The dawn of digital mirrorless cameras

I think its pretty exciting times right now for photography.

Digital mirrorless has three big challenges over digital single lens reflex:

- The EVF (electronic view finder) needs to have no noticeable delay, sufficient resolution, and sufficient quality. The best available EVFs (Olympus OM-D, Fuji X, various Sony) seem to have solved this problem suffiently, though future improvements are still possible.

- With mirrorless, we have a much shorter distance between optics and sensor. Current digital sensors cannot handle light falling in at an angle very well. The only camera that can handle this relatively well right now is the Leica M, but even that one is far from perfect. All other companies have to instead create optics that basically work like those made for DSLRs,

- With mirrorless, there is no space left for a specialized separate AF sensor. This leads to inferior autofocus performance. There are a couple of solutions around for this:

A) Contrast Autofocus, which needs no calibration, but also doesnt have a clue about the direction the focus has to be moved, leading to "pumping" (moving backward and forward). Olympus had optimized this with autofocus frequencies (recomputation of the focus) of up to 240 Hz.

B) Phase Autofocus on the Sensor. Like a DSLR Autofocus Sensor, the image sensor of the Mirrorless can have phase detect autofocus, which measures the angles light are falling in and thus detects in what direction to move the optics and by how much to move it. This however is done by masking light falling from certain angles on the sensor. That means only a couple of pixels do the phase detection, and the phase detection is much weaker than for DSLRs, i.e. doesnt work in low light.

C) Combined Contrast and Phase Autofocus. This tries to combine the advantages of contrast (needs no caliration) and phase (knows the direction to move) autofocus. Surprisingly few companies have tried this (AFAICS only Nikon with their Nikon 1 system, and Sony in some of their cameras)

D) Dualpixel. This is currently only available for some Canon DSLRs (the 70D was the first one). This is used when the mirror is locked up (socalled lifeview mode) and the DSLR acts like a Mirrorless (with the backside monitor as EVF). Necessary for example for video.

E) Bokeh Evaluation. Panasonic recently came out with the idea of evaluating the quality of out of focus areas to compute the focus. Kind of improving the ordinary contrast focus with a knowledge about how far to move the focus, just like with phase detect autofocus. I dont know if it is also possible to know into which direction the focus has to be moved. This only works with one camera right now and only with certain Panasonic lenses. However, first reports state it works really well.

I think sooner or later these challenges will be solved and DSLRs will be replaced, even for people who shoot action in low light.



What are the advantages of digital mirrorless cameras over DSLRs ?

- Smaller size, lower weight.

- Reduced cost. The optical system for the OVF of DSLRs is actually an extremely complex thing and needs precise alignment.

- Cheaper and higher quality optics for wide angles. Unless you are forced to avoid too steep angles, at which point to have to make wide angles work just like for DSLRs (i.e. socalled "retrofocus" constructions)

- Better viewfinder. Not only can the viewfinder be intelligent, displaying all kinds of information such as magnification of the focus point or realtime histograms, it can also be large and bright, even if the sensor itself is small. For OVFs this is only possible in dependence of the sensor size.



Though will they ? Mirrorless also have two huge problems:

- Increased requirement for power. Either you have to accept larger batteries, or you have to accept less photographs per battery charge.

- Increased heat at the sensor. Because the sensor has to run nonstop for the EVF, over time it might heat up a lot, which results in increased noise. There are already video cameras out there that use active cooling of the sensor, however this doesnt really lower the requirements for power either.



I wonder how the world will look like in 5 or 10 years. Will DSLRs indeed vanish completely ?

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