You need a much higher PPI than 500. These displays are tiny. Epson have just announced a sub one megapixel display (1024x768, only one quarter of the pixels found on a retina iPad display) to equal Sonys top of the line OLED viewfinder. It's diagonal measurement is 0.48 inch. That 2666 PPI. We need much more than that to make it lifelike.
Maybe at some point when the technology has been perfected, offers considerably dynamic range, and reaches around 500DPI such that the visual acuity of someone with 20/10 vision can't see any pixels...then they might be ready to replace OVFs en-masse.ok... but i am typing this on an ipad with a 264ppi density, the Galaxy X IV phone is 440, 500 isn't too far in the future
Are 1200 or 2600 ppi EVF's in use in consumer-grade cameras today? And it seems my calculation was wrong before for the required PPI. We can derive the necessary PPI using a little math, though... If I use the visual acuity for a person with 20/10 vision (which for most people with corrective lenses these days is the case, including glasses, hard contact lenses, and for the most part soft contact lenses), we have 0.7 arc seconds, or 1/86th of a degree (normal 20/20 vision is about 1 arc second, or 1/60th of a degree). Turning degrees into a scalar distance and computing for resolving power:
tan(A) = opp/adj
tan(deg) = size_of_pixel/distance_to_screen
tan(1/86) * distance_to_screen = size_of_pixel
If we assume a one inch distance from the eye to the EVF, resolving power of the eye (the smallest resolvable detail in inches) would be:
P = tan(1/86) * 1" = 0.0002"
Or in terms of pixels per inch:
1"/P = 1"/0.0002" = 5000PPI
That assumes a 1" viewing distance, or a fairly standard 25mm. There are cameras with smaller viewfinder eye relief than that...some as small as 10-11mm. To account for that:
PPI = 1"/(P*D)
1"/(0.0002" * 0.43") = 11,268PPI
A 2600ppi display would definitely be getting there for 20/20 vision and a 1" relief, but if my calculations above are correct...for 20/10 vision we would really need 5000ppi (O_o...sorry, I guess I dropped a zero somewhere before) and a 1" relief. If viewfinder eye relief is smaller than 1", then for 20/10 vision we might need as high as 12,000PPI!!! (Is that even possible? Each RGB pixel would have to be 2.1 microns in size, each subpixel element would be 0.7 microns, or 700nm, in size...at that size we are getting down to the wavelength of red light!!)
Assuming there are consumer-grade EVF's with 1200ppi or even 2666ppi, what are the refresh rates like? Color depth? I'd read several things about Sony EVF's clipping blacks or producing poor tonal range in the shadows. As far as I knew, that was Sony's latest and greatest EVF, but I could be wrong. That just demonstrates some of the DR problems I'm worried about though...you simply don't have ANY issues like that with an OVF. About the only issue I can think of with an OVF is the potential for blinding yourself in one eye if you look at the sun through the lens...but, well, that's operator error. ;P
Pixel density (and I mean full RGB pixel density, so 5000ppi would be the lower end limit as far as I am concerned) is only one factor. You still need to improve the dynamic range and color depth of such displays, improve their refresh rate, etc.
There are also other caveats that come into play with EVF's that have nothing to do with the design of the viewfinder screen. When it comes to low-light photography, the quality of the rendered image will drop, as you have to use the image sensor, with all of its limitations and flaws, to record the light coming through the lens. You'll experience increasing noise and banding as sensitivity cranks up to compensate for lower light. With an optical viewfinder, your eyes will do the adjusting for low light after a short while, and are far more adept at seeing in low light than an electronic image sensor could ever hope to be. I'd never be able to do night sky photography with an EVF...even with the large LCD screen on my 7D, I can't see anything except the brightest stars, and when cranking up ISO you still don't see any more as noise starts to take over and drowns everything out. I have to let my eyes adjust to the dark, but when they do, I can see hundreds of stars through the optical viewfinder, frame and focus my shots, etc.
I could probably keep going...the limitations of EVF's vs. an optical viewfinder are considerable, and many of them are not just due to the design of the viewfinder screen itself, some are due to the limitations in sensor sensitivity. The limitations of the sensor extend into other areas of mirrorless technology...for example low-light AF. FP-PDAF pixels in mirrorless sensors are moderately capable in good light, but they are part of the sensor. Image sensors are orders of magnitude less sensitive to light than specially designed phase detection AF sensors. The kind of low-light AF capabilities we enjoy today with -2EV and in some cases even -3EV AF without an AF assist light are at the very least years ahead of FP-PDAF, and given the nature of image sensors, which must be primarily tuned for a different purpose (capturing quality images), I wonder if FP-PDAF will ever be quite as good as a dedicated AF unit in a DSLR.
Sure, I think progress is good, and I think the diversification of options is also good. However, mirrorless technology is premature for widespread use and replacement of DSLR tech. I'd say radically premature for use in professional grade mirrorless cameras that could potentially replace DSLRs...at least at current DSLR prices (one could always spend $50 grand on some kind of top of the line mirrorless with all the bells and whistles if they really want something mirrorless that will service modern professional photography needs, assuming such an offering is made available.)