Glass Vs. Air For Close Focus
Q When would it be best to use macro diopters vs. extension tubes? I do a lot of backpacking, and I’m looking to make my camera kit as versatile as possible with the least amount of weight. –Seminar Participant
A A great variety of tools and techniques will bring you closer to your subject, but the fact that you’re looking to stay compact and lightweight for backpacking will narrow the choices somewhat.
Close-up diopters haven’t been very popular in recent years, because many of our lenses now focus quite close. So the next question to ask is, “How close do you need to get?” If you just want to fill the frame with a medium-sized flower, the internal capability of many lenses should suffice; a close-focus-capable lens, such as the Canon EF 100-400mm ƒ/4.5-5.6L IS II USM, which focuses to 3.2 feet at 400mm, will give you a magnification of 0.32X (1/3 life-size), or, if you put a 1.4X tele-extender on it, approximately 1/2 life-size. But now we’re putting a lot of weight in that pack! If you need more lightweight magnification, here are the pros and cons for diopters and extension tubes.
A close-up diopter is a single- or two-element lens that screws into the filter threads on the main lens to alter the close-focus capability. They’re most often designed to be used with medium-telephoto zooms, such as an 80-200mm or a 70-300mm optic. When attached to a lens of this type, the focus distance to the subject stays constant and the magnification increases as you zoom out to the telephoto end of the focal length. You can fill the frame by being close to the subject, and magnify the subject by increasing the focal length. The final magnification at 300mm with a Canon Close-Up Lens 500D (double element) is nearly 1X, with a focus distance of 19.7 inches. Canon offers close-up diopters in 52mm, 58mm, 72mm and 77mm filter sizes. A less powerful version is the 250D, designed for lenses of lesser focal length; it comes in 52mm and 58mm filter sizes. Canon’s diopters start at about $100 and go up to $176 at the larger filter sizes. Generic close-up lenses are available from some major filter makers, and vary in size and magnification power.
Close-up diopters are light, small, and can be purchased to work with a variety of lenses, depending on the filter size. The disadvantage is that while being relatively sharp in the center, none gives stellar results at the edges, and the single-element versions have poor resolution overall.
An extension tube has no glass—it’s only a hollow tube, and its function is to increase the distance between the main lens and the film or sensor. This enables the lens to focus closer, meaning that you can increase the size of the subject in the frame by moving closer to it. Extension tubes come in varying sizes from 8mm (Nikon PK-11A) to 36mm, and individually or in sets of three, typically a 12mm, 20mm and 36mm. Be sure to get tubes that maintain the automatic aperture and metering connections to the attached lens.
The advantages with extension tubes are that they can be employed with any lens to allow for closer focusing (note that this could be a problem with ultra-wide-angle lenses of a focal length less than the extension tube’s length), and the quality of the lens isn’t impacted because the extension tube contains no glass elements. They’re slightly bulkier and heavier than close-up diopters, but the difference is minimal. I always carry a 25mm extension tube in my bag in case I need to get closer with a telephoto lens.
The Magic In Focus Stacking
Q When moving the camera to focus-stack a macro subject, I can see that the subject changes size as the camera gets closer. How do you get sharp results when the numerous captures making up the composite are all different? Is there something the photographer has to do to make sure that the final image is at its sharpest rendering? –Field Class Participant
A You’re correct; the subject does get slightly larger as the camera moves in closer for each slice of the focus stack. The magic fix happens in the software that assembles all of these focus slices to make up the final composite. Be aware that you may lose some of the area around your composition as the software aligns the subject and crops the edges of the completed image. The software programs that I recommend for assembling a focus stack are Zerene Stacker, Helicon Focus and Photoshop (in that order).
When capturing a series of images for stacking, be sure that the subject doesn’t move. The software can compensate only for very slight alignment variations, although this problem can be fixed manually using the software’s retouch function. It’s tedious work. Understand that if you’re doing a deep-focus stacked composite, the closer elements of the image will obscure areas behind them as they “bloom” out of focus. Some of these anomalies can also be fixed in the software or in Photoshop, but it’s a pain.
There’s a learning curve to achieving really good focus-stacked images, so practice and be attentive. And remember this general principle: You can’t take too many images in a focus-stacked composite, but if you take too few, you’ll have an unsharp final result.
Q I’m thinking of buying a tilt/shift lens, but I’m not sure if it will be of significant use, other than the occasional landscape and architectural photograph. Can you give any other reasons to invest in this lens? Which of the focal lengths do you think are the most useful? –Seminar Participant
A Tilt/Shift (T/S) lenses have a variety of uses for both problem-solving and achieving special effects.
First and foremost, tilting the front elements of the lens changes the orientation of the plane of focus to make better use of the available depth of field (DOF), that is, the range of sharp focus. If you want to know why this works, research the Scheimpflug principle.
Let’s say that the wind is blowing and a fast shutter speed is necessary to stop the movement in the grasses or trees of a landscape, but you also need DOF. By tilting the T/S lens, you can maximize the DOF at a wider aperture and still use a faster shutter speed. The tilting of the focal plane is also useful in close-up and macro photography. The more efficient use of the DOF can bring parts of the image into focus that otherwise wouldn’t be sharp.
Another use is the placement of a narrow band of sharpness through an image by reverse-tilting the lens to achieve an overall miniature look; the band of sharpness becomes minimal, so a cityscape can be rendered as a toy village. We’ve seen a lot of this lately. This technique also can be used to emphasize an in-focus area within a generally out-of-focus composition.
The shift function of these lenses is less well known. I like to use it for capturing panoramas, where the position of the camera body is fixed, but the lens is shifted all the way to the left, centered, and then shifted all the way to the right. The three images will match perfectly for a panorama rendering, even if the camera/lens is pointed significantly up or down. This works the best with APS-C-sensor cameras, as the difference of the shifts is more pronounced.
Further, the shift function of a wide-angle tilt/shift lens can solve the problem of inward-leaning distortion of vertical elements in a composition that results when pointing the lens upward, such as when photographing architectural elements of a building or trees in a landscape. The perspective can be corrected by leveling the camera/tilt-shift lens combination, then raising (shifting) the front of the lens until the tops of the vertical features are in the frame.
The available focal lengths of T/S lenses are 17mm, 24mm, 45mm and 90mm for Canon cameras and 24mm, 45mm and 85mm for Nikon users. Schneider, Rokinon and Lensbaby also make T/S lenses. For landscapes, I regularly use the 90mm and 24mm Canons. I find the 45mm to be the least useful for nature photography.
But, wait, there’s more. You can use diopters or extension tubes on T/S lenses (primarily the 85mm/90mm versions) to increase their macro capabilities. And, of course, you can focus-stack your T/S captures to achieve even greater DOF, such as in a typical landscape featuring a foreground of tall, bright blossoms, moving across a cascading stream, extending into a larger field of flowers where a bear and her cubs pause, motionless, through an evergreen forest, against a backdrop of pink-tinged snow-covered mountain peaks and a rosy, cloud-streaked sky. In my dreams.