HSS (High-Speed Sync) and image quality

High speed without HSS
Apparently, although I haven't confirmed this, at very high shutter speeds, another method (avoiding HSS) is to envelop the entire shutter operation with the flash duration, by setting a variable-duration flash to full power. Flash distance from the subject is then used to vary exposure. I'm not sure why flash output waveform isn't visible as a decrease in light across the image (i.e. "shutter creep"), since higher shutter speeds don't actually increase the curtain speed but instead narrow the opening that passes over the sensor. Here is a video that I don't fully understand: Breaking The 1/250s Sync-Speed Trick! - YouTube

If you understand that, information would be appreciated. I guess I'd be curious to see if his image looked different if he held the camera upside-down here.

As a final note, remember an alternative to high-speed may be to use an ND filter, if your goal for high-speed is simply to preserve bokeh in a bright scene.
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I watched the video, originally and had posted on a similar issue on another thread. The video, in general is not very helpful. It just explains that in order to combat banding due to the rapid closing of the second curtain that you need to have either a.) a longer flash duration to "beat" the second curtain, or b.) have an HSS light that fires the multiple pulses of light as the curtains are closing.

And in regard to color, how much to be seen is going to be negligible. In the shots I used, it was an ungelled strobe. In order to get white balance correct, I should have used a CTO gel, but all I was demonstrating was HSS. In midday sun, where HSS is most utilized, gels are not likely to be used because the color temp of the flash is similar to the ambient color temp.

I've come to equate this thread similarly to the way I treat my patients (I'm a student nurse). Understanding the anatomy and physiology of patients (equivalent to the technical specifications of flash is important), however how useful remains to be seen. Ask a veteran nurse of 20 years how myofibrils work in the muscle - in most cases, they won't remember. Because I ran through my thread similarly about 2-3 weeks ago, what I learned is that a.) I can combat motion and the HSS barrier with my current setup and b.) how do I utilize it and c.) how does it affect my images.

I used to own a $20 RF trigger off of ebay. While it didn't work consistently, when it did work, it was MUCH simpler to shoot with. I rarely focused on all the other nuances of HSS and shadows, etc. Granted, I'm learning more, my new system allows me to do much more. Finding what works for you, and how to best utilize it will be more valuable than remembering information that won't tell you how to set up your shot.
 
Here's an example of why I'll end up using HSS more often than normal.
85mm ISO 100 f/1.4 1/500

$Shiloh Resized.jpg

Because I was in my garage, I wanted to have the least amount of background in focus as possible. I needed my strobes with a soft box and grid because of the "look" I was going for and there was just too much ambient light being allowed by the wide aperture. Even at 1/400, there was still significant background showing up. Once my modifiers were in place, I adjusted the SS accordingly. I was able to do this not because I know everything there is to know about the way my strobe works, but because I know how to utilize my system.
 

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Here's an example of why I'll end up using HSS more often than normal.
85mm ISO 100 f/1.4 1/500



Because I was in my garage, I wanted to have the least amount of background in focus as possible. I needed my strobes with a soft box and grid because of the "look" I was going for and there was just too much ambient light being allowed by the wide aperture. Even at 1/400, there was still significant background showing up. Once my modifiers were in place, I adjusted the SS accordingly. I was able to do this not because I know everything there is to know about the way my strobe works, but because I know how to utilize my system.

I'm a bit confused why you took that shot at f1.4? There's nothing noticable to render out of focus that I can see,in fact it's black.
Did you post the wrong pic maybe?
 
No, I did it on purpose. In test shots, I stopped down, but it a.) gave me a greater depth of field, and b.) changed the light on my subject.
 
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Here's an example of why I'll end up using HSS more often than normal.
85mm ISO 100 f/1.4 1/500



Because I was in my garage, I wanted to have the least amount of background in focus as possible. I needed my strobes with a soft box and grid because of the "look" I was going for and there was just too much ambient light being allowed by the wide aperture. Even at 1/400, there was still significant background showing up. Once my modifiers were in place, I adjusted the SS accordingly. I was able to do this not because I know everything there is to know about the way my strobe works, but because I know how to utilize my system.

I'm a bit confused why you took that shot at f1.4? There's nothing noticable to render out of focus that I can see,in fact it's black.
Did you post the wrong pic maybe?

Let me ask you this then:

Had I shot this image at full power, with a soft box and grid, ISO 400, f/9 1/250, would it have been "right?"
 
No, I did it on purpose. In test shots, I stopped down, but it a.) gave me a greater depth of field, and b.) changed the light on my subject.

Interesting.
I would have done it differently,but that's what makes the world go 'round.


"Let me ask you this then:

Had I shot this image at full power, with a soft box and grid, ISO 400, f/9 1/250, would it have been "right?""


I definitely wasn't telling you what to do,just asking why.
"Right" will always be subjective I guess.
I probably would have started at around f5.6 and iso 200.
 
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Thanks again for the help. I just wanted to report back a little bit of research on high-speed flash operation.

Variable-duration vs. Variable-voltage
These two types of flash can typically be distinguished as follows:

Variable-duration flash
Small-battery powered flash (power control via flash duration is more energy-efficient, and so usually used with batteries)
Handheld and camera-mounted speedlites (these are typically small-battery powered, just due to physical dimensions)
Xenon gas-filled flashes (xenon-filled flashes are more efficient and work at lower voltages, and are used for increased battery life)
IGBT controlled flashes (insulated-gate bipolar transistors offer high-efficiency high-speed current switching in current small electronics)

Variable-voltage flash
Studio monoflash units
Voltage-controlled studio strobe
Units with integrated modelling lamps
Wall-powered flash


How this affects your image
Flash color and duration is affected by the type of flash and its configured power output setting. Here is a very useful reference for understanding that: Paul C. Buff, Inc. - Flash Duration

Both types of flashes exhibit color changes when power is adjusted. However, that change is different for each. One reason is the materials used for the flash. Another, possibly non-intuitive reason is this: A variable-duration flash trims the trailing end of the output (when the capacitor has already discharged and the voltage has diminished) as necessary to reduce total light output. This causes the average flash voltage to actually be higher as power decreases of a variable duration flash. A variable-voltage flash unit diminishes the voltage for the entire duration of the flash, but also causes the the voltage to be more consistently distributed through the flash.

Both types of flashes also change the visible duration as power is adjusted. Variable-duration flashes obviously reduce duration with reduced power, although not at a linear rate - most of the power is spent early. Variable-voltage flashes result in a "slower" flash at lower power, because the initial output is dampened (the waveform is smoothed) as voltage is reduced. Thus a greater percentage of the power is spent late in the flash. The reason for this can also be seen in the photo above.


Relationship to sync-speed and "HSS"
At full power, total flash duration for both types of flash are commonly equivalent to exposure times from 1/400 - 1/600 (although most of the light has already been emitted by 1/2000). A Canon 580EX II (variable-duration) flash set to 1/128 power will only last a total of about 1/60,000 of a second. A similar Yongnuo flash is about twice as fast. ()

Typical camera "max flash-sync speed" (the shortest exposure for which the leading shutter has finished opening for a useful period of time before the trailing shutter begins to close) ranges from 1/150 - 1/350. This duration and shutter "curtain speed" is slightly slower than the typical flash duration, by design. Making the shutter open and close operations more "instantaneous" to raise this sync-speed is not tremendously advantageous in typical consumer equipment. As you have seen above, flash devices are also fairly variable in function beyond these speeds - they have variable output pattern by device manufacturer and model, and that output pattern is asymmetric. As a result, for a conventional flash to be consistent from photo to photo and from image top to bottom (or left to right), the entire flashpower must be spent while the shutter is fully open.

However, with "high-speed-sync" (HSS) flashes, the flash is actually pulsed rapidly over the entire duration the shutter is open AND partially open.

Unfortunately, this reduces maximum flash power for two reasons:
1) Now, rather than the entire flash output reaching the sensor, only a portion of the sensor is revealed to the flash at any point. The shutter speed is now modifying flash power.
2) The "pulsing" action typically increases total duration to cover the entire time from shutter open to shutter close. This reduces the flash output at any given point (the flash hardware is generally not designed to survive or be electronically capable of full power operation for these longer durations)
This PocketWizard wiki image shows a 600EX-RT output in HSS mode:
View attachment 63676

High speed without HSS
Apparently, although I haven't confirmed this, at very high shutter speeds, another method (avoiding HSS) is to envelop the entire shutter operation with the flash duration, by setting a variable-duration flash to full power. Flash distance from the subject is then used to vary exposure. I'm not sure why flash output waveform isn't visible as a decrease in light across the image (i.e. "shutter creep"), since higher shutter speeds don't actually increase the curtain speed but instead narrow the opening that passes over the sensor. Here is a video that I don't fully understand: Breaking The 1/250s Sync-Speed Trick! - YouTube

If you understand that, information would be appreciated. I guess I'd be curious to see if his image looked different if he held the camera upside-down here.

As a final note, remember an alternative to high-speed may be to use an ND filter, if your goal for high-speed is simply to preserve bokeh in a bright scene.


That is deep!
 
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