That app is, indeed, for Canon EOS DSLRs-- the EOS M is pointedly non compatible. But it's the Live view that's displayed, not the viewfinder.
I use my iPad to stream Amazon Prime video to my AppleTV-- technically I could use my Macs to watch the same streams, but they wouldn't be HD. This proved a welcome surprise, as many of the other services like Macs-- but demand additional payment for streaming to the iPad.
The shutter was a mirror. At the time did they have a shutter behind the mirror, or use the mirror as the shutter?
Wikipedia's article on the history of SLR camera
Early 35 mm SLR cameras had similar functionality to larger models, with a waist-level ground-glass viewfinder and a mirror which remained in the taking position—blacking out the viewfinder—after an exposure, returning when the film was wound on. Innovations which transformed the SLR were the pentaprism eye-level viewfinder and the instant-return mirror—the mirror flipped briefly up during exposure, immediately returning to the viewfinding position.
Now, when the viewfinder blacks out, that means that the mirror has been raised to take a picture. If the mirror did not return instantly, or even worse, did not return until the film was rewound, this would mean that the shutter would be the only thing keeping the film from being overexposed. To solve this problem You could add a film door, and use a leaf shutter, but this complicates matters.
Mirrors are heavy. Shutters are light enough to be moved in small fractions of a second.
In a twin lens reflex camera, the mirror reflects the light entering the viewfinder lens, to the viewfinder screen at the top of the camera. The mirror doesn't need to move. because there's another lens below for the film.
In 1959 Nikkon called their fast versions of 3.5 cm, 5 cm, and 10.5 cm lenses the three sacred treasures. Tastes have changed.
You are happy with an f2.8 lens? Seriously? If they could make a f1.8 or faster lens without making it insanely big, they would. It's a compromise and not necessary with the better sensors/smaller bodies.
Sigma has recently released a f 1.8 zoom lens. It's merely the 17-35mm range, though. f2.8 is useful because many of the existing bodies have focal points that are extra precise at f 2.8 or faster. So if a photographer uses the existing "holy trinities", that functionality is never lost. As for faster apertures,
Nikon does have a 200 mm f/2.0 that is big, heavy, and expensive. It once produced a 300 mm f2.0 that had those three qualities in spades. Apparently, they were quite useful in cinematography, and many of them were converted to different mounts.
The problem with long, ultrafast lenses is math.
Want a f2.0 85mm lens?The effective aperture must have a diameter of 42.5mm.
Want a f2.0 300mm lens? The effective aperture must have a diameter of 150 mm.
And of course, the front element must be large enough to let that much light through-- the afforementioned 300 mm lens has a 160mm front thread-- big, and heavy. (Photographers have slightly different expectations about the 400mm 2.8 lens, which requires a similarly sized effective aperture.)
Someone asked why the 300mm/2.8 lens was significant. The reason for it is the 300mm/2.8 and the 70-200mm/2.8 lenses are pretty much lenses that set the bar or standard for optical clarity, so to speak, for both the Nikon and Canon camps.
According to DXOMark, the top scoring lenses for both the Canon 1Dx and the Nikon 810E are both made by Carl Zeiss-- e.g Carl Zeiss Apo Planar T* Otus 85mm F14 ZF.2.
The top scoring Canon is, indeed, the 2.8 300mm. But Nikon's best lens is the 2.0 200mm. Now, it has a 2.8 400mm and 2.8 300mm that are almost as good-- but it has a number of portrait lenses up there as well.
(The 70-200mm zooms are almost second rate in comparison. Besides, people have accused the Nikkor of being slightly short.)
If you're a sports photographer, I suppose I understand why you might judge a lens manufacturer on the basis of its 300mm f 2.8. But that's not necessarily the most exquisitely designed lens in the lineup.
Ah, ok. As for portraits-- the 200mm f/2 is said to be commonly used for head shots.
I own a D7000, the D90's successor. It has an optical viewfinder, and a mirror. When I press the shutter button, the mirror flips up, blanking out the viewfinder, the shutter is tripped for a fraction of a second, and then the mirror flips down again, letting me see through the viewfinder again. The viewfinder is a purely optical device, relying on a pentaprism to show an upright version of what the film or sensor will be exposed to.
After turning off the camera, and even after removing the batteries, the viewfinder will still let me look through the lens-- not a great advantage, mind you, but it is a consequence of the technology, It does save on batteries, though.
In a mirrorless camera, the viewfinder is a tiny lCD display, showing what the camera sensor is recording. The viewfinder will not go dark when the shutter is pressed, and it will even show the effects of in camera electronic filters. I don't have such a camera, but I would imagine that the viewfinder would be blank if I turned off the camera and removed the batteries.
You can make a smaller, lighter camera, if you ditch the flipping mirror for a screen on the back or a electronic viewfinder. An electronic viewfinder is even useful for recording video-- on my D7000, the optical viewfinder is completely blanked out during video mode, as otherwise the mirror would get in the way.
Why would a 300 mm lens be critical to Samsung's success? It's too long for portraits, especially on a APS-C sensor.
IIRC, samsung cameras don't have mirrors, and therefore are not DSLRs.
One more, thing, the mac uses compression to avoid swapping-- CPU cycles are cheap, IO cycles are expensive.
see this ars technica article for an explanation-- yellow might actually mean--"compressing" and red might actually mean "swapping," though In any event, using 7.99 GB out of 8.0 GB (my situation), is perfectly normal.
Oh No, I'm using 9.5 MB of swap! Whatever shall I do?
On the Mac, free ram is wasted ram. If it's not otherwise assigned, it usually gets used as cache.
Apple keeps changing the activity monitor around, but in the latest-- Yosemite, there's a little plot that shows "Memory Pressure". If it's green, don't worry about it. If it's yellow, you are actually running out of memory, and might want to quit some processes. If it's red, the machine is swapping to disk, and if you are still using spinning rust, this can mean a massive slowdown.
Seriously, that's how it works
You have 4K Blurays? I have quite a few, and I've not encountered a single disc that offers more than 1080p.
for a couple 3.5" hard drives,
2.5 inch SSDs are plentiful.
Also a real desktop can get much faster CPUs than an iMac.
From what I've heard, i7-4790k is a real screamer... It really does depend on whether you can use more than 4 cores.