Mirrorless vs DSLR

Started Nov 9, 2013 | Discussions thread
jfriend00 Forum Pro • Posts: 11,573
Re: Mirrorless vs DSLR

stevo23 wrote:

Frame Speed Limitation - Yea, maybe there are limitations, but I'm not sure we've reached the peak. After all, how many times a second do the valves in your lawnmower cycle up and down? I suppose mirror-less has a limitation too, what is it? It would be interesting to know what the limit is now that we've eliminated mirrors. The Sony A7 is 5 fps, the OMD at 10? What was the fastest DSLR? 11? 12?

Here are things that can limit the frame speed:

1.  Mirror speed with auto-focus.  This is basically how fast can the mirror flip up, flip down, stabilize, give the camera a little time for you to see through the viewfinder and for AF to get some data.  Moving the mirror faster also requires more power (it's a physics thing with energy required to accelerate/decelerate the mass of the mirror).  This limitation obviously only applies to mirrored dSLRs.

2.  Sensor read-out.  How fast can the data from the entire sensor be readout while maintaining low read noise.

3.  Processing speed of the RAW data off the chip - converting it to digital and then making a RAW file and/or JPEG out of it.  Nikon's current generation of dSLRS (other than the D4) seem to be all limited to around 144MP/sec (D610, D800, D7100 - all 6fps at 24MP).  This implies there's either something in the sensor design or EXPEED 3 interface to the sensor that can only go this fast. We are hoping to see this speed increase with the new EXPEED 4 chip which claims it can process 24MP at 12fps.

4.  Card write speed.  How fast can images be written to your memory card.

5.  Buffer size.  If the read-out speed (2) is greater than the processing speed (3) or card write speed (4) which it usually is, then you can go faster if you have some place to buffer either the data off the chip or the converted images before being written to the memory card.

6.  Sensor initialize time.  Some sensors take some time to go from a live view mode to a single digital capture.  This "initialization" time is often seen as a momentary blackout of an EVF while taking a picture.

The Nikon 1 can do 14MP at 30fps so there are ways to go fast.  It doesn't have a very large buffer though so you get less than 2 sec at 30fps.

There seems to be some sort of practical limitation for dSLRS around 12fps.

Mirrorless can go much, much faster than the 12fps if their design is optimized for that (at least 30fps in the Nikon 1 already) where the upper bounds in the future are all processing related (not mechanical) so they can probably go much higher in the future with nothing more than semiconductor improvement if there's a market willing to pay for that.

I don't know enough about what determines read noise to know if there might be some limits with read-out speed in order to keep the read noise down.

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