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Technical

June 2011

One of the hallmarks of Canon is its ongoing commitment to, and investment in, research and development. While investment is spread across all sections of Canon's research – from medical products to business and office systems and astronomy uses – because the majority of Canon's business involves lenses in one form or another significant investment is put into developing new lens technologies. What is learnt in one area of lens research can often be applied to problems that need solving in another. David Newton takes a look at the key lens developments Canon has introduced to its L-series of professional EF lenses between 2009 and mid-2011.

The last two years have seen several new technologies introduced into the Canon EF lens range, all with one goal – to ensure that the image quality captured is as high as possible. Since 2009 we have seen a major new lens technology appear, as well as some adjustments and modifications to existing lens technologies to improve them even further.

Hybrid Image Stabilizer (IS)

Introduced with the EF100mm f/2.8L Macro IS USM lens in 2009, the Hybrid IS system takes the Image Stabilizer system found in other Canon EF lenses and improves on it specifically for macro photography.

The general rule of thumb states that to avoid camera shake you should use a shutter speed that is equal to, or faster than, the reciprocal of the lens focal length. Or, in simple terms, turn the focal length into a fraction with a 1 on top – so 200mm becomes 1/200, which looks a lot like a shutter speed. In fact, 1/200sec is the minimum shutter speed that you should use when hand-holding a non-IS 200mm lens. With macro photography, due to the increased magnifications involved, this rule of thumb needs to be tightened a little more so, if possible, you should use an extra stop or two faster than the reciprocal shutter speed.

 

The location of the IS unit processor and camera shake sensors found in the EF100mm f/2.8L Macro IS USM lens.

In normal photography, the magnification and angle of view mean that all camera shake looks simply like rotation around a point. Even though the camera is, at times, shifting in a parallel plane to the subject the shift is hidden by the focal distance. This type of camera shake is called 'angle shake' and it's what is corrected for by normal IS systems.

However, when photographing macro subjects the focus distance is much smaller, and the magnification higher, so those small shift movements that are present in all hand-held picture taking, where the camera moves parallel to the subject, become much more obvious. It's these shift movements that the Hybrid IS system corrects.

To be able to correct the two different types of camera shake in macro shooting, the IS unit for the EF100mm f/2.8L Macro IS USM makes use of mostly the same technology as normal IS sensors. However, in addition to the vibration gyro (which detects angular motion), there is also an acceleration sensor that is used to detect the parallel 'shift' motion. By utilising the data from both sets of sensors, the Hybrid IS unit is able to detect, and compensate for, camera movement in three dimensions.

Clearly, with two different sensors both picking up data about the motion of the camera, there is some scope for overlap – where the acceleration detects some angular motion and the angular gyros detect some shift motion. To avoid this problem, the IS algorithm for the Hybrid IS unit has been developed to differentiate between the two types of motion and their effect on each sensor.

 

The IS unit used in the EF100mm f/2.8L Macro IS USM lens.

The effect of this on your photography is that in normal shooting, the EF100mm f/2.8L Macro IS USM lens offers up to four stops of Image Stabilization; at half life size (0.5x) magnification it gives up to three stops; and at full life size (1x) it gives up to two stops of IS allowing for sharp hand-held shooting, even in true macro photography.

Fluorine lens element coating

 

The front and rear lens elements of the EF70-300mm f/4-5.6L IS USM lens are coated with a non-sticky Fluorine coating.

All Canon lenses feature one of a number of different lens coatings. Indeed there are often different coatings used on different lens elements. One aspect of a lens coating's function is to help to keep the lens protected and free from dirt and dust – especially on the front and rear lens elements that are frequently exposed to the world's natural elements when changing lenses.

Canon has used Fluorine coatings on the low-pass filter in front of its CMOS sensors in all of its recent EOS DSLR cameras. However, the EF70-300mm f4-5.6L IS USM lens is the first lens to offer such a coating. The Fluorine coating is designed to reduce the likelihood of dust and dirt sticking to the lens element and also to make it easier to clean should any dust or dirt manage to adhere.

The coating works in two ways – firstly, it reduces static electricity so that small particles are less likely to be attracted to, and become attached to, the surface. Secondly, it is 'hydrophobic' so it repels moisture and makes cleaning water drops, like rain, off a lens much easier.

Cleaning lenses that are coated with Fluorine is much easier too. Often you'll find you only need a blower bulb and a soft, dry, cloth to remove any dust that has become attached. In fact, if you use a solvent to clean the lens you may find it harder because the coating will reduce the solvent to very small beads of liquid that are harder to wipe away.

The Fluorine coating is applied over the top of other lens coatings and is added to both the front and rear lens elements as these are the ones most likely to come into contact with dirt.

The Fluorine coating is now being incorporated on many new Canon lenses, for example: the EF1.4x III and EF2x III Extenders, the EF300mm f/2.8L IS II USM, the EF400mm f/2.8L IS II USM, the EF500mm f/4L IS II USM, the EF600mm f/4L IS II USM and the EF8-15mm f/4L Fisheye USM.

Fisheye zoom lens first

Announced in August 2010, and due to be available in autumn 2011, the EF8-15mm f/4L Fisheye USM is the first zoom fisheye lens available for an interchangeable lens SLR camera to offer photographers both circular and full frame options.

 

At its widest focal length (8mm) the Canon EF8-15mm f/4L Fisheye USM lens offers a 180º degree field of view in all directions.

At the fully wide setting of 8mm, this lens projects a circular image with a 180º degree field of view in all directions. However, once you zoom in, the circular nature of the lens disappears and it becomes a full frame fisheye with a rectangular image where the field of view is 180º diagonally. This is true no matter what camera you use, as even on Canon's APS-C sensor DSLR cameras, like the EOS 7D, the angle of view will be a diagonal 180º – index marks on the lens indicate where you achieve a fisheye 180º diagonal field of view for both APS-C and APS-H sensor cameras.

With cameras that have a smaller than full frame sensor, there is a zoom limiter to stop you being able to zoom to the full 8mm; this avoids you creating images that are somewhere between circular and full frame, where you may have what appears to be heavy vignetting in the corners rather than something that appears fully circular. However, this is not essential to use and is only provided for use as photographers see fit.

To really help you to exaggerate the perspective a fisheye lens can provide, the EF8-15mm f/4L Fisheye USM lens features a close focusing distance of just 15cm from subjects.

Power Focus (PF)

Canon's super telephoto lenses have long featured the ability to jump to a preset focus distance by turning the playback ring located in front of the main focus ring. However, with the advent of video in DSLR cameras, the requirement for smooth focus pulling has seen the playback ring modified to provide this functionality.

 

A close-up on the EF600mm f/2.8L IS II USM super telephoto lens – it's one of several new Canon super telephoto lenses that offer Power Focus (PF) via the Focus Mode switch that features AF, PF and MF settings.

The Focus mode switches on lenses that feature Power Focus have a third position other than AF (Auto Focus) and MF (Manual Focus) – this is PF. By selecting PF on the mode switch and turning off the focus preset settings, the playback ring can be turned, causing the focus motor to electronically drive lens focusing. Being an electronic drive it is a smooth and continuous pace and allows for accurate focus pulls either from one subject to another, or from out of focus to in focus.

The speed of this change can be controlled at two rates by turning the playback ring to a greater or lesser degree. The direction in which you turn the ring determines the direction of focus pull.

Since it uses the USM focus motor, these focus changes are completed in near silence so there is no noise to affect sound recording. It also means that you have to exert less force on the lens helping to eliminate camera shake during focusing.

IS Mode 3

IS Mode 3 is a new Image Stabilizer mode that has been added to Canon's Mark II super telephoto lenses – the EF300mm f/2.8L IS II USM, the EF400mm f/2.8L IS II USM, the EF500mm f/4L IS II USM and the EF600mm f/4L IS II USM (note that these lenses have been announced but have not yet come to market). Mode 3 is specifically designed for shooting fast moving sports where you may need to move the camera rapidly from one subject to the next.

In these situations, you can find that the view through the viewfinder doesn't quite keep up with you moving the camera because the Image Stabilizer, even in Mode 2, thinks that the motion is camera shake that should be corrected. This can make composition difficult, as you don't have a clear view of the subject.

The two original IS modes, Mode 1 and Mode 2, work by detecting camera shake and moving lens elements to correct the optical path of the light passing through the lens. Mode 3 works in the same way, but the crucial difference is that the IS motor only kicks in once you actually take the picture.

 

A close-up of the EF400mm f/2.8L IS II USM lens. IS Mode 3 is activated by pushing the sliding STABILIZER MODE control to 3.

On a half-press of the camera shutter button, the lens calculates the IS that will be required, but doesn't apply it to the correcting elements, so you have a clear view of the scene without the fractional delay you would normally see when moving between erratic subject. Once you fully press the shutter button to take the picture, the IS elements are released to correct for any camera shake.

Like Mode 2, which is designed for panning with moving subjects, Mode 3 will detect panning motion and then only apply Image Stabilization at right angles to this direction of movement. This makes it an ideal option for all kinds of sports photography where you may be panning with moving subjects, or moving between erratically moving subjects.

Mark III Extenders

As a development of Canon's EF Extender Mark II models, the EF1.4x III and EF2x III take the performance of the previous generation of extenders and improve on it in key areas, while tailoring them to suit the requirements of shooting with digital SLR cameras. A new optical design helps to eliminate chromatic aberration, resulting in sharper images that show less colour bleed along high contrast edges.

Digital cameras have slightly different lens requirements to those of film cameras, so the Mark III Extenders employ different lens coatings to help to reduce the flare and ghosting that can be caused by stray light passing through the lens and either refracting off internal elements, or reflecting back off the sensor in the camera.

Both extenders also employ Fluorine coating to help to keep the front and rear elements clean, thereby avoiding dust and dirt on the lens that may degrade image quality with flare.

The handling of the extenders has been modified too – the lens release button is now better placed and easier to use, while being out of the way and less likely to be knocked.

 

The Mark III versions of Canon’s EF1.4x and EF2x Extenders offer a number of benefits over their predecessors including processors that relay information from the attached lens back to the camera to ensure improved AF performance.

However, the biggest change is within the electronics of the extenders. Both models feature integrated processors to collate and transfer all the information from the lens back to the camera. This includes data about focal length, focus distance and Image Stabilization. The advantage of this is that the camera can adjust settings like AF Microadjustment (if you are using it) to suit the combination of lens and Extender. It also means the AF performance when using extenders is improved compared to the previous generation of extenders when used with earlier generations of Canon telephoto lenses.

To achieve the maximum benefits of this new processor, you need to ensure that you attach the lens to the Extender first, and then attach the whole lens and extender combination to the camera. This way the camera will see a combined "Lens + Extender". If you add the extender to the camera first the camera will recognise it, but will then not be able to deduce that a lens has been added to the front of it.

As with the previous Canon extender models, the lens mounts are dust and drip proof, but in the Mark III Extenders, the lens mount features more screws to provide a stronger and more durable attachment to the camera and lens.

The EOS maxim

Even in two short years, and despite reaching the milestone of 60 million EF lenses in February 2011, Canon's R&D lens department has certainly not been sitting still. It continues to innovate and bring new technologies to market to ensure the lens range available and the quality of the lenses on offer lives up to the established EOS system maxim of "Quick and easy operation with high image quality".