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Old Jan 31, 2004, 8:03 AM   #1
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Default 420EX Flash Hi Speed Sync/Recycle Times

Hi All: I've got the DRebel w/24-70 Canon lens (Never in all of history has such nice equipment been sqaundered on someone so photographically inept as myself). I've been trying to get some stop action photos of my sons' swim meets and been having troubles getting the shutter speeds fast enough, even with the f2.8 available on this lens and iso's of 400. I've found that iso 800 looks fairly grainy. It turns out that the poor ambient lighting in the pool presents a formidable challenge. I've read the book on the 420EX but I still don't understands it (I'll reread it a few more times before it finally sinks in - just a little). In essence, do I want high speed sync selected on the flash when trying shoot with fast shutter speeds?

Next question: I would like fast recycle times on the flash. I've read that fresh alkalines are the best, but I've also read that fully charged NiMH are faster? I've got two sets of 1700mah NiMH's from my CP990 left over, but it seems? that they may be actually slower than the alkalines were.

I continue to learn more all the time, much of it from this forum! Thanks. gary
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Old Jan 31, 2004, 8:54 AM   #2
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Quote:
Originally Posted by tuthill
In essence, do I want high speed sync selected on the flash when trying shoot with fast shutter speeds?
No! you want regular X-sync (ie 1/200s max)... even @ 1/60s the flash pulse itself will be much faster than the shutter speed to freeze the action. High-Speed sync are designed for fill-in in bright outdoors and not for freezing action... It's designed to synchronize with the narrow slit of the shutter @ high-speed and can result in multiple ghost pictures beside reducing the range of the flash!

Quote:
Note an important point - FP mode does not help you freeze motion; the name “high-speed sync” is a bit misleading in this regard. Normal flash photography is very good at freezing motion on film, since the flash burst is so incredibly brief. However when you use FP mode flash the flash unit pulses the light output to simulate a longer-duration burst of light. Since the flash burst is not particularly brief you can’t freeze motion as easily, even with high shutter speeds. The mode is called high-speed sync since it lets you synchronize flash exposure with high shutter speeds, not that it lets you take high-speed photographs.
http://photonotes.org/articles/eos-flash/#fp

BTW the NiMh rechargeable cells are fine... I've used up to 2100mAh, if any they should make the flash recycle faster as well as providing more shots!
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Old Jan 31, 2004, 11:11 AM   #3
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Thanks NHL: Clearly I've got a lot of reading from the link you included. I intend to at least attempt to get through that this week. I read your reply and picked up the camera/flash just to try what you saild. Indeed, when the flash is attached, when the camera is set to Tv (shutter priority) I'm not able to speed the shutter any faster than 100-200/sec. But, when I switch the flash to hi speed sync, it lets me take a photo of my computer at 1/4000th second. The photo looks grossly ok to me but I didn't really look closely for ghosting, etc. I'm really confused on this. When I'm in a relatively dark pool building and want to freeze action, should I be using a flash? That's what seemed to work for me on my Nikon but maybe I'm mistaken. I'll keep reading and experiementing. If I can't use hi speed sync and without it I can only use 1/200t second or slower, I shouldn't have gotten the flash in the first place. gary
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Old Jan 31, 2004, 11:38 AM   #4
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tuthill

I have the 420EX and Rebel and use high speed sync. I can stop bball players so I don't see why you can't stop swimmers. I read the notes as well but rely more on practical application. Mostly 1/500 or lower; lenses: 50mm 1.8 & 75-300 USM; 420 set to H. No way I'd have gotten these without the flash...don't return yours.

See results: http://www.brrd.ab.ca/nnorway/2004basketball/Junior%20High%20against%20comp%20(jan14).htm

http://www.brrd.ab.ca/nnorway/2004basketball/Junior%20High%20against%20bashaw%20(jan21).htm

http://www.brrd.ab.ca/nnorway/carrweb/speedskating.htm (no flash here)
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Old Jan 31, 2004, 12:25 PM   #5
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Using a flash will indeed stop motion, even if the shutter speed is 1/60. The idea is that the flash is so much brighter than the ambient light that the image sensor will capture light only from the flash, and hardly anything from the ambient light. Since the flash pulse is so short, it'll stop freeze motion.

In high-speed FP mode, the flash duration is just as long as the shutter speed. If you pick a high enough shutter speed you'll obviously also stop-freeze. However, FP mode costs you half or more of your flash output.

You can also read the short articles on:

http://www.photozone.de/bindex3.html

In the lower left corner are links to standard and high speed flash sync.

Barthold
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Old Jan 31, 2004, 9:42 PM   #6
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Here's another an example between High-Speed Sync vs a single slower X-sync pulse.

This may also explain why the recycle time of the flash takes longer as well... :P
Quote:
The problem with "high speed sync" for action photos is that it works by making the flash slow down. Since the camera's shutter can't open fully in less time than its max normal sync speed, the film can't be exposed all at once at high shutter speeds. Exposure must be controlled by the shutter's slit travelling across the film, exposing different parts of the film successively. Instead of giving one almost-instantaneous burst of light, the flash gives a sequence of many pulses of light, approximating a continuous light source during the time the shutter is open. So instead of freezing motion with the fast electronics of the flash, motion is stopped by the much slower and less effective mechanics of the moving shutter curtains. The maximum shutter speed is in the neighborhood of 1/4000 or 1/8000, but the fastest flash duration at ordinary sync is much faster. When using high speed sync, fast shutter speeds are only available at wide apertures and close ranges, precisely the conditions where ordinary auto flash produces its shortest durations.
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Old Jan 31, 2004, 10:08 PM   #7
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Hi NHL, that's a cool link. Thanks. The key point to remember is that a regular flash (standard sync) is about 1/20,000. Five times faster than the fastest shutter speed of the 10D. Thus for stop-motion indoors use standard sync!

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Old Feb 1, 2004, 5:22 AM   #8
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Barthold

The other keypoint in all photography is how well one controls the lightings: Since a flash can freeze an action @ slower shutter speed, one can "lighten up" the background (instead of blacken out) by judiciously selecting the desired speed to provide a balanced fill with ambient light.... :lol:

BTW this is a link on how High-Speed Sync is correctly exploited with your f/2.8 lenses: http://eosseries.ifrance.com/eosseri...k_synchfp.html
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Old Feb 1, 2004, 8:12 AM   #9
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Oh man, do I have some reading to do! Does using the 420EX in standard mode (not high speed sync) limit the camera's shutter speed? It seems with mine it's limited to 1/100th or 1/200th of second when the 420EX is attached and the camera set to Tv and aperture is displayed at 2.8. I'll keep working on this but at present, it looks like the high speed sync is a must. Like I said earlier, with the poor ambient lighting and the speed of the swimmer's arms, I'd like at the very least 1/500th second, and 1/1000th is even better. gary
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Old Feb 1, 2004, 8:17 AM   #10
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Oh man, do I have some reading to do! Does using the 420EX in standard mode (not high speed sync) limit the camera's shutter speed? It seems with mine it's limited to 1/100th or 1/200th of second when the 420EX is attached and the camera set to Tv and aperture is displayed at 2.8. I'll keep working on this but at present, it looks like the high speed sync is a must. Like I said earlier, with the poor ambient lighting and the speed of the swimmer's arms, I'd like at the very least 1/500th second, and 1/1000th is even better. gary
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