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Archive 2004 · Why there is a limit 1/160 ?
  
 
Charles_cz
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p.1 #1 · Why there is a limit 1/160 ?


I've just got my flash lightning setup. I try to figure out how everything works.

I have 3 AB800, trasmiter RR1TX and RR1RX recievers for each light from the same company. Camera 20D to shoot with.

I am not sure if I've got this right. My camera sync speed is rated 250. At least that is what I was able to find. The manual for Radio Remote One says that I am allowed to use Maximum shuter speed 1/154 or slower.

When I try to use faster shutter speed (above 1/160) I will get part of the picture or entire picture black.
Can anybody explain me why in plain english?

When I trigger flash lights with my 550EX I can use any shutter speed I want. Is that limitation of the radio remote one or I just don't have enough knowledge to understand this. That is possible since I have just started.

Is there any way to shoot with higher shutter speed with the remote setup I have? I have cats and I would like to shoot some action shots. I guess I can use my 550EX to trigges the flashes but I want to understand what is going on here.
Thank you for advice. Charles



Sep 22, 2004 at 01:29 AM
papageno
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p.1 #2 · Why there is a limit 1/160 ?


Trippers have some delay---they are allowing for that. I can't explain it.
As to freezing action, with most flashes the speed of the flash is what freezes the action. The reason for using higher shutter speeds is to keep ambient light at bay.
Traditionally, flashes work at roughly 1/1000 to 1/40,000 . Generally, less power is faster.....



Sep 22, 2004 at 06:49 AM
Dave Baker
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p.1 #3 · Why there is a limit 1/160 ?


Charles_cz wrote:
When I try to use faster shutter speed (above 1/160) I will get part of the picture or entire picture black.
Can anybody explain me why in plain english?


The flash duration, as already mentioned, is really really short (1/1000 of a second or less).

Your shutter is open for the amount shown on the dial (the 1/160 of a second) but it's never a purely open/closed arrangement. With a focal plane shutter, one side opens, the opening "travels" the length of the frame, and then it closes behind.

What happens is you need to open the shutter for long enough to be sure it's all the way open for the actual time that the flash bursts. If it's still in the transition then you get a shadow over part of the frame (where the shutter curtain currently is).


So - this is ok:

1) shutter starts to open
2) shutter full open
3) FLASH!
4) shutter starts to close
5) shutter fully closed


And - this is not ok:

1) shutter starts to open
2) FLASH!
3) shutter fully open
4) ....



Sep 22, 2004 at 01:46 PM
Charles_cz
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p.1 #4 · Why there is a limit 1/160 ?


Thank you .. Charles


Sep 22, 2004 at 08:30 PM
redcrown
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p.1 #5 · Why there is a limit 1/160 ?


News Flash - Most studio lights (monolights) have long durations. Sometimes as long as 1/30 second. They do not freeze action. I was surprised to learn this recently when I tried to shoot a girl while she flipped her hair. There was a lot of blur. Using a 550ex flash I saw no blur.

So I hit the bulletin boards looking for an explanation and vendor sites looking for secs. Got the explanation that monolights are slow. Few vendors publish specs, but I found some and confirmed 1/30 to 1/100 flash duration is common (lower power = faster). There is one brand (can't remember the name) that has 1/3000 and they charge about 3x the normal price.



Sep 24, 2004 at 05:48 AM
Charles_cz
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p.1 #6 · Why there is a limit 1/160 ?


Thanks redcrown, that's something I was experiencing. I am glad you brought it up! That's one of the reasons I asked this question. I tried to shoot some movement and I've got motion blur. I was confused because everyone told me that flash will freeze the motion. I guess that is not case with my AB's. Anybody has more info or specification on AlienBees lights.

I now understand how flash and camera works but it does not help me to freeze an action.
Charles



Sep 24, 2004 at 06:26 PM
 

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Daschund Woof
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p.1 #7 · Why there is a limit 1/160 ?


Charles,

I don't know what kind of action you're trying to freeze, the AB 400 has a flash duration of 1/6400 (or at least that's what they say on their website). You can see all their specs here:

http://alienbees.com/allspecs.htm

Daschund



Sep 26, 2004 at 05:01 AM
Photon
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p.1 #8 · Why there is a limit 1/160 ?


Studio flashes (whether monolights or pack and head units) often have a longer flash duration than shoe mount units - it's part of the reason that they can have a max output that is several f stops greater than a portable flash. However, I've never seen one with a duration of 1/30 second. My Paul C. Buff (White Lightning) units have maximum durations in the 1/400 to 1/800 second range (it varies with the power of the unit, and of course the duration becomes shorter when you set the flash at a lower power level). This is from memory, but those numbers are at least approximately accurate.

If you want to stop fast action (and a hair flip can be pretty fast, as can a cat), set your flash to half or quarter power (or still lower if you can get by), and you'll have good freezing ability.

Daschund, the specs on that website may be minimum flash duration, at minimum power. I know the older WL Ultras specified durations (at full power) slightly longer than 1/1000 sec, but maybe they've gotten things faster. If I can find the manual for my X-1600, I'll see if it gives details for duration at different power levels.



Sep 26, 2004 at 05:42 AM
redcrown
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p.1 #9 · Why there is a limit 1/160 ?


Here is how I tested. I took a world globe and spun it while firing shots as it slowed down. First I did it outside in the bright sun with very fast shutter speeds. At 1/1000 sec the globe image was well frozen when rotating "fast". Then I repeated the test indors with my Novatron M500 monolights at full power. At roughly the same speed, the motion blur was heavy. I kept benchmarking sun vs. monolights until I determined that the Novatron units at full power were equal to a "sun-lit" shutter speed of about 1/125.

Not real scientific because I used a ticking sound the globe made while spinning to manually "by ear" sense the speed. But for me, it's academic, because if I have a model casually run her hand through her hair I'll get blur. I'm almost always at full power because I'm firing the lights through a softbox with baffels.





Sep 27, 2004 at 04:49 AM
Pavel
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p.1 #10 · Why there is a limit 1/160 ?


how long was your shutter speed and how much ambient light was there? Was it enough to light the shot to get the blur?


Sep 30, 2004 at 01:11 AM
RDKirk
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p.1 #11 · Why there is a limit 1/160 ?


I can't believe you've found electronic flash units with a 1/30 second duration. That's slower than old flash bulbs. That would have to be a unit along the lines of a half million watt seconds. Not possible. Recycling would blow your circuit breakers.

What is more likely is that you've got really bright ambient lighting or your camera is set on an automatic exposure setting--something that's letting the room light affect the exposure in addition to the flash. Your camera should be set on manual with the shutter at its highest shutter speed (exception: A radio remote might require a slightly slower speed). You control exposure with the aperture.

Alienbees units are all well shorter than 1/1000 of a second, and they do stop any motion a human would be doing in your living room.



Oct 06, 2004 at 04:04 AM





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