Why don't SLTs allow the mirror to flip up?

Started May 19, 2012 | Discussions thread
McLuhan
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Re: Why don't SLTs allow the mirror to flip up?
In reply to IcyVeins, May 20, 2012

Well, high iso performance is definitely bent to the amount of light that the sensor receive(strength of the original signal) along with other factors(signal/noise ratio(SNR) for a single pixel due to technological improvement, the density/size of pixel, whether the photo suffer from heavy underexposure which make darker area more noisy,even the noise-reduction optimization and output engine for JPG). Appearently current SLT technology has to compromise 1/3 EV of light which reduces the strength of the signal, which has an negative impact on the RAW file SNR once above iso 800, reflected in DPR RAW comparison of A77/D3200. That's partially why sony puts the 16.1 MP sensor from nex-5n to A57 to get better high iso performance.

However, it is nevertheless more unacceptable to lose faster autofocusing system in dim light event/sport shooting by abandon the phase detection and swith to slower contrast AF(at least for current sony installation, M4/3 does somewhat better at the moment) because the genre you are shooting naturally requires accurate responsive AF performance and higher shutter speed(which pushes the iso up usually). So if you have to choose between a clearer shoot and an out-of-focused shoot, I bet you may still like the latter. If the picture is noisy, post process the image and reduce the size and you get it. It is a lot harder to put it right if the picture is out-focused due to either slow focusing system or motion blur due to unsafe shutter speed.

Currently Sony may still have difficulty in making super quick CDAF esp in dim light or integrating PDAF on main imaging sensor without affecting the imaging process just like the rest of the major players(well, interesting Nikon 1 system for making hybrid focusing system possible on mirrorless) So the translucent mirror still needs to stand in the way. Or the whole point of SLT technology will be lost. Until either super quick CDAF or main sensor PDAF technology is commercialized, SLT will be the way, I am afraid.

If manual focusing is suitable for your genre, I guess it would be shooting still objects, which does not require high shutter speed anymore, then just keep the iso/shutter speed down and use a tripod, or use multi-frame stacking with resonable iso to hand hold the camera(still very bad behavior for people trying to expect wonderful result without using base iso and a tripod but everyone just does so when traveling for leisure even they have their tripod on their shoulder, just laziness, lol, in museum where photography is permitted yet tripod/flash is prohibited, iso 800 is still your good choice). The a77 RAW under iso 100 is nearly free from SNR loss due to the translucent mirror, you actually get a free 1/3 EV stop ND filter for free...

Currently I wish they can somehow create a way which bounce the 1/3 EV light back to the main imaging sensor after the PDAF sensor has tasted it to minimize the SNR degradtion due to Lowered signal strength, I don't know whether it is possible, the mechinical structure, however, may be even more complex than SLR, just my personal guess. Still, use RAW and post processing at the moment when you need to push it near or even above 3200, or a tripod when shutter speed is not a problem and you never even need to think about SNR issue when using base iso. Or...swith to the upcoming A99, as this possible 24 MP FF has bigger pixel size and looser pixel density will help with the high iso SNR using existing technology, but to complicate the issue is not the SLT way.

 McLuhan's gear list:McLuhan's gear list
Sony SLT-A77 Sigma 30mm F1.4 EX DC HSM Samyang 8mm F3.5 Aspherical IF MC Fisheye Samyang 85mm F1.4 Aspherical IF Tamron SP 70-300mm F/4-5.6 Di USD +1 more
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