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Understanding Flash Sync Speed and High Sync Speed

March 3rd 2014 1:30 PM

What is flash sync speed? How does it work and what are its limitations? The video below takes you through a quick and simple explanation of why you get the black band on your image when using flash and how to avoid it.

 When You Click The Shutter Button

Most DSLRs have a two curtain mechanism in front of the sensor. When you press the button, the sensor is exposed. First, one curtain goes up exposing the sensor, and the second curtain follows to hide the sensor after which they both reset their position. The amount of time that the sensor is exposed is based on your shutter speed setting. A slower shutter speed will leave your sensor fully exposed, while a faster shutter speed could mean that only a sliver of a window will be open between the curtains.

When Your Flash Fires

Typically, when you press the shutter button and the first curtain goes up, the flash will fire a single burst of light and the second curtain closes. If your shutter speed is set too high when the flash fires, only the uncovered section of the sensor in that moment will be exposed. The areas of the sensor that are obstructed by the curtains during the flash fire will remain unexposed and you will have black bands or shadows across your image.

Maximum Shutter Speed Sync

Cameras have what is called maximum shutter speed sync. It is the fastest shutter speed you can set on your camera where both curtains will fully expose the sensor when using flash and avoid the black bands. Most cameras have this setting at 1/180th of a second or 1/200th of a second.

shutter too fast

f/2.8, shutter speed 1/500 with off camera flash creates a black band.

High Speed Sync

Some higher end cameras and flashes have a setting that allows the user to override the maximum shutter speed limitation without sacrificing the image. In Canon, this feature is called High Sync Speed (HSS) and in Nikon it’s called Auto FP. When this feature is turned on, the flash fires more than one burst of light like a strobe effect. It begins before the first curtain goes up and ends after the second curtain closes. This allows all the little sections to be exposed resulting in an image with no bands.

HSS flash sync

f/2.8 shutter speed 1/350 to get background colors leaves subject a little dark.

HSS flash

f/2.8 shutter speed 1/350 with HSS option turned on. Flash on camera.

Note: When a Canon flash is attached to a Canon camera (or Nikon Flash to Nikon camera), the camera will set the limit on the maximum shutter speed which protects the user from accidentally getting black bands. It won’t allow you to go past the maximum shutter speed unless you turn on the HSS feature.

Drawbacks to High Speed Sync

1. Heavy battery use – because the flash fires more than one burst of light in rapid fire it consumes batteries quickly.

[REWIND: THE BEST BATTERY TO USE FOR FLASHES]

2. Expensive Equipment – combinations of third party triggers like Phottix and Yongnuo with third party flashes give you the power to do off camera flash affordably. But in order to make use of the HSS and Auto FP features, you will have to invest in triggers and flashes that can accommodate that function like the newly announced Yongnuo 622N-TX and the Canon 600EX-RT Speedlight Flash and they are generally a higher investment.

[REWIND: WIRELESS FLASH TRIGGERS ON A BUDGET]

Conclusion

Keep your shutter speed at 1/200 or slower when using flash unless you have the HSS (Canon) or Auto FP (Nikon) feature turned on which allows you to raise your shutter speed when using flash.

Michelle is a Southern California Portrait and Wedding Photographer. When she’s not geeking out with a camera she’s nerding out in her IT world. All other moments in the day are spent with her two wonderful children.

See her work on The COCO Gallery
check out her blog at frexNgrin

Comments [6]

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  1. Kelvin Strepen

    Now, I understood, Michelle Ford. Thanks for your writing.

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  2. Alexander J.E. Bradley

    Thank you so much for this video. I have been shooting High Sync flash photography for some time. I throw milk on people and capture the moment the milk in in flight, and impacting on the face of my subject, but to freeze the milk in motion I need to shoot at speeds of about 1/1000 – 1/2000, so I employ high speed flash sync. I just never really understood how it actually worked until now. I did however think that the flash power output had something to do with the ability for this functionality to work. As in, shooting on my SB800 at Full Power, it takes 1/880 to fire, I would obviously be limited to shooting below this speed for it to work? Or is this irrelevant because it will multi flash when it shoots.

    Here is a link to some of the work I have been using with fill flash at speeds of generally 1/1000. http://www.alexanderjebradley.com/lait.html

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  3. Chance

    Some flash units, primarily moonlights, have an extended flash duration. This actually allows for HSS to occur.

    I use a Canon 5D, Neewer strobes, and Pixel King tx with Pixel Opas transceivers. It’s a great combination for someone on a budget. The neewer strobes are more than enough fill light and work great at night

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    • Michelle Ford

      chance, thank you for that. i’ll dig around and see what i can glean about neewer.

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  4. Rick

    There’s a third drawback that is probably worth mentioning; at least with Canon’s implementation of HSS, you lose some flash output when turning it on.

    An example: You want to use a specific aperature and ISO. And, you have your flash at full power and shutter at 1/200 s. But while that gives you good fill, the ambient is too much. So you set the shutter to 1/400 s and turn on HSS. But now, the flash will have less output, so you’ll need to adjust accordingly.

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    • Michelle Ford

      you are right rick. i didn’t realize this at first but the more i read about it, the strobe effect actually has an impact on the amount of light it pushes through.

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