How Shutter Speed and Aperture Relate to Flash

This illuminating tutorial is guaranteed help you take better photos.

In this information-packed photography class, Karl breaks down the relationships between flash power, aperture settings and shutter speeds.

You’ll learn about:

  • Understanding flash sync speeds
  • The relationship between ambient light and flash
  • The relationship between aperture and flash
  • First- and second-curtain flash synchronization

You’ll learn how each of these can work together to influence the final image.

In this class:

  • How shutter speed works in photography
  • Sync speed vs flash duration
  • Leaf shutter vs focal plane shutter
  • Shutter speed and aperture
  • The impact of ambient light on an image
  • Controlling flash exposure
  • Combining studio and ambient light

If you enjoy this class, check out Understanding Flash Power and Fast-Flash Jelly Headshots.

Questions? Please post them in the comments section below.


  1. HI,

    Does the new global shutter system in the Sony a9 eliminate the issue with flash sync or is it a new workaroud?

  2. Hi Karl, how does the first curtain / second curtain work on cameras that only have digital shutter and are not mechanical ? Thanks.

    1. Hi, first or second curtain simply refers to when the flash will be fired, either at the start of the exposure or at the very end of the exposure so this is just controlled electronically so should make no difference whether it is a mechanical or electronic shutter.

  3. I was told that when working indoors, he first step is to set the camera so that the ambient light is removed, so take a photo at F8, SS 100, ISO 100 and that photo will be black. From there turn on your flash and you can start taking photo’s. Do you need to do this?

    1. Hi, as often is the case it depends on circumstances as occasionally you also want to include some of the ambient light in the scene too. However I always think it is good practise to understand how much is ambient and how much is flash. A good example of this can be see in this class where I have to mix both but also need to establish which is which: – The settings you mentioned above would be a middle of the range starting point as ambient light can vary greatly. I tend to decide what I need my aperture to be for creative depth of field reasons first and then shoot at varying shutter speeds and ISO to establish what the ambient light levels are. If you restrict yourself to f8 straight away then you’re also restricting your creative decisions for depth of field. Once you’ve established your DOF and aperture you then work everything around that whether it’s an increase or decrease in shutter speed, a decrease or increase in ISO or even adding ND filters to your lens. The class I mentioned above will give you a good idea of how I deal with these sort of problems.

  4. Hello Karl,

    I have a question: When I use my godox V1 as an optical slave to shoot with my Canon T3i I cannot go above the 1/250 sync speed (I do not have any trouble when the flash is attached to the hot shoe). Is this because of the optical trigger? How can I fix this?

    Thank you!

    1. Hi Ramina, I’m afraid the working specifics of different flash systems is not something I can answer as many of them are different. You would have to consult your user manuals or the manufacturer for that sort of information. As you know we teach techniques, lighting, visualisation and the art of photography. The limitations you are experiencing will be a solvable as it would be very strange for a system to prevent you from choosing whatever shutter speed you want if you are working in manual mode.

      1. Thank you for your reply, Karl. I have this limitation even when I only use my camera’s pop up flash, It does not let me go beyond the max sync speed in full manual mode. So I think when I use the pop up flash as an optical trigger my camera still applies the same limitations because the pop up flash is firing to fire the external flash. Thank you again.

  5. I’ve always had the issue of experiencing a cap on my shutter speeds when I was connected to my FJ400 strobe. Despite being in HSS mode on the trigger, strobe, and in camera, I could adjust my shutter to 1/250 or higher, but the camera would automatically readjust to 1/200 once I engage the shutter to take the photo. Not sure why this is. I currently use a Canon R6II but also experienced this issue when I used my previous Canon Rebel T8i model

    1. Hi, if you are in full manual mode on your camera then this shouldn’t happen as the camera should give you total control, it may be that there is a sensor on the hot shoe where the trigger or flash goes that over rides this but that would defeat the purpose of having a full manual mode. Check in the camere menu settings if there is an over ride for flash sync speed.

      1. Wow I tried the same thing with a speed lite instead and didn’t have that issue. The FJ-X2m flash trigger must not be registering with my camera. Will research if there is any other accounts of this issue online.

  6. Another observation is that HSS works differently in different camera systems. Canon is very primitive because is elongates the flash duration as you explain. However Nikon HSS is the most sophisticated and adopted by Leica. The HSS flash output is in pulses so requires a lot of power. The faster the shutter speed, the more power you need for more pulses.

  7. Probably the best explanation on the world wide web.
    Just one issue. Focal plane shutter only travels forwards. This means both curtains travel in the same direction. So waving the black card apart from each other is not correct because they are moving is opposite directions! Also most focal place shutters run horizontally not vertically. Only later cameras had vertically running focal plane shutters.

  8. Hi Karl,

    I have a question regarding the flash function settings. Are options for first and second curtain flash synchronization available in Nikon Camera as well or not?

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