Over the years I have published a number of articles about achieving sharp focus in digital photography. I have spent much time discussing the use of focus stacking, blending several variably focused images to obtain otherwise impossibly wide depth of field. It is a perfect example of how digital photography has opened creative options that are not possible with film. In special situations, focus stacking is a powerful tool, but most of the time sharp focus has more to do with careful adherence to good technique, which applies to both the film and digital processes. This week I would like to discuss just a few tips that may improve your photographic focus. Let's start with the digital cameras and those giant LCD screens
|Zoomed Live View Focusing|
It may be surprising, but some people actually still gaze through a viewfinder to compose and focus their images, but with the proliferation of larger sharp LCD screens many cameras have dispensed with the optical viewfinders all together. The LCD provides an excellent real-time view of the scene and, when zoomed in, can be helpful in the fine adjustment of focus, especially in low light, but the viewfinder is better for routine focusing when a quicker response is necessary.
Although helpful in some special situations, manual LCD focusing is general awkward. The screen works best to compose the image while relying on auto-focus to control; the focusing.
One major challenge LCD focusing is the difficulty seeing the image clearly in bright light. It is a simple thing, but adjusting the LCD brightness to its maximum level can make a difference. Just remember to have a spare battery on hand, since the bright screen will more quickly drain power from the camera.
Through the Viewfinder
If your camera is still blessed with a good viewfinder, it offers some definite advantages for manual focusing. It is less bothered by bright light, but I find that, on occasions, I still have to shield the eye cup from glare using my hand or hat visor. Here a few other points to consider on your search for perfect focus.
If, as you gaze through the viewfinder, you never seem to get the scene to appear sharply in focus, the first step should be to adjust the diopter. Most cameras have a knob on the side of the viewfinder which adjusts the optics to match your vision. Start by focusing the best you can and then turn the knob until the view becomes clear. The adjustment will vary from person to person and with or without glasses. My diopter knob tends to easily get knocked out of focus, so I need to readjust every so often.
Using Focus Points
My vision isn't as sharp as in my youth and the act of manual focusing is additionally complicated by my variable focus glasses. The result is that I have come to depend more on my camera's auto-focus capabilities. The accuracy and adjustments of auto-focus are different on every camera, but in general, modern digital cameras do a remarkable job at nailing the focus. The key is to grab your manual and take the time to understand how your particular camera focuses and then practice until the adjustments become automatic. The key issues include: the locations of the focusing points, how to select the individual or groups of focus points and which points are most accurate. Not all focus points are of equal accuracy. On my Canon 5D Mark II the center point is a "crossed" type, which means that it is sensitive to both horizontal and vertical lines. The other focus points are sensitive to either horizontal of vertical lines and are about one half as sensitive as the central focus point. When possible, I use the center point, but at times the peripheral sensors work better to nail the focus when the subject is away from the middle of the field. I have previously discussed the use of the full field of focus points to allow Hand-Held Focus Stacking . Auto-focus is steadily improving and new cameras may have more focus points and a greater number of more accurate sensors. Grab that manual and figure out how your auto-focus does its magic and then practice, practice.
Following FocusOnce you have mastered your camera's auto-focus peculiarities, the next step is to read on in the manual about the various focus modes. My camera has a "One Shot" mode used to hold focus on stationary subjects, as well as two action modes, "AI Focus" and "AI Servo" used to maintain focus on moving subjects. It is a profound mystery to me that, when in AI Servo mode, the camera is able to adjust focus as a subject changes its distance from the camera. Even more remarkable, when in AI Focus, the camera can detect when a stationary subject starts moving and follow it from there. It doesn't always work perfectly, but the fact that it succeeds so often is a miracle. Many cameras have these capabilities and if yours is so blessed, do it the honor of learning how to use it. Just think of the tack sharp images you will get as that ravenous Lion hurtles toward you with ever shortening points of focus centered on his gleaming white teeth!
Although the broad concept of infinity may be impossible for our feeble minds to fully grasp, when focusing a camera the location of infinity seems quite comprehensible and finite. By definition, infinity focus is the point of focus beyond which all more distant objects remain sharp regardless of how far away.
|Mount Monadnock - Infinity Focus|
It would seem that all you should need to do, to focus on infinity, would be to rotate the lens barrel as far as it will go toward the little infinity squiggle. Older lens had a hard stop at the infinity point, but today, most lens can rotate beyond infinity. As Buzz Lightyear would say, "To infinity and Beyond!". In auto focus the lens is designed to stop at infinity, but when manually focusing it is possible to go too far so that proper focus needs to be pulled back and confirmed visually. Lens manufacturers give various reasons for the removal of the hard stop at infinity, including compensation for changes in the glass related to variable temperature, reduction in wear on the auto-focus mechanism and, undoubtedly most important, reduction in the price of manufacture. They argue that the ease of manual focus is less important now that most people are using their very capable auto-focus systems. Regardless of the reasons, the simply rule is to be careful when manually focusing to infinity. Again read your manual and experiment with the settings. In good light it is easy to focus visually on a distant object and then check the lens to see precisely where infinity lies. Many lens', including my workhorse 24-105mm, have a little check mark at the infinity point.
Be aware, on many zoom lens (those described as "Varifocal"), the focus will vary as the focal length changes. Zooms that maintain focus while zooming are called "Parfocal". My 24-105 is of the Varifocal variety, and so I can't zoom in to focus and then expect to be able to hold sharpness as I pull back.
The hyperfocal distance is the closest point of focus beyond which everything will appear sharp. This distance varies depending on the focal length and aperture. The hyperfocal point is key to capturing those dramatic landscapes, with both foreground detail and distance vistas in sharp focus. There are various precise and a few approximate approaches to determining this distance, but I well save this more involved discussion for another blog.
As I mentioned at the beginning, Focus stacking is a technique in which multiple, variably focused, images are blended to create a potentially limitless depth of field. I've discussed this approach in previous articles, but it should be noted that this is another area in which digital photography has expanded creative capabilities and broken bonds to the physical limitations of our expensive optics.
Focus Stacking I
Focus Stacking II
Hand-Held Focus Stacking
Hopefully these few tips will be of help in achieving consistently sharp focus. The key is to use careful technique to control both the sharpness of your focal point and also the size of the full depth of field.
And finally if you feel that you have done everything right and your images are still uniformly fuzzy, make sure that you are holding the camera steady. Perfect focus can't compensate for even a little camera jiggle. Get a tripod! and more than that, actually use the damn thing!!
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