June 5, 2012

off-camera flash in low light – choosing your shutter speed

In the article on maximum flash sync speed, a question came up whether this is where we’d be at even in low light.

The answer is, that we’d most likely be at a shutter speed where the ambient light shows up. To remain at max flash sync speed in low light, isn’t the immediate best choice, for the background would usually go too dark. And we would like context. Our photographs usually look best with our subject in surroundings we can recognize, or complements our subject in some way.

Regarding our choice of max flash sync speed, this is the best go-to camera setting when you use flash in bright ambient light. High-speed flash sync kills too much of our flash output, to be our first choice, unless we are specifically chasing the higher shutter speeds or wider apertures. If you use a softbox or umbrella (or some light modifier) with high-speed flash, then you stand the risk of the flash simply not being able to pump out enough light to match the bright light. For this, generally our sweet spot is maximum flash sync speed.

Shutter speed choice when using flash, will vary depending on what we’re photographing, or trying to achieve. In low light, we’re most often dragging the shutter. But we have to be able to adapt what we do, against what we’re trying to achieve with our photos.

As recap example of using flash in low light, let’s have a closer look at the top image:


I was busy photographing a model, Molly K, as part of a forthcoming review of the Canon 600EX-RT speedlite and Canon RT-E3 speedlite controller. For a final image, I wanted her against the awesome backdrop of the early evening Manhattan skyline.

The photograph above was my first test shot: 1/30 @ f/5.6 @ 800 ISO.  You can’t use your camera’s light-meter in a general way, since there are dark areas and bright areas. Selectively metering and guesstimating, along with a few test shots, will get us there. I eventually settled on 1/20 @ f/5.0 @ 800 ISO for the settings of the final image.

Working at shutter speeds as low as 1/20 hand-held, will strike fear with some photographers. Alternately, some might be okay with it, saying that “flash will freeze the movement.”  Well, yes … but not necessarily. It depends. Or if this was a Facebook relationship status, it would fall under “it’s complicated.”

We’ve discussed shutter speed choices with flash in that article, for various scenarios. But let’s look specifically at flash with low light.

Flash will only effectively freeze motion, if
– the ambient light on your subject is 4 stops or more under the (proper) flash exposure, and
– there isn’t a bright area behind your subject that will reveal there was movement.

In the example above – a straight-forward portrait of our model, there isn’t any movement to contend with, except for potential camera shake. This is where a stabilized lens works wonders. The Nikon 24-120mm f/4 VR (B&H) and Canon 24-105mm f/4L IS (B&H), are both superb lenses for general photography. With the image at the top, there was minimal available light on her, so the flash froze any potential camera shake. Along with a the stabilized lens, a careful stance and breathing, this all ensured that I get crisp images.

Since she wasn’t going to move or jump, the brighter sky behind her wouldn’t show the blur of movement.  Flash will freeze action, as long as the subject isn’t moving against a much brighter background – for then we will see some kind of ghosting effect, or parts of our subject might disappear into the brighter areas.

Doing another test shot at my final settings of: 1/20 @ f/5.0 @ 800 ISO, I could easily confirm that camera shake would not be a problem. In this case flash would freeze any movement, whether the model’s or my own. On top of that, I was shooting at a focal length of 24mm, and in comparison, especially with a stabilized lens, a shutter speed of 1/20th isn’t all that scary.

camera settings:  1/20 @ f/5.0 @ 800 ISO

I used a softbox to camera-right, with the Canon 600EX-RT (B&H). The speedlight was in manual exposure mode, and was controlled by the ST-E3-RT Speedlite Transmitter (B&H).

I didn’t specifically meter for the flash. From experience, I have a good idea of how powerful my light will be at specific distances with that softbox. With manual flash, we have that specific relationship between Aperture + ISO + Distance + Power, to give us the correct flash exposure. And this remains consistent, even if we shoot on another day in another place.

 
equipment used:
Canon 5D Mark II;  Canon 24-105mm f/4L IS (B&H)
Canon 600EX-RT (B&H);  ST-E3-RT Speedlite Transmitter (B&H)
Lastolite Hot Shoe EZYBOX Softbox Kit (24″x24″) (B&H)

 
related articles:
max flash sync speed
the advantage of a higher max sync speed
tutorial: high-speed flash sync
using high-speed flash sync / Auto FP   (model – Aleona)
dragging the shutter
shutter speed choice with flash
– shooting in low light – flash and incandescent light
when aperture does NOT control flash exposure
‘urban legends’ of flash
shutter speed does not necessarily control your background exposure!

 

 

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{ 19 comments. } Add a Comment

1 Felipe Anciaes June 5, 2012 at 1:29 pm

Neil, I’m a fan of yours! I can’t wait for a new post at Tangents every week! Thanks a lot! Please, keep it like that!!

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2 Eva June 5, 2012 at 4:50 pm

Neil,

Thank you for your generous reply to my question. I was honestly very surprised to see the new post you created staring right at me on the front page. It cleared up the smoke, so thanks again! :)

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3 Boston Wedding Photographer June 5, 2012 at 6:19 pm

Great stuff Neil, good location and model.

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4 mo11211 June 5, 2012 at 7:28 pm

Thanks for another informative article.

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5 Rick June 5, 2012 at 11:45 pm

Could you explain why you used ISO 800 when you had a f/4 lens? You could have used a larger aperture and a lower ISO. Presumable a lower ISO would have produced a better image quality. Was it because your f/4 lens performs better when stopped down to f/5.6?

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6 Neil vN June 5, 2012 at 11:50 pm

Rick … 800 ISO isn’t a particularly high ISO anymore, and I felt more comfortable using the lens slightly stopped down, than wide open. But at some point here, these settings become fairly arbitrary, and the difference between f/56 and f/5 and f/4.5 become incremental. Same with 400 ISO and 500 ISO, for example.

Neil vN

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7 parv June 5, 2012 at 11:52 pm

The choice of shutter speed is not my problem around low levels of ambient light (as shown above), the amount of flash intensity is when both darker & lighter tones are present. The results are unsatisfactory when I do try: shadows are crushed and/or highlights are overexposed when trying to expose for face, skin tone.

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8 Neil vN June 5, 2012 at 11:58 pm

Parv .. this is exactly the reason it is essential that we shoot in RAW. Then we can control the contrast and local contrast, etc, in post-processing. Much less stress.

Neil vN

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9 Jo June 6, 2012 at 1:30 am

Love.It. I just love how you think out loud in these posts. It must be the right learning style for my brain because it just makes sense. Thanks Neil!

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10 andrew June 6, 2012 at 2:55 am

I second what Jo says in the above post.

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11 Desmond June 6, 2012 at 2:52 pm

The 5th line “And we would like context” …. was that meant to read “And we would LOSE context” ?

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12 Neil vN June 6, 2012 at 2:58 pm

Yes, we would lose context at settings where the background goes too dark. Which is why I said, “and we would like context”.

Neil vN

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13 patrick clarke June 6, 2012 at 4:13 pm

neil i notice that the lower body is in shadow
how would you correct this if you were shooting a bride and you would like the gown better exposed ?

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14 Neil vN June 6, 2012 at 4:16 pm

I purposely feathered the light from the flash here to get that light fall-off to her feet.

So to get more even light, you’d hold the softbox more evenly, and you can also pull the softbox further back from your subject, in order to get more even light. But … then the light becomes more contrasty.

Neil vN

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15 sam June 6, 2012 at 4:30 pm

Thanks Neil. What power was your flash set to? 1/2 power? or 1/4 at closer distant to subject?

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16 Neil vN June 6, 2012 at 5:21 pm

Sam, I didn’t take particular notice of my actual power setting. Too many things would affect my exposure for it to make any real sense to list the power setting of the flash. The two baffles in the softbox would affect exposure. Also, in the way that I asked my assistant to feather the light, would also affect exposure.

Neil vN

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17 annemarie June 7, 2012 at 1:06 am

Neil, Just want to say thank for this and the numerous really helpful articles. I like it when you also show how it would be without flash (some writers just show the final pic) and sometimes when you show how it could go wrong.

Consistency with Aperture + ISO + Distance + Power? That sounds interesting. Have you written on this, or will you one day?

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18 Neil vN June 7, 2012 at 2:43 am

Annemarie … see the Amazon link at the bottom of the article there, to my books on flash photography? You have some homework. ;)

There is also this list of all the articles on this website, on the topic of flash photography.

Neil vN

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19 Joshua July 2, 2012 at 8:01 pm

Neil,

Thanks for the great article. I got 2 questions.

I was shooting a wedding with people dancing and the room has some background spot lights. I was using 1/320 and f3.2 with ISO 2000. I tried to adjust with the ISO as I need to freeze the dance motion and wanted to keep a relatively narrow depth of field to isolate the subject. I found it very hard balance the bounced flash light to properly show the “context”.

Also, during dinner time, the head table is backed by a wall (with like 3 feet distance), I found the “context” got all wash out by my flash. I tried to adjust my bounced light to different angles and directions but didn’t help.

How would you do that?

Thanks,
Joshua

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