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Focusing And Depth Of Field

Updated: May 13, 2019

With the advent of DSLR (digital single lens reflex) cameras that have the complexity of mini-computers, many of the functions which used to be done manually have been automated. Functions such as exposure settings, focus, choice of ISO, etc. And for general photography, these "auto functions" work just fine.

But when you strive to take photos that are top notch, you usually want them to be "sharp", or finely focused thru out the frame. There are quite a number of basic things you can do to help produce sharp photos: use a tripod, lock up the internal mirror, use an external trigger device or use the 2 second shutter timer, etc. But they are all for not if you aren't accurately focusing on your subject.

One of the basic concepts in photography that one must come to understand is the concept of " Depth of Field " and what camera settings effect it. The definition of Depth of Field (DoF) is:" the zone of acceptable sharpness within a photo that will appear in focus." You can adjust the depth of this sharply focused area purposely, to create the effect you want. I started to explain it here but then I found an article that was really well written, with lots of good graphics. Kudos to it's Bulgarian author, Stefan Surmabojov: Anything you need to know about DoF is explained there.

One other concept a landscape photographer must grasp in conjunction with DoF is Hyperfocal Distance. This is also sometimes called " double the distance ". The technical definition is" the closest focusing distance that allows objects at infinity to be acceptably sharp." This is a very complicated subject, explained using formulas and charts; I have included a link here to an article by Spencer Cox that goes into great depth to explain it.

In practice, most photographers use the " double the distance " method. To find the hyperfocal distance focus point for a given scene, you can simply double the distance between your lens and the closest object in your photograph. If the closest object is 10 yards in front of you, focus on an object 20 yards away. Take the picture and in the LiveView screen, evaluate the the photo foreground to distant background for sharpness/focus. This will be much more critical when using wide open apertures ( small F numbers) since wide open apertures have a shallow, or narrow DoF. Smaller apertures, F/ 8 to F 16 or higher for example, have a much deeper DoF. ( remember DoF article ) This naturally results in more sharpness from near to far. But you should still evaluate the effect of your chosen hyperfocal distance by reviewing your photo in the Liveview screen.

One of the most useful features on DSLR cameras is the LIVE VIEW screen. Get used to using it extensively, both for taking the photo and then reviewing the results. Several reasons for this recommendation:

1. the LV screen gives you a larger view than what you see thru the viewfinder

2. when you use the LV screen the internal mirror is locked up to minimize shake, and the viewfinder is blocked.

3. you can magnify the screen image up to 10 times to really check how well the image is focused

4. you don't have to bend your neck to see the image.

The way I use the liveview screen when taking a landscape photo is:

1. Compose your picture using the LV screen

2. Magnify the view up to 5x or 10x

3. Using the up/down and side to side arrows, move thru the picture from foreground to far background, evaluating for sharpness. You may have to refer back to your camera's manual to figure out how to adjust the magnification and how to move around the image .

4 Switch the lens over to manual focus This is often a small switch on the side of your lens.

5. Use the focusing ring to adjust focus, then do not touch it again once you are satisfied with sharpness of image.

6. Return to normal magnification on the Live View screen.

7. Double check your composition

8. Take the picture using external trigger or 2 second shutter delay

9. Review the photo taken for sharpness; use the 5x or 10x magnification again. Move around the screen checking foreground, mid ground and background.

From Here To The Moon I estimated the distance to the rock in the foreground, then doubled it. I focued on the small sagebrush clump behind it. Under magnification, the picture is acceptably sharp from the foreground rock and flowers, to the moon above the distant peaks. It was shot at F 13.

If the foreground is soft, or not acceptably sharp, pick another focal spot a little closer and shoot another photo. If the background is soft, you can pick another focal spot a little more distant than the previous one; you can also narrow down the aperture ( increase the F number) to give a deeper DoF.

Two considerations to using the LV screen. It will use more of your battery, but as a practice, you should carry 1-2 extra charged batteries at all time. And to help you view the screen and evaluate the image, you can use a loupe, a 3x magnifier that fits over the screen to help you better see the fine details. Here is a link to one on Amazon, (I am not an associate site for Amazon, I get no money for this referrral)

I hope this blog has given you some insight into an important aspect of taking photos which is often rushed thru. I hope it gives you cause to slow down, take a few extra minutes before and after pushing the shutter. And always remember to slow down and just enjoy the beautiful landscape you are taking photos of.