Canon call their lenses designed to only work on the small sensor digitals EF-S. Presumably the S is for small sensor. Nikon call theirs’ DX, since they call their small sensors DX and their full-frame sensors FX. For convenience in this article I will refer to Nikon lenses designed for full frame as FX, even though I don’t believe Nikon does.

When a lens is designed there are a number of criteria that the designer must meet. One of these is what’s called the image circle, the area at the film/sensor plane that is to be fully illuminated, sharp and with aberrations well corrected.

Lens coverage area differences with full frame and small sensor digital SLR cameras. Note that is is a very simplified diagram and does not reflect the way camera lenses actually form an image.

The EF and FX lenses are designed to create an effective image circle that covers the full 35mm frame. This has a diameter of approximately 43mm, which is the distance across the diagonal of the 36mm x 24mm sensor/film size. This is why a 50mm lens is considered ‘normal’ on a full frame 35mm camera, as it is the closest common focal length to the diagonal size.

EF-S and DX lenses are designed for the smaller image circle of the small sensor in the 450D, 50D, etc models. The sensor is 22.2mm x 14.8mm, which has a diagonal distance of 26.7mm. This is why if you put an EF-S lens on a full frame camera you get a circular sharp image with a dark outer area.

Designing a lens for a larger image circle is harder. It typically uses more lens elements and more expensive ones because of the need for more aspheric or special glasses to keep the image sharp and evenly lit over the larger image circle. This makes the lens larger, heavier and more expensive. Basically it comes down to this, creating a lens for the smaller sensor is easier and cheaper than it is for the big sensor at the same level of lens performance. This is also the case with lenses for medium and large format cameras.

A 50mm EF or FX lens on a small sensor camera has the field of view of an 80mm on a full frame camera. A 50mm EF-S or DX lens also has the same field of view as an 80mm would on a full frame camera. If you go to the Canon and Nikon websites they clearly state this, for example “Uses optics designed to take advantage of the small image circle to give a 17-85mm (equivalent to a focal length of 27-136mm in 35mm format), 5x zoom ratio” for the 17-85 EF-S.

Canon’s tilt and shift lenses, for example, are designed with an even larger image circle than full frame, so that with the lens shifted off center and/or tilted, part of the image circle will still cover the whole sensor.

0.5 second, f16 and 100ISO, Sigma 70mm Macro on Canon 400D

Macro photography is a great and interesting area of photography. Technically covering the area of close-up photography where an object is reproduced on the sensor at a size of at least 1:1, these days it is also commonly used to refer to all close-up photography. Because of the close distance (relatively if not in actuality) from the subject to the lens, rangefinder or compact cameras were not ideal for it because the viewfinder would not reflect exactly what the lens is seeing. However, with the advent of digital, and thus the possibility of a live preview of exactly what the lens is seeing on the large LCD on the back of the camera, compact cameras now become quite convenient for macro work.

0.5 seconds, f5 and 100ISO, Sigma 70mm Macro on Canon 400D

Another positive for many compact cameras is the amazing degree of close focusing ability many possess. Some digitals can focus so close that they can actually achieve focus on an object touching the front element of the lens. Of course, an issue with compact cameras is the small sensor size, which causes noise issues. This is partly compensated for by another positive that derives from the small sensor size, lens focal length. Because of the tiny sensor size, compacts need very short focal length lenses. In a given situation, shorter focal length lenses give you greater depth of field in practice (see the separate article on depth of field for the correct definition and more explanation). This is why compact digitals have much greater depth of field in actual use than a 35mm full frame camera or even a digital SLR.

1.5 seconds at f5.6 and 100ISO, Sigma 70mm Macro on Canon 400D

Digital SLRs are dependent on the lens you fit to them for their close-focusing ability. Basically a macro lens has to allow for more lens extension to focus more closely. You can also achieve this lens extension by using extension tubes or bellows. A macro lens is designed to maintain good optical quality as a greater lens extension is used. Many zoom lenses come with macro capability, which can be extremely useful. However, maximum image quality is usually achieved with a dedicated, single focal length lens. Macro lenses come in focal lengths from 50mm (sometimes less) up to around 200mm, with the most common in the 50-100mm range. These will have greater effective focal lengths on most digital SLRs. A longer focal length gives you more working distance from the camera to the subject for a given framing. This working distance can help in close quarters, with some types of subjects that may be scared away or are dangerous and in getting light onto the subject (too close and the lens can cast shadows).

1/6 second, f5.6 and 100ISO, Canon 100mm Macro on Canon 400D

I have a Canon 100mm f2.8 macro lens, which I love. But I have also been working recently with a Sigma 70mm f2.8 macro lens, which is fantastic. Both can get to a 1:1 magnification without extension tubes. Both are very sharp lenses, both autofocus on the Canon very well, even at macro distances.

My macro rig includes several Canon cameras, a macro lens, extension tubes and a homemade light

The great joy of macro photography is that it is a form of photography that you can do in most situations. In the field you can do macro photography on flowers, plants, insects, rocks, sand, rusting metal, you name it, you can macro shoot it, so long as you can get close enough. If the weather is too cold or too unsettled or dangerous for photography, set some things up indoors and happily shoot away while the gale blows outside. Whatever your passion in photography you can find something similar that you can shoot, from lovely florals to crystal landscapes, insect portraits to fungal forests. There are people who spend their entire photographic career shooting macros only, and never run out of great subject matter. I’ve recently been exploring crystal and rock macro shots and exploring the potential for crystal landscapes by combining images. This is fun and a diverting, and quite creative and is a great way to spend time when housebound.

Here is a piece of amber from my collection (1.5 seconds, f22 and 100ISO, Sigma 70mm Macro on Canon 400D)

Macro lets me get up close and personal with the insects trapped in the amber

So what exactly do you need for macro photography? A digital compact camera will work fine. One with a tilting LCD screen can be a great help when working in certain situations, but is certainly not essential. Likewise a good tripod is a help for certain types of subjects. I use a large Manfrotto model, where the center column can be removed and inserted horizontally. Whilst not the same as a macro rail, it allows me to easily move the camera forward or backward at will. A macro rail is a massive aid in accurate positioning of the camera, and is something I will add to my kit at some point. Naturally when you are working on some sort of tripod, a cable release or wireless remote is also useful. Now, of course, a tripod is not essential. You can do great macro work handheld.

The beauty of digital is immediate feedback

If you use a digital SLR, then you either need a macro-capable zoom, a true macro lens, extension tubes or a bellows, or close-up accessory lenses that screw onto the filter threads of your lens, to begin. There are various pros and cons to all of these, from price to flexibility. Many of you will already have a macro-capable zoom lens. I am a big believer in exploiting the potential of what you have before running out to purchase something else. So whatever you have, try using it. The cheapest additional purchases are extension tubes and close-up lenses. Extension tubes seem to give the best result of well corrected single focal length lenses, but they can also work well on zooms. Close-up lenses, particularly if good quality ones, are a good option on lenses which do not currently focus close enough for your purposes. I have happily used them on my Canon 100-400mm IS L series lens for a long working distance. The thing is to experiment. Close-up lenses can also be used on compact cameras.

Depth of field is an important creative control in macro photography. See the special article on depth of field
1/25 second at f2.8, 100ISO, Sigma 70mm Macro on Canon 400D

In the three images below we show how increasing depth of field has a major impact on the resulting image

Lighting is important for macro work, as you often want to work at small apertures for a greater depth of field. I’ve used everything from a torch to ‘paint with light’, an external flash gun, like the Canon EX flash units that can be wirelessly controlled, a ring flash, tungsten lights, gold and silver reflectors and my own made ‘light pipe’ unit.

Here I use my lighting rig to light the front of the object (1/6 second, f2.8, 100ISO Sigma 70mm Macro on Canon 400D)



Whereas here we have the lighting set to come through the subject. (0.7 sec, f2.8, 100ISO, Sigma 70mm Macro on Canon 400D)

Some of the accompanying photos show a lighting rig I wired up for macro work. It is a very simple rig, just two bright, white LEDs with battery packs and a switching potentiometer that both switches the LED on and off, and also can dim it somewhat. I mounted two of these into a box with wire that allows me to position the LEDs as I need. Wire is not as easy to use for this as flexible, gooseneck fittings but it is a lot cheaper. The LEDs can be positioned as needed and provide enough light for macro work of small objects. They are small enough to hide behind transparent or translucent subjects or can be positioned to the sides of the lens to light opaque subjects. To make one of these all you need are the LEDs, battery packs, a switch or switching potentiometer, wire, a box and soldering iron, which are available at any electronics shop that sells parts.

2.5 seconds, f16 and 100ISO, Sigma 70mm Macro on Canon 400D

1/2 second, f11 and 100ISO, Sigma 70mm MAcro on Canon 400D

A camera lens will actually only focus one single, flat (if it is a good lens) plane perfectly. As you move away from the plane of sharp focus, objects become gradually more blurred. In practice we can tolerate a small amount of blur (called a circle of confusion, from the blurred circle of light you get if you focus a point source of light, like a star). How much blur we can tolerate is determined by how much we will blow up the image in printing or projection. Common values for this circle of confusion range from 0.025mm to 0.033 mm. The reason larger format images appear to have larger depth of fields is because you do not need to magnify them as much to get a resulting print size.

Aperture F number (or the f stop) is calculated by dividing lens focal length (fl) by the diameter of the aperture (a) (F number = f.l. / a). What this means is that for a given F number, a telephoto lens (long focal length) will have a larger aperture diameter (if you like, size of the front element of the lens reflects this) than will a wide angle lens. That’s why an f2.8 28mm lens is not as physically wide as an f2.8 400mm lens. For depth of field, it is actually the lens aperture diameter and not the focal length that matters, but you can see from the above how we can effectively think in terms of focal length because of the relationship between F number, aperture and focal length.

The basic lens equation is 1/subject distance + 1/focal plane distance = 1/focal length. The focal length (fl) is the distance from the lens that a subject at infinity will be brought to focus. Subject distance (s) is the distance from the lens to the subject we have focused on and focal plane distance (fpd) is the distance from the lens to the film or sensor plane in the camera. The above equation explains why a lens extends as you focus on closer subjects (fpd must get larger to compensate for s getting smaller, since fl remains constant). It also explains why adding extension tubes or a bellows to a lens allows it to focus on closer subjects (it increases fpd or focal plane distance).

A point of light is not, in practice, brought to a single point on the film plane, but to a tiny (hopefully) circle. The size of this tiny circle of blur (circle of confusion) is defined by the diffraction characteristics of the lens (and its aperture) and by the quality of the optical corrections in the lens. In many cases it is not, in fact, a perfect circle, due to the actual shape of the aperture and to any aberrations in the lens. As an object moves out of focus, this circle of confusion gets larger. One aside here – some lenses are marketed as having great out of focus blur, by having a carefully designed aperture iris that is as close to a perfect circle as the engineers can make it. It offers more pleasing out of focus images.

Images appear to us to be sharp when this circle of confusion is smaller than we can resolve with our eyes. This explains why an image can look sharp from a distance but becomes blurred as we get closer to it, we are finally close enough for our eyes to resolve the circle of confusion. Thus there is no such thing as a completely sharp image. The closest we can get is a photograph of a completely flat object, like a map or painting. Even here, there will be a fundamental level of sharpness caused by the lens characteristics.

When you focus on a subject at distance s, an object closer to the camera (sn) will be brought to a focus further from the lens (behind the film plane). This means that at the film plane the circle of confusion will be larger. A subject further from the camera (sf) will come to a focus in front of the film plane. This also means that at the film plane the circle of confusion will be larger. The size of the circle of confusion turns out to be directly related to the physical aperture of the lens and how far the subject is away from what we have focused on. What this means is that to maintain a certain maximum circle of confusion size (effectively how sharp we want the image to look), as we increase the lens aperture (or the lens focal length) we get less distance off the focal point in acceptable focus.

So what all the above translates into is the following:
*    For a given lens, you get a greater depth of field as you stop down to smaller apertures (go from f2.8 to f11, say)
*    At a given aperture number, say f2.8, a telephoto lens will give you less depth of field than a wide angle lens, because the physical lens aperture will be larger for the longer focal length lens. This is provided you keep the lens to subject distance the same
*    The actual size of the depth of field decreases as the camera gets closer to the subject it is focused on (it can be 10 feet or 3m at a distance and only inches or centimeters up close)

Shot with a 50mm lens

Shot from the same distance with a 100mm lens

Shot with a 100mm lens from twice the distance

All the above also explains why compact digitals seem to have a much greater depth of field than digital SLRs. For a given effective focal length (say 50mm in 35mm camera terms), a camera with a smaller sensor will use a smaller focal length to achieve this than a camera with a larger sensor. Given the smaller focal length, at a given F number, the smaller sensor camera will use a smaller aperture, giving a larger effective depth of field. This is why many complain of not being able to use the same shallow depth of field techniques that we are used to using with 35mm cameras for things like portraiture.

For those who want a more mathematical discussion, see Norman Koren’s excellent article.

Film

Film is certainly, on the surface, the cheapest option. You probably
already have a film camera of some sort, but new ones are very
reasonably priced. You will have read that film is so much higher
resolution than any digital camera around. That is true up to a point.
Film is an analogue device, meaning that it is not sampled at fixed
points, like a digital camera does. This does mean that, theoretically,
there is more information in a piece of film. However there are two
things that can get in the way of you having all this data to play with.

Film has a fine structure called grain. It looks like noise. Slow
films, like ISO 100, have smaller, more even grain and so is less
noticeable unless you enlarge massively. Fast films, like ISO 400 and
above, have large grain that is more noticeable at lower enlargement
levels. What this means is that above a certain resolution, determined
by the speed of the film, smooth areas of the image, like skies, become
noisy. There is still information there, it is just noisy.

Another issue with film is what resolution you can scan it at. Now you
can always get the film scanned at very high resolution. The down side
is that this can be expensive and you are not doing it yourself, so you
do not have control. However, this is a very valid approach for many
people. If you scan yourself, the option is to scan the prints or the
film. Scanning the prints is a viable option but don’t believe you are
going to get incredibly high resolutions by scanning this way, even if
your flatbed scanner is capable of it. Prints are a second generation
and is limited by the optical, and increasingly the digital, resolution
of the equipment used to produce them. Anything above 600 dpi is
probably pushing it for most prints, especially drug store ones. You
can buy a film scanner that will go to much higher resolutions.

One last issue with film is dust and scratches. Film is prone to
attract dust and can be easily scratched. Removing these marks can add
significantly to the time you spend scanning images.

Digital Cameras

The sensors in digital cameras capture a specific amount of
information. A two megapixel camera captures that many pixels, usually
no more and no less. As discussed last issue, you can increase the size
of the image file by interpolation, but you can only do this so far.
Digital camera images have no grain. At a low ISO setting (for cameras
that allow you to vary this) and with fairly short exposures, like in
daylight, the images from a digital camera are beautifully smooth. As
the ISO setting is increased and/or you take longer exposures, noise
starts to appear. You also get more noise the hotter the camera is.
Many cameras now have some sort of noise removal processing built into
the camera, which does help.

Pictures from your digital camera are available immediately. There is
no processing and scanning to do, they are just there. Now this is only
truly the case when your camera is saving the image in a standard file
format, like JPEG or TIFF. Proprietary formats, like RAW, need to be
processed by special software before you can commonly use them in, say,
Photoshop or PhotoPAINT, or processed by Photoshop’s own Camera RAW
plugin. This still takes less time than having film processed but does
add a delay.

Compared

Digital camera images are very seductive. Most people find it very hard
to go back to film once they have had a taste of the immediacy and
smoothness of good digital images. But film is cheap (except when you
shoot a lot) and is still in some ways the best to do long duration
trips with. Digital cameras allow you to vary the ISO setting from shot
to shot, something you can’t do with most films. However, you will be
very hard pushed to blow a two megapixel point and shoot digital camera
image up to 1m x 1.5m in size. The higher resolution digitals are very
capable and it is my belief that top end camera, like Canon’s EOS-1Ds
Mark II, with a 16.7Mpixel sensor are the equal of film in a 35mm
camera.

The truth is that there are pros and cons with both. Which works for you depends on funds, expectations and usage.

This extreme blowup is from a Nikon
D1x camera set at ISO 100. You can see that the sky is very smooth,
typical of all digital cameras at such a setting.

This shot, taken with a Canon G1, is
a similar extreme close-up and shows the noise that appears in all
digital camera images with very long exposures, here over 4 seconds. In
fact the G1 has handled this better than most.

This extreme blow-up is a tiny
section of an ISO 100 slide. Even here you can see both the grain and
tiny dust particles that stop the sky being nice and smooth, as it
would have been with a digital at a low ISO setting.