Art reproduction workshop
ARTSpace will present a free workshop from 2 to 4 p.m. Saturday at the Soldotna Public Library to demonstrate the new Soldotna Rotary/ARTSpace art-copying installation to produce JPEG files documenting their portfolios. The service is free to use, but only available to people who have a Soldotna library card and who have had previous training and authorization to use this loaned equipment.
The workshop also will cover how to turn these JPEG files into photo books to be used as deposits to the library’s new long-term archives of local artists’ work, as catalogues of artists’ exhibits and as permanent deposits with the Library of Congress when registering copyright.
By Joe Kashi, for the Redoubt Reporter
Achieving correct exposure, focus and color balance are key to making successful photographs, but too often the results don’t match what we saw and intended. When our photographs become predictably unpredictable, it’s time to first check and calibrate our cameras and lenses, rather than checking prices for new gear.
Checking and calibrating your cameras and lenses is much less expensive and likely more useful. Modern calibration systems and software make this a fairly straightforward task.
First, let’s check lenses for correct optical alignment. This should be done as soon as you buy any new lens so you can return it immediately if it’s not properly assembled during manufacture. Most reputable online sellers allow direct return during the first 30 days after purchase. If you miss that window, you’ll have to settle for the manufacturer’s service, which is often erratic, rather than immediate replacement or credit.
If a poorly assembled lens is already out of warranty, it’s usually less expensive to simply replace it than to have it professionally serviced and adjusted. In most instances, a poorly assembled lens must be aligned at a factory service center, if at all. The only exceptions are some of Sigma’s prograde “Art” series lenses, which are user-adjustable if you buy Sigma’s USB “dock.”
To test a lens for correct optical alignment, stand in front of a brick wall or some other perfectly flat, highly textured surface. Aim your camera at the center of the wall in front of you, as level and parallel to the ground as possible. Be sure that you are facing the wall squarely, at a 90-degree right angle.
Use a tripod and remote release, if you have one, or the camera’s two- or three-second self-timer. Set the camera to the mirror-up or other antishock mode and focus as carefully as possible, with the autofocus area centered in the middle. Shoot several frames at the widest lens aperture and also at a commonly used aperture, such as f 5.6 or f 8.
Examine each frame carefully at 100 percent magnification. The center should be crisply sharp. If it’s not, you have a focusing problem with the camera, in addition to any optical problems. Assuming the lens is crisply sharp in the central region, compare the left one-third frame and the right one-third frame, as well as comparing the top one-half frame and bottom one-half.
Is there a major and consistent difference in sharpness between the left and right or top and bottom? Does the difference continue to be unacceptable at f 4 to f 5.6, even though you’re sure the camera is carefully pointed squarely at the wall? If you find major and consistent differences in sharpness, it’s quite possible you have a poorly assembled lens resulting from variances in manufacture. It should be returned ASAP.
Even the best lenses typically show slightly soft corners at wider apertures and some minimal amount of misalignment. Your decision to retain or return a lens depends on whether any misalignment is severe, consistent and constant, or only a minor difference that largely abates when the lens aperture is closed a bit. Inevitably, edges and corners will be less sharp than the central regions of most lenses, particularly at wider apertures. However, in a correctly assembled lens, the sharpness should degrade smoothly and consistently in all directions. Finding that one side or the other is always much less sharp than the opposite side is strong indication of a poorly manufactured, “decentered” lens.
Assuming your lenses seem to be acceptably aligned, then it’s time to check whether your cameras are focusing them correctly. Misfocus is common and makes good lenses look bad.
Misfocus can occur in both digital SLR and mirrorless cameras, but it’s more common with SLR-type cameras that incorporate moving mirrors and separate “phase detection” autofocus hardware. These mechanical devices are susceptible to jarring out of calibration during regular use and to factory misalignment. However, a careful user can easily readjust their focus.
Most SLR cameras can be adjusted to match the focusing characteristics of several individual lenses, but you will need to separately test each lens with that camera and then make adjustments specific to each lens. The most common SLR focus calibration and adjustment tool is the “Lens-Align Mk II,” available for about $70 at Amazon, B&H Photovideo and other major online vendors.
Using the “Lens-Align,” you can tell whether your camera is focusing a particular lens correctly or to a point in front or behind the subject. One or two tripods and a bit of trial and error will be required for each lens, but the end results are worth the effort. Often, you’ll find that your lenses seem much sharper after adjusting your camera’s focus for each lens.
Zoom lenses can be a bit trickier than single-magnification “prime” lenses when adjusting focus, because their focus problems may shift as magnifications are changed. If your camera allows you two adjustment points for each zoom lens, then that’s especially precise and should be used, if possible. Most cameras do not allow multimagnification zoom adjustments, so I typically use an intermediate zoom lens magnification as my base point when making an initial adjustment with the Lens-Align tool and then check both the wide-angle and telephoto magnifications to verify that focus alignment does not shift as the lens is zoomed.
It’s a good idea, after making your initial adjustment with a wide lens aperture, to make another alignment test exposure with the lens stopped down to f 5.6 or f 8. Some lenses, especially older designs, had a tendency to shift focus when the aperture closed. If that occurs, then redo the camera’s focus calibration with your lens aperture set to the most frequently used opening.
Mirrorless cameras can be checked, as well, with the Lens Align tool, but mirrorless cameras typically do not have, nor need, lens-specific focus adjustments. That’s because most mirrorless cameras autofocus using data directly from the imaging sensor. Such “contrast detection” autofocus is inherently immune to the sorts of hardware misalignment that troubles moving-mirror dSLR cameras. However, it’s still possible for mirrorless cameras to misfocus by mistakenly fixating on some high-contrast edge behind or in front of your intended focus point.
There are two solutions that work around contrast-detection autofocus problems. The first is to use a tiny autofocus spot and focus lock to manually select the most important focus area, then hold that focus lock until the photo is taken. The second would be to use a central array of about nine or so larger autofocus areas that would average the focus over all those focus areas, and thus be less susceptible to being fooled by a few high-contrast edges behind your main subject.
Next week, we’ll take a look at calibrating your camera, monitor and printer to show precisely accurate, vibrant color. It’s actually quite easy with modern measurement hardware and calibration software.
Local attorney Joe Kashi received degrees from MIT and his law degree from Georgetown University. He has published articles about computer technology, law practice and digital photography in national media since 1990. Many of his articles can be accessed through his website, http://www.kashilaw.com.