Canon 1D Mark IV Optics

Canon EOS-1D Mark IV Optics

Lens Compatibility

Like all other Canon EOS-1 series cameras, the Canon EOS-1D Mark IV accepts the full range of EF lenses available for full-frame cameras. Because its APS-H sensor is larger than those of Canon's consumer and enthusiast SLRs, it can't use the EF-S lenses Canon manufactures for use on APS-C cameras. The same applies to lenses with sub-35mm image circles available from third-party manufacturers as well.

The APS-H sensor on the Canon 1D Mark IV means that it has a smaller angle of view (by a factor of 1/1.3x) than a full-frame camera with any given lens. While most properly called a "crop factor," the 1.3x ratio is most commonly referred to as the "focal length multiplier," since that's how it works in practice: Any lens used on the Canon 1D Mark IV will have the same field of view as one with a 1.3x greater focal length will when attached to a 35mm camera. For example, a 100mm lens on the Canon 1D Mark IV will show the same field of view as a 130mm lens on a camera with a 35mm frame size.

The Canon 1D Mark IV also offers Lens Peripheral Illumination Correction, which corrects for lens shading (commonly called "vignetting"), producing uniform exposure across the frame by compensating for the light falloff seen with some lenses in the corners of the frame. Lens Peripheral Illumination Correction first appeared in the Canon 5D Mark II, and has since featured in several of Canon's consumer and enthusiast DSLRs. Peripheral Illumination Correction makes its EOS-1 series debut in the 1D Mark IV, and works with over 85 different Canon lens models, in both Raw and JPEG workflows. For JPEG shooting, the correction is made at capture time, while Raw shooters can access the function in Canon's Digital Photo Professional software. DPP offers the highest degree of correction. In-camera correction of JPEGs operates with somewhat reduced strength, especially when shooting at higher ISO sensitivities, given that the correction can make image noise more pronounced. From the factory, the 1D Mark IV body ships with correction data for 29 lens models. Canon's EOS Utility software allows correction data for further lenses (including models as-yet unreleased) to be uploaded to the 1D Mark IV, with the camera body able to hold data for as many as 40 lens models.

Canon 1D Mark IV: Overhauled AF system

The Canon 1D Mark IV incorporates an overhauled AF system, with a new low-noise AF sensor with improved AF points, refined servo tracking algorithms, automatic correction to increase focus accuracy under artificial lighting, and a variety of new custom functions that better allow AF operation to be tailored to individual photographers' requirements.

Canon 1D Mark IV Autofocus System: New Sensor

The Canon 1D Mark IV's new AF sensor has 45 points, just like it's predecessor from the 1D Mark III, but now allows all but six of these to act as f/2.8 cross-type points, so long as they're addressed manually. In addition, the Mark IV reverts to allowing all of the points to be addressed manually, doing away with the concept of "AF Assist" points that can't be directly addressed, and are only available when selected automatically, or when using tracking autofocus. (A custom function still allows the number of points available for manual selection to be reduced in this manner, however.) In normal operation with automatic selection, there are 19 cross-type points with the same arrangement as in the Mark III.

The 1D Mark IV's 45 autofocus points are arranged in an oval-shaped pattern. The center point has a double line design that allows it to better detect the subject even when extremely out of focus, and is a cross-type sensor that's vertical line sensitive up to f/4, and horizontal line sensitive up to f/8, allowing it to continue operating as a single axis sensor even when using lenses or lens / extender combos with a maximum effective aperture of between f/4 and f/8. The center row of AF points, including the center point, all include a thin line sensor allowing vertical line detection at f/2.8 or faster, improving AF detection precision, and better allowing the 1D Mark IV to focus on low-contrast subjects.

The photo above (courtesy Canon USA, Inc.) shows the sensor from the new EOS-1D Mark III. Notice how all four sensor arrays are the same size, both vertical- and horizontal-sensitive elements now covering the full AF area. This is how the Mark III manages to distribute cross-type AF points across the entire AF area, rather than just in a cluster around the center. The two full-size AF arrays on the left and right contain elements corresponding to the pink-marked vertical-sensitive AF points in the diagram below

As previously noted, the 1D Mark IV's selection of cross-type AF points varies between automatic and manual selection, with 19 cross-type points available for automatic selection, and 39 cross-type points available for manual selection. This is achieved by making the the vertical line-sensitive portions of the sensor with switchable reading positions, effectively sharing the same vertical line sensitive portions between multiple adjacent AF points. The single-axis points -- of which there are 26 during automatic selection, and six when selecting an AF point manually -- are horizontal line-sensitive sensors that operate at maximum apertures up to f/5.6. Two of these points -- those directly above and below the central cross-type AF point -- are dual line types that operate with increased precision and performance. For the cross-type points, all but the center cross point function as high precision cross types with lenses of f/2.8 or faster, and their horizontal line sensors (vertical detail sensitive) offer triple the precision of their vertical line sensors. When using lenses that are between f/2.8 and f/5.6, these cross-type points fall back to operating as single-axis vertical line (horizontal detail sensitive) points. There's an exception to this rule, however. Six specific lenses or lens / extender combinations allow cross-type focusing with 39 AF points, as low as f/4. These are detailed in the table below.

New since the previous 1D Mark III is a dedicated light source detection sensor, located on the back of the 1D Mark IV's pentaprism, which is used to finetune the behavior of the AF system based on color information, reducing AF problems often encountered when shooting under artificial illumination. Without this correction, a lens system will bring different wavelengths of light into focus on different planes. High-quality camera lenses are usually well-corrected apochromats, so this isn't a problem at the image sensor. The relatively simple optics (lenses and prisms) in AF systems are another matter, though, so it's very likely that long (red) wavelength light would produce a different focus point than would short (blue) wavelength illumination. By taking the color of the light source into account, the camera can compensate for this tendency.

The AF sensor itself has also been tuned in terms of noise performance, increasing its signal to noise ratio, and providing a cleaner signal from which to make focusing decisions. No specific information on the level of improvement has been provided by Canon, and it's important to note that the sensitivity range of the AF sensor is unchanged, at EV -1 to EV 18 (at 23°C/73°F, ISO 100), but Canon states that the improved noise performance of the AF sensor should yield higher accuracy and greater stability when dealing with extremely bright or dark subjects, or when shooting subjects with low contrast. One final note related to the AF hardware is that Canon has now implemented stricter standards for autofocus adjustment in its manufacturing process, although no specifics have been provided as to what changes this entails.

The workload of processing the wealth of available information from the AF and light source sensors to perform autofocus calculations is shared between two 32-bit RISC processors -- the Canon 1D Mark IV's main 40MHz CPU, and a dedicated 48MHz autofocus CPU.

Canon 1D Mark IV Autofocus System: Updated AI Servo Autofocus Algorithm

The remainder of changes in the Canon 1D Mark IV's autofocusing system are to be found in the camera's firmware -- specifically, the focusing algorithms, and the custom functions that let photographers tune the camera to their own specific needs.

Canon has apparently made considerable changes to its focus-tracking algorithms, as the 1D Mark IV's servo autofocus mode merits a new name: AI Servo II AF. The basic tracking speed of the Canon 1D Mark IV is the same as that of the Mark III, but its handling of subject motion, lost focus, and integration of information coming from the lens have all taken a step forward, according to Canon representatives.

AI Servo II is Canon's name for their predictive autofocus system, which tries to extrapolate future subject position from past subject motion so the AF system can move the lens elements smoothly to follow it. For instance, if a subject is moving toward the camera at some constant speed, AI Servo would determine that the lens needed to move a certain amount between each AF "look." By moving the lens elements more or less smoothly, the amount of additional correction in each AF cycle will be that much less, making it easier for the camera to follow rapidly-moving objects. Predictive autofocus control begins operating immediately that the camera detects subject motion -- for example, after runners launch from their starting blocks. From that point onwards, the subject's motion is tracked and predicted. AI Servo II AF should better be able to handle a variety of common situations.

The 1D Mark IV's AI Servo II AF algorithms now better recognize sudden, abnormal changes in focus distance that would imply the subject may have been briefly obscured by a closer object, or that the AF point has briefly slipped off the subject and onto the background. Where the Mark IV determines this to be the case, it will continue its tracking based on the last good result, ready to pick the subject back up when it falls under the AF point again.

Another difference in the Canon 1D Mark IV's AI Servo operation has to do with how it deals with lost focus in a continuous-mode shot sequence: If the AF system detects a focus error for one of the shots in a series (which presumably means you had C.Fn III/2 set for shooting speed priority), the AI Servo system will disregard the focal setting associated with that shot in its motion-prediction calculations. By throwing out bad data, the AI Servo algorithm can greatly improve the accuracy of its predictions.

As noted in the discussion of custom functions below, a significant feature upgrade in the Canon 1D Mark IV's AI Servo mode is that you can now specify which of the AF points you want the camera to begin its servo tracking from, and once tracking begins, the subject will be followed by a cluster of up to 18 AF points that can move anywhere on the AF array. If the subject is briefly lost or obscured, it can be recollected by any of those 18 points, and tracking resumed. As the subject is tracked, the Canon 1D Mark IV shows the currently-active AF point in the viewfinder.

Canon 1D Mark IV Autofocus System: New Custom Functions

A new addition to Custom Function III-3, AI Servo 1st / 2nd Image Priority, allows 1D Mark IV shooters to mimic the behaviour of the original EOS-1D, EOS-1D Mark II and EOS-1D Mark II N digital SLRs when shooting image bursts. All three of these cameras would prioritize shutter release over focus lock for the first shot, ensuring that it was captured at the moment the shutter button was pressed even if the camera felt that autofocus lock hadn't quite been achieved. For subsequent frames, though, they'd favor focus priority over frame rate, ensuring that as many shots as possible in the burst were correctly focused. The 1D Mark III changed this behaviour to allow focus priority for all shots, and either focus or shutter release priority for the first frame followed by drive speed priority for subsequent frames. The 1D Mark IV now adds the original behaviour as a fourth option.

For focusing on subjects that occupy a small portion of the frame, or when shooting through obstructions such as a chainlink fence or a race drivers' helmet, a new Spot AF function is available that reduces the point size. Accessed through Custom Function III-6, this should make autofocus easier in these situations, but also brings a reduction in AF speed, and can potentially make it harder to achieve an AF lock.As a (rather subtle) reminder that Spot AF is activated, the AF point will blink with increased brightness when focusing.

Of course, the opposite is an equally common situation -- some subjects will occupy a larger area spanned by several AF points, or will move fast enough that it's difficult to keep them under one specific point. The 1D Mark IV offers another Custom Function that recognizes this, and expands the focus area to include surrounding points C.Fn. III-8 allows three different ways in which the AF point expansion can operate. The left/right AF point option allows the focus points immediately to the left and right of the manually selected point(s) will come into play if focus lock can't be achieved with the selected point. A second option surrounds the selected AF point with a ring of adjacent points.

The third option is a little more complex. In One-Shot AF, it will attempt to set focus from the select point(s), but if this fails, will try the six adjacent points, then the 18 adjacent points, and finally the entire AF array. In AI Servo AF, a much larger 18-point expansion is used, and once subject tracking begins, this expanded area will follow the subject across the entire AF array. If the subject is briefly lost or obscured, the 1D Mark IV will resume tracking only when the subject is detected by the group of points that were last tracking it. This differs from the behaviour in automatic AF point selection, where tracking could resume from any AF point on the array, potentially switching to a different subject unintentionally. In all cases, if the three AF point expansion modes, if the selected point is at the very leftmost or rightmost edge of the frame, then the expansion points will only be added on the inside of the manually selected point(s), and won't wrap around to the other side of the frame.

As previously described, the Canon EOS 1D Mark IV changes the AF point selection behavior of the Mark III, which only allowed direct selection of 19 AF points, and relegated the remaining points to "assist" status. The Mark IV returns to the behaviour of previous cameras, allowing all AF points to be selected manually, and instead allows the number of selectable points to be reduced via Custom Function III-10. Several options are available, removing all but inner 9, outer 9, 11, or 19 points from manual selection, but regardless of the option chosen, all points remain available for automatic selection or tracking operations. The two 9-point options and 19-point option replicate those from the 1D Mark III, while the 11-point option comes from the 1D Mark II/n.

Custom Function III-15, which controls autofocus assist from external flash strobes, has also had a new option added. The IR AF assist beam only option prevents flash strobes such as the Speedlite 270EX from providing autofocus assist. These strobes don't include an infrared assist beam, and hence perform AF assist by firing a succession of low-power flash bursts, which could prove objectionable in some environments. The new option prevents this becoming an issue.

Finally, the new Custom Function III-16 allows AF point selection to be linked to camera orientation. This can prove helpful when shooting a variety of landscape and portrait orientation in succession. The camera can remember different AF point selections for landscape and portrait-mode shooting, and will switch back and forth between these selections automatically as the body is rotated. (It's actually possible to switch between three different point selections -- one for landscape, and two for portrait -- since the 1D Mark IV differentiates between portrait-mode shooting with the camera turned clockwise or counter-clockwise.)

Dust Reduction Technology

First introduced on the Canon Rebel XTi, Canon's system-wide approach to reducing the impact of dust on the image sensor is also included on the Canon 1D Mark IV, with a slight update to the anti-static coatings used.

A key feature of any SLR is the ability for the user to easily swap lenses. This expands creative options enormously, but every time the lens is removed, dust from the environment is free to enter the camera body. From there, it's only a matter of time before some of it makes its way to the surface of the sensor ,where it casts shadows that appear as dark blobs in your images. In truth, it's the anti-aliasing filter that collects dust, rather than the sensor itself, but common parlance refers to "sensor cleaning." For the sake of familiarity, we'll generally refer to sensor cleaning here, but will make mention of the anti-alias or low-pass filter as seems appropriate. Every DSLR ever sold has offered a sensor-cleaning mode, in which the mirror is locked up and the shutter opened to permit the sensor to be cleaned with compressed air, a solvent-carrying swab, or other means. As the market has matured and more DSLRs have found their way into the hands of novice users, it has become clear that some automated way of dealing with sensor cleaning is needed.

The principal approach other manufacturers have used to deal with dust has been to make the system self-cleaning, vibrating either the anti-aliasing filter itself or a protective cover glass lying above it, to shake loose adhering dust particles. Once dislodged, a strip of sticky material at the bottom of the sensor cavity or mirror box catches and holds them. This approach was pioneered by Olympus, but has since been adopted by Canon, Nikon, Pentax, Panasonic, and Sony, in various forms. Some cameras use a dedicated piezoelectic element to provide the vibration, while others perform double duty with the sensor shift mechanism used for their image stabilization, with widely varying vibration frequencies and efficacies. In addition, some manufacturers have adopted coatings on the low-pass filter intended to prevent dust particles from adhering in the first place.

Canon's EOS Integrated Cleaning System employs a piezoelectric, vibratory cleaning method when the power is switched on and off, as a primary part of the overall strategy. To avoid missing the action when first starting up, the Canon 1D Mark IV aborts its power-on cleaning cycle as soon as the user touches the shutter button. This insures that you won't miss a critical shot due to sensor cleaning. It's also possible to trigger the cleaning system to operate manually -- either as well as, or instead of, the automatic startup / shutdown operation.

Previous EOS-1 models have also used an anti-static coating on the anti-aliasing filter to make it harder for dust to gain a foothold in the first place. The 1D Mark IV uses Canon's latest generation fluorine-based coating, which purportedly improves this dust resistance property. Dust particles frequently carry static charges, so the anti-static coating avoids one of the key mechanisms by which dust particles adhere. Canon has also adopted a special shutter-curtain coating designed to greatly reduce the shedding of particles, and a different plastic in their DSLR body caps, one less prone to creating shavings that can drop into the mirror box.

No matter how good an automatic cleaning system, there are going to be some stubborn dust particles that it can't dislodge. To deal with these, the Canon 1D Mark IV has the ability to shoot a dust reference photo, and then transfer that information to Canon's Digital Photo Professional software, which can use it to eliminate the shadows cast by dust particles on the images. Canon's "Dust Delete" processing works for both JPEG and RAW format files. The dust map ("Dust Delete data") that the software uses to perform its magic is stored in the headers of files created by the camera. There's thus no need to keep track of a separate dust image file, the information is always available in the file headers, assuming you've actually performed the dust-mapping process. You can update the Dust Delete data any time you think the camera might have been exposed to dust, or after you've manually cleaned the sensor. The latest dust map is automatically incorporated into the EXIF headers of all JPEG images, or the headers of any RAW files.

Located in Shooting Menu 2, the Dust Delete Data option displays a screen that shows when the last Dust Delete reference image was captured. Selecting OK on this screen initiates a cleaning cycle, after which the camera prompts you to take a picture of a blank white surface. (The camera automatically defocuses the lens and sets the aperture appropriately, to produce the best possible dust image.) The camera then processes this data, and reports whether it was successful or not. If the surface you used to capture the image wasn't sufficiently uniform, you'll get an error message, but if the image was good, you'll see a confirmation screen. The Dust Delete Data just generated will now be included in the headers of any JPEG or RAW images captured, until you decided to capture a new dust reference image.

We don't have any quantitative way of evaluating dust-removal systems, but based on Canon's description of it, their anti-dust technology does appear to go a step or two beyond anything else currently on the market, providing a more comprehensive solution to the problem of dust in DSLR images than we've seen to date.

Don't count on the anti-dust system to do everything, though.

Despite the many advances in Canon's anti-dust technology, though, we feel compelled to point out that we've thus far seen no anti-dust system that completely eliminates the need for sensor cleaning. Sooner or later, you're going to need to clean your sensor, so we strongly recommend purchasing a good-quality sensor cleaning kit right along with your DSLR. Automated anti-dust systems like Canon's will certainly help with some of the dust, typically the dust that the nylon brush-based cleaning systems can also handle. Inevitably, though, you'll encounter dust that sticks to the sensor's cover glass tenaciously; dust that only a wet/dry cleaning approach can remove. We ourselves use and recommend products from Copper Hill, which we've found to be both highly effective and among the most reasonably priced on the market.

The images above were taken from our standardized test shots. For a collection of more pictorial photos, see our Canon EOS-1D Mark IV Photo Gallery .