Harmonizing ambient light with OCF

[Stradawhovious]

Ok, I get the premise of OCF when you are using it to overpower ambient light, such as in a studio setting, or indoors when you don't want the ambient light to come into play.

What about outdoors? What about just using OCF for fill, to get the correct exposure of nice blue skies and a backlit subject?

Anyone have any good learning tools for that one? (onilne, books, personal experience, etc)

My assumption is that TTL metering is going to be virtually useless if you are metering for the backgound, so you will want to work the strobe in manual...... But then again, I really don't have much of an idea about anything so I could very easily be wrong. I also don't have/can't afford a decent light meter at the moment. That is certainly on the hit list, but not in the near future. I have been told that my fun money has basically dried up for the time being.

I plan on taking the kids out and getting some practice at this soon, and would like to at least have a direction heading on this subject so I'm not shooting blind.

Thanks in advance!

 

[gsgary]

When mixing ambient and flash you have 2 exposures, shutter speed controls ambient light(slow shutter more ambient, fast shutter less ambient) aperture controls flash, without a flash meter it will be trial and error but once you have and ambient about even you can start playing with your shutter speed to darken the background by using a higher shutter speed or if you want to blow out the background lower your shutter speed but with a speedlight you will never overpower the sunlight on a very bright day

 

[Robin Usagani]

Why would TTL be useless? The flash meters trough the lens, then shoot a preflash and see how much light reflected back trough the lens, then it sets the flash exposure automatically. It doesnt matter what you are metering. The only thing that reflects back to your camera is the subject UNLESS the background is close by or you are indoor. If you think it is too harsh then jsut lower the FC.

 

[AustinPhotographer]

I don't know what kind of equipment you're working with, but I do this all the time with a pretty simple shoe-mount system. I shoot Canon and have an ST-E2 IR transmitter, a 430exII, a 580exII and an MR 14EX ringlight. It's really great for getting different results fast, since all you have to do is vary your shutter speed/aperture/iso, and the flash system does the work of calibrating light output to ideally illuminate what you sampled. Faster shutter speed - darker background, slower shutter speed - lighter background. I did a shoot for a press kit I developed for one of my clients, and used this technique to get the right balance. Check it out -

I set up the camera to capture the orange glow and silhouette of the trees on the running trail, sampled the runners and shot around 15-20 passes to get a good capture. I had a ringlight on the camera, and my 580 and 430 on either side (you can see a little flare on the guy's face).

Justin Wallace Photography

 

[Stradawhovious]

Thanks for the clarification!

Let me take this one step further, and tell me if I'm overthinking this, or if my brain is tricking me into thinking I'm smart.....

What's to stop a guy with more time than money from making a chart for this?

Bear with me here.... Let's say that I have a speedlight and a shoot through umbrella set 4 ft from my subject. In a dark room I get good exposure with the strobe set at 1/2, and the camera set at 1/125 and f/8. (numbers at random, let's no pick them apart too much....)

Now, I'm outside, sunny day, shooting in the shade. I meter the background, and the camera tells me that at f/8 I want a shutter speed of 1/125 to properly expose it, but my subject has a shadowy face. Assuming I can trust my camera's light meter, I should be able to put that same speedlight, 4 feet away, through a shootthrough umbrella at 1/2 power and get a decent exposure on the subject, as well as my background... right?

IF this is the case, what is to stop me from working up a spreadsheet of exposure settings with differenct combinations of distance, shutter speed and aperture? (yes, ISO too..... I won't forget that little guy!)

It would take some time, but might be really handy to help dial in the exposure in the field.... or at least get close fast.....

Feel free to point and laugh if this is too far fetched, or I'm just overanalyzing a simple situation.

Why would TTL be useless?

If I'm shooting off camera, I use a cheap trigger/radio system that doesn't send TTL data.

If I'm shooting with the flash on the camera, it's a moot point. My D7000 and SB-600 combination seems to do a really good job with that.

 

[Big Mike]

You can use TTL metering for this, but it may change a lot, based on where your subject is in the frame and how reflective they are. Once you get the hang of it, you'll likely find that manual flash control is preferred because it's consistent and predictable.

As mentioned, the real key to figuring this out...is realizing that every flash photo is actually two separate exposures....the ambient exposure and the flash exposure. Aperture and ISO affect both exposures equally, but shutter speed only affects the ambient exposure (as long as stay under the max sync speed)...and the flash power & distance will control the flash exposure.

So when you want to balance them, or just find the ratio that you want...you can use those settings that only affect either the ambient or flash.

So as an example, you set up your shot at meter for the ambient light. If you want a slightly darker background (for nice blue skies etc.) then you'd probably under expose the ambient a little bit. If you want to turn cloudy skies into dramatic skies, then under expose the ambient even more. Then determine the flash exposure that you will need to properly expose your subject. Now, you probably won't want to use the aperture or ISO to adjust your flash exposure because that will change your ambient exposure as well....so you can adjust the flash power and/or move the flash closer or farther from your subject.

There are some things to keep in mind. If you want to underexpose a bright scene, you'll want to use a fast shutter speed...but you may run up against the max sync speed limit (probably 1/200 or thereabouts). So you can't go higher than that...so to get that under exposure that you want, you'll have to stop down the lens. But as you do that, you'll require more and more power from your flash. For example, to get the ambient exposure that you want, you may have to use something like 1/200, ISO 100 and F16. But at ISO 100 and F16, you flash (at max power) may only have a working distance of 5 feet...so you'd be OK...IF you can get your flash that close. If not, you may have to open the aperture a bit, thus sacrificing the ambient exposure that you want.
This is where you have to be watchful of what's affecting your flash output. For example...umbrellas, softboxes and all of those silly flash accessories will rob you of flash output...you may find that you have to use bare flash (hard light). You can help your cause by zooming the flash head (if you flash does that). It concentrates the light into a tighter area, giving you more (localized) output...but make sure that you get enough spread to cover the area that you want to.

So when you put this all into practice....you may be wishing that you could just turn the power of your flash up....which is why it's nice to have those powerful (expensive) flash units like the 580EX or SB900. This is also why I tend to use a studio strobe with a battery pack. It's got lots of power when I need it.

This was shot under a bright, overcast afternoon sky....and lit with a studio strobe and flash unit. Not really and example of 'good balance' but just an example of when a lot of flash power is needed.

 

[Big Mike]

Bear with me here.... Let's say that I have a speedlight and a shoot through umbrella set 4 ft from my subject. In a dark room I get good exposure with the strobe set at 1/2, and the camera set at 1/125 and f/8. (numbers at random, let's no pick them apart too much....)
Now, I'm outside, sunny day, shooting in the shade. I meter the background, and the camera tells me that at f/8 I want a shutter speed of 1/125 to properly expose it, but my subject has a shadowy face. Assuming I can trust my camera's light meter, I should be able to put that same speedlight, 4 feet away, through a shootthrough umbrella at 1/2 power and get a decent exposure on the subject, as well as my background... right?
IF this is the case, what is to stop me from working up a spreadsheet of exposure settings with differenct combinations of distance, shutter speed and aperture? (yes, ISO too..... I won't forget that little guy!)
It would take some time, but might be really handy to help dial in the exposure in the field.... or at least get close fast.....
Feel free to point and laugh if this is too far fetched, or I'm just overanalyzing a simple situation.

You are on the right track. If you get 'proper exposure' with those setting and that lighting power/configuration, then it should also give you enough light in an outdoor situation. But keep in mind that little things like the position of the flash head and the umbrella can affect the light that ends up getting to the subject.
Of course, the ambient light that you run into when outdoors, will really determine much of the exposure settings that you'll need to use...so making a chart may be helpful...but you'll need to be able to adapt quickly.

I think that the more common situation is that after doing this a few times, you just get a feel for where your light needs to be and at what settings. For example, from experience...you may 'know' that with the flash at 1/2 and 4 feet away, F8 will give you pretty good exposure...so that's a good place to start. If you have to move the flash farther away, you know that you'll need to open the aperture, turn the flash up or turn up the ISO.

 

[AustinPhotographer]

I get what you mean, and I think that kind of chart would be a lot of help in reaching a starting point for adjusting all of your settings outside. Sun/shade/clouds/time of day all vary so much that it might be tough to dial everything in for a perfect exposure the first time around.

To address your point about using the same settings outside as you were inside, you would be spot on assuming that flash were firing at the exact moment you sampled your subject with your camera's light meter. When you used your 1/2 power 1/125 f/8 in the studio, I doubt the camera gave you those numbers when you sampled the subject since it didn't know the flash was coming. If you aren't on TTL, then your cameras going to assume no lighting parameters will change from the time the subject is sampled to the time the shutter opens, while in your case they're changing dramatically due to the supplemental strobe lighting.

If you're blasting out your subject outside with fill light, just turn the power down a bit, move the flash&umbrella further away, speed up your shutter speed, narrow your aperture, crank down your iso, or any number of things until you get the right balance

 

[Village Idiot]

The easiest chart to do, would be to make one up based on the modifiers you shoot and your lighting style. It would have to be based on experience. You can do one for your guide numbers of your flashes, but when you start sticking different modifiers on them, it's going to start affecting the light output and sometimes you may want to overexpose or underexpose a certain flash.

I lied, the easiest thing to do is to get a light meter, but with enough experimentation and experience, it becomes second nature. Set your lights up, take a test shot, adjust, and you're good to go. I'm a really technical person and I know how to use guide numbers and understand differences in exposure and ambient, but I find it easy enough to take that approach.

 

[Derrel]

One of the easiest ways to balance the ambient light exposure with the flash exposure outdoors is to use an older-technology flash metering system, like AUTO-thyristor flash, like those made by Vivitar, Sunpak, and Metz. You set the camera's ISO, f/stop, and shutter speed to the prevailing lighting conditions outdoors, and then adjust the ISO setting on the flash to either a higher or a lower ISO setting than the camera is using. Typically, what I would do is set the camera's ISO to 100, the aperture to f/11, and the camera's synch speed as fast as possible, typically 1/200 or 1/250 (depends on the camera), and then adjust the flash in AUTO mode to the f/11 setting, and then set the ISO around two full stops HIGHER than the camera's ISO value, or even a slight bit more, approaching three stops higher than what the camera is set to.

So, camera all set for ISO 100 exposure at f/11. NON-dedicated flash set to AUTO-thyristor mode, power setting the f/11 value, but the ISO deliberately set HIGHER, to 400, 500, or 640, to provide LESS flash than ambient, and only fill in the shadowy areas. THis is an old-school method that has been used for 40 years or so...it is how I learned to shoot balance fill-flash back when only a few Olympus and Nikon cameras had TTL flash metering capabilities.

 

[RockstarPhotography]

You can also use this equation to get you in the ball park

GN (guide number = distance x f stop.

That's flash at full power, adjust your guide number accordingly.

That's also using the iso your gn is rated for

 

[Big Mike]

I also used (and learned) with an Auto-Thyristor flash and adjusted the exposure the way Derrel mentions.

I now ultimately believe that manual flash is a better method, but the auto-thyristor flashes were pretty good.

 

[Big Mike]

You can also use this equation to get you in the ball park
GN (guide number = distance x f stop.
That's flash at full power, adjust your guide number accordingly.
That's also using the iso your gn is rated for

Don't forget to take into account the zoom of the flash head. Don't forget to figure in how much output is lost when using the modifier (umbrella etc.), don't forget to figure in a filter if using one.

 

[RockstarPhotography]

You can also use this equation to get you in the ball park
GN (guide number = distance x f stop.
That's flash at full power, adjust your guide number accordingly.
That's also using the iso your gn is rated for

Don't forget to take into account the zoom of the flash head. Don't forget to figure in how much output is lost when using the modifier (umbrella etc.), don't forget to figure in a filter if using one.

yup, and also make sure your using the same unit of measurement as your guide number. Its really just to get you in the ballpark, and you can adjust from there. Its a place to start. If using a modifier you may want to bump the power up a bit.

 

[Village Idiot]

You can also use this equation to get you in the ball park
GN (guide number = distance x f stop.
That's flash at full power, adjust your guide number accordingly.
That's also using the iso your gn is rated for

Don't forget to take into account the zoom of the flash head. Don't forget to figure in how much output is lost when using the modifier (umbrella etc.), don't forget to figure in a filter if using one.

It also doesn't work if you have a stronger light source overpowering it. That's the biggest problem when trying to shoot outside in daylight. Certain times of day will be much better for overpowering the sun, but that's the downfall of a speedlight, they don't always have enough power to cut it. That's why there's other options like more powerful lights and other tricks.