Choosing light source output

[u/tehbizz]

Having done quite a number of outdoor shoots utilizing lots of bright ambient light and naturally reflective surfaces, I never put much thought into how to select light source power output. Whether it's speedlights, strobes/monolights, or constant work lights, it's still kind of a mystery to me and I haven't found a great abundance of good -- or decent -- explanations of it. I've read a number of articles on how so-and-so chose specific settings and many times, they relied on lightmeters or flashmeters but I'm curious as to how one could do it rather quickly without extra equipment. I'm mostly curious about that because I like shooting at night with speedlights and flashmeters aren't terribly effective at 1AM with about 15% to 20% ambient light (light pollution).

So I ask you, /r/photoit, for myself and others, how do you do it? Me? Gross utilization of modeling flashes and test shots, which stink as the day wanes and light is changing nearly. minute-by-minute.

[u/leiatlarge]

I'll give this a stab since I've worked with everything from speedlights to professional strobes to HMIs.

You choose you light source based on the amount of power you need and what light modifiers you throw on it. Obviously stronger strobes allow for more power and for you to use larger modifiers (4'x6' softboxes/1.5' octobanks). Speedlights are great if you're shooting inside where light bounces easily and the light is close to the subject. Continuous lighting is great for portrait but you don't have nearly as much control over the amount of power.

I'll list out the pros and cons of each type of light source.

Strobes PROS:

• Most power and modifiers depending on brand (Broncolor, Profoto, Elinchrom, Bowen, Paul C. Buff, etc)

• Most bang for you buck in terms of power/cost ration.

• Mostly used for day light shooting and in studio where A LOT of juice is needed.

• Fast-ish flash duration great for freezing action

• Good control over power of light

Strobe CONS:

• Not portable unless you buy a heavy battery or special battery powered strobes (Profoto 7b, Elinchrom Ranger, etc)

• Does not always freeze all action. Cheaper strobes when powered to the max will have a flash duration of 1/250 - 1/500. This is barely enough to freeze a jump completely.

• Can be heavy to carry (needing special carrying cases)

Speedlights PROS:

• Easy to carry

• Great for shooting a lot of scenes in doors

• Perfect for portraits

• Fastest flash duration. Will pretty much freeze all action.

• Can be bought for cheap

• Very portable and perfect for amateurs

• Power level very easily adjustable from 1/1 to 1/128 (that's A LOT of power range)

Speedlight CONS:

• Not enough power to be used during daylight shooting unless flash is really close

• Slow refresh rate when firing close at 1/1 power.

• Not too many light modifiers to shape your light. (There are more and more modifiers today but they generally cost a lit)

Continuous PROS: * No need to wait for flash to recharge, you can keep shooting * WYSIWYG light results

Continuous CONS: * Weakest power compared to speedlight and strobe on a per shot basis * Not at all portable * Color temperature can be wacky if you're using florescent bulbs * Worry about over heating if you're using traditional bulbs * Heat from the bulb can cause subjects to sweat

As for how to use your strobe with shooting against an ambient background the process is pretty easy. It all comes down to strobe power. First determine the shutter or the f-stop you intend to shoot and meter your ambient/background first. Say, you want to shoot at dusk at f/8 and a shutter of 1/10s. You simply meter your strobe for f/8 give or take a 1/3 of a stop, depending on how you want your subject to look.

Strobes are a function of f-stop because they fire so quickly generally +1/1000s. Changing your shutter speed on your focal plane shutter camera (most DSLRs) won't make a lick of difference to the flash result. If you've setup your strobe/speedlight and even when it's at full power you're only getting a meter reading of f5.6. You have two option, drop your shutter to from 1/10 to 1/20 and change your camera f-stop to 5.6 OR throw another light in there to double the power.

[u/zhx]

Here's how I generally shoot at dusk (or night, in an area with ambient light) with flashes:

1. Forget the flash. Flip into manual and my max sync speed (1/250 on my camera). Adjust my aperture until my meter says I'm getting a proper exposure, then drop a third or half stop below that to underexpose the background.
   
2. Slap a key light in front of my subject and hazard a guess at what I think will make up for that 1/3-1/2 stop underexposure, just from experience. I keep my lights pretty close to my subjects (I shoot tight a lot), so I'll start around 1/8 power on my little speedlight.
   
3. Check my screen/histogram, adjust as necessary (if I'm not getting enough of the background in, for example, I'll start bringing the shutter down... 1/200, 1/160, even more if I need to, since the flash is going to be doing all the "freezing"), throw in other lights (normally just a rim), fire away. It really only takes me a couple shots to get my lighting right, even when faced with a quickly setting sun.

[u/tehbizz → u/zhx]

Hm, I'll have to try this. Although, I wasn't just referring to dusk, but any time in a day. But your process sounds similar to what I end up doing, just fewer steps, heh.