Closeups and Image Magnification

Let’s speak of closeup photography in the broadest possible context, in which the photographer isolates a subject and renders it large enough to substantially fill the field of view. Thus closeup techniques are those one will use in the majority of photo situations, unless one shoots mainly action or wide perspective scenes. Taking a photo of a bird at 20 yards distance or a flower at 1 foot distance poses similar problems, uses similar techniques, and possibly even the same lens. In both situations, the focus will be closer than hyperfocal distance of the lens, hence closeup.

Just as we do with our eyes when we want to examine something closely, we make a closeup image by moving the lens as close to the subject as necessary for the subject to fill the field of view. But just as with our eyes, each lens has a closest focusing distance (distance from sensor/film plane to subject), limiting how close we can get.

What if one needs to make the subject even larger?  One always has the option of taking the shot from farther away than desired (smaller subject image), then cropping the image in post-processing to increase size. With a high pixel count sensor and good light, the resulting image will be satisfactory for all but the largest blow-ups. But for the best result, one needs to get closer, so that the subject fills the frame and uses all the available sensor pixels.

To get closer than the lens allows, special macro tools are used to lessen the lens’s closest focusing distance, either by adding extension between the lens and the camera, or by adding a pre-focusing supplemental lens on the front of the camera’s lens. One can define macro photography as a subset of closeup photography that improves the closest focus of the lens in order to render a full frame image of a small object. This improvement can be integral with the lens, as in specialized macro lenses, or added before and/or after a suitable general purpose lens.

The general purpose lenses most suitable for closeup photography will largely mitigate the nearness problem via a close focusing design that provides enough magnification for most all subjects. Such designs may internally apply both techniques above. Assuming one’s general lens kit is chosen with closeup imaging in mind, much closeup work can be accomplished by simply choosing the appropriate focal length lens from one’s kit, where the smaller the subject, the more focal length is needed for magnification. The full variety of focal lengths may have use, depending on acceptable working distance and on the field of view angle one needs to enable seeing the complete image.

Working distance is the distance from subject to front of lens, proportional to focal length. It is an important consideration, since providing subject lighting and avoiding disturbance of live subjects requires some minimal distance.

Background rendition is an important concern, since a closeup by our definition highlights a sharply-focused subject against a likely out-of-focus background. The closer the focus point, the more likely the background will lose focus. Bokeh, the visual appeal of an out-of-focus background, is much better in some lenses than others. Good bokeh and close focusing distance are ideal attributes of a lens used for closeups. To further control background, it is sometimes necessary to use a longer focal length to limit the background field of view, or to re-orient the camera direction to change the background, or to modify the background lighting, or even to provide artificial background.

At the wide end of the spectrum, single lenses by themselves are mostly all that one needs for closeups. With my kit, to take pictures of household items for posting to eBay, I use the manual focus 28mm f/2.8 AIS for its excellent near-field performance: minimum distortion/aberration and maximum contrast, color rendition, and sharpness. It has a close focus distance of 9″ by itself, the smallest in my kit; this feature is the principal reason for its utility as a closeup lens. It’s 38 years old, but still one of Nikon’s superb lenses. Below are product images from this lens, demonstrating both the available sharpness, and by poor example, the importance of proper lighting technique and background selection/rendition.

Similarly, for natural light portrait closeups of people, I still use my 40 year old MF 85mm f/1.8 portrait lens, utilizing its ideal field of view (on my DX body) for head shots. It is 2 stops faster than my two AF zooms that cover this FL. The consumer-friendly Nikon system fully supports these old lenses on the latest digital bodies. This lens has very good bokeh, and is excellent wide open on a DX body. It’s downside is its 40″ minimum focus, more than twice that of more modern lenses, not an issue for portrait images, but ruling out this lens for macro use.

For small objects, one naturally reaches for a longer focal length to gain magnification and also free working distance. For very small objects, one likely needs macro attachments to modify the light path, reducing the closest focus distance of the chosen lens. For people who specialize in macro photography, the major lens manufacturers make specialized macro lenses that have built-in mechanisms for reducing closest focusing distance. The high price of such special purpose lenses make them poor values for photographers who only take an occasional closeup picture (a good used 105mm macro lens can be had for around $250, with new ones $500-$1000). For the rest of us with 35mm SLR cameras, there are different types of add-on adapters that will bring the subjects closer. They are smaller and lighter than a separate macro lens, and hence more likely to be in our kit when we need them.

Supplementary lenses, called closeup lenses or diopters, reduce the closest focusing distance of the lens behind it. They operate like magnifying reading glasses. My kit has the excellent Canon 500D closeup lens (two achromatic elements), which can screw onto the front of either my 24-85mm or my 80-400mm, and supports focal lengths of 70-300mm. It is a +2 diopter lens, so it will focus at ~20″ (500mm) regardless of what lens it is used on, so long as the lens focus is set to infinity. It makes it possible for my telephoto lenses to focus much closer than normal, and this is responsible for the magnification of the image. When on the 80-400mm, it is ideal for closeups of larger objects such as flowers. Here are some sample images taken with a hand-held 80-400mm lens with 500D closeup supplemental lens (moderate zoom, between 80-150mm). Note the focal plane was not entirely parallel to the dragonfly’s long axis, in order to get more front detail. This is generally a no-no in macro photography, and the lens should have been stopped down more to compensate.

Alternatively, one can keep the closest focusing distance of a lens fixed, and increase the focal length (image magnification) by adding a tele-converter (extender) behind the lens. The excellent Kenko 300 Pro 1.4x extender converts my 80-400mm lens into a 110-560mm lens. The disadvantage of this approach is that it costs a full stop of light, so is not viable in poor light.

I have one macro lens in my kit, a 55mm f/2.8 micro (see article on my rebuild of this lens) which goes to 0.5X (1:2) magnification all by itself, thanks in part to a close focus distance of 9.8″. It is also an excellent general purpose lens, my only 35mm ‘normal’  focal length primary lens. With very small objects, depth of field becomes a critical issue. That is why specialized macro lenses such as this almost always have a very small f/32 aperture available (my two long lenses also go to f/32: 80-400mm, 200mm). We have now discovered a third attribute of the best candidate general purpose lenses for macro closeup photography: close focus distance, good bokeh, small aperture.

To increase the distance from lens to focal plane (effectively decreasing the closest focusing distance), there are adapters called extension rings (no glass inside, just hollow tubes; pure extension). The PK-13 extension with the 55mm goes to 1X (1:1) life size magnification. One can also add a PN-11 extension (noted for its built-in tripod collar) to get even closer. These adapters are fixed length and couple to the camera’s exposure controls. There are also variable-length bellows extensions that will give finer control. One may never have a need for this level of sophistication; they are too bulky for field work and most are not able to be coupled to the camera’s exposure and focus controls.

External lens extension maintains the working distance of the lens, but contributes a small light loss (negligible in long lenses). Note that both methods for reducing lens closest focus distance, supplemental diopters and extension tubes, remove the ability of the lens to focus at infinity. The more the reduction in lens closest focus distance, the nearer and narrower the new focus zone.

The following picture was taken with the 55mm hand held at 1/500s, f/11. The background was cropped as much as possible; this lens is quite analytical, so its bokeh is not very appealing. The small flower, less than the diameter of a penny, was moving slightly in the breeze.

Mounting the PK-13 extension ring behind the 55mm micro to extend its macro range to 1:1, I tested the extreme ranges of the hand-held camera and lens, using f/32 aperture for the maximum depth of field possible and ISO 3200 to get the shutter speed up to 1/125s (since this was a lens that I had rebuilt, I was interested in its performance). This tiny flower is slightly more than half the diameter of a dime. Bokeh quality increases with extension, so this is my preferred macro configuration with this lens. For magnification up to life size, using extension with the smallest f/stop can produce good results. But going beyond 1:1 with extension exaggerates the lens diffraction effect, so with the PN-11 added, f/32 would not be a good choice.

My set of Kenko extension tubes can enable closer focus with the 80-400mm. They can be used by themselves, singly or in combo, or in combination with the 500D supplemental lens. They fully couple with the camera, supporting autofocus. Here’s a small backyard flower not quite 1/2″ diameter, shot handheld at 400mm at f/20 and 1/60s, with VR and AF engaged, with Canon 500D supplemental, and with Kenko 36mm extension. Because I shot at 400mm, I got slightly better than life size, but not quite enough to fill the frame; this is about a 2/3 crop of the original.

But what if the subject is ‘really’ tiny? Stack those lenses. Using a stacking adapter that allows filter rings to be mated, a shorter lens can be reverse mounted on the front of a longer lens, where it acts as a high power supplemental closeup lens. The very good, compact 200mm f/4 lens, face-to-face mated to the (reversed) 55mm 2.8 micro, produces sharp 3.64X macro performance through 11 glass elements (pictured below). These very sharp lenses provide quality reproduction, with the 55mm stopped down slightly to f/4 in this combination. A quick picture of a rosemary blossom with the stacked lens illustrates the resulting magnification, but not good macro photography. It takes sliding-rail mount on a tripod and a remote shutter release, together with a good bit of technique and patience to take an excellent macro image with this setup, due to the tiny working distance and depth of field (insufficient for this subject). The sliding rail mount is helpful to position the camera precisely without having to move the tripod.

Although physics dictates very small DOF at high magnification, there is an optical sectioning solution called focus stacking. One takes several exposures, varying the plane of focus across the subject. The stack of exposures is input to a software application, which produces one image, a composite of all the in-focus parts of the stacked images. As few as three slice frames will make a marked improvement in overall focus of some subjects, but 5-10 frames is more typical and 20 or more are used for very finely detailed results of subjects of considerable depth. Two programs are available for OS X, priced around $100. The sectioning frames can be taken with hand-held camera at fixed focus, moving the camera slightly for each slice frame. Or, electronically controlled sliding rail mounts can be used for tripod work. This gets pricier, at upwards of $600 for hardware and software.

A further interesting development, not yet ready for prime time, is a specialized camera design making an image that can be focused by post-processing software. This approach uses only a small subset of the sensor pixels to render any specific focus point, so the quality will be less than professional unless a large camera with very large sensor pixel count is used. An affordable and usable camera capable of high quality imaging using this technology is probably a few years off.

The following chart shows the efficacy of the different lens/adapter combinations with which my small kit can go life-size and beyond. In general for larger subjects such as flowers, a telephoto with supplemental closeup lens is easiest and works best. The supplemental really tames the lengthy close focus distance of the 80-400mm zoom, producing usable magnification up to better than 1:2 at 400mm and going 1:1 with 36mm added extension, with AF-S and VR enabled. That’s the max hand-held magnification I hope to achieve, and this combo goes with me into the field. For tiny flowers, smaller insects, and any other subject of 1″ or less, the 55mm micro with some combination of adapters seems to fill the bill, but working distance is minute; this lens doesn’t travel in my walking kit.

The chart rows are in order of decreasing subject size. Note, at high magnification, working distance can be less than an inch, probably too close for successful imaging of some subjects.

Subject Size (long dimen.) Life-Size DX Magnification Lens Combo Working Distance
≥10” ≤0.1X Any lens
5” 0.2X 400mm ~92”
3” 0.32X 560mm (400mm with 1.4X) ~92”
2” 0.5X 55mm Micro ~4”
1.7” 0.6X 500D on 300mm (80-400mm) ~20”
1” 1X 500D on 300mm (80-400mm) w/ 36mm ext. ~20”
1” 1X 55mm with PK-13 ~2”
0.35” 2.9X 55mm with PK-13 and PN-11 ~1.5”
<0.18” 3.64X 55mm reversed on 200mm <1”

More about Magnification

It may seem, when looking at camera ads and specs, that sensor size affects magnification. It doesn’t. The DX sensor, being only 2/3 the size of a full 35mm frame (FF), can render subjects at life size that are up to 1” long (versus up to 1.5” for FF), perhaps making it seem that the DX is a more powerful magnifier. But the same 1.5” object would need to be reduced to 2/3 of its actual size to be seen entirely in a DX frame. My camera uses a DX-format sensor, so the perspective offered by my lenses is that of a 1.5x focal length lens on an FF sensor (i.e. 85mm on DX gives the same perspective as a 127.5mm on FF). This is not a gain in magnification, but a reduction of perspective.

Sensor pixel density does affect magnification capability, the magnification that occurs during image enlargement when making a final image on media. For small subjects like insects, one will generally want the final image to be larger than life size. The number of pixels in the image determines how large the image can be made and still retain lifelike quality. This is why one seeks to make full-frame images of the subject of a closeup, to ensure the subject is represented by all the available pixels in the camera sensor.

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