Photography Boot Camp – The Exposure Triangle

Posted in Photography Boot Camp on November 25th, 2010 by MadDog
No Gravatar

I’ve been thinking for a while of writing some posts about basic photography skills. I don’t claim to be an expert, just an old-timer who learned the craft from a patient and skilled father. The amazing cameras which we have available to us today allow a budget-pinched but earnest enthusiast to create very high quality images. It requires only a very modest investment to gain knowledge and acquire skills which can vastly improve the visual appeal of everyday photographs. The bonus is that, with these new skills and an understanding of what is going on inside the camera, a new world of possibilities flings its doors wide and invites the adventuresome to step in and start snapping.

So, as I find myself inspired to do so, I’m going to create a series of posts for Photography Boot Camp. I’ll cover only the basics, because they are all that are necessary to begin the adventure. Today I’ll try to explain the Exposure Triangle as briefly and succinctly as I possibly can. I’m going to stay away from technical jargon as much as possible. It is the concepts which are needed, not the fancy vocabulary. The concepts of the Exposure Triangle have not changed since the birth of photography. This is where it all begins.

Okay, what is  it?

As the name implies, there are three things to consider when trying to get the proper amount of light into your camera so that the image is correctly exposed – the picture is neither too light or too dark. Those things are:

  • How sensitive is the sensor?  (This is what used to be called “film speed”. It is now called ISO.)
  • How big is the hole through which light travels to the sensor? (This is still called aperture. It’s measured in “F-stops” which is usually shortened to “f” something, such as f4.5.)
  • How long is the light coming through the aperture allowed to remain shining on the sensor? (This is still called shutter speed. It is measured in seconds or fractions of a second.”

Here is the way the relationships between these three values are usually displayed:

The arrangement in a triangle reminds the photographer that when one value is changed then at least one of the other values must also be changed to achieve the correct exposure on the sensor. Everything must be kept in balance in order for the EXPOSURE value in the centre to rest at zero.

We’ll start with the easiest one to visualise, shutter speed. As the diagram indicates, the shutter speed will determine whether moving objects in the image are “frozen” or blurred. Have a look at these two images:

In this image, the shutter speed was “fast”. I set the camera for 1/500 of a second. You can see the individual blobs of water.

In this shot, I changed the shutter speed to 1/8 of a second:

Now the water stream appears fuzzy and indistinct. This is what is called motion blur.

At this point one might ask, how do you set the camera to do this? Most cameras give you the option to select what is called an “Shutter Speed Priority” mode. Your camera usually controls aperture, shutter speed and ISO automatically. However this does not allow you very much creativity. The camera calculates what seems best for overall good quality images. The Shutter Speed Priority mode allows you to force the shutter speed to the value you want to either freeze the action or allow it to blur. An important point here is that if you choose a slow shutter speed, say 1/30 of a second or slower, you will have to either brace the camera firmly against a stationary object or use a tripod. Otherwise the entire image will be blurred because of the movement of your hands. Most of today’s cameras try to compensate for hand movement, but there is a limit to what they can correct. This is called Image Stabilisation. It affects motion of the camera itself, not motion of objects in the view of the camera.

Using the priority modes of your camera, Shutter Speed or Aperture, allows you to control those single variables while your camera still tries to calculate the other two variables to give you the correct exposure

Okay, let’s have a look at aperture. As the diagram indicates, the primary effect of aperture is the control of how much of the view of the camera from the lens to infinity is in focus. This is called Depth of Field. You can think of it as “deep focus” versus “shallow focus”.

Here are two images which illustrate the idea:

The above image was shot at an aperture of f2.8. Perhaps I should stop here and give a little explanation. The symbol ƒ is the official way to indicate the “stops” of the aperture. You can pretty much forget that unless you want to get into the jargon. All that you really have to know it that the number represents a backwards measurement of the size of the hole through which the light is falling onto the sensor. In other words, the bigger the number, the smaller the hole. The bigger the number the less light is getting through. There’s a technical reason for this upside-down way of expressing it, but it doesn’t matter for our purposes here. I’m keeping it simple, because that’s the way I like it (Uh-huh, uh-huh).

Where the inverse numbering silliness does make sense is when it comes to Depth of Field. The bigger the number, the more is in focus. In the first image, shot at f2.8, the coin is blurry as is the other side of the kitchen. In the image below, shot at f8.0,  the coin and the distant windows are much more in focus:

To control the aperture, and thus the depth of field, the easiest way is to use the Aperture Priority mode of your camera. You can set the aperture for the depth of field which you desire and your camera will try to calculate the shutter speed for you to get a correct exposure. Some cameras might also automatically change the ISO, if necessary.

For shots containing both near and far objects which you want to be in focus use a large value for your aperture. However, if you have a friend standing near you and you want the background to be blurred, use a small value.

We are now down to the last variable, ISO. The primary reason for taking manual control of ISO is to allow you to shoot dimly lit scenes without using your flash. You can see some examples here, here and here.

So, what is the downside of using a high ISO setting to make the sensor more sensitive to light? Why not just make it as sensitive as it can get and leave it like that? The problem is that high ISO settings invariably increase the noise in the image. Okay, what does noise look like? Here is an portion of an image shot at an ISO of 80. As you might suspect, that low number indicates that the sensor was not feeling very sensitive:

This is a perfectly good image.

Here is the same portion of the same image shot at an ISO setting of 1600. This is pushing the limits of the Canon G11:

The noise in the image is plainly visible. It affects the apparent sharpness of the image as well as the colour balance and the contrast. If you couldn’t get any more light on the scene and you did not want to use flash, this might be acceptable. Very expensive cameras with very large sensors can shoot with very little noise in near darkness. Oh, if only I could afford one. Drool is dripping off of my chin.

Most cameras now have a Low Light mode of some kind. I usually keep my camera set on the lowest value for ISO so that I have the least possible amount of noise and only take control of it or use a Low Light mode if I want the “mood lighting” effect that you can get indoors with available light.

I”m running out of steam, so I’m going to leave it there. I hope to come back with more of Photography Boot Camp later. If you find any of this useful, please leave a comment here or comment on my Facebook link to this post.

Tags: , , , ,

Direct Comparison – Canon G9-G10-G11

Posted in Photography Tricks on January 28th, 2010 by MadDog
No Gravatar

This post may cause some of you to reboot. Sorry for that. Not everybody is a photography geek. However, since I find myself today with all three of my Canon G series cameras at the office, I decided to make an extremely unscientific comparison of them. Canon has been all over the map with megapixels in the G series. The G9 was 12 and shot pretty good pictures. The G10 went to 15 and gave amazing detail in good light conditions, but was too noisy for the low light levels that make such sweet available light shots. The G11 gives you  10 megapixels. Why the backtracking? To give you a better all-round experience. Fifteen megapixels are overkill for most uses. And, the “buckets” are too small to catch enough photons to keep the sampling fair. Remember, all this dancing around of pixel counts was done without changing the size of the sensor.

Anyway, that’s way too much detail for most folk and the geeks already know what I’m talking about. Here’s a series of three shots at my bolted-to-the-wall computer in my office. All were shot at ISO 1600, which is adequate for most indoor shooting without flash as long as there are no kids or pets in the shot and you can brace a little to avoid motion blur. Just the ticket for those romantic, candle-lit dinners. All of these are a small portion of the centre of the frame – about a 300% enlargement:

Here’s the G9:

It’s noisy, no doubt, but it’s not unmanageable. I’ve made no compensation for megapixels here and the shots are compressed with JPG, so it’s not a technically sophisticated comparison, to say the least. Non-photographers probably won’t even notice the differences.

Here’s the G10 image:

We have to click all of these to really see the detail. If you do, you will probably note much more noise and a generally poorer image. That’s because of trying to cram 15 million pixe3ls on something smaller than your little finger nail.

Here’s the G11 image:

I would certainly call this better than the G9 or G10. There’s less noise and it is of the manageable kind, using a good noise filter such as Noise Ninja Pro. The detail level is better and the whole thing simply looks better.

So much for low light. How about normal shooting? I grabbed this image in front of my office today on the G11:

Nice and clean for a snapshot, but it doesn’t tell us much.

Here’s a blowup from the G9:

Pretty crisp. You can read the PNG on the plate.

Here’s the G10:

Not so hot. I didn’t get the apparent size the same, but you an still tell that it appears a bit blurry compared to the G9. Again, more pixels doesn’t necessarily make a better camera.

Here is the shot from the G11:

Frankly, I can’t see a lot of difference here. That’s to be expected. At high light levels, we shouldn’t expect to see much, although my imagination whispers that there is more detail in the shadows and highlights for the G11. This is is one of the Holy Grails for point and shoot cameras – low noise, high dynamic range. The extra detail in the shadows and highlights make a huge difference when you’re trying to achieve magnificence on a budget.

So, what does MadDog think?

Well, first MadDog wonders if anybody cares. I took this shot with the G11 in miserable lighting conditions at ISO 1600. The G11 has a swivel screen, so you can do all of those exciting things with a camera that you’ve only dreamed about. Just don’t tell me about them. I’m as happy as a clam. I can’t wait to get it into its UW housing and take it diving on Saturday.

I’m probably going to start carrying my G11 as my daily camera, though I’m a bit nervous about that, given the security situation here. When my G9 was stolen and thrown to the pavement, it still worked, except in the UW housing, Still they are tough cameras. I can’t think of many cameras with which you could club a thug unconscious and then take his picture.

I’ll still use the G10 when I need massive detail. Good light and lots of pixels can’t be beat for some jobs. But, my new sweetheart is the G11.

I’m so fickle.

Tags: , , , , , , ,