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ilkka_nissila wrote:
I think there are a lot of opinions expressed in this thread that are more justified based on partisan/brand fan/sports team fan than an understanding of the technology.
Canon chose to implement phase-detection autofocus across the sensor so that each photodiode corresponding to a pixel is replaced by a pair of photodiodes which receive light from different sides of the image field. All photodiodes contribute to both the image (averaging the pair) and distance (focus error) calculation for autofocusing. This contrasts with the Nikon / Sony approach which most other manufacturers use where a small number of photodiodes are allocated to phase-detection only and the majority are allocated to image formation only. Advantages of the first approach (dual pixel autofocus) is that independently of where the subject is, both phase and contrast information is available as the subject moves across the frame, and by averaging the phase difference data across patches, it's possible to get very high SNR even in low light to the phase information. A disadvantage is that the camera has to process twice as much data from the sensor to do focusing (and in an early part also image formation). Advantages of the second approach include less processing needed to perform phase-detection autofocus and the option of creating higher-resolution cameras (since in the first approach, the images produced have a pixel count one half of the photosite count of the sensor whereas in the second approach, almost all the photosites are used for image formation). As a result Canon's high-speed cameras are based on 48 million photosite sensors producing 24 MP images (but with a smooth AF response to subject positional changes) and their 45 MP cameras (with 90 million photosites) aren't quite as fast in terms of sensor read time or performance overall (and may have heat limitations due to the vast amount of data collected and processed). Sony/Nikon have fast cameras that are 45-50 MP since those are based on 45-50 million photosites. But there is a thread on the Nikon forum complaining that focusing on the eye is in some cases erratic. Some say it's due to subject-detection algorithm issues, I believe it is due to the fact that sometimes there is a phase-detection sensor directly on the eye and at other times it's slightly off, leading to focusing on something else with strong contrast and/or brightness in terms of vertical lines. I find the Nikon (Z8) focusing to focus sometimes on background vertical lines such as grass if the subject is in the foreground, small, and backlit, whereas Nikon cameras with cross-type autofocus sensors such as the D6 focus much more reliably on the subject in such situations. This is also happening when photographing concerts with the vertical microphone stands often catching focus rather than the face or eye of the performer. Thus I applaud Canon for finally bringing cross-type phase-detect sensors to mirrorless cameras in the R1, and I hope the other manufacturers (Olympus/OM Digital was actually there before Canon) will follow suit and implement this very important technology as soon as possible.
Sometimes it's just not possible to implement technologies that would give best of all worlds results in a single camera and manufacturers have to weigh the advantages and disadvantages of different solutions and one way in which they compete with one another is by making different choices. Canon implemented dual-pixel autofocus in products even before they could use it for continuous autofocus, but they've gotten through that hurdle and today despite of the processing requirements, their cameras are among the best and most liked in terms of how the autofocus works. Other manufacturers have advantages in different areas (such as Sony in making a high-performance, high-resolution A1 in a compact package and Nikon in offering some unique lenses and overall a lens system that emphasises the upper intermediate level lenses and not only the most basic consumer and the most advanced high-end lenses). The customers have a lot of choice today and the performance and results of cameras of all these brands are excellent, which leads me to wonder why there is so much negativity in online gear forums. Pick up a film camera and try to shoot some action, or even a 1st-generation digital camera and you might find that the manufacturers have done a fantastic job in advancing the technology of photography to where we are today. I would even argue the cameras are too good and leave too little to the skill of the user, so it has in some ways become a boring task to take photos.
With regards to the lenses, I am completely puzzled at the forum complaints about Canon's high-end supertelephoto lenses while they seem to be producing excellent results in the hands of skilled photographers. Although Nikon has built-in TCs in the 400 and 600 mm lenses, this seems to have increased the cost of those lenses by about $3000 per lens. This was the case also with the Canon 200-400/4 Extender and Nikon 180-400 TC: those lenses cost almost twice that of the TC-less previous generation (Nikon 200-400/4). The manufacturers really milk every dollar they can from those who want that convenience. I think Sony's and Canon's decision not to include TCs in their 400/2.8 and 600/4 is perfectly reasonable as it makes those lenses substantially less expensive and slightly lighter as well. I've always had the opinion that TCs are a perfectly good way of ruining an excellent lens into mediocrity and certainly wouldn't want to pay so much to get that option. And I'm speaking as a Nikon user. I completely understand that if the photographer doesn't have any choice in a given situation and needs the focal length, and if the finer points of the image quality are not as important as getting the shot then they would want that built-in TC in there. But I don't specialize in long-lens photography and so the price is a very real issue. Having that built-in hot-swappable TC there makes these lenses from difficult to get and justify into completely out of question. A specialist would perhaps in many cases have a different view, as this would be their primary lens, but I argue that having (or NOT having) that built-in TC is very much a legitimate compromise to make from the manufacturer's part.
My guess that we'll see at the Paris Olympics the usual split of 50-60% Canon, 20-30% Sony and 20% Nikon among the accredited photographers. They will know what they're doing and get the results. Probably none of them will be aware of or complain about Canon's supposedly inferior long lenses, because they know these lenses are really good. ...Show more →
Thank you for taking the time to contribute to the discussion with a balanced perspective.
FWIW, some of the focusing difficulties you described with the Z8 I have also experienced with Canon mirrorless cameras. Backlighting just seems to be a more challenging scenario in general for mirrorless and I do think my DSLRs locked focus more confidently in those conditions. Perhaps it is a difference of non-cross (mirrorless) AF points vs. cross points (DSLRs). That said, there are so many other ways in which mirrorless has outperformed DSLRs in the two years since I transitioned, there is no way I would go back. While I was initially skeptical about slow lenses, breaking free from the DSLR f/5.6 AF limitation has really opened up possibilities for interesting lens designs from all of the brands.
Some of the negativity here is very simple: certain photographers have a perceived need for more resolution than less, especially those frequently working in reach-limited situations. Meanwhile, Canon only has one high MP FF option that in some criteria is a compromise solution. A higher resolution sensor also offsets, to some degree, the need for TCs and lack of an integrated teleconverter in Canon's super-teles, by allowing deeper crops for those who can benefit in this way. It is interesting though that if Canon will not chase high MP in their flagship category, that users of such cameras will likely have greater reliance on TCs to fill the frame as much as possible. And here super-tele lenses with integrated TCs would be a benefit in fast-paced situations (or a solution like the rumored 1.0-2.0x TC). This is actually how I think my 200-400 on a 24MP sensor works best. And I do use the integrated TC a lot during sports events. But if I was instead using a higher resolution camera, the 'freedom' to crop deeper would somewhat offset the need for the TC (because my images are often not delivered at full camera resolution). And indeed, when I did a trial of the 100-300/2.8, this was frequently how I used it for some sports - simply pressing a button to activate APS-C crop rather than losing a lot more time physically adding or removing a TC. Having an integrated TC here would have been attractive as a 24MP FF user. It leaves me wondering a bit what will happen with the 200-500/4, if it ever materializes. With the R1 being 24MP and likely Canon's flagship 'action' camera for at least 4 years, there should be a greater argument for an integrated TC with this lens.
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