Lenses for compact system cameras

The exaggerated perspective of a fisheye lens.

Leading manufacturers publish ‘roadmaps’ showing both currently-available lenses and those that are in development and expected to be released within the next 12-18 months. These documents are easily located with a Google search on ‘lens roadmap’ and selecting the brand that interests you.

Lenses for CSCs have been designed to use the main image sensor to provide autofocus (AF) information plus a live preview of the scene. This is different from the AF systems in DSLRs, which are usually slower to focus in live view mode. Consequently, most CSCs can focus as quickly in live view mode as when the viewfinder is used ““ and lock-on can be very fast and accurate.

In addition, most CSCs can provide a magnified preview for accurate manual focusing, as well as other focusing aids. This allows old, manual focus lenses to be fitted to modern cameras and has led to the development of a wide range of adapters, some accommodating obscure and obsolete mounts. Cash-strapped photographers can look to the secondhand market for fast, fixed focal length lenses, which can be purchased without much financial risk.

Establishing a System

Once you’ve chosen a camera, the next step is to select lenses to match it. Camera manufacturers make this easy by offering ‘kit’ lenses; typically starting with a general-purpose zoom lens that ranges from medium wide to medium telephoto in focal length and adding a tele-zoom lens that ranges from 55-250mm for cameras with APS-C sensors or 40-150mm for M4/3 cameras.

Most manufacturers make it easy to start a camera system by offering one or two zoom lenses with the camera body. (Source: Olympus.)

The Olympus lens roadmap with separate sections for the Four Thirds system lenses produced for its DSLR cameras (which can now be used by the new OM-D E-M1 camera) and the Micro Four Thirds lenses for its OM-D and PEN cameras. (Source: Olympus.)

Buying kit lenses when you buy a camera body will save money and enable you to cover most popular subject types. But it may not give you the lenses you need for certain types of subjects and although the lenses may perform well within their design limitations, they aren’t premium products.

Most photographers include at least one kit lens in their systems for everyday shooting. However, they often look for higher-specified lenses to handle special subjects. And this is where allocating your budget becomes important.

Crop Factors and Focal Length

Sensors in most digital cameras are smaller than a traditional 35mm film frame, so images are cropped by the ratio of the sensor size to a 35mm film frame, effectively increasing the effective focal length of the lens. The table below shows typical crop factors for the main sensor sizes used in today’s CSCs, based on the dimensions of the sensor.

When a lens designed for 35mm format is used with a smaller sensor, several other parameters can be affected, aside from the obvious reduction in field of view. Depth of field may be increased; perspective will be altered if you have to move away from the subject to cover the same field of view as a 35mm lens on a 35mm sensor.  

The enlargement applied by smaller sensors will also increase the risk of camera shake, which can cause blurring in shots. So the focal length that can be reliably hand-held at a given shutter speed should be reduced by the crop factor.

Blurring of defocused areas is decreased with smaller sensors. However, because many lenses produce higher resolution in the centre of the frame than around the edges, using a lens designed for a 35mm camera on a camera with a smaller sensor crops away the ‘soft’ edges, leading to higher resolution across more of the frame. This can be advantageous for landscapes, architectural photography and copying artworks or documents.

The illustration above shows how smaller sensors can act as a kind of zoom adjustment. The main image shows the subject as it would be captured with a 36 x 24 mm ’35mm’ sensor. Stepping in the black rectangles outline the view that would be shown with a lens of the same focal length on an APS-C sensor, a M4/3 sensor, a 1-inch sensor and a 1/2-3-inch type sensor. The reduction in the field of view has the effect of magnifying the central area of the subject with respect to the image frame.

Olympus or Panasonic?

While owners of M4/3 cameras can choose between Olympus and Panasonic lenses because they have the same lens mounts, it is usually best to stick with the same brand as the camera body. There are two reasons: stabilisation and aberration corrections.

Most Panasonic lenses have in-lens stabilisation while Olympus builds stabilisation into each camera body. Consequently, if you fit an Olympus lens to most Panasonic bodies you won’t get stabilisation. Fit a Panasonic lens to an Olympus body and you can choose whether to use the stabilisation system in the lens or the camera.

Both camera manufacturers install firmware corrections for distortion and chromatic aberration (and maybe other aberrations) in their latest cameras ““ but only for their own lenses. This won’t matter much to photographers who shoot raw files as they aren’t adjusted. But for JPEGs, it will make a difference.

Stabilisation

Different camera manufacturers have different approaches to image stabilisation. Canon, Fujifilm, Nikon, Panasonic, Samsung and Sony build stabilisation into their lenses; Olympus and Pentax build it into the camera body, using a sensor-shift system that moves the sensor mounting to counteract camera shake.

Thanks to the latest technologies the differences between the systems are largely irrelevant to most photographers.   Any small differences in steadying performance are barely detectable; it’s better to concentrate on whether the system offers stabilisation across as many planes as possible. (Olympus’s 5-axis stabilisation system is a good example of a refined and very capable in-camera stabiliser.)

Lens-based stabilisation can be slightly more effective in dim lighting and with low-contrast subjects, particularly with long telephoto lenses. However, stabilised lenses are often larger and heavier than lenses without stabilisation and they cost more to make.

In-camera sensor-shift stabilisation works with all lenses you fit to the camera body and delivers better results in movie mode. Manufacturers using this system make lenses that are lighter and mechanically less complex, so they’re cheaper to manufacture. As this technology improves, you need only upgrade your camera body, which is much less expensive than upgrading a suite of lenses.

Additional Lenses

If you love shooting close-ups, it will be worth investing in a macro lens. If you’re into sports and/or wildlife a high-power telephoto lens will be desirable. Alternatively, you may be drawn to a fisheye lens for its ability to cover a very wide area or a tilt/shift lens for tabletop or architectural photography.  

Lensbaby makes an interesting range of special effects lenses that can tilt the plane of focus to make some areas sharp while others are very out-of-focus. They provide an easy and reliable way to manipulate depth of field and create miniature effects and soft-focus backgrounds in portraits. And you can align the lens to make the plane of sharpness, horizontal, vertical or diagonal.

Olympus’s 5-axis sensor-shift stabilisation moves the image sensor to compensate for a wide range of camera movements.(Source: Olympus.)

A macro lens will allow you to shoot close-ups of very small subjects.  

Some of the interesting special effects lenses in the Lensbaby family. (Source: Lensbaby.)

Lens Hoods  

Shooting without a lens hood can result in flare (which causes a loss of contrast and colour saturation) and ghosting (which produces polygons, starbursts, rings, or circles across the image). Zoom lenses are often flare-prone as they have more internal elements and multiple surfaces tend to produce more scattering.  

A lens hood will ensure the light that reaches the camera’s sensor isn’t contaminated by scattering and internal reflections within the lens. Very wide angle lenses usually come with hoods attached to the outer barrel to ensure they remain correctly orientated as these hoods are very shallow.

The effects of flare include veiling, loss of contrast, and ghosting.

Some manufacturers provide hoods with their more expensive lenses, but not with the cheaper, entry-level lenses. Others make you purchase the hoods separately.  

Most hoods sell for between about $25 to $100, depending on the size of the hood and what it is made from. Theoretically, there shouldn’t be much price differential between plastic and aluminium hoods but plastic ones are generally cheaper. Modern plastics are very robust and shatter-resistant as well as less likely to be dented by impact shock than lightweight metals.

For very wide angle lenses, like the Panasonic fisheye lens shown above, the lens hood is usually shallow and attached to the outer barrel so it remains correctly orientated. (Source: Panasonic.)

Lens Adapters

Adapters let you fit a lens from a different brand on your camera body or use lenses designed for larger sensors. Some manufacturers still rely on them to fill critical gaps in their ranges.

Many adapters are very basic and require you to use manual settings for both focusing and exposure control. Others come with AF-confirm chips that permit focus confirmation and may also support some metering modes. Autofocusing with adapters is usually slow and drains battery power.

Before buying an adapter, it’s important to understand some of the problems they present.  

1. Fitting an adapter increases the size and weight you have to carry.

2. You will probably have to adjust the aperture and focus manually.  

3. The distance scale may not indicate the actual focusing distance.   Always check focus before shooting.

4. Adapters containing glass lenses introduce two more lens-camera interfaces, which can distort the image through side-to-side or top-to-bottom tilt. They can also cause some quality loss and reduce light transmission. (Glassless adapters should cause little or no loss of image quality.)

5. Lens adapters vary widely in quality. Basic ones are made from cheap aluminium and may have variable thickness. Some have poor or no blackening and/or baffling and a cheap coating that flakes off. A well made lens adapter is all metal with chromed steel and/or anodised surfaces and appropriate baffling. The mount should have uniform thickness to within a few microns to prevent image blurring.

6. The thickness of the adapter must match the camera’s flange focal distance (between the back of the lens and the sensor). You may find it difficult to find out what this is so it’s best to purchase adaptors from a specialist retail store.

7. Third-party adapters aren’t covered by the camera’s warranty so you use them at your own risk (and any damage they cause is your responsibility).

Adapters fit between the lens and the camera body, enabling you to use a lens with a different mount. This weatherproof E-System DSLR to MFT adaptor is designed to allow Olympus’s Pro & Super Pro DSLR lenses to be used on M4/3 cameras.

 

Excerpt from  Compact System Camera Guide.