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Why does the size of your light source matter?


Keywords: flash, studio, lighting, filter, guides, tips

This is part 3 of the learning to light series with Josh Larkin. 

Despite what you may have heard, size matters and that is especially true for your light source.

Portrait photographers often use large modifiers -- think 50" softboxes, 43" umbrellas, etc. -- to soften the light hitting the subject. And that's what we want most of the time (film noir shooters excluded), nice soft light that transitions slowly from highlights to shadows. Take the umbrella off of your light source, adjust its power output or your aperture or shutter speed for a correct exposure and what do you get? Hard light. Your beautiful transitions are gone, replaced by the hard line where your light ends and the shadow begins. That's what happens with small light sources.


Soft light made by an apparently huge light source. 1/250th f/7.1 ISO 100

The thing is, that huge softbox or umbrella will create hard light as well depending on how far it is from the subject. Why? Because it's all about the apparent size of the light. Not to you, as the photographer, but to the subject. If you have an umbrella handy, give it a whirl. Move the light stand back a good 15 feet from your subject and fire away. Hard light, guaranteed. Move it in to about three or four feet, soft light. At three feet away, that 43" umbrella is a huge light source that bathes your subject in light from multiple directions. From 15 feet, it's not so big anymore. In fact, it's kind of small, and the light is essentially hitting your subject from one direction.

Another way to think of this is to talk about the biggest light source of them all: the sun. Now, sure, the sun is a big light source, but, it's approximately 93 million miles away from the earth, so it therefore acts like a small light source. However, add an overcast day into the mix, and you essentially have a gigantic softbox over the light source, diffusing the light and allowing it to hit the subject from various angles, thereby making nice, even, soft light.

The basic idea is this: big light equals soft light, small light equals hard light. And as it turns out, that's a pretty easy concept to demonstrate. I decided to shoot a small Egyptian statue I had on hand. The figurine stands about five inches tall, so since it's really the apparent size of the light that dictates whether we'll get soft or hard light, I didn't need to go with an umbrella to get nice, soft light, I just needed to make the light appear big to the small statue. To do so, I mounted up a 10 x 14 inch Lumiquest Softbox LTp to my Nikon SB-600 speedlight and positioned it on a light stand at about 45 degrees camera right.

The lede shot was taken with the front of the softbox positioned 10 inches away from the figurine. At that distance and from the perspective of the small statue, this is a not just a big light source, it's a huge light source. I shot this at my D7000's max synch speed, 1/250th of a second, f/7.1, ISO 100. My SB-600 was zoomed to 24mm and dialed down to 1/8th power. Notice the transition from the lit side of the statue to the shadow side. Pretty smooth right? Now look at the shadow being cast by the statue. It's not that easy to see where it begins and where it ends because there's a gradual transition from the white board into the darkest area of shadow.



Slightly harder light from an apparently smaller source. 1/250th f/5.6 ISO 100

For shot two, above, I moved the light back to 28 inches from the subject. To compensate for the loss of light, I opened up my aperture to f/5.6. The exposure is a little darker on this shot, but what we're looking at here is the quality of light. While I wouldn't exactly call this hard light, it's definitely harder than the lighting in shot one. We can see that the transition across the statue's face is more abrupt, and in the shadow being cast by the figurine, the line between the lit and unlit area of the board is becoming much easier to discern. Same light, same light modifier, different apparent light size.


Now that's some hard light. 1/250th f/4 ISO 100

Okay, now we're at 66 inches from our subject, and to get a better exposure I've bumped my f-stop to 4 and flash output to 1/4th power. That gave me a good exposure for sure, but at just over five feet from the subject, my 10 x 14 inch softbox is starting to look like a pretty small light source to the statue. Have a look at the hat on the statue. In shot one, there's no real discernable transition between the lit and unlit areas of the hat. In shot two, the transition is still subtle. In shot three, it's much more obvious. How about the cast shadow? To my eye, it's pretty clear where the light ends and the shadow begins along much of the length of the shadow in shot three. Apparently, my softbox isn't so soft when it looks small to my Egyptian friend.

So as I said at the start, size matters. Practically speaking, there are a number of ways you can utilize this to improve your images depending on the look you're trying to achieve. For example, when we bounce our flash off of a ceiling or a wall to diffuse the light, we're creating a huge light source, right? Well, maybe we don't want it quite so huge. Solution, use the zoom head on your flash to tighten the beam spread, which essentially makes your ceiling or wall a somewhat smaller light source than when you hit it with the zoom opened up. Working on the fly but want to get good soft light in a portrait with only a small softbox such as I used above? Get that thing in close -- I'm talking like a foot from your subject -- boom, soft light from a small source that appears big to the subject.

Finally, did you happen to notice that blue/gray background getting lighter as I moved my light back from the subject? I did, and I think I might try and tackle the reason why that's happening in my next lighting post. Until then, thanks for reading and let us know in the comments what you think!

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(3 Votes )

Originally written on October 29, 2012

Last updated on January 24, 2021

User User


Virginia Tucker (dogmamom) on July 11, 2014

I'm listening! Good article. If I were to buy ONE piece of lighting at a time (after a flash unit!), what would be the top five items, in your opinion? I'm on a budget and can't do it at once but it's a goal. I'd like to have a small, somewhat portable (to fold it up when company comes over) hobby studio in my home.

Dale Maas (marnigirl) on October 30, 2012

Donor Ribbon awarded for his generous support to the Fundraising Campaign 2014 Donor Ribbon awarded for his very generous support to the Fundraising Campaign 2015 Ribbon awarded for his generous contribution to the 2017-2018 fundraising campaign

Josh, Thank you so much for taking the time to answer my questions. Your answer is great at helping me get on the right track. For me, at least, this guide is of great benefit. I am due to go to a flash workshop with Arizona Highways on Nov 2,3 and hopefully that workshop, coupled with your input will allow me to get a starting grasp on 'Flash'. Thanks again, Dale

User on October 30, 2012

Hi Dale, I'm going to get into specific settings in a few more posts as I wanted to cover some of the more theoritical aspects of lighting before getting into the practical side of things. However, to get you going, you're correct that your pop up flash will be firing if you're using it as a commander. In your camera's menu for for Commander mode, which I believe is e3 on the D300, you can set the mode that the pop up flash is firing in, though. You'll be able to choose between TTL, M (Manual), and -- which means the flash fires at so low of a power output it won't contribute to the exposure but it will fire your SB700. Nine out of ten times that's where I have my popup set, unless I want to use it to add a bit of fill, in which case I set it to Manual in the menu and dial the power down to about 1/2 of the output of my designated flash. As for how I arrived at my settings, for these initial posts I've really only been concerned with the effect my flash has on the scene, so right there I knew that my camera should be set up so that no ambient light plays a role in the exposure. If you're familiar with shooting indoors without flash, you'll know you need to have a shutter speed somewhere around 1/60, a low f/stop, and likely ISO of 400 to get in the ballpark. But since I want no ambient light in the exposure, if I crank my shutter to my camera's max synch speed, 1/250th and keep my ISO at 100, then no matter what aperture I'm at if I don't fire a flash I'll get a totally black image. For the lede shot, since I knew the light was going to be right up close to the subject I knew I'd want a smaller aperture to control some of the light entering the camera, so I went with 7.1. For my flash power settings, again, with the light being close I knew I wouldn't want it at full power, so I started at 1/8th. In looking at my notes from this shoot, I actually started at 1/8th power but with an aperture of f5.6, but in looking at the LCD I could see this was too bright, so I knocked the aperture down to f7.1 to darken the image a bit. For shot two, since I moved the light back from the subject, I knew I'd lose some of the intensity from the light, so I simply opened up my aperture a bit to f5.6. In the final shot, the light is so far away that I had to move the aperture to f4 and crank the flash power to 1/4th in order to get a correct exposure. When I started learning this stuff, and still now, I couldn't afford to drop a few hundred dollars on a light meter, so I approached it by setting things up the way I thought it would work, firing a few test shots and then chimping the camera and making adjustments as needed. After awhile, it just started to sink in where I'd need to set my camera and flash settings depending on the subject, light source, distance, etc. I'll be looking much more closely at exposure settings in some future posts, but until then, know that I'm working in manual mode on the camera, shutter at max synch speed, and aperture and flash power adjusted based on what I'm seeing in test shots. In fact, if you're following along and you set things up at 1/250th, f5.6, ISO100, flash one to four feet from your subject and through a modifier, you can safely start with your flash power set to 1/8th. If the resulting image is a little dark, either bump the flash to 1/4th or open the aperture, a stop or two. If it's too bright, dial the flash power back a bit or close down the aperture. Cheers -- Josh

Dale Maas (marnigirl) on October 29, 2012

Donor Ribbon awarded for his generous support to the Fundraising Campaign 2014 Donor Ribbon awarded for his very generous support to the Fundraising Campaign 2015 Ribbon awarded for his generous contribution to the 2017-2018 fundraising campaign

I follow your train of thought (mostly :), but what is happening with the popup flash that is on your camera? Unless I am totally in left field, I cannot use my SB700 as a slave unless the popup flash on my D300 is activated. Please advise. This 'flash thing' is something I want to get a grasp on, but seem to have a hard time getting my head around it. Secondly, how did your arrive at the settings you used on your shot. Any input will NOT be to basic for this student. Thanks, Dale