Photography Tip #6: ISO

The ISO setting on your camera is a measure of how sensitive your camera sensor is to light.  In the days of film (Okay, I know. I know. Film is still very much around.) you would see the ISO number indicated on a roll of film listed as the film speed.  With film you were stuck with that ISO setting until you finished the roll of film.  On your digital cameras today you scan switch ISO settings with each image you take. This gives you great creative freedom.  You can choose from ISO 100, 200, 400, 800, 1600, and even higher within any given shoot.  But what do these numbers mean?

It's actually very simple. A low ISO (100) is not very sensitive to light.  A high ISO (1600), on the other hand, will be very sensitive to light, so you can take pictures without flash in much dimmer settings than you could at the lower ISOs.  

To make this crystal clear, it's time for yet another analogy from Bryan Peterson's book Understanding Exposure. (You really should run out NOW and get a copy for yourself.  It's super user-friendly.  Besides, I'm thinking he should probably give me some kind of kick-back for how often I refer his book, right?)  Anyway, Bryan Peterson uses the analogy of worker bees to explain how ISO settings affect your images.  

Imagine you have 100 worker bees on hand to gather the light in an image and deliver it to your camera's sensor.  Those would be some speedy worker bees, right?  Well, now imagine you have 200 worker bees to gather the same amount of light.  It would take those bees half as long to gather the needed light as the 100 bees took.  400 bees would gather the light 4 times as fast.  800 bees would gather the light 8 times as fast.  You get the picture.  So, each time you double your ISO setting you can halve the shutter speed.  So, you will be able to use a faster shutter speed in low light.  This is probably the most important aspect of ISO.

How does this affect your photography?  Let's say your aperture is set as low as your lens will allow at f/1.4.  Unfortunately, you forgot your tripod at home, so you are limited at how low you can set the shutter speed (since you will be hand-holding the camera).  You won't be able to set the shutter speed as low as your camera's light meter suggests in order to get a proper exposure when you are in a dimly lit room.  

How can you get more light onto the sensor so that you can shoot at a higher shutter speed and forego the tripod? Simply increase your ISO settings on your camera.  If it is set at ISO 100, try ISO 200 first.  If you still need a faster shutter speed, try ISO 400.  Continue adjusting the ISO settings until you reach a fast enough shutter speed to shoot without a tripod.  It goes without saying that each time you adjust your ISO settings you will also have to adjust your shutter speed until your camera's light meter indicates a proper exposure.

(Not sure what a light meter is?  Grab the manual that came with your camera and figure this out fast!  Understanding your light meter is crucial to learning how to shoot manually.)

You should also know that colors will be most saturated and images will be sharpest at the lower ISO settings.  In most cameras you will also see increased "noise" or graininess in images where higher ISO settings are used.  For this reason, since I shoot using available light, I always try to shoot in conditions that allow for an ISO setting of 100.

How do you know what the slowest shutter speed is that you can shoot your particular lens at without having to use a tripod?  That's pretty simple as well.  Generally speaking (unless you have a VERY steady hand) your shutter speed should not fall below the lowest mm reading on your lens.  For example, if I am shooting with my 50 mm lens, I should try not to shoot without a tripod if the shutter speed is lower than 1/60th of a second.  Shutter speeds faster than that should result in images that are pretty clear when hand-held.  If you are using a 24-70 mm lens, you should not shoot slower than 1/25th of a second without a tripod.  If you are using an 85 mm lens, your lowest shutter speed should be 1/100th of a second.  Anything slower than that requires a tripod.

So far we have learned about Shutter Speed, Aperture, and ISO settings. Together these three make up what Bryan Peterson (there's that name again) refers to as The Photographic Triangle.  Simply put, a correct exposure is a simple combination of these three factors.  

But what is a correct exposure?  That all depends on the desired result. Do you want to freeze the action, then place priority on a fast shutter speed and adjust your ISO and aperture settings until your camera's light meter indicates a correct exposure.  Do you want to record the tail lights on passing cars as a blurry streak of red and yellow? Then, place priority on a slow shutter speed.  Do you want to isolate one candle on top of a birthday cake?  Then, place priority on a large aperture (small f-stop) adjusting your shutter speed and ISO settings afterward to indicate a correct exposure. 

Any number of combinations of ISO, Shutter Speed, and Aperture can result in a correct exposure.  Only one of those (usually about six or seven different options) combinations is what Bryan Peterson refers to as The Creatively Correct Exposure.  And that, my friends, depends upon you - the creative force behind the lens.

Here are some general guidelines about which ISO setting to use:

Outdoors in brightly lit sunlight - ISO 100

Outdoors but in overcast light - ISO 100 or ISO 200

Shooting indoors without flash - ISO 100 if possible, use higher ISOs when needed

One last note:  When adjusting your ISO settings, always remember to change it back to ISO 100 at the end of the shoot - unless, of course, you are purposefully trying to increase the grain in your image for artistic affect.  Just remember, the preferred ISO for highest sharpness, color saturation, and image clarity is ISO 100.  That should be the starting point for every shoot.

Photography Tip #2: Understanding Shutter Speed

I'm about to embark on a basic lesson for manual shooters (for those of you wanting to learn how to use the manual settings on your camera).

First up is a lesson on shutter speed.  The shutter speed is the length of time the light coming through the lens opening (or aperture) of your camera is allowed to stay on the film (or sensor) of your camera during any given exposure.  These speeds are expressed in seconds or fractions of a second.  i.e. 2, 1, 1/2, 1/4, 1/8, 1/15, 1/30, 1/60, 1/125, 1/250, 1/500, 1/1000, 1/2000, etc.

These numbers are read as two seconds, one 15th of a second, one 60th of a second, one 1000th of a second, etc.  The smaller the bottom number is in a fraction, the slower the shutter speed will be.  And vice versa, the larger the bottom number, the faster the shutter speed will be.

What it boils down to is this: A faster shutter speed can freeze the motion of a fast moving subject, and a slower shutter speed can blur that moving subject to give the impression of motion.

How is this useful to the average mom or hobbiest?  Let's say your daughter is swinging on the swings at your local park, and you want to get a clean shot of the joy spreading across her face (while she is moving).  Simply select a high shutter speed (at least 1/250 sec. or faster) to freeze the action and be sure to focus in on her face.  

In contrast, to capture the motion of your daughter swinging (think a nice blurry arch), choose a lower shutter speed.  Just keep in mind if you choose to use a shutter speed lower than 1/60 sec, you may want to mount your camera on a tripod to make sure the other elements in the picture remain sharp.  

The following series of pictures illustrate how adjusting your shutter speed can make a dramatic affect over the feeling of an image.  

In this first image, I started with a slow shutter speed of 1/6 of a second.  You will see that the fan blades are blurred.  It gives the impression that the fan is moving, but you can barely see the fan blades themselves.

I then switched my shutter speed to a slightly faster speed of 1/50 of a second.  You still see the blur of the fans in motion, but you can now begin to see the actual fan blades themselves.  The faster shutter speed is starting to freeze the action. 

In this last image I set the shutter speed to 1/800 of a second - a very fast shutter speed.  This stops the blades in their track and gives the impression that the fan is not even moving at all.  

This is the power of shutter speed.  Now you know how those professional sports photographers can get tack sharp images of a race car driving around a race track at over 100 miles per hour.  Put this knowledge to the test and imagine the implications this will have for your son's soccer games.  You can even get a great portrait of your child - without having to ask them to get off the swingset.  They can have their fun while you have yours! 

There's just one last (but very important) point to cover.  You might have noticed that along with the changing shutter speeds in these three pictures, the aperture (or f-stop number) was also changed.  That was necessary to make sure the exposure of each image stayed the same. Had I not changed the aperture the picture would have gotten darker and darker as I increased the shutter speed.  

Does all this talk about aperture have your head spinning?  No worries, I'll take on that beast next time.  For now, just have fun with your brand spanking new knowledge of shutter speed.  Go, grab the kids, head out to the park and freeze some of your own swing action!  Enjoy!