LESSON 2: Priority is Your Friend!

Focal length, aperture, and are the three biggest choices we have to make when capturing a subject or scene exactly as we want the rest of the world to see it. All are equally important in expressing our own creative visions, and all must be thoughtfully chosen before we can create that “Perfect Picture”.

In this lesson, we are going to cover aperture and more specifically, aperture priority mode, and show you why this can cover most shooting situations. I find I have my camera set to Av (Aperture Priority) about 90% of the time as I feel it allows me the most creative flexibility for my style of shooting. About the only time I don’t use it is when I am shooting sports and want to freeze action, and in the studio using strobes where the camera’s flash sync speed is limited to between 1/125-1/250 sec.

There are several reasons for this and the first is that it allows me to totally concentrate on my subject and composition without having to worry about changing light conditions and improper . I only need to be concerned with , and point of focus. Both of which I can change quickly and easily without taking my eye off the subject or checking my exposure meter.

Shooting in natural light, the conditions can change very quickly. Not only is our light source, in this case the sun, moving but we have to deal with other factors such as clouds moving through, shadows from trees and other objects, etc, that are always changing as the sun moves or the wind blows.

Portland Head Light House f/10, 1/25sec, 70-200mm lens@70mm Av

I can’t tell you how many times I’ve been completely lost behind the viewfinder, entranced by my subject, that I didn’t notice my exposure meter moving and either under or over exposed an image. The reason for this was my camera was set to manual and while caught up in the moment, I simply forgot to adjust my shutter speed for the changing light. I hate to admit that but it does happen to just about every photographer I know, no matter their experience level.

To use Av to its fullest potential, we must first have a THOROUGH understanding of how aperture size, lens type, and even lens construction, effect depth of field.

First of all, we need to know that DOF (depth of field) is not split evenly in front of and behind the focus point. It’s is closer to 1/3 in front, 2/3 behind the point of focus. This can be extremely critical when shooting with very shallow DOF! Many times, manual focus will be needed to ensure we have exactly what we want sharp in an image.

Second, and this is the biggest issue we see in classes and on workshops, is that even at the same aperture, DOF is different for each type of lens! Many times we have had students ask why they didn’t achieve the same look as an example image when they shot it at the same exposure setting listed. The answer is because of the lens used. Think of it this way, in the days of film SLR’s and today’s full frame DSLR’s, a 50mm lens is considered a “normal” lens. Basically what this means is that looking through the viewfinder with a 50mm lens on, you will see a FIELD OF VIEW of about 45 degrees which is similar to what our eyes normally see. Objects will appear correct in size and distance. Now, put on a wide angle lens and suddenly the FIELD OF VIEW is expanded and not only are we taking more in through the viewfinder but objects appear smaller and more distant. Put on a telephoto lens and just the opposite happens. FIELD OF VIEW is compressed and objects appear closer and larger. You’re probably asking yourself what all the “FIELD OF VIEW” talk is about and what does it have to do with aperture and DOF which is what we are supposed to be learning about here, right? The answer is this, with “expanded” field of view (wide angle lens) comes “expanded” DOF, and with “compressed” field of view (telephoto lens) comes ‘compressed” DOF. It’s that simple! Well….. kind of.

Now to make it a little more complicated, let me add the following.

DOF can be different even at the same focal length and aperture! What? How is that possible? I know I just explained how field of view, or basically the focal length of the lens, is equally important as aperture in determining DOF so how can two lenses with the same field of view and aperture have different DOF? The answer is lens type and lens construction. If I take a 28-70mm lens and a 70-200mm lens and set them both to 70mm, f8, which one would have greater DOF? Hmmmm….. from what we learned above, it would make sense that the 28-70mm (wide) lens would have more DOF at the same aperture as the 70-200mm (telephoto) lens would and it does if we focus on an object from the same distance (same field of view!) with each lens. However, every lens has a “minimum focusing distance”, that is, the closest the front element can be to a subject and achieve sharp focus. DOF is shallower the closer we are to the minimum focusing distance of any lens and becomes greater as we focus out toward infinity. Since wide angle lenses have much closer minimum focusing distances than telephoto lenses do, we can get much closer to the subject with the 28-70mm set at 70mm than with the 70- 200mm set at 70mm. This “compresses” the field of view and therefore shrinks the DOF! Now, if we take and add an extension tube to the 70-200mm lens and make the minimum focusing distance equal, the DOF then becomes greater on the 28-70mm lens! Confused yet? We’re not quite done……

Macro lenses have extremely close minimum focusing distances and therefore less DOF at a given aperture than a regular lens. Adding extension tubes to a regular lens will allow closer focusing just like a macro lens but you will lose DOF as well as the ability to focus out to infinity. The closer you get, the shallower the DOF so when approaching 1:1 or life size magnification, DOF can be reduced to several millimeters even when stopped down all the way. Aperture choice and focus point are critical in this situation so keep this in mind!

One last point before we move on.

Believe it or not, sensor size can affect DOF! It’s not as drastic an effect as what we have covered so far but it is important to know.

Earlier I mentioned that FOV was referenced to 35mm film and full frame digital cameras. Most of today’s DSLR’s have sensors that are smaller than a piece of 35mm film. We usually see this expressed as a “crop factor” or the dreaded “magnification factor”. Most cameras have a 1.5 (Nikon) or 1.6 (Canon) crop. Basically what that means is that the sensor is roughly ¾ the size of a piece of 35mm film so you get a narrower field of view from a lens as you would on a full frame or film camera. In other words, if you were to set up a full frame camera next to a crop frame camera and put 50mm lenses on both of them, the images from the crop frame camera would appear as if they were shot with a 75mm (Nikon) focal length or an 80mm (Canon) focal length lens. Now, we all know that the DOF will be greater at a given aperture on a 50mm lens than on an 80mm lens, right? So, which image will have greater DOF? Are you sure about that? If you said the one from the camera with the smaller sensor (80mm FOV) you’re right! Take a bow as you’ve managed to follow all of this correctly so far!

But wait a minute…. We’ve just spent all this time learning how narrower field of view affects DOF so the image with the 80mm field of view should have shallower DOF not GREATER! That is correct, but think about it carefully. We shot both images with a 50mm lens. We are only seeing the equivalent field of view to an 80mm lens on the cropped sensor camera. To get the same size image with the same field of view we would have to put a LONGER lens on the full frame camera which would then give us less DOF for the same field of view! So, the smaller the sensor, the greater the DOF at a given focal length and aperture.

I know this was a lot to take in, but trust me, it will all make sense as we move through the rest of this lesson. By fully understanding how all of these factors affect DOF, you will truly be able to make the most out of your camera and lenses using Av!

One of our workshop participants right after I explained DOF to him! f/3.2, 1/800sec, 120-300mm lens @300mm Av

As stated earlier, Aperture Priority allows you the freedom to focus all of your creativity on your subject without having to worry about changes in exposure values. As long as you know what aperture you need for the DOF you are trying to achieve, the camera will take care of the rest. However, you do need to be aware that certain rules still apply such as shutter speed being lower than the focal length of the lens. In this situation, you can easily cause out of focus images due to camera shake. If you are unable to get a fast enough shutter speed because of the lighting you are shooting in, you have a couple of choices. First, get out your tripod! Most people are amazed at how much sharper their images are when they actually use one. If you are shooting in a place that doesn’t allow them, left it at home, or just can’t set one up, raise the ISO on your camera to see if you can get a usable shutter speed. Most of the newer DSLR’s have incredibly good high ISO so you don’t need to worry about noise as much. You will want to be careful not to underexpose at higher ISO’s though as that can really amplify the noise in the dark areas of an image. While I like to shoot at ISO 100 whenever possible, I would much rather bump it up to get the shot I am after than not get it at all. It’s always a good idea to check the setting BEFORE each shoot in case you forget to set it back to 100 after shooting in low light!

f/2.8, 1/80sec, 28-70mm lens@70mm Av Notice the “noise” in the background of this image. This was shot on an older DSLR with the ISO@800 I was not able to set up a tripod at this location and the light was so low that I couldn’t get a fast enough shutter speed for hand holding without going to 800ISO The noise here is unacceptable. Fortunately, today’s DSLR’s have even less noise at higher ISO’s than this. Lets take a look at some images shot in Av and discuss why it was the right choice for each shooting situation.

I love shooting portraits in natural light. Indoors or out, there are always going to be distracting elements that we need to be aware of. To remove these distractions from a scene, we need to either move the subject, or use an aperture that blends them into the background. Both options work but many times the light dictates where the subject needs to be and moving them isn’t an option. In this case, using a lens with a large maximum aperture and shooting wide open is the answer. With the camera in Av and the lens wide open, I am free to concentrate on my subject and not worry about what’s behind them. Also, as I move around, I don’t have to think about changes in exposure and my subjects will be more relaxed if I am not constantly interrupting the flow of the shoot to make adjustments.

f/5.6, 1/200sec, Av

f/1.2, 1/400sec, 85mm lens, Av By choosing to shoot with the lens wide open and at the minimum focusing distance, the subject becomes separated from the background. Not only does this help eliminate distractions, but it adds a lot of depth to the image.

f/4, 1/200sec, 70-200mm lens@200mm, Av Using a telephoto lens with a large aperture and close to the minimum focusing distance helps to eliminate unwanted background elements from the image. The added distance from the subject usually makes them feel more relaxed as well

f/5.6, 1800sec, 50-500mm lens@500mm, Av For subjects that are uncomfortable around the camera, an even longer lens accomplishes the same thing. The background here was trees and a chain link fence. Using the lens wide open blends all of the distracting elements into a nice smooth background.

f/2.8, 1/500sec, 28-70mm lens at 70mm, Av Again, by shooting with the lens wide open and at minimum focusing distance, not only can you direct your viewers eye exactly where you want, but you can give your images a lot more depth.

Here are a few more portraits. All shot in natural light with the camera in Av. If you have any questions, just post them in the QnA.

f/4, 1/22sec, 70-200mm@200mm, Av

f/2.8, 1/400sec, 70-200mm@200mm, Av

f/2.8, 1/800sec, 28-70mm@70mm, Av Kathleen and I both share the joy of . While Maine and Washington are quite different, each has an abundance of natural and man made photographic opportunities. Whether isolating a single bloom in a field of flowers, capturing a wind battered lighthouse along a rocky shoreline, showing the great expanse of a mountain side lake, or even the grand scale of a volcanic peak, with our cameras in Av, we are able to easily capture the beauty that surrounds us. We usually find that we are shooting these scenes with our lens fully open, or stopped down as far as possible.

I will point out that some people feel that you lose sharpness when shooting at small due to diffraction. There are many studies on this topic and I will be happy to point you in that direction if you wish to read up on the subject. Basically, it will vary with the quality of the lens, quality and size of the sensor, and the AA filter that is over the sensor. My personal experience is that the added DOF that shooting at smaller apertures far outweighs the effect of diffraction with the lenses and camera system I use. The best way to find out the limits of your equipment is to shoot the same scene at every aperture your lens has and view the results. The results will more than likely be different for each lens you own so plan on taking some time if you want to try this!

Shooting in Av again allows us the freedom to really concentrate on composition without having to worry about subtle changes in light as the sun rises and sets or clouds drift by. And remember to always bring your tripod when shooting in any of these situations!

f/22, 1/00sec, 17-40mm@17mm, With my camera on a tripod, I manually focused on the rocks at the front of the scene. With my aperture at f/22, I knew I would get maximum DOF.

f/11, 1/250sec, 70-200mm@200mm, Av With my camera still mounted on my tripod and in the exact same spot as above, I switched to a telephoto lens. Notice how the telephoto “compresses” the scene as compared to the wide angle image above.

f/32, 1/4sec, 105-210mm@210mm, Av Once again with my camera mounted on a tripod and using manual focus, I stopped the lens all the way down and selected a shutter speed that I knew would give me the effect I was after. The color here comes from a blue and gold polarizer.

f/5.6, 1/1600sec, 120-300mm@300mm + 2XTC, Av During a workshop on the coast of Maine, we were sitting on some rocks pretty far from the surf. This man came up and started fishing with the waves pounding the rocks in front of him. I put on a 2X teleconverter and set the focus on his back. With the camera in Av, I just had to time the waves right to get the shot I wanted with the correct exposure.

f/4, 1/160sec, 17-40mm@40mm, Av With the close minimum focusing distance of my wide angle, I was able to get very close to this leaf and still get a large FOV while keeping DOF fairly shallow.

f/16, 1/60sec, 17-40mm@36mm, Av. Using a wide angle lens and manually focusing on the rocks directly in front of the lens, I knew that stopping down to f/16 would give me the DOF I wanted. An image like this is a great place to try DOF preview!

f/20, 1/250sec. Av

f/11, .3sec Av

f/16, 1/125sec Av

f/22. 1/20sec Av Another favorite type of photography for Kathleen and I that Av lends itself well to is macro photography. This is always where I find myself so caught up in the intricate details of the subject, that I never remember to check my exposure meter! Shooting in aperture priority solves that problem for me. I also find that I am more likely to experiment with DOF and focus point when I am not worry about exposure. Keeping one finger on the control dial, I can quickly change aperture without ever taking my eye off the subject. This keeps me from losing focus, or accidentally moving the camera which can be critical when working with such narrow DOF. Depending on the focal length of your macro lens, you might also find yourself blocking some available light as you work your subject. Shooting in Av will take care of that as well! If you find yourself unsure about what aperture to use or what point to focus on, try using the DOF preview feature. What this does is stop down the lens to the selected aperture without firing the shutter. You can look through the viewfinder and adjust the aperture to get the DOF you want as well as see what areas of the subject are sharp. By holding down the DOF preview button and focusing at the same time, you can be certain that you have your point of focus exactly where you want it. You will notice that the viewfinder gets very dim as you stop the lens down. It can be difficult to work with at first but as you use it more, it will become much easier. Having the ability to see the entire DOF at every aperture and being able to place it exactly where you want in the image is a very powerful tool that you will find yourself using more and more once you learn how to use it.

f/18, 1sec, Av

f/3.5, 1/8sec, Av

f/22, 1sec, 28-70mm@70mm+20mm extension tube, Av Using DOF preview, I manually focused on the closest point in the image I wanted sharp.

f/22, 2sec, 28-70mm@70mm+68mm of extension tubes, Av I stacked all three extension tubes together to get as close as possible. Manual focus, DOF preview, and mirror lock up were all used in this image.

f/8, 1/40sec,

f/8, 1/250sec, 70-200mm@200mm+36mm extension tube, Av I shot this looking out the back door of my house during an ice storm. By using the telephoto lens + extension tube, I was able to focus very close and blur out the background nicely. If you look in the drop, you’ll see the hot tub that is also in the bottom right of the frame. You can see why I needed very shallow DOF here!

f/22, 4sec, 180mm macro lens, Av Manual focus using DOF preview, mirror lock up to prevent camera shake from “mirror slap”, tripod and shutter release.

As you can see, Aperture Priority allows all of the creative flexibility of shooting in Manual while allowing you to really concentrate on your composition and focus without the distraction of adjusting exposure. Once you have determined and set the aperture value that is needed for the image you are creating, you are free to fire away knowing that the camera will take care of setting the correct shutter speed even under changing light.