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01-20-2009, 12:41 AM   #1
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Flash + Manual setting

Hi there,

I shoot with a Pentax K100D, and use a Sigma EF-530 DGST flash. I've just started using the flash, and have some promising results, but I'm very frustrated when trying to use my aperture priority and manual settings with it. I used the flash to shoot a roller derby game, and my photos kept either over exposing, or lacked good definition. My main problem was I could not put my TV faster than 1/180 when my flash was activated. To keep my photos at a better light level, I tightened my aperture, but this was at the expense of my depth of field, and took a lot of excitement out of my pictures. To get any results, I was shooting TV 1/90 and F 8.0, but with the amount of movement, a lot of the photos lacked crispness, and had blur from movement in it. Am I completely confused, or should there be a way that I can have a faster shutter speed when operating my flash...?

01-20-2009, 12:52 AM   #2
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Actually, I feel really silly now. I read into it and now realize that the sync speed is only 180, but I'm still really upset about this. Does anyone have any suggestions for how I can accomplish better photos with my flash?
01-20-2009, 06:36 AM   #3
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There is something called high speed sync which allows you to use shorter shutter times. Read up on it. As far as I know both camera and flash must support it.

An article about flash and high speed sync.
01-20-2009, 06:45 AM   #4
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You can activate high-speed sync on the Sigma flash by pressing "+" or "-" until "FP" appears on its LCD display's upper line. Note that you cannot use Auto-ISO with high-speed sync.

01-20-2009, 06:54 AM   #5
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in reading the post, it almost seems like you are trying to use the flash for "fill" as opposed to the flash being the primary light source.

A flash itself can be very short duration, less than 1/1000 of a second, and can "freeze" the image

the trick is, to have the lens stopped down enough, and shutter speed at the maximum possible, so that the frame is 2-3 stops under exposed, and let the flash only expose the subject correctly. For some sports, if this is the objective, true TTL flash may be better, but that is only available on the *istD and *istDS.

The other option, is high speed sync, used as a fill flash.

You will need to read your manual for this, option, and note that your flash power is greatly reduced with HSS because it must divide the flash power over 5-6 pulses, and therefore the GN for HSS is reduced.
01-20-2009, 12:59 PM   #6
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QuoteOriginally posted by nezvanova Quote
I shoot with a Pentax K100D, and use a Sigma EF-530 DGST flash. I've just started using the flash, and have some promising results, but I'm very frustrated when trying to use my aperture priority and manual settings with it. I used the flash to shoot a roller derby game, and my photos kept either over exposing, or lacked good definition. My main problem was I could not put my TV faster than 1/180 when my flash was activated.
That shouldn't have been a problem - the flash duration itself is so short, even with a shutter speed of 1/60 you'd still be freeing the motion, as long as the shutter speed was fast enough to cut out most of the ambient light. And if 1/180 wasn't enough to cut out the ambient light at the aperture and ISO, you could lower ISO rather than close down the aperture. I kind of doubt a roller derby arena would be lit well enough that this 1/180 at ISO 200 would have been letting in any significant amount of light even for most lenses wide open.

So if you were getting overexposed pictures, that shouldn't have been from too slow a shutter speed, but rather, from the flash system trying to redner everything like daylight, which is what it normally shoots for. If you don't want that, simply dial in some negative flash compensation.

QuoteQuote:
To get any results, I was shooting TV 1/90 and F 8.0, but with the amount of movement, a lot of the photos lacked crispness, and had blur from movement in it.
There is no way you should have been getting enough ambient light at those settings - even at ISO 3200 - for the shutter speed to have had any effect whatsoever on motion. The flash is only going off for 1/1000 of second or whatever - that's either enough to stop the motion or it isn't, bt changing shutter speeds wouldn't affect that one bit.
01-20-2009, 04:31 PM   #7
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I did change my ISO settings, and settled at 800, because 200 was too low, and the resolution at 1600 was too grainy for what I wanted. I can post samples of what I wound up with at the settings I was successful with.
01-20-2009, 11:15 PM   #8
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QuoteOriginally posted by nezvanova Quote
I did change my ISO settings, and settled at 800, because 200 was too low, and the resolution at 1600 was too grainy for what I wanted.
In what sense was 200 too low? The flash wasn't powerful enough to illuminate your subject? Yeah, in that case you'd need higher ISO. Still unless this is an incredibly brightly lit environment, there is practically no way ambient light would be overexposing your picture at ISO 800, f/8, and 1/180". The flash was essentially the *only* light source, meaning if it was brighter than you wanted, you could have dialed in negative flash compensation - and shot at a lower ISO too.

01-21-2009, 12:37 PM   #9
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I guess I really need to just sit down with my flash and my manual and work out it's settings and how they work. I was sort of winning it at that last shoot, and I left with some successful results, but not as many as I would have liked.
01-21-2009, 02:59 PM   #10
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I too had similar problems trying to shoot hummingbirds at a feeder on my porch. 1/180 of a second was way too slow to freeze their wing motion. I needed fill flash for the pop in their colors due to a backlit situation. eventuelly got frustrated without finding a solution. I had thought about setting up halogen worklights on stands to increase light levels, but didn't try it. Too bad they don't let you have a moron mode where the camera lets you do whatever you want without telling you you are a moron for even trying. I'm still not sure why i would care that my flash duration was longer than my shutter speed. Oh well, the hummers will be back again.
01-21-2009, 03:14 PM   #11
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after a certain shutter speed, the sensor (or film) is not exposed entirely, instead, light hits the sensor as a moving slit of light.

since the flash fires for only a brief moment in time, it will only illuminate that one slit, so you'll get a picture only partially illuminated in the form of a rectangle (depending on how fast your shutter speed is)

here

http://ca.youtube.com/watch?v=7CHgBuKmfog

look closely, the shutter is fully open for a brief moment in time, but if you increase the shutter speed, most mechanical shutters simply cant move that fast, so to compensate the second shutter will start to close before the first reaches its end cycle.
01-21-2009, 04:46 PM   #12
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You could set the flash to trailing curtain, so the people's image trails into the flash exposed image. But I understand that limits the Tv to 1/90?
01-23-2009, 08:39 AM   #13
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my probobly dumb question would be if the flash duration is 1/400th os a second(random speed picked out for the example) but the shutter speed is 1/1000th of a second, wouldn't the image be evenly illuminated as far as the camera is concerned?
01-23-2009, 10:49 AM   #14
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QuoteOriginally posted by shuie Quote
my probobly dumb question would be if the flash duration is 1/400th os a second(random speed picked out for the example) but the shutter speed is 1/1000th of a second, wouldn't the image be evenly illuminated as far as the camera is concerned?
No, because the shutter is not fully open at any speed >1/180. The trailing curtain starts to close before the leading curtain has reached the end so you just illuminate a slit.

High Speed Sync actually strobes the flash for 1/180 of a second so you take several flashes as the slit moved across the frame.
01-23-2009, 11:01 AM   #15
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No

QuoteOriginally posted by shuie Quote
my probobly dumb question would be if the flash duration is 1/400th os a second(random speed picked out for the example) but the shutter speed is 1/1000th of a second, wouldn't the image be evenly illuminated as far as the camera is concerned?
No, as Gooshin stated earlier, at above 1/180th the shutter is never completely open during the exposure. Camera shutters have a leading curtain that moves across the sensor to expose it, and a trailing curtain that then moves to cover it back up. 1/180th of a second is the fastest shutter speed where the whole sensor is still exposed at once. At shutter speeds faster than 1/180th, the trailing curtain starts to move across the sensor, covering it up, before the leading curtain is completely open. At very fast shutter speeds, there is basically a slit of exposed area between the shutter curtains that moves across the sensor very quickly.
The problem with using a flash at these speeds is that the flash is a very quick burst of light, so only part of the sensor gets exposed. High speed synch is achieved by having multiple flash bursts to expose the sensor evenly as the slit moves across the sensor.
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