Friday, October 01, 2010

How to: Track Ambient Automatically While Using Manual Flash

Here's a cool tip that some of you might not know about. If you are using manual flash (for consistency) you can still work in a quasi-auto mode in an environment where the ambient light level may be moving around on you.

It works great for using manual flash against fast-dropping light after sunset, for instance. And you can control the flash and ambient very easily from your camera.
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First off: As always with manual flash, you'll need to keep the flash-to-subject distance consistent. This either means shooting a relatively static set, or having an assistant track the subject with your flash.


Use Aperture Priority

In this mode, your aperture stays wherever you set it, and that means that your manual flash exposure will also remain constant. The shutter speed varies according to the ambient light. So it will track automatically.

This also gives you a neat control function over both flash and ambient exposures.

Let's say that your flash is putting an exposure value of f/5.6 on your subject, and the ambient (say, for the sky in the background) is f/5.6 at 1/60th of a second.

By setting the camera on AV f/5.6, it is going to choose a shutter speed at or very near 1/60th, which is just want you want. If you want to vary the sky value, simply do this with the exposure compensation dial. Your sky will track at your preferred lighting ratio -- even as the ambient light drops down after the sunset.

If you need to alter the exposure on your subject, simply adjust your aperture. Going to f/5.6 1/2 would drop the exposure on your (manually flashed) subject by half a stop. Going to f/4 1/2 would brighten them up. You get the idea.

And all the while, the relative brightness of the ambient background would track at whatever ratio you previously chose. Which is pretty sweet when your ambient is dropping by the second as dusk turns to dark. Because that is when the color of the light can get really interesting (and fast moving) and you do not want to be wasting time getting exposure readings off the sky.

And all the while you are keeping full control of your flash exposure, which is absolutely consistent.
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UPDATE: I would think this goes without saying, but several commenters have correctly noted that you need to make sure your shutter speed does not creep up above your sync speed.


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30 Comments:

Blogger Miika Ylhäinen said...

Wow this is really cool! Haven't thought about it, but makes perfect sense. Sometimes when you are shooting mid-day on a semi cloydy day, when sun is behind a cloud one second and fully exposed the other, balancing the ambient is a real PITA.

October 01, 2010 12:16 AM  
Blogger AlexJB said...

An excellent point! Thanks for this post. I've struggled sometimes to follow the lingo that you typically use for describing how to manage exposure. I tend to use aperture- and shutter-priority modes to control depth of field or motion blur. So it helps to have you connect the principles for combining ambient and flash with letting the camera's meter do the work!

October 01, 2010 1:36 AM  
Blogger Fredrick3929 said...

I've thought about that before and i'm guessing it would be optimal to use evaluative metering just because you would probably get whacky exposures say if you used partial or spot... & centered metering.

October 01, 2010 2:39 AM  
Blogger Lars said...

I had never thought of that. Thanks. But it makes sense and I sort of feel silly for not having thought of it.. Well it just goes to show that those constantly working with flash (you) have a lot more to contribute than those who mainly read about flash (me). And thanks for the Kick A** site!

October 01, 2010 3:24 AM  
Blogger mark said...

The tricky part for me was getting the camera to meter properly for the ambient at aperture priority the camera tries to expose for my subject as well and i ended up with an ugly mix of ambient and flash on my subject.

The solution that worked for me was spot metering for the ambient first then adjust the EV compensation to get that value when i focus on my subject. Once that was done all i needed was dial in the flash and then it was sunset strobist heaven.

October 01, 2010 4:16 AM  
Blogger Andy said...

Excellent idea - thanks for that!

October 01, 2010 4:25 AM  
Blogger Ian said...

It surprises me this advice doesn't show up more often, its a great way for tracking falling ambient. Care needs to be taken at sunrise with the max shutter speed obviously and that always comes as the best light in the sky shows itself.

October 01, 2010 4:33 AM  
Blogger The23rdman said...

This is something I do when shooting families on location when the sun is coming in and out. Makes the shoot flow so much easier.

October 01, 2010 6:44 AM  
Blogger Wibo said...

This is great. I learned the full manual way from you.
And this technique using the aperture priority mode I learned from (the books by) Joe McNally.

I still use manual mode a lot.
I use aperture priority when the light is constantly changing and I'm having flashes in there on fixed positions.

October 01, 2010 6:45 AM  
Blogger Graham Ashford said...

This work well as long as you stay under your camera's maximum flash synch speed. Let's say you are at 1/160 and the ambient jumps a full stop - your camera will want to shoot at 1/320, which depending on your camera /flash setup will give varying results.

If you have HSS/FP set on your flash, it may not give as much light as you are expecting, underexposing your flashed subject.

If you do not have HSS/FP set, your camera will either stay at 1/200 (on Canon) overexposing the ambient by 2/3 stop, or shoot 1/320 with a nice black strip on the bottom of your flashed subject.

October 01, 2010 7:35 AM  
Blogger Paulo Rodrigues said...

Now why the hell didn't I think of blogging that!

Here is another tip that I posted on my blog a while back.

If you have your ambient correct and want to adjust your flash exposure, you can use the Ael button to lock the exposure. Then when you hit your wheel to change the aperture the ambient will stay the same.

http://paulophotoblog.blogspot.com/2008/11/auto-exposure-lock.html

October 01, 2010 7:54 AM  
Blogger roncastle said...

I am not believing this post. I have a family session booked for this Sunday for a sunset shoot, and won't have anyone around to help me. I was brainstorming with myself this morning before I got out of bed on how I could make it go as smooth as possible. I actually came up with the idea of using AV to track the waning sunlight levels, and then I see your post. Two great minds!!!

October 01, 2010 8:03 AM  
Blogger Gustavo Santos said...

I did exactly this when shooting interiors, balancing available light and flash. Just had to worry about getting the flash exposure right, and a simple EV adjustment would set the available light to the levels I wanted!

October 01, 2010 9:04 AM  
Blogger Alex said...

Right here we go...

I think that for Dutch it's workable but not great. give it a 6.5 out of ten

I read your blog in English, but I'm a multilinguist plus a teacher of English, so...

It does translate your words to a very very formal register, but that is because we use a formal form and an informal version of the word 'you'

Plus, it often doesn't get technical words, but that is to be expected.
Then again it doesn't get the word ambient for which I can think of a couple translations :S

My recommendation is not to worry about it too much for the Dutch.
We as Dutchmen in general speak proper English as it is, but the ones who are inclined to read your work are often even more educated than Joe Blow.

So I would leave the Dutch out of your equations.

Cheers

October 01, 2010 9:26 AM  
Blogger David Cutts said...

Just watch the sync speed, yeah after sunset, but at a high iso ...

October 01, 2010 9:59 AM  
Blogger tundracamper said...

What timing! I am taking some homecoming photos of my kid this evening and will use this exact procedure.

One thing to keep in mind is when the shutter speed gets high - like in daylight. If the shutter speed gets above 1/250, you get into the high-speed sync area, which most flashes in manual mode can't handle.

October 01, 2010 10:45 AM  
Blogger Rob said...

Kind of like a "halfway to Mcnally" deal. Maintain control of the flash exposure and let the camera follow the ambient automatically instead of turning it all over to CLS. DUH!
Really straight up and easy to do. A real lightbulb (pun intended) moment!
Thanks Dave!

October 01, 2010 11:12 AM  
Blogger Mike said...

I love these types of posts David. Little tips like this really help the novice like myself, to "see the light" so to speak. I hope to see more posts like this in the future. This is what separates Strobist from other lighting forums and blogs!

October 01, 2010 11:40 AM  
Blogger Jonathan Histed said...

It is necessary to understand how the meter in your camera works to get predicatble (and useful) results: (and I'm not talking about the normal 18% grey issues). I shoot Canon-(a 400D): and generally use Evaluative metering. I often take shallow depth of field portraits, so tend to set a single focus point to coincide with the subject's eye. I press the shutter: the camera first focuses then the evaluative metering reads the exposure from the focus point: leading to odd effects, as the camera is taking no account of the difference between the background and the subject. Indeed: this problem seems to bedevil using flash with any kind of auto program on the camera. Whether the camera decides the background or the foreground is to be "18% grey" markedly effects the overall outcome, and is I think the main reason why people object to ETTL: what it was the camera took the readings off is sometimes not obvious: leading to apparently random exposures. The camera clearly does clever stuff internally just to make matters worse when it comes to using ETTL: which is not clearly documented, making all forms of automatic exposure fraught with problems.

To focus then recompose with a half depressed shutter seems the wrong way to go. You quickly start waggling the camera back and forth between frames, and indeed your selected focus point may still miss the background once moved for composition. Any suggestions as to the best way of handling this one? I have yet to play with the options for separating the fixing of exposure, FEL, and focus from the half depressed shutter... but I suspect that is the only way to go... What do people find works ergonomically the best ?

I may of course have completely misunderstood the Canon metering system and I stand to be corrected by people who know better. I believe similar issues must exist with the Nikon system: but that is foreign territory for me…

October 01, 2010 2:20 PM  
Blogger Richard said...

Another killer tip. Thanks for sharing!

October 01, 2010 3:11 PM  
Blogger Peter Libby said...

This is an unrelated "comment."

Since this is the first time I have commented on anything, let me just say an all-caps THANK YOU! Thank you, David, for this site and all of its collected wisdom. I no longer feel timid about exploring the use of flash, and the use of speedlites in particular, and now my photography is improving because of it.

Apparently it is true: When David Hobby speaks, a lot of people listen. You have been telling us for some time now to get ourselves a free sample pack of Rosco gels. Well, so many people have been scooping up all of the freebies, that Midwest Photo and Amazon (and probably others, too) no longer offer these "samples" for free. Nope, they now charge about $9-10 and it is now called the "Strobist" pack.

Now, that is what I call influence.

Peter Libby

October 01, 2010 5:40 PM  
Blogger Bernhard A S said...

In the old film days the Canon EOS 1 and 3 Models allowed you to take a flash exposure reading and it showed on a little bar graph in the viewfinder the difference in f/stops between flash and ambient exposure.
To widen or narrow the gap between the two, you did not have to take your eye off the viewfinder.

In the digital days the feedback is by the LCD screen and the camera makers do not see a market for such gadgets anymore.

I have to admit that I fully embraced the control via LCD and I go fully manual these days whenever I set the light.

If the distance between model and flash varies one can fine adjust with the aperture setting.

I usually use the fill flash as commander (a SB 900) Even when dialled low it reaches everywhere and I never had issues with not triggering the other manual or SU4 flashes.

So if the distance between subject and main light changes I adjust first the aperture on the camera and then the manual fill flash setting. The display of distance on the fill flash can be used as a rough guide, when dialing the manual setting up and down.

For example I want the fill flash to be 1 stop down, so I first get the setting for the correct distance with the current aperture and then dial it down a stop.

Sounds complicated when explained but try it it is quite intuitive once you get the hang of it.

October 02, 2010 8:22 AM  
Blogger TK said...

I used this technique in this afternoon photo session. It, however, didn't work well for me - the background was too bright with the pattern metering. I had to change to the manual mode instead. Here is one photo after using the manual mode: http://www.flickr.com/photos/26423920@N00/5045990385/

October 03, 2010 2:26 AM  
Blogger Jeebsion said...

I've been using such method for quite some time now ... it's definitely a good advice/pointer .. can see a bit of my cycling editorial shots at http://www.jeebsion.com/blog/?p=702 ...

October 03, 2010 4:43 PM  
Blogger rsprung said...

The German translation seems pretty readable, if a little awkward. It could definitely help a non-proficient English reader.

One correction though: If you hold the mouse over the text, it does not give you a better translation. It offers you the opportunity to improve the translation. As many readers as you have around the world, that might work out pretty well.

October 04, 2010 12:49 PM  
Blogger Kevin Camp Photography said...

I use a similar technique shooting sports with flash. I set the camera up with my SB-600 down low on my monopod connected via dedicated cord in manual mode at 1/4 power. Set exposure for f4 for normal shots. If player comes toward me I step up the aperture value to choke the flash and keep from blowing out, if the play goes away from me, I drop down to f2.8 to get more power out of it. Still have to shoot at ISO1250 or 1600 for night football but far better than ISO2500 or higher. The relatively low power settign allows me to get several rapid flashes before the flash has to recover. Low mounting position of flash removes red-eye and gets some light under the helmets too. Players never even notice it.

October 06, 2010 10:52 AM  
Blogger Ian said...

See there IS a reason why the Exposure Comp button is so, so handy on Nikon's!

I just dial a 1/3- 2/3 down depending on how dramatic I want the shot to be.

October 07, 2010 9:24 PM  
Blogger Peter F. Castro said...

Seems good in theory and would have to check it out. Would seem to benefit bodies that don't have pro-like features and all the control buttons/dials outside. I am used to just thumbing over the shutter speed. I am shooting at a nightclub tonight and may try it there as ambient changes quite a bit. Even if it's not a perfect system it's a neat tool to keep in mind which I hadn't before. Gracias again, DH :)

October 09, 2010 7:34 PM  
Blogger Fardan Raffii said...

a very good point

thanks strobist.com

October 13, 2010 7:47 AM  
Blogger Callum Winton said...

I think as a footnote it's worth noting that to do this successfully and consistent;y you'll need to set you camera to full frame metering.

With the sunset/rise behind the subject then they're more than likely to be in the shade
If you focus then re-frame your subject to a 1/3 in the frame then you may be alright, but if you keem them central (thinking covershot) then spot or even center weighted may try to drastically drop the SP to expose the subject correctly.

CW

November 07, 2010 11:49 PM  

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