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Old Feb 1, 2004, 8:25 AM   #11
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You're limited to 1/200th in standard X-sync mode; However, you do not need to go higher than this to freeze the swimmer arm, ie the flash pulse itself is much faster than the shutter speed! Going to higher shutter speeds will decrease the output on your flash in the High-Speed mode (ie the Guide Number is lowered proportionally with each shutter speed increase) and will limit your range. This also explains why it takes so long for your flash to recharge: the flash has to stay on longer at a 50kHz rate with a reduced output to stay in sync with the shutter slit!

As an example the GN on my 550EX is 55 at normal sync, but is considerably reduced to 19.4 @1/500s and only 13.8 @1/1000s... IMO you're out of range (42/2.8 = 15m max. @ ISO 100 on X-sync) and rely solely on the shutter speed to freeze the action... Time to switch to a more powerful 550EX or a Sigma 500DG Super may be (same cost as the 420EX)?
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Old Feb 2, 2004, 12:28 AM   #12
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NHL,

Another link I didn't know about. Thanks! In normal sync mode, does the camera use the pre-flash to figure out how powerful the flash should be, given the aperture and shutter speed? Say if in manual mode I set it to F2.8 and 1/60, the camera will try to figure out the flash output?

Thanks,
Barthold
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Old Feb 2, 2004, 5:12 AM   #13
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Barthold

Except for manual, the camera will command the strobe unit to ouput a preflash in all the automatic modes (ie P, Av, Tv, etc...) and use this info to compute for the real exposure.

In manual, you're on your own (ie no pre-flash)! For single flash it's still pretty easy to work with by dividing the GN by the distance to find the aperture setting for all X-sync shutter speeds: for example @ 7.5m it's f/5.6 (ISO100) with your 420EX at the tele position. For Normal or Wide angle the GN is of course smaller...

When you have multiple units, this'll get harder and the camera E-TTL in auto is the best since the camera will also command the slaves to issue their own imperceivable pre-flashes as well and modulate them wirelessly accordingly. In manual however you'll probably need a handheld flashmeter, but with experiences you can probably get away with... if the secondary units are set only as integer ratio of the main unit. 8)

Again: http://eosseries.ifrance.com/eosseri...ork_ssfil.html
... this system is now improved with the 1D mrkII now that the distance info is also figured in (I believe they had licensing problem with Minolta and then Nikon on this... ditto with the built-in auto pop-up flash a while back). The Minolta 7xi blazed the trail here in the past decade with the built-in flash poping-up, fired, and auto retracted after the shutter is released! :P
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Old Feb 2, 2004, 9:45 AM   #14
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Default Reply to your question about batteries....

I like to use the Duracell lithium batteries.
They are expensive, but they last a long time and are very lightweight.
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Old Feb 2, 2004, 11:46 PM   #15
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NHL,

Thanks! I'm not sure how you got to F5.6 in your example though (guess I need to look up the GN number for my 420EX :-)). I typically like to shoot in Av mode, control over the DOF is important to me. But sometimes I also want a faster shutter speed using the flash, since there's enough ambient light that a slow shutter speed causes blur. Thus that means manual mode (I think).

Thanks,
Barthold
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Old Feb 3, 2004, 4:11 AM   #16
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For the 420EX:
GN = 42(in m) or 138 (in ft) @ ISO100
GN = distance * aperture -> 42 / 7.5m = f/5.6
or you can find the distance 138 / f/2.8 = 49.2ft

There's a caveat however, the GN is given at the maximum zoom position, if you look in your flash manual there's lower GNs for each focal lenght as it get wider...

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I typically like to shoot in Av mode, control over the DOF is important to me. But sometimes I also want a faster shutter speed using the flash, since there's enough ambient light that a slow shutter speed causes blur. Thus that means manual mode (I think).
Yes... in manual mode you can set both the shutter and the aperture, and the flash (in TTL) will modulate its output to match the aperture value. The flash does not pre-flash in manual (M), but it still preflash (to my surprise) on TTL and exposed the images correctly when the camera is on manual!

BTW the distance scale on the 550EX move in accordance with the aperture wheel on the back of my 10D in manual... pretty nifty. 8) 8) 8)
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Old Apr 13, 2004, 11:53 PM   #17
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Hey, just found this thread, have some questions. I've been experimenting with my newly purchased 550EX on my D-Rebel. I found the following:

1) Used my EF 50 f1.8 II lens indoors in light not quite bright enough to use without dipping too low in the shutter speed to avoid "hand-shake" effect taking pictures of friends at a party. I I found using the High-Speed Sync flash with wider apertures (1.8-2.8) and higher shutter speeds provided the most pleasing pictures, with good amounts of background blur, and not making pictures seem to "saturated" with light.

2) Using that same lens in a darker enviroment (in a pool hall), found the use of lower shutter speeds (i.e. less than 1/200) regardless of aperture gave the best pictures. Pictures taken with High-Speed Synch flash didn't seem right, sometimes washed out on one side, and the histogram was often to the left).

Is this consistent with "rules of thumb" around flashes? In other words, the worse the lighting conditions, the less likely High-Speed Sync flash will work? (or be appropriate)

Thanks!
Graeme
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Old Apr 14, 2004, 9:14 PM   #18
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Quote:
Originally Posted by Graeme Shiomi
Is this consistent with "rules of thumb" around flashes? In other words, the worse the lighting conditions, the less likely High-Speed Sync flash will work? (or be appropriate)
Correct. Basically your guide number (flash power) is automatically reduced by more than 1/2 because of instead of outputing one powerful blast, the unit is now producing smaller pulses of flash following the shutter slit as it moves across the surface of the CCD or film.

High-Speed Sync is best suited for outdoor fill at close distance with high shutter speed -> larger aperture -> less DOF ("with good amounts of background blur")!
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Old Apr 17, 2004, 7:47 PM   #19
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Quick question.
Can you use a 380EX Speedlite flash with the EOS 300D camera?
Had contacted Canon and it was suggested not to use this.
Was under the impression all EX units were compatible.
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Old Apr 18, 2004, 6:17 AM   #20
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Quote:
Originally Posted by Nutmeg
Quick question.
Can you use a 380EX Speedlite flash with the EOS 300D camera?
Had contacted Canon and it was suggested not to use this.
Was under the impression all EX units were compatible.
Not in the automatic mode...
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