The Perfect Aperture, Shutter Speed or ISO To Use For T2i HD DSLR Video

First off, let me say that my headline is very misleading. Simply put, there is no single absolutely "correct" or "perfect" shutter speed, aperture or ISO setting for any given scene.

I wrote the headline this way on purpose to reflect the second most popular Google search query leading visitors to my Web site. As you can see in the screen grab below, " Crow Digital Media" is the number one query but right there at number two is: "how to know what aperture to use when filming T2i." Up until now I haven't had any content answering this question, for several good reasons.





Interesting...I wanted to investigate this question in depth to see if my gut instincts on this topic are "correct" (there's that word again!) or if I'm crazy as a loon.

Something seems very off base about the question itself. For instance, why didn't they ask what the "correct" ISO or shutter speed is? Basically, the question comes down to exposure - I think the real question they have is "what is the correct exposure for this particular scene and how do I get it?" And I have a very precise answer: "it depends."

EXPOSURE IS A CREATIVE CHOICE, RARELY A TECHNICAL ONE
This is the crux of my view on the matter. Any exposure that isn't so blown out or underexposed that it takes away from your view of what the image should be is, in my view, "correct."

There is software and hardware called Waveform Monitors that allow you to determine if your video follows the "Broadcast Safe" standards set by the Institute of Radio Engineers (IRE) and their 0-100 scale. These technical requirements tell you if your whites in the scene are "too white" or the darker areas "too black" but even those standards are designed for TV broadcasts in the United States - they were never meant to be applied to footage destined to be shown on a movie screen, in Europe or to a video on YouTube. In other words, they don't really apply to you unless you want to show your stuff on TV or cable.

WE ARE CREATIVE FILMMAKERS ALLOWED TO MAKE CREATIVE EXPOSURE CHOICES
Remember that scene in the movie "Apocalypse Now" when Marlon Brando, playing the terrifying and presumably insane Colonel Walter E. Kurtz, moves his face out of the shadows and then just barely into the light to confront Martin Sheen, the Army officer sent to kill him? Would anyone say that scene was "under exposed?"

Had our Canon T2i traveled back in time to be on that movie set, its built-in light meter would no doubt have said a big "YES" but it would be as incorrect as it could be. Why? Because that scene was carefully lit and filmed to fulfill the director's vision. The shadows were used to great effect so that we could hear Brando's voice coming out of the dark before we ever saw his shaved head move into the smoke filled light. Had the scene been filled with more light we would have lost that chilling moment.

What exposure does my scene need in order to best tell the story is the question you should be asking yourself first. Next we'll talk about how to achieve it with your T2i.

GIVE ME THE CAMERA SETTINGS ALREADY!
Okay, Okay, here comes the geeky stuff all you gear heads (like me!) really wanted to know in the first place. No matter if you are taking still photographs with your T2i or filming 1080p HD video, your exposure is controlled by three settings that all work together:

• Shutter Speed


• Aperture or "F stop"


• ISO

Changing any one of these three settings will make your video darker or lighter. You do have your T2i set to fully manual exposure control for video don't you? If not, go into the camera settings and make that change right away. Yes, it means more work for you but it's worth every bit of initial pain and learning to master your craft.

For me, one of these settings almost always stays the same no matter how I set the other two. Because of the "180 degree rule" my shutter speed is basically kept at 1/50th of a second since 99% of the time I film my video at 24 frames per second to help achieve a more filmic look. The only time I would change it off 1/50th would be if I wanted to do a slow motion scene in which case I would have to first set my T2i to film at 720p/60 fps and then I'd change the shutter speed to be closer to 1/30th of a second.

So that leaves me with two controls with which to adjust the overall lighting in my scene as captured by the camera: ISO and aperture.

One of the great things about shooting video with HD-DSLRs is the amazing range of ISOs we can now select from; anything from 100 to numbers in the thousands depending upon your camera. A rule of thumb is to stay below 800 ISO in order not to introduce too much noise but, as always, rules were made to be first understood and then broken.

That leaves aperture. In my mind, aperture is your greatest tool. Different lenses will give you different aperture options but the lower the aperture number the more light will be let into your scene.

TURN ONE UP, THE OTHER DOWN
I find this process very similar to color grading your video footage, if you raise one value up, your next move is generally to move another slider down. Likewise, let's say I want to achieve a shallow depth of field look to my footage of outdoor plants and flowers filmed on a sunny, California afternoon. That's my creative vision of the scene.

To achieve it, the first camera adjustment I make is to lower the aperture setting to something like 2.0 for the shallow depth of field but now my entire picture is blown out, there's simply too much light hitting the camera's sensor. I want to keep my new aperture setting and I can't change my shutter speed because it's already set to 1/50th where I like it - so that leaves only my ISO settings.

So in this case to compensate for the blown out scene I would want to lower my ISO until I get the image I want.

But what happens if I dial my ISO all the way down to 100 and the image is still too bright? In that case there is one other option. You can purchase Neutral Density (ND) filters that screw to the front of your camera's lens and cut down the amount of light by up to 8 full stops. There are even a couple of manufacturers that make adjustable, rotating filters that give you anywhere from 2-8 stops of...errrr..."less light."

So basically I am always juggling different combinations of aperture and ISO settings to get the image I want, sometimes using a set of ND filters to help out when shooting outdoors on bright sunny days if I want to keep my aperture setting open to achieve that shallow depth of field look.

DIFFERENT SETTINGS, SAME EXPOSURE
Because shutter speed, aperture settings and ISO can act to negate or enhance each others effects in sort of a push/pull relationship, it's mathematically possible to film two different video clips that look nearly exactly the same yet each clip used different exposure settings.

In fact, author Bryan Peterson points out in his famous book on photography titled "Understanding Exposure" that depending upon the lens attached to your camera, you will have no less than six different aperture/shutter speed combinations that result in the same overall exposure (you may notice differences in the overall sharpness and definition of the image however.)

All Aperture/Shutter Speed Combinations with the same “Exposure Value” number are more or less equal. This chart doesn’t take into account ISOs.

Even though video shooters may be more likely to manipulate aperture/ISO settings than aperture/shutter speed, the same idea applies.

THE T2i THINKS IT KNOWS WHAT EXPOSURE YOU SHOULD USE
I can't tell you how it works but the software inside your camera has a formula it uses to determine what the "correct" exposure should be. But really it's only an estimate and it can't take into account your creative choices like wanting to purposely darken or lighten a scene. Still it tries.

If you press the shutter button halfway down and hold it (even while in video mode) you will notice a rectangular marker underneath a small, ruler-like graphic called an "exposure compensation meter." It measures from -2 on the left to Zero in the middle and +2 on the far right.



From the camera's perspective, it wants you to have that rectangular marker set at Zero, if it's at +2 it means it thinks your image is 2 points overexposed. Therefore the camera thinks that if you can lessen the amount of light in the image by 2, you will have achieved "correct" exposure.

This can be done by lowering the ISO, closing down the camera's aperture so less light is let in or changing your shutter speed to a higher number meaning the shutter is actually open for a lesser amount of time. You could change all 3 values, two of them or just one - the camera doesn't really care. In fact, you could not change any settings on the camera itself and instead screw on one of those ND filters to let in less light into the front of the lens and that would work too.

There's a two button combination you can use (the AV +/- button and the scroll wheel) which together will allow the camera to semi-automatically adjust your overall exposure up or down to get that marker right in the middle.  I've recently begun testing  to see if I can determine what values the camera changes in order to "correct" the exposure but so far the results are inconclusive.

But remember, our T2i's light meter is only a tool, WE are the filmmakers and may decide to overrule the camera's helpful suggestion.

EXPLORERS OF LIGHT AND LIGHTBOXES
Canon has assembled a prestigious panel of some of the best photographers in the world under their "Explorers of Light" program. While most of us will never be members of this select group, we are all still explorers of how light works and how light or darkness can be used to achieve our vision.

It occurs to me that I haven't mentioned one other huge area of lighting and that is the use of artificial light or reflectors. By changing our camera settings we are changing the way our camera reacts to the light in a scene, but there's always the option of changing the light we are working with, by adding to it, taking light away, changing the color of the light, reflecting it or even diffusing.

On a Hollywood film set that's what the Director of Photography is in charge of, as DSLR cinematographers we should learn from their bag of lighting tricks. After all, we are now filmmakers.

NOTE:  I'll be releasing a video on this topic in the next couple of days, it's already in editing!