Question: How do aperture and shutter speed change with the amount of available light?

Answer

Why? Well, I'm going to be digging into some fairly low-level photographic concepts here, and I've been building up to this point over the past couple of issues.

If you don't read those issues first, a lot of what I cover here might seem confusing. It's like trying to learn how to swim by jumping into the deep end of the pool.

Having said that, let me help you on your way:

• November 2006 - What is Aperture?
• December 2006 - What are F-Stops?
• January 2007 - What is Shutter Speed?
• February 2007 - The Aperture/Shutter Speed Balance

OK - ready to get started?

You have two ways that you can control the amount of light that lands on the sensor of your digital SLR camera: you can make the aperture of the lens wider or narrower, and you can make the camera's shutter stay open for a short or long period of time.

Now we're going to toss in the most important variable: the amount of available light.

Let's begin with the most common scenario: you're taking a photo on a bright sunny day of a static subject (I'll talk about moving subjects in a later issue of the newsletter). In this case there is plenty of ambient light so you're not going to have to open the aperture wide or keep the shutter open for long for the sensor to collect enough light.

Remember, the amount of light we're after here is just enough to create a balanced exposure. If we let in too much light we wind up with an over-exposed photo, and if we let in too little the photo will be under-exposed.

Let's start by setting a fairly narrow aperture of f/16. Since there is plenty of light outside, the correct shutter speed for a correctly exposed photo should be about 1/250th of a second.

Let's add this information to a table that we can build upon as the light changes:

Available Light	Aperture	Shutter Speed
Bright Sun	f/16	1/250

This is a good start. But imagine now that instead of a bright sunny day, it's partly overcast. If we just leave the camera set to f/16, 1/250 we're going to wind up with a photograph that is under-exposed, since the ambient light is dimmer.

We now have one of three options:

1. Open the aperture wider
2. Slow down the shutter speed
3. Widen the aperture AND reduce the shutter speed

In the December issue of the newsletter, I talked about how apertures are measured in f-stops. Well, we're going to take that concept a bit further today and delve into stops of light.

When you begin to think about the amount of available light in terms of stops (rather than just saying "whoah, it's BRIGHT out here!") then the changes you have to make to aperture and shutter speed to get a correct exposure start to make sense.

In order to keep things simple for now, I'm only going to be using a half-stop scale.

Here's the aperture scale with half stops (full stops in bold):

2.8

3.5

4.0

4.5

5.6

6.7

8.0

9.5

11

13

16

19

And here's the shutter speed scale with half stops (full stops in bold):

1000

750

500

350

250

180

125

90

60

45

30

19

Let's say that the difference in the amount of available light between a clear day and one that's partly overcast is one FULL stop of light. Let's also go back to our three options for changing the camera settings, and add some more details:

1. Open the aperture by one full stop
2. Slow down the shutter speed by one full stop
3. Widen the aperture by a half stop AND slow down the shutter speed by a half stop

And here's how our camera settings might look when we apply each one of these three different options:

Available Light	Aperture	Shutter Speed
Bright Sun	f/16	1/250
Partly Overcast	f/11 (one stop wider than f/16)	1/250
	f/16	1/125 (one stop slower than 1/250)
	f/13 (half stop wider than f/16)	1/180 (half stop slower than 1/250)

That's enough tables and numbers for you to kick around for now. Even if you're using your camera in AUTO mode, you can still see the aperture and shutter speed settings the camera is choosing in the viewfinder.

Pay special attention to these two numbers as the amount of available light changes, and you'll begin to understand how aperture and shutter speed work together to create balanced exposures.

Online Digital SLR Lessons

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Latest Digital SLR(s)

This show is always the time when camera manufacturers announce all of their latest models, including many that are still in production but are soon-to-be-released.

This year was no exception, and saw the confirmed introduction of 3 new digital SLR camera, along with a host of "pre-production" models.

The four new cameras announced at PMA were a high-end professional camera from Canon (the EOS 1D Mark III) and two new models from the Olympus company, which never ceases to surprise me with their level of innovation.

Since the Olympus cameras are better suited for the consumers this newsletter is for, I'm going to focus a bit more on them and will let you go looking for more information on the EOS Mark III if you so desire.

The two new Olympus cameras (to be released in June and July) are the E-410 and the E-510.

Besides including many of the features that are common on digital SLR cameras today (including 10 megapixel sensors), these two pack in a bunch of additional features that are designed to produce better images and make the cameras more versatile.

Both feature the Olympus dust control system (called a SuperSonic Wave Filter) and live view LCD screens (that allow you to preview an image before you take it). Even though this feature is quite common on compact digital cameras, it is NOT on SLRs and these two cameras join a very select group of live view digital SLRs.

Finally, the E-510 will also include a built-in image stabilization system (already available on cameras from Pentax, Samsung and Sony). The image stabilization reduces the effect of camera shake and helps you take clear photos in low-light conditions without using a flash.

The big news about the E-510 is that it will be the first digital SLR camera to include ALL of these special features. While the Sony A100 came close, it lacks the live view LCD screen that will be available on the E-510.

Even bigger news is that both cameras will retail for less than $900, making them enticing options to consumers seeking a new digital SLR camera.

Digital SLR Camera of the Month

Aimed at the semi-professional market, the Nikon D200 has all the bells and whistles that you could possibly hope for in a digital SLR camera.

Key to this camera's appeal are its fast 5-photo-per-second continuous shot rate, 11-point autofocus system and instant response times. You'll notice that the theme of these features is SPEED.

Since the D200 is one of the fastest consumer digital SLR cameras you can buy, this makes it the best digital SLR for action photography.

But it doesn't stop there. The polls are in and users of the D200 are just plain thrilled. In a comparative analysis of several different user review web sites, the D200 has emerged as the top rated digital SLR camera, due to an impressive number of rave reviews.

If you're just beginning your journey into the world of digital SLR cameras then the D200 is probably a bit much - you really don't need all of the features and functionality that this camera offers.

If, however, you've been using a digital SLR camera for a couple of years and feel like you're ready to make the move to the next level, then the Nikon D200 is sure to please.

Accessory of the Month

It's a lens, but not a lens in the traditional sense because...well, it's flexible. Literally.

Lensbabies come in a variety of mounts so they can attach to cameras from different manufacturers. The images they produce are completely unique and use what's called "selective focus".

You are actually able to twist and turn Lensbabies so that singular elements in your photos are in focus while the rest blurs out completely.

If your photography is all about capturing crisp, clear, life-like images then Lensbabies are definitely not the right accessory for you. But if you're branching out into more abstract forms of photography and want a lens that can really enhance your creative vision, then it's worth your time to take a closer look at these amazing lenses.