Now this really isn’t a HDR question per say but it is a very relevant one since a good portion of HDRs are landscapes or objects that we may need a very deep depth of field for. In fact shallow DOF images are not really that great but of course there are exceptions.
Depth of Field
So let’s examine how to get the maximum Depth of field and also how and what should be our subject of focus.
First lets go over what makes up Depth of Field (DOF from here out) DOF is determined by: Aperture, Focal Length and Distance to subject. The smaller the aperture, (higher the f/number) the deeper the DOF. The wider the focal length, the deeper the DOF, The farther away you are from the subject, the deeper the DOF (Of course in all cases the opposite is true.)
So for the most part, a good amount of all landscapes and HDR of architecture or objects are shot with wide angle lenses. So we’ll take that part as a given. The distance to subject can vary greatly. So that leaves Aperture and you may think, well for the deepest DOF, I’ll just crank it down to the smallest aperture I have.
Well, that would be wrong. The problem being; Diffraction. Diffraction causes loss of sharpness in our image and it comes from using too small an aperture. Some is good, more isn’t better. Now there is a long and involved story behind it but I will let you Google that part. But I’ll just say that it is dependant on your sensor size on how far you can go. For a Full Frame DSLR, you should Max out at about f/16, for a crop sensor DSLR, about f/11 and for point and shoot camera, about f/8. Can you go more? Yeah you can get away with it sometimes and sometimes you need to when you are trying for long shutter speeds for the image. But the above guidelines are pretty good.
So now that we know how to get a deep depth of field, let’s look at focusing techniques that best take advantage of that.
All too often when people take Landscape images they just focus on the distant horizon or “Infinity” on our camera’s focusing scale. And that may be fine. But sometimes that is the last place we want to focus. It really depends on the composition of our image and the element within that image.
Let me give you one piece of advice, This way you can sleep at night, not toss and turn and worry about one more thing. If your subject of the image is the mountain range or the lake or the sunset over the ocean and there is no subject in the foreground. Focus at infinity…done.
But, if you take the advice that I offer in my …See class, “Always have a subject in the foreground and leading lines to your background”, well, now you have something to think about.
Hyperfocal Distance is a distance to focus on, based on Focal Length and Aperture that will have the maximum DOF possible with that lens at those setting. When focused at the Hyperfocal Distance, your DOF will extend from ½ the Hyperfocal Distance all the way to infinity.
“But I stink at math how can I figure out Hyperfocal Distance?” Well luckily there are many charts and programs and website to do that math for you. On the web you can go to dofmasters.com and right there you can plug in your camera, focal length and aperture and not only will it give you the Hyperfocal distance. You can also use it to figure out DOF for other shooting situations.
But of course you don’t always have your computer around when you are out shooting. Well then do what I do, get a DOF ap for your smart phone. Check the ap store for your particular phone for DOF calculators and I’m sure you will find one no problem. The good thing about an ap on your phone rather then just using a website on your phone is even if you are in remote locations away from any signal, your ap will work.
Focus in Practice
Let’s take look at how this all works in practice.
With the lens focused at 2 feet, our image is in the field of acceptable focus from 1 foot (half the Hyperfocal distance) all the way to infinity. The pencil can is sharp and if we look at the zoom you can see that the 12 Inch mark is clear. If we look at the background we can see that it falls well within the field of acceptable focus (remember that the point of focus is the only part that is perfectly sharp)
Now lets move the cup closer to the camera, in fact let’s make it extreme and place it at the minimum focus distance of the Canon 17-40L lens: .75’
Placing the focus on the Pencil Can, We can see the can is perfectly sharp. The distant background is now slightly out of focus.
Setting the focus at the Hyperfocal distance, the background now comes into the field of focus and the pencil can looses some of its focus.
Placing the focus at infinity is the worst scenario and with the background in focus but no sharpness or focus whatsoever on the pencil can, our subject.
So here is where you need to make a decision. For me, I would place focus on the subject itself. Because of the size and scale of the subject in the overall image, I want that totally sharp and would give up a little of the background focus
Making the decision
Here are some Guidelines to help you make that decision.
- If your subject is in the background and no items of interest in the foreground: Focus at infinity done, sleep at night.
- If you have a foreground subject but not one clearly defined subject, focus at the Hyperfocal distance
- If you have a clearly defined foreground subject that is at or closer to the camera than the Hyperfocal distance, focus ON the subject.
- If the composition and scale allows, place your subject at the hyperfocal distance. Best of all worlds
Here are some examples of when you would use what.
In this case with a clear and difined subject that was closer than my hyperfocal distance, I chose to focus on the subject, the tennis ball
In this image I have a foreground subject but it isn’t a single subject or point and I need the maximum depth of field. So I focused at the hyperfocal distance. Which in this case was on a 1.6X crop camera, 10mm Lens, f/20 and the hyperfocal distance was 11 inches
Ok, so we are done right? Almost, what if I have tried everything and becauee of the combinations of focal length and distance to subject and aperture I just can’t get that deep deep DOF I need! Am I out of luck? Nope, your last ditch effort is: Focus Stacking.
Focus stacking is something that is done often with Macro photography. Because of the close distnace to subject and focal length used the total DOF is often inmm. So peopke will use sophisticated prograns to stack images shot at different focus distance to blend into a single image with greater DOF. Well we don’t need to get that compliacted and we can take just two images, One focused on our subject and one focus at our background and blend those tow together using layer masks just like I showed you for adding adjustment layer masks.
This image was done just that way because I wanted to clouds and the mountain behind the poppy field to be in better total focus.
Hope that helps,