That is it. The flash speed will freeze your subject matter so movement wont be a consideration unless the ambient light is high enough to affect exposure. The flash speed does not need a relative shutter speed to perform the correct exposure, trust us and try it.

Good luck...and post your results please.


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