User Tools

Site Tools


photo:sensor_readout_speed

sensor read out speed and silent shutter mode

Introduction

  • digital camera sensors currently read from one side to the opposite side and how long this takes is the sensor read out “speed” (actually, the transit time as the speed would refer to the scan rate or how many rows per second are read) and this can have major ramifications on many aspects of the camera's performance.
  • larger photosites take longer to read out
  • the higher the bit rate, the longer it takes to read out - hence some full frame cameras will reduce the bit depth of your raw files from 14 to 12 bit resulting in slightly lower dynamic range
  • more rows of photosites takes longer to read out
  • some cameras are designed to prolong photosite readout at higher ISOs (eg. Panasonic GH5 above ISO 800)
  • thus, readout transit time can be expected to be longer with larger sensors
  • eventually sensors will have a global readout whereby all the pixels are read simultaneously which will resolve this problem, and these are available in some cameras but these sensors are more complex and tend to have more image noise at present.

How can you test sensor read out speed?

What happens with slow sensor readout?

when shooting in electronic shutter mode

  • if the camera pans or the subject is moving quickly, the subject will become distorted depending upon the direction of movement but usually by creating slanted lines which is called rolling shutter and things get even worse when you shoot propeller blades!
  • when shooting in artificial light you may get banding due to the AC frequency of the light's output
    • this can be minimised by choosing a shutter speed which reduces it (slow shutter speeds increase the number of bands but reduces the intensity of them such that shutter speeds longer than the flicker rate should largely eradicate the banding), or turning on the “Anti-Flicker” mode which most modern digital cameras now have
  • when shooting with electronic flash, only part of the image may have flash exposure unless the shutter speed is slower than the readout speed
  • a slow readout speed may limit the burst rate and the fastest shutter speed in electronic shutter mode
  • a slow readout speed will also contribute to EVF blackout during burst mode
  • on these cameras, even using electronic first (or front) curtain shutter can cause issues such as slanting lines 1)

slow or no AF during burst shots

  • one aspect that is often not considered is on sensor AF performance - with mirrorless cameras or dSLRs in Live View mode, the on-sensor AF sensors have to wait until the full image has been read off the sensor before the AF can get another go at checking focus.

Comparison of sensor readout speeds

  • traditional film movie cameras with a rotating mechanical shutter have a rolling shutter of only 5ms for 24fps 180 degree shutter (equates to 1/200th sec)
  • most mechanical shutters in modern cameras have a flash sync of 1/250th sec or 4msec (ie. only at shutter speeds slower than this is the whole film or sensor area exposed to a burst of light)
    • Nikon D810 dSLR has flash sync of 1/320th sec or 3msecs but see here for oscilloscope demo which shows the transit time is actually shorter at around 2.5msec
    • motor-driven mechanical shutters are slower than spring actuated shutters and thus cameras such as the Panasonic GM series had flash syncs of only 1/50th sec

modern digital cameras with fast sensor read outs

  • Arri Alexa Mini is 3msec 2)
    • around 6-7msec or 1/152nd sec; fastest shutter 1/32,000th sec; fastest burst rate
    • scan rate appears to 640,000 rows/sec 3)
    • this is the only full frame camera with a stacked sensor design to allow such a fast sensor read out
  • Canon C300 II is 6msec 4)

modern cameras with medium sensor read out speeds and minimal rolling shutter

  • Sony FS7 is 14msec 5)
  • Fujifilm XT-3 - readout is “1.5x faster than previous models” and can shoot at 20fps and it maintains Live View (30fps in 1.25x crop mode)
  • Panasonic GH5 4K video stills camera has 20msec or 1/50th sec (perhaps 13msec6) ) at ISO 800 and lower or at 6K, and 40msec or 1/25th at higher ISO 7) and fastest burst rates are 12fps (AF-S) and 9fps (C-AF), but only 7fps for Live View while electronic shutter goes to 1/16,000th sec
    • around 20msec or 1/50th sec according to flash sync (NB some sources on web quote 10msec but this is not what I get); fastest shutter 1/32,000th sec; fastest burst rate 60fps; banding in artificial light at shutter speeds faster than 1/200th sec;
  • Fuji XT-2 around 21msec 8)
  • Leica SL around 22msec 9)

modern cameras with slow sensor read outs and thus problematic rolling shutter

photo/sensor_readout_speed.txt · Last modified: 2019/07/06 21:30 by gary1