Question about freezing motion

[JoelKlein]

Hi everyone,
I was playing with a Dreidel, spinning it, and using a Z8/14-24 to capture the Dreidel frozen while it’s spinning at its fastest phase.

My observations:
Using a shutter speed of only 1/250, ISO 64 f/2.8 with a speed light, I was able to freeze the motion.
But, without a flash, I wasn’t able to freeze it even with a high ISO, or a much faster shutter speed. Why? What is the logic?

With a flash 1/250 sync = Frozen

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With a flash in 1/800 high speed sync = blurry!

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Higher ISO instead of a flash = blurry

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Flash at its lowest power = Frozen

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[Cameron T]

The brighter the object, the less time you need to freeze it. super bright object = less time needed.

Same reason you can use higher shutter speeds in bright daylight.

 

[JoelKlein]

The brighter the object, the less time you need to freeze it. super bright object = less time needed.

Same reason you can use higher shutter speeds in bright daylight.

Same brightness using ISO wouldn’t freeze it at 1/250 while a flash would.

Ambient lighting is strong

 

[Cameron T]

Same brightness using ISO wouldn’t freeze it at 1/250 while a flash would.

Ambient lighting is strong

Doesn't matter, the flash is many times stronger, rather obviously.

There are plenty of videos and tutorials that explain this in more detail.

Why does the flash freeze a picture?

Why does a flash freeze a picture even if I use a shutter speed like 1/10 sec? I don't understand it, because the light will hit the sensor the whole time, not just when the flash is fired.

photo.stackexchange.com

How to Freeze Motion With Flash Photography

When it comes to freezing motion, shutter speed is normally the parameter of choice. However, if you are shooting in the studio and you have full control of the light, using flash can actually be the better choice. This excellent video tutorial will show you how to freeze motion using flash...

fstoppers.com

etc

 

[DRwyoming]

My observations:
Using a shutter speed of only 1/250, ISO 64 f/2.8 with a speed light, I was able to freeze the motion.
But, without a flash, I wasn’t able to freeze it even with a high ISO, or a much faster shutter speed. Why? What is the logic?

With a flash 1/250 sync = Frozen

When the flash light is dominant in a scene the flash duration becomes the effective shutter speed. Depending on the flash strength and distance to subject that might be a flash duration and hence effective shutter speed of 1/5000 to 1/10000 of a second or even shorter.

The technique of using flash duration to freeze action is used all the time in things like photographing hummingbirds so that their fast moving wings are frozen in time. The 1/250" shutter speed has a big impact on how the ambient light can light up the background and overall scene but assuming the ambient light doesn't dominate the scene the flash duration sets the effective shutter speed for the main flash lit subject.

If you reduce the ambient light so you could shoot at say 1" or even longer without fully exposing the scene you could still freeze fast action with the flash as the flash duration would really set the effective shutter speed for everything not fully lit by ambient lighting.

 

[JoelKlein]

I never knew this! Can you believe it?!
But wait, why when I used flash high speed sync, at shutter speed of 1/800, it didn’t freeze it like 1/250?

Why use 1/160 in studio? To darken the ambient light?

 

[DRwyoming]

What is the logic?

If you dig a little deeper, flash photography when there's some reasonable amount of ambient light is really an example of double exposure with the first exposure created by the ambient light at the camera's shutter speed and the second exposure with the flash duration setting the much faster effective shutter speed. If the flash exposure is much brighter than the ambient exposure you don't really see the much darker image created by ambient light but if the two light levels are closer in terms of stops of exposure you can start to see both exposures in the image.

I don't do much multi-flash hummingbird photography these days as I prefer natural light images with modern cameras that can reasonably handle higher ISO settings but here's a few older images. They're both shot with the camera set to 1/250" but in the first image the flash lighting was dominant and you don't see much or any of the exposure based on ambient light. In the second image the ambient light exposure is closer to the flash exposure and you can see the ghosting of the fast moving wings. The sharp wings are the flash exposure and well frozen in time but the blurred wings are what the ambient lighting provided at the set 1/250" shutter speed.

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[JoelKlein]

Is there a way to calculate flash duration? Effective shutter speeds produced by the flash?

 

[Doug Herr]

... why when I used flash high speed sync, at shutter speed of 1/800, it didn’t freeze it like 1/250?

High-speed sync (HSS) is multiple lower-powered flashes as the shutter curtain slit moves across the image area, so you ended up with more ambient light illuminating the Dreidel. HSS can result in distortion of fast-moving objects similar to the rolling shutter effect.

 

[John Navitsky]

the flash is basically a second shutter. the brighter the flash setting the longer the duration. if you have a flash like a godox ad200, you can turn on a setting that will show you the duration when in manual mode (not ttl).

 

[DRwyoming]

I never knew this! Can you believe it?!
But wait, why when I used flash high speed sync, at shutter speed of 1/800, it didn’t freeze it like 1/250?

It's been a while since I shot with High Speed Synch but as I recall the way my cameras provided high speed synch above the normal flash synch limit was to pulse the flash while the shutter was open. I'd have to review that as I haven't delved into that in a long time but as I recall it's not a single flash burst.

Why use 1/160 in studio? To darken the ambient light?

That's a natural impact of lowering the camera shutter speed, ambient light becomes less important to the resulting image but it may also depend on the studio flashes you're using and the best synch speed for them.

BTW, one way to get your head around this is to think of what would happen if you darkened your studio completely and only used flash (one or more) to light your subjects. You could leave the shutter open for many seconds if the room was completely dark but when the flash fired it would set the effective shutter speed for anything in the scene. IOW, in a completely dark room with little to no ambient light you could leave the shutter open for very long times (in film basically indefinitely, with digital there are limits due to electronic noise for very long exposures) and the flash would be the only real light source so it would only expose the scene for the duration of the flash burst.

When you start introducing ambient light at more reasonable levels then it's really a double exposure situation like shown in the previous post. But you can use that to your advantage in several ways:

- Full Flash images have the ambient light so far down that you can ignore it. Your studio setting with flash synch set to 1/160" is likely a case of that unless your studio has very bright ambient lighting or you run the ISO pretty high. In this case flash does all of the lighting and you can ignore whatever ambient light is in the studio. If you meter a scene like this without the flashes it should show up as underexposed by several or many stops as the only real lighting is what the flashes provide.

- Fill Flash which many outdoor photographers use sets the flash exposure somewhat below the exposure from ambient light just to fill in shadow areas like eyes underneath the brim of hats. In this case you typically meter the scene and set the camera settings for proper exposure and then set the flash manually or via a through the lens flash metering (e.g. Nikon's iTTL) to something like negative 2/3 to maybe negative 1.5 stops or so depending on how much fill you want. You might even fill closer to ambient to remove most if not all shadows if desired.

- Key Flash where the ambient is slightly underexposed and the flash lighting is for the main subjects. This can make those main subjects jump off the page as they're maybe half a stop to a stop or more brighter than the background. In this case you meter the scene without flash to be underexposed a bit and then set your flash manually or though iTTL or equivalent to have positive exposure compensation so the flash lit subjects are brighter than the background. This is used all the time in advertising and things like magazine covers where the models really jump off the page as our eyes are drawn to those brighter subjects lit by the flash.

 

[DRwyoming]

Is there a way to calculate flash duration? Effective shutter speeds produced by the flash?

Flash duration depends on the specific flash in use and to some extent the type of flash with studio flashes being a bit different than Speedlight style flashes in terms of the shape of the pulse of light that's delivered and what that means in terms of total integrated light over the flash burst.

I've mostly used off-camera Speedlight style flashes like Nikon's SB-800, SB-900, SB-600 and the like. Here's estimated flash durations at different fractional flash power settings for the SB-800 from its manual.

The estimated flash durations are given in terms of fractional power so it's much harder to estimate when running in an automated flash mode like Nikon's iTTL. I'll use iTTL with positive or negative flash exposure compensation (depending on whether I want Key Flash, Fill Flash and the like) for a lot of stuff where exact flash duration isn't my biggest concern. But for things like hummingbird photo setups where I want to freeze the wings I'll go to full manual flash control and figure out the scene before the birds come in so that I have decent control over flash duration.

 

[John Navitsky]

godox ad200 flash at full 1/1 power, flash duration 1/220s

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flash at 1/256 power, flash duration 1/15380s

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[tclune]

godox ad200 flash at full 1/1 power, flash duration 1/220s
<snip>

flash at 1/256 power, flash duration 1/15380s
<snip>

AIUI, flash duration is a bit of a saw-tooth with a long tail. At full power, you have a high peak and a lot of tail: at low power, you get the top little bit of the peak and essentially no tail. The upshot of this is that full power lasting 1/220 s does not suggest that it is similar to a shutter speed of 1/220 s -- the vast majority of the light is in the first millisecond or so.

 

[bleirer]

This guy, Harold Edgerton (Dr. Strobe), started it all, I think. Stopping bullets in flight and more.

Harold Eugene Edgerton

Learn more about the photography of Harold Eugene Edgerton.

www.icp.org

 

[Geoff_G]

As mentioned above there are '2 exposures' to take into account....one from ambient lighting and the other from the flash lighting. Flash duration is short so SS has no effect on flash strength (a sync speed of 1/250 Sec allows the flash to happen when the shutter curtain is fully open, any faster than that means some part of the image does not receive flash illumination bc it's blocked by the moving shutter curtain). As Dave's chart shows, flash duration is what changes the flash output level. In some case flash duration is important (as in Dave's example). In other case flash strength is what matters, not flash duration.

Getting to simple...
With a flash acting as a 2nd light source it can be set to dominate the scene or just add to it (ie, fill in flash). Flash exposure/duration is very short so exposure is set with aperture, flash power, and distance to subject, SS is basically out of the equation. But SS determines background exposure so the overall scene exposure is set with SS whereas subject exposure is set with flash.

 

[bleirer]

Negative comments sure put a damper on people asking questions.

 

[BillW]

This guy, Harold Edgerton (Dr. Strobe), started it all, I think. Stopping bullets in flight and more.

Harold Eugene Edgerton

Learn more about the photography of Harold Eugene Edgerton.

www.icp.org

When I was an undergraduate, I had to take a laboratory class in order to graduate. I was a math major, so not a natural in a lab.

Harold Edgerton and his assistant, Charlie Miller, offered a high speed photography course that met the lab requirement. I decided to try it. We took photos of bullets crashing through apples and playing cards, water and milk droplets and other short-lived phenomena. A great course and lots of fun.

Professor Edgerton was mostly retired at that point, but a very nice guy with great stories. He never lost his sense of wonder about what he could discover with the equipment he invented.

The technique to photograph a bullet crashing through an apple or playing card was to line up all the equipment, turn off the lights, open the camera’s shutter, and fire the gun. A microphone was used to trigger the flash from the sound of the gun. The flash had short duration and would easily stop motion of a bullet. Given it was Professor Edgerton’s lab, we had pretty good equipment to use.

 

[JoelKlein]

I have 3 Ad300 pro’s and 1 600

 

[JoelKlein]

To be perfectly honest, the fact that you dont already know the answer to that, while charging people for your photography is a bit concerning.

Seems you never ran a baby’s and kids/family studio business.

All light are coming from the flashes/softbox’s. Ambient room light isn’t in the equation. Camera shutter is set to 1/160. Sometimes if a bit less light is needed, it’s easier/faster to crank the camera shutter to 1/200 which effectively results in a bit darker exposure with the same lighting power settings.
All we need to know, is a solid understanding of all lights/softboxes what they do, and how to manipulate them to get the light where it’s needed.

Freezing Dreidel’s motion with flash, isn’t required to the above business.
What is required, is knowledge of HSS, because we have recall button set to open the lens to f/1.2 and up the shutter speed without needing to fiddle with the flash trigger settings.