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mburns's Journal: Samsung Digital Camera Compared to my Yashica

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I am very interested in the question of what kind of digital camera can match the quality of a 35mm film camera. In the context of the new high definition digital post processing, how many pictures with a standard information content can I take with a camera in one second of open shutter?

In the end, I compute that my (consumer grade) Samsung ST65 has 2.6% of the performance of my Yashica. So what I ought to do in practice is to load the Yashica with slow film, attach the telephoto lens extender for most pictures, use a tripod and cable release, focus carefully, and use the best nondigital processing for prints.

The answer can only be had, I think, by comparing the shutter speeds of different digital sensors and frames of film on the same picture, using the same lens aperture area, at the same pixel count and signal to noise ratio. (The faster shutter speeds are better even for pictures with no motion, because then more total information can be fed to digital post processing from the same use of the camera. You can take the picture twice and combine the information in post processing when the shutter speed is doubled. Ignore this shutter speed rating if you will, but then there are no quality differences left between cameras in the modern context.)

Cameras not matching this test design, but having similar technology to what is tested, should then be expected to perform more or less well in proportion to the area of their apertures, and in proportion to their pixel counts. The pixel count applies again, as a reduction in exposure time due to the lower magnification that is needed for the picture.

The signal to noise ratios account twice as a factor for rating cameras; it takes post processing using four photographs to double the ratio. These ratios can be extrapolated as proportional to the linear size of a pixel for the different sensors. And films have a constant signal to noise ratio, but it is said to be twice as good for print films compared to slide films.

Larger total areas for the sensor format count inversely, because the exposure is slowed.

The effective sharpness of the lens aperture seems to not vary intrinsically with the size of the film frame or sensor.

Other references do not focus on the shutter speed comparison. They neglect the aperture area and magnification, and the signal to noise ratio is only accounted once as a factor. But all of this yields a systematic bias.

Refer to this authority:
http://www.clarkvision.com/articles/digital.signal.to.noise/

This page compares ISO 50 Velvia slide film to the digital sensor in the Canon 1D II camera. For the same signal to noise ratio as the film achieves, it rates the Canon sensor at ISO 1220. In shadows, the Velvia only rates at ISO 15. The advantage for the Canon is 24.4.

For the next factor, look at:
http://en.wikipedia.org/wiki/Velvia

This page implies an equivalent pixel size of 4.7 microns for the Velvia film, 160 lines per millimeter at 50% of full contrast. The Canon sensor has pixels that measure 8.2 microns. The Canon yields 8.2 million pixels with its APS-H format, and the Velvia film gives the equivalent of 39 million in the 35mm size. This fact applied twice, the rating here for the Canon is 0.0144.

http://en.wikipedia.org/wiki/Image_sensor_format

The APS-H format is 1.29 times smaller than the 35mm size, 1.66 in area. For the same aperture area and the same picture, the shutter speed is faster by this factor.

Since the signal to noise ratio is the same for the two cameras, we multiply the three factors to get the advantage for the Canon digital camera in the shutter speed for equivalent information with the same aperture area. This is a factor of 1.02! Compared to print film, the factor is 0.25, because the film's signal to noise ratio is doubled. Digital cameras compete better in the shadows of a picture.

http://www.cacreeks.com/films.htm

Holding the aperture areas constant, frames of film perform better with increasing area. Beautifully detailed photographs do not require longer shutter times. The shutter speeds do not increase sufficiently with ISO rating to beat the decreases in pixel number counted twice. ISO 800 film has half the bit rate of ISO 100.

When pixel sizes are unchanged, the ratings also improve with area for digital sensors. And increasing pixel numbers improves the ratings even for the same format size. Post processing can implement these tradeoffs differently, especially when multiple exposures are made.

So, comparing my Yashica with the slow slide film and a 59mm f1.7 lens to my Samsung ST65 with 14.2 million pixels, a crop factor of 5.6 and a 24.5mm f5.9 lens, my Samsung can only create 0.0258 of the same work of art as the Yashica in the same shutter speed. I calculate this by comparing the Samsung to the Canon camera.

This calculation is copied from the "units" command line calculator.

  You have:
  (24.5mm/5.9)^2/(59mm/1.7)^2* # the light available
  (5.6/1.29)^2* # the smaller image is brighter
  14200000^2/8200000^2* # recalibrated number of pixels
                                                                                                    # counted twice for information
                                                                                                    # and faster exposure
  (1.45micron/8.2micron)^2* # recalibrated adjustment for noise
                                                                                                    # done twice
  1.02 # calibration point for slide film
                                                                                                    # to digital camera
  You want:
          Definition: 0.025803348

--
Michael J, Burns

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Samsung Digital Camera Compared to my Yashica

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