Monday, December 16, 2013

3.3 - Balancing Flash/Ambient Indoors

In last week’s post I discussed the basics of exposure with ambient light (i.e. without the use of a flash).  I wanted to give a basic overview of exposure before jumping into balancing multiple exposures.  As the Lighting 102 course explains, when shooting with ambient light the idea of exposure is fairly rigid.  There is correct exposure for a given setting.  Straying much from this correct exposure and the photo becomes either under- or over-exposed (too dark or too light). 

In contrast, flash photography has multiple exposures: an exposure for the ambient light and an exposure for each flash used.  The idea of “correct” exposure gets a little murkier because each lighting source has it's own exposure.  Is the “correct” exposure based on the overall ambient light exposure, the subject, the background, or any combination of these?  There isn’t really a simple answer as it is completely up to the photographer to decide what they are trying to create.

As a general rule of thumb for any photo is that the main subject should be fully exposed. That is to say that if the subject is a person, the person’s face should be properly exposed.  The exposure of everything else in the photo is then free to be manipulated to the desires of the photographer.

The following exercise will illustrate the balancing act between flash exposure and ambient light exposure with a simple one-flash setup.  The aperture, ISO and flash power are held constant (f/5.6, 200, ¼ respectively) and the shutter speed alone is used to balance the exposures.   Remember that aperture affects both the ambient and flash exposures; shutter speed only affects the ambient exposure.  Therefore by modifying only the shutter speed the flash exposure remains constant but the ambient exposure can be modified.

The first shot of the exercise is to the left.  I think it's a wonderful example of taking the ambient light out of the equation.  This is a base line for the exercise, and assures that no ambient light will be affecting the shot as the flash is first introduced.  This wonderful first shot is taken at 1/200 at f/5.6 and the ambient light is approximately 6 stops under-exposed.   How do I know that it is 6 stops under-exposed for ambient?    I took a second test shot in Av and the camera calculated that a correct ambient exposure would be at a shutter speed of 0.4 seconds.  Then it is just a matter of counting up the stops.

Shutter Speed: 1/200 second
Now the flash is added (through an umbrella).  The couches and wall in the background are being lit by spill light from the flash.  The shot was still taken 6 stops below the ambient exposure so the light has to be coming from the flash.  From this point forward I will slow up the shutter speed to start bringing in the ambient light.

Shutter Speed: 1/125 second
This is the same shot taken at 1/125 (2/3 of a stop slower).  It doesn’t look all that different from the shot at 1/200 and there are two reasons for this:

1.     Since I started so far below the ambient exposure 2/3 of a stop isn’t enough to begin to bring in much ambient light, and

2.     Shutter speed does not affect flash exposure.

Shutter Speed: 1/40 second
The ambient light doesn’t begin to be exposed until about 1/40th of a second.   This is the shutter speed that begins to allow the ambient light to fill in the flashes shadowy areas.

To the right is the shot taken at 1/40th of a second.  The difference between this shot and the one at 1/125 is very small but the ambient light is (just barely) beginning to be exposed.  Again, everything is staying consistent (aperture, ISO and flash power) but with the slower shutter speed more ambient light is allowed in.

Shutter Speed: 1/6 second
Here it is again at 1/6th of a second.  You can start to see why there isn’t a single “proper” exposure for the ambient light.  The subject is exposed and the amount of ambient light exposure is completely up to the photographer’s discretion.

Shutter Speed: 0.4 second

Again at 0.4 seconds, which is what the camera calculated as the "correct" ambient light exposure.

Shutter Speed: 0.6 second

And again at 0.6 seconds.  I could keep cranking up the ambient exposure but I think you are starting to see the point of the exercise.  I hope that you can see that the idea of proper exposure is quite different when working with flashes.  As long as the subject, the cameras in this case, are properly exposed, the background exposure can be anything you want it to be.

If you decide to try this exercise out on your own be sure to set the subject in an area that is less exposed to the ambient light than the background.  Place it in a "shaded" area if you want to think about it that way.  Doing this prevents the ambient light from over-exposing the subject as you open up the shutter.  This concept works just the same outdoors where you have to compete with the sun.  Also please check out the Lighting 102 course by David Hobby here.

Below is a photo of the basic lighting setup that I used for this exercise.  I originally had the curtains opened during my first attempt, an instruction that I missed in the L102 course, and had to redo the exercise.  Hopefully you can learn from my mistake.

If you have been following my blog you may be confused on why this post wasn't about working outdoors.  In last week's post I explained the difficulties of working outdoors in Michigan during December.  In fact, the high daytime temperatures are struggling to get above freezing, and there is 6-inches of snow on the ground now.  This does not mean that I'm blowing off the two exercises dealing with balancing flash with the sun.  Instead I have something special planned for these two outdoor exercises that won't require me to suffer out in the cold. This "something special" is going to take a little bit of time, and with the holidays quickly approaching, there is going to be a small lag in the posts.  Look for the post on these exercises shortly after the New Year.

Until then,  thank you again for reading and I hope that you have a wonderful holiday season.

Monday, December 9, 2013

Exposure Basics

The next exercise in the Lighting 102 course deals with balancing flash exposure with twilight.  Completing this exercise has been difficult for me because of the time of year.  We are nearing the winter solstice and where I live that means that twilight is around 4 in the afternoon.  Since I work a day job, that happens to support my photography hobby, the time of day the sun sets limits me to working on the weekends.  This is my long-winded way of saying that I can’t write a post about my progress through the next Lighting 102 exercise because I haven’t actually done it.  I also thought that before I write a post about balancing flash exposure with ambient light exposure that I should give a quick overview of exposure in general. 

When I began this blog a few months ago, I had told myself that I wouldn’t write a post about exposure.  It’s not that exposure is a complicated concept but it takes a while to discuss and there are literally hundreds of books on the subject.  I convinced myself that there wasn’t a need to repeat a subject that has been so thoroughly covered by others.  I have since thought differently but today’s post will only be a little review on exposure and will be in layman's terms. 

Simply said, exposure is the quantity of light captured on your camera’s sensor (or film if you’re old school).  Regardless of the type of camera, only three things determine exposure: Aperture, Shutter Speed and Sensitivity.  If you understand these you can say good-bye to full-auto modes and "creative modes" forever. 

Aperture is the opening in a lens that allows light to enter the camera.  Aperture works much like the iris (colored portion) of an eye.  As an exercise, stand in front of a bathroom mirror and stare at one of your eyes. Then cycle the bathroom light on and off and watch how the iris expands and contracts as it adjusts to the changing light. Camera lenses do the same thing except instead of a pretty iris they have a series of fins, or the diaphragm, to restrict the incoming light.  If you have an SLR with a “depth of field preview” button you can see the lens’ diaphragm by looking through the front of your lens and hitting the button (as long as your aperture isn’t set to the lens’ maximum). *  Below is a series of shots to illustrate.
f/2.8                                    f/5.6                                       f/11
Depth of Field Preview Button
Aperture is expressed in f-stops and they are fractions. Therefore, f/2.8 is a larger aperture than f/11.  A larger aperture (smaller number) will allow more light to enter the camera than a smaller aperture (larger number).  Aperture affects more than just the amount of light entering the camera but I'll discuss that later in this post.

*The “depth of field preview” button is on the front of the camera to the right of the lens just under the lens lock release button (at least on my Canon).

Shutter Speed
Cameras have a shutter made up of multiple little doors. The shutter is opened for a given amount of time and allows the light to expose the camera sensor (or film).  You can think of the camera’s shutter as your eye lids if you’re like me and love analogies.  On a SLR you can see the shutter by taking off your lens and lifting up the pentamirror or pentaprism.  If you choose to do this just be careful, that’s a sensitive piece of machinery that you’re sticking your finger into.  If you don't know what a pentamirror or pentaprism is, I don't suggest doing this at all, just trust me that the shutter is made up of multiple pieces. 

Shutter speeds are measured in seconds or fractions of seconds.  Longer shutter speeds allow more light in and shorter speeds less light.  The important thing to remember is that shutter speeds, much like aperture, are also expressed in “stops”.  I’ll get into why after I get through a little sensitivity training.

Remember this stuff? (wiki)
Sensitivity is measured in ISO.  The sensitivity of a digital camera’s sensor is adjustable.  In contrast, a roll of film has a set ISO sensitivity rating.  On film cameras the only way to adjust the ISO is to remove the roll of film and load another with the desired ISO rating.  ISO actually stands for International Organization for Standardization, (I figure that if I took the time to look that up on Wikipedia I might as well share it) and is a way to measure how much light a type of film needs to become exposed. When digital cameras were developed someone smart decided to measure the digital sensor sensitivity using the same system.  ISO is measured in whole numbers, finally whole numbers!  What’s even better is that a lower ISO value is less sensitive than a higher ISO number so it’s intuitive.  This means for instance that ISO 100 needs more light to get proper exposure than ISO 400.  You also may have guessed that ISO, just like aperture and shutter speed, is expressed in “stops”.

The reason Aperture, Shutter Speed, and ISO are all expressed in stops is because each stop affects the exposure equally.  This means that opening up the aperture by one stop effects the exposure the exact same as slowing down the shutter speed by one stop.  Below is a table of full stops for all three:
Aperture (f-stop)
Shutter Speed

Moving down the table each f-stop allows exactly half as much light into the camera as the previous setting, each shutter stop allows twice as much light, and each ISO setting needs twice as much light for a given exposure.  For instance, if the correct exposure in a given situation is f/5.6 with a shutter speed at 1/125 and an ISO of 200 and you wanted to open up the aperture to f/4 (1 stop), what could you do to get the correct exposure?  If you only opened up the aperture, the photo would be one stop over-exposed so to correct it you could either speed up the shutter by 1-stop (1/250) or decrease the ISO by 1-stop (ISO 100).

f/5.6, 1/125, ISO 200 = f/4, 1/250, ISO 200
f/5.6, 1/125, ISO 200 = f/4, 1/125, ISO 100

Dave this is so confusing, why can’t I just leave my camera in auto mode and let it figure it out?  The camera’s auto modes stink because they doesn’t allow any changes to the camera's built in functions.  I compare it to forever driving with an instructor, sitting shotgun that has his or her own brake and tells you where to go.  I’d say get the f-stop outta my car!  Digital cameras have sophisticated built-in light meters built and they should be taken advantage of but not in the auto mode or any of the "creative" modes!  Those darn “creative modes” drive me just as crazy!  Most digital SLRs (DSLR), however, have three semi-auto modes that are great to use. 

Canon EOS shooting modes (wiki)
In Canon world, the "semi-auto" modes are P, Av, and Tv.  These are Program, Aperture priority and Shutter priority (T for time, I guess), respectively.  All three allow you to use all the built-in functions of your camera that you paid good money to have: White Balance adjustment, Picture Style, ISO adjustment, focus point selection, etc. and even whether or not you want the built-in flash to fire.

In Program once you depress the shutter button half way it will select an aperture, a shutter speed and ISO (if ISO is set to auto) that will produce correct exposure. Then by turning the selector wheel you can scroll through aperture/shutter speed combinations that will produce a proper exposure.  The disadvantage to Program mode is that if you want to keep shooting in a specific aperture or shutter speed you need to crank on that wheel each time you take a shot.

Aperture also affects a photo’s depth of field.  In laymen’s terms this is how much of the photo is in focus and how much of the photo is out of focus.  As a rule of thumb for portrait work you want to shoot with a large aperture (small number) to blur the background and make your subject stand out.  For landscape work you want the entire scene (foreground and background) in focus and by “stopping down” your aperture (larger number) you increase the depth of field to accomplish this.  To shoot with a consistent aperture, use Av mode.  In Av mode the camera will adjust the shutter speed as the light changes to give you correct exposure without changing the aperture.

Shutter priority (Tv) works much the same way as Av mode, except you set a shutter speed and the camera adjusts the aperture and ISO (if ISO is set to auto).  For instance, this mode is helpful when shooting sporting events.  In this situation you know you want a fairly fast shutter speed to freeze the motion but you don’t want to keep adjusting the aperture as the amount of light changes.

Helpful Tip:  As a rule of thumb the inverse of your focal length is the slowest shutter speed recommended if the camera is hand held.  In layman's terms, with a 50mm lens one can shoot at 1/50 without worrying too much about camera shake.  With a 250mm lens that shutter speed drops down to 1/250.  The more zoomed in the lens is the more susceptible it is to camera shake.  If you have a steady hand, or your lens has vibration reduction (VR-Nikon) or image stabilization (IS-Canon) built in, you can slow up that shutter speed slightly.  Shooting with shutter speeds largely slower than the inverse would require a tripod, or other means, to steady the camera.

Manual Mode (M)
DSLR’s also have a Manual mode.  In this mode the user manually sets the desired aperture and shutter speed.  All of my photos that I’ve taken for the Lighting 102 course have been shot in Manual (M) mode.  Shooting in Manual does not somehow make one photographer superior than another so I don’t say this to be egotistical.  I shoot in Manual for this class because some of these exercises require that photos be taken purposely under- or over-exposed.  Also while I am learning off-flash photography I need to be able to control everything and modify one thing at a time until I get my desired exposure.  However, I will take a test shot in Program priority to take advantage of the light meter and get me in the ballpark of where I need to be for an ambient light exposure.

Most DSLRs have the ability to set the ISO setting in either Auto or a specific ISO setting (200, 400, etc) in any of the semi-auto modes or manual mode.  In Auto, the camera will set the lowest ISO possible to achieve proper exposure.  As another rule of thumb, the lowest possible ISO should be used for any shot.  The lower the ISO the better quality the image will have.  Quality cameras will have great photo quality up to ISO 400 or even 800.  Beyond ISO 800 and image degradation will begin to be noticeable, but don't be afraid to crank up the ISO if you are shooting in very low light situations. A grainy photo (loss of image quality due to high ISO) is better than a fuzzy out-of-focus one. 

If this hasn’t confused you enough in the next post I’ll be discussing multiple exposures which complicates matters even further.  In flash photography not only do you have the ambient light exposure but you also have an exposure for each of the flashes used.  It’s madness but its so much fun!!!

Monday, December 2, 2013

Umbrella Specular Portrait

This is the second assignment of the Lighting 102 course and I'm still working with specular highlights.  This assignment is more structured than the Cooking Light assignment as the instructor, David Hobby, has a specific technique to try out.  He specifically states that this assignment is a portrait of someone using a single soft light source and positioning it so that it becomes a specular highlight on a dark semi-reflective surface.

While hunting for my next subject I came across this photo on a social media website.  My sister-in-law took the photo, and without knowing it she produced a purrfect (sorry) example of this technique.  When I spoke with her about using her photo in this blog she told me what shot she was aiming for and that, “The little bugger ruined the shot at the last instant by closing his eyes and sticking out his tongue”.  She may have just been sharing a funny anecdote of the shoot but it certainly wasn’t ruined.  Think of it this way, if you were trying to get a photo of a cat closing it’s eyes and sticking out its tongue, I’d tell you good luck! 

The conversation reminded me of some advice that I read a while back.  The advice went along the lines of don’t be apologetic of your work.  I think self-critique is a great way to improve your photography but you certainly shouldn’t give a list of all the perceived faults when someone offers you a compliment. I don’t think the author of this advice meant to suggest that you need to be an insufferable self-promoter but when someone compliments a photo of mine I catch myself saying “yeah, but…” far too often.  I tell people, “yeah, but I could’ve done this", or "I should’ve done that”, instead of just saying thanks and telling a funny story about how the shot came to be, like my sister-in-law did.  It’s good to constantly look for ways to improve your photography but it's also important to not be too hard on yourself.

The photo of Einstein is also the inspiration for my own work during this assignment.  I decided to make this a family pet themed post.  I certainly couldn’t post a photo of a cat without a photo of a dog!  Again, the goal of this assignment is to get a specular highlight on the background to produce a halo effect behind the subject.  Below are a couple examples of my work with my dog Apollo.  I could get him to close his eyes or stick his tongue out but never at the same time! :)

For the background I used my dining room table flipped on its side.  I then set up my shoot-through umbrella and took a series of test shots at different angles to get an idea of the size and location of the specular highlight on the background.  Once I got that figured out I placed a chair directly in front of where the highlight would be and bribed Apollo into position. 

This all worked well as long as he was sitting, but it didn’t take long for him to lie down and get comfortable.  At this point I needed to work a bit on the fly.  I found that keeping the umbrella close to the camera allowed me to better predict where the highlight would show up.  This was a bit of a test in visual geometry.  If you remember your geometry instructor teaching about angles of incidence and angles of reflection and wanted a real world example, here it is.

If you'd like to read more about this assignment or see other people's work you can find it here on the Strobist L102 blog.

I think that if the goal of the L102 course, over the past few weeks, was to get me comfortable working with specular highlights then it was a success.  I feel that I’ve learned a ton about off-camera lighting so far and I’ve only gotten through the first two ways to control light: position and apparent size.  The next section of the L102 course is about Balancing light and follows the same structure of a series of exercises followed by an assignment. 

I want to thank you again for reading and please be sure to ask any questions in the comments section below.