Autofocus is also a fairly important reason. The Autofocus in SLRs uses many dedicated AF points with a secondary mirror that connects to the phase detection sensor. This is faster and more accurate than what is used with Live view. In live view, Contrast Detect is used, which in most cases is still slower and less accurate, especially as the available light falls off (either from a darker environment, or from a lens with a smaller maximum aperture).
Lenses are a big factor too, at a certain point you are limited by the maximum resolution of the glass/sapphire/flourine whatever. High resolution / sensor area cameras run into this issue. larger lenses allow for larger sensors, which means lower demands on the glass. Typically, SLR lenses are nicer in the first place, or at least have higher end products available. For very high-end photography, you still see medium format cameras for this reason.
This isn't exclusive to SLRs. These days, all the top mirrorless cameras have on-sensor phase-shift AF sensor pixels across the entire frame. Also, not all cameras use contrast detect in Live View. For example, Sony's DSLRs were the first (and maybe only) DSLRs to use a secondary PDAF sensor for Live View. Yes, you can get slightly faster PDAF on an SLR, but the gap is very narrow these days. The often mocked Nikon 1 mirrorless series can AF track just as well as most consumer DSLRs.
>> Lenses are a big factor too
Once again, this isn't exclusive to SLRs. This is more about sensor size than whether the camera has a mechanical mirror box inside.
No, it is not, but, for a given price point, you will likely get faster AF with an SLR today than all but the most expensive mirrorless cameras. Especially with motion tracking. I know that there are some cameras that say they'll be faster, but having tested a bunch in the real world, I had a very hard time finding any that worked as well as SLRs in as wide a range of conditions.
>>This is more about sensor size than whether the camera has a mechanical mirror box inside.
Yes, though it is more complex than this. It also has to do with the distance from the sensor to the back of the lens. This doesn't require a mirror, but most mirrorless cameras are focused on reducing the size of the package, so they try to reduce this distance so they can shrink their lenses. This is not an absolute advantage of the SLR, but the form factor currently lends itself to this characteristic, while mirrorless bodies are typically trying to optimize for something else. (of course, many mirrorless cameras can use adaptors to full-frame SLR lenses, and the results can be great image quality, but typically bad performance on autofocus.)
source: Spent several days with A7R, A7R2, Canon 6D, 5D3, 5DSr. Tested lenses Canon 11-24, 40mm, 24-70ii, 70-200, sony 70-200. Ultimately bought the 5DSr, due to more reliable functioning, ergonomics, lenses, battery life, etc. Despite genuinely wanting to shed the weight.
>> No, it is not, but, for a given price point, you will likely get faster AF with an SLR today than all but the most expensive mirrorless cameras. Especially with motion tracking. I know that there are some cameras that say they'll be faster, but having tested a bunch in the real world, I had a very hard time finding any that worked as well as SLRs in as wide a range of conditions.
Practically speaking, most non-enthusiasts don't turn over their cameras every two years. So there are plenty of DSLRs in the wild that mirrorless cameras can outperform. My Nikon V1 (hardly a new camera) can outperform a Canon 5D1 in AF speed in just about any situation, and rightly or wrongly, my V1 is considered to be a joke by many enthusiasts.
It's about as fast as my APS-C DSLRs from 2008 and 2010 -- and keep in mind, that a DSLR from 2008 is probably more than fast enough for most non-enthusiasts today. Newer mirrorless cameras can perform about as well as slightly older consumer DSLRs in terms of AF. And for most people, it's a fair compromise for the size differential.
>> Yes, though it is more complex than this.
No disagreement there, but you're speaking from the context of an enthusiast. From a bigger picture perspective, most buyers of consumer DSLRs (which are the majority of DSLRs being sold) aren't pixel peepers. They just want better photos of their kids and pets, etc. Most of them could be easily satisfied with an iPhone 7+ with portrait mode or a Sony RX100MK1.
The benefits you speak of are very true for a segment of photographers but I question whether they apply to the person who simply wants better quality images than they get from their smartphone or cheap point and shoot.
>a DSLR from 2008 is probably more than fast enough for most non-enthusiasts today
I was selling some older DSLR equipment recently and it made me think that someone wanting to learn photography with a "real" camera today can do quite well with older gear. It won't autofocus as well or have as good a sensor but it can be plenty good to learn on. Lenses of course don't degrade in value quite as much but there are plenty of lenses that enthusiasts may sniff at but are plenty good for a beginner.
Thank you! I wasn't aware of the various methods to autofocus. It makes sense that having a mirror to send light to a dedicated sensor would be better.
I remember an older camera my mother used to have used some sort of ultrasonic device for ranging -- I remember it would make a 'click' sound anytime it was focusing.
Lenses are a big factor too, at a certain point you are limited by the maximum resolution of the glass/sapphire/flourine whatever. High resolution / sensor area cameras run into this issue. larger lenses allow for larger sensors, which means lower demands on the glass. Typically, SLR lenses are nicer in the first place, or at least have higher end products available. For very high-end photography, you still see medium format cameras for this reason.