Friday, August 15, 2014

Day 79, Learning 79: Maximizing Sharpness and Detail

These days we probably place too much emphasis on sharpness and detail; the masters of old certainly weren’t as obsessed with it as we.  Even while I try to remind myself that sharpness isn’t everything, I find myself justifying my obsession by saying I can always unsharpen an image, but it’s harder to sharpen a blurry one.

True sharpness is a cross-platform endeavor

I’ve known the basics of how to achieve sharp images for years, decades; but as a professional I’ve learned the importance of maximizing sharpness in a very conscious way across “platforms.”  Sharpness isn’t dependent solely upon your equipment, your focus, your camera settings, or your editing skills-- it’s a combination of all four.  So today I’m covering them all.

Equipment / Lens.  Manufacturers tout the sharpness of their lenses, and it’s a vital player in the game.  Without a sharp lens you’ll never get truly sharp, detailed pictures.  In truth, though, most lenses are pretty sharp nowadays-- or at least pretty sharp at a specified focal length and/or aperture.  Inexpensive lenses can often be as sharp as expensive ones.  No matter what you buy, it’s worth researching what others have written about the “sweet spot” for sharpness.  Typically, though, lenses don’t perform at their best near the edges of their capacity.  They tend to be sharpest between f/5.6 and f/16, and if it’s a zoom at neither the widest or the narrowest.  A few test shots will probably tell you what you need to know.

Equipment / Lens Hood.  This five dollar accessory (I use this collapsible version) can make a world of difference, even when you’re not shooting with the sun pointing into the lens.  We see objects in the world because light is reflecting-- and refracting-- off of them.  We are literally walking in a world of refracted light.  Strong, directional light on a clear day causes the light to refract before it reaches your sensor, and blurs your image.

Focus.  There’s not too much to say about this.  Your camera’s auto-focus probably does a pretty stellar job.  Certain lens-camera combinations can require fine-tuning, an option available on high-end DSLRs.  Another factor to consider is the where to focus.  In portraits, the closest eye is the common target and for good reason.  If the eyes are sharp, then the image appears in “focus” even if the rest is blurry.  This dynamic comes into play when saving a slightly blurry image during image editing.

Settings / Aperture.  Only a few lenses are tack sharp wide open.  Strangely, these lenses aren’t necessarily the most expensive ones.  The Nikon 75-150mm f/3.5 is very sharp wide open and costs $150 used.  Typically, however, you need to close your aperture two stops before you get close to maximum sharpness.  For most lenses, sharpness declines around f/18 due to diffraction.  “Diffracted light” is light that is reflected at an angle after striking a surface.  When you narrow the diameter of the aperture, you are essentially forcing the light through a narrow opening and a small portion of that light is bouncing.  A wave length that should fill one pixel of your sensor spills onto another, muddying the sharpness of your image.  Most lenses, therefore, are sharpest between f/5.6 and f/16.

Settings / Shutter.  This is a no-brainer.  A slow shutter speed allows the tremor in your hands-- or the movement of the subject-- to blur the image.  The common rule of thumb is your shutter setting should be equal or greater than the millimeter of your lens: 50mm lens, 50th of a second.  This is (basically) true for a full-sized sensor, but the rule deteriorates quickly.  The higher the MP on your sensor, the higher the shutter speed needs to be (Nikon D800 owners discovered this in a hurry).  The real villain is pixel density-- not the number of pixels overall. The closer those pixels are to each other, the more they are affected by motion blur and diffraction.

Settings / ISO.  High ISO equals noise.  Noise competes with detail.  Yes you can reduce noise in post, but you’re also reducing the natural texture.  So if we want sharper images, shoot as close as possible to your camera’s base ISO (typically 100 or 200) and with proper shutter speed and aperture.

Editing.  There are a number of sharpening tools in a variety of software editing programs and they all adjust essentially the same thing.  What’s surprising is that they can be remarkably different in terms of effectiveness.  It’s important to understand that sharpening tools essentially increases the contrast on perceived “edges” in the image (any place there is a sharp change in color).  Lightroom’s sharpening tool works well with non-portrait images; I find it to be ugly on people.  Photoshop offers a quick sharpen tool (the triangle tool) for when the image is pretty sharp but I want to quickly hit the eyes or hair. 

I typically set the Strength between 15 and 25 to minimize noise.  More sophisticated options are the UnSharp Mask and Smart Sharpen filters.  These adjust the edge contrast and are best used with a Mask so you can paint the sharpness exactly where you want it.  The most powerful tool in my opinion, is the High Pass Filter located under “Other” in the Filter menu.  For portraits I recommend setting the Radius between 2.5 and 3.5 (though you may need to go higher based upon the image), and the Blend Mode for the layer to Overlay.  Then apply a black Mask (holding the Alt key while clicking on the mask icon) and paint in the areas of sharpness.  In my experience, the high pass filter can virtually adjust the plane of focus by as much as two millimeters if I’ve missed my focus. The eyes, as I mentioned earlier, define our sense of focus in a portrait.

Not every image needs to be in sharp focus; that’s a myth sold to us by camera and lens makers.  It’s reinforced by the fact we view images on our computers now.  What used to be a 4x6 inch image now starts at 5x7 with infinite zoom capabilities.  Most people, however, still print at 4x6.  When I pick up my camera, I’m aware that sharpness is an aesthetic variable just like depth of field and I plan accordingly.  Often I default to a “sharper is better” decision because I can always blur in post, but even then the degree to which I pursue sharpness varies.  The picture below was one of my client’s favorites (and mine, too).  I clearly missed my focus mark.  But that error adds an ethereal quality to the image, and an intimacy that wouldn’t exist if the eyelashes had been in focus.  

What’s your favorite “fuzzy” image?

No comments:

Post a Comment