Understanding Sync Speed, and ND Filters vs HSS – Slice of Pye Ep. 10
Welcome to the live series we’re doing bi-monthly on Profoto’s Instagram called “Slice of Pye”. We’ll be covering a myriad of topics, discussing lighting principles, and showcasing a ton of Profoto gear in action over the course of the next year so please join us over on IG Live!
Tune in to our next episode: August 21st at 2PM PST!
In this episode, we’re focusing on high-speed sync. We’ll cover how it works and when to use it in addition to discussing the difference between using an ND filter vs. high-speed sync. Watch the full episode here:
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In this episode, we’re focusing on the high-speed sync capabilities of Profoto products. Not only do we cover how it works and when to use it, but we also discuss the difference between using an ND filter vs. high-speed sync.
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- Profoto B10
- Matthews C Stand
- Profoto 3′ RFi Octa Softbox
- Profoto Air TTL Remote
- Tiffen 4 x 4″ Water White ND 1.2 Filter (4-Stop)
Why/When Do We Want To Use High-Speed Sync?
When you are shooting outdoors and your intention is to maintain a wide aperture and shoot at a shallow depth of field, you are going to be letting tons of light in. For our test shot in the video, you’ll see our settings are at 1/200th of a second, f/1.4, ISO 400 which is letting a lot of ambient light in giving us a brighter exposure.
When we’re shooting in mid-day sun and a wide aperture, you are going to have to compensate and raise your shutter speed. The problem is, as soon as we get past 1/200th of a second (for most cameras) the flash is unable to fire when the first curtain opens before the rear curtain closes. Let me clarify before this gets confusing.
Curtains? What Are Those?
When you hit your shutter button and your sensor is exposed you have 2 different ‘doorways’. You have one shutter window that releases (first curtain) when you first click your shutter button and then one following after (rear curtain) that closes. While that first curtain goes up, the flare fires during that opening, and then the other one closes, and that’s what exposes the sensor. When you speed up the shutter speed, the gap of time in between the first curtain and rear curtain is so small that the flash can’t fit in a shot. You’ll see a bar that comes across the top or bottom edge of the image which is because the flash is firing through the curtain while part of the image is being blocked. If you need more clarification we cover this in-depth in our Lighting 101 course here.
The Downsides of High-Speed Sync
The solution to avoiding the bar the top and bottom of the image is to switch into High-Speed Sync, but there is a slight issue that occurs. The flash isn’t going to be giving you its full power. As soon as the curtain starts to open the flash is going to pulse, it will start rapidly firing to get an even amount of light into the frame before the rear curtain closes. What that means is dramatically less flash power, as you see demonstrated in the episode.
The alternative is to forego a shallow depth of field and drop down your ambient light exposure and compensate with your aperture and ISO settings rather than adjusting your shutter speed. You obviously lose that wonderful bokeh that is created with a shallower depth of field, so let’s discuss our options.
How To Shoot With High-Speed Sync
Our first step is to set our flash to HSS, if you are using a remote trigger the option should be available on the actual remote, if not you can trigger it on your flash menu system. Once you do that you’ll be able to adjust your shutter speed accordingly while maintaining a shallow depth of field.
The ND filter is going to cut both our flash power and our ambient light exposure. Depending on the type of filter you purchase, you are likely to get a bit better performance using an ND filter because the flash power won’t have to pulse as quickly. Here we are using a 4-stop ND filter which is what I take with me for most of my portraiture work.
To learn more about the fundamentals of lighting check out our Lighting 101 workshop that deep dives into lighting principles!