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Continuous Drive mode

Apart from the smaller viewfinder the other (and possibly more important) difference between the A850 and A900 in terms of specification is a smaller buffer size, which results in a slower continuous shooting speed. In the tables below you'll find the results of our continuous shooting test with both cameras. All other speed parameters such as power on and power off times or image browsing are identical.

To test continuous mode the camera had the following settings: Manual Focus, Manual Exposure (1/640 sec, F2.0), ISO 200. Measurements were taken from audio recordings of the tests. Media used was a 16 GB Lexar Professional 600x UDMA CF card.

The tests carried out below measured the following results for JPEG and RAW:

  • Frame rate - Initial frame rate, this was always 3.0 fps (+/- 0.05 fps)
  • Number of frames - Number of frames in a burst (for JPEG there is no limit with a fast card)
  • Buffer full rate - Frame rate if shutter release held down after burst (buffer full)
  • Write complete - How long after the last shot before the CF lamp goes out

Burst of JPEG Large/Fine images

Timing
A850
A900
Frame rate 3.0 fps 5.0 fps
Number of frames no limit 175
Buffer full rate n/a n/a
Write complete n/a (immediate) n/a (immediate)

Burst of JPEG Large/X.Fine images

Timing
A850
A900
Frame rate 3.0 fps 5.0 fps
Number of frames no limit 125
Buffer full rate n/a n/a
Write complete n/a (immediate) n/a (immediate)

Burst of RAW+JPEG (Large/Fine) images

Timing
A850
A900
Frame rate 3.0 fps 5.0 fps
Number of frames 14 11
Buffer full rate 1.2 fps -
Write complete 8.5 sec 11 sec

Burst of RAW images

Timing
A850
A900
Frame rate 3.0 fps 5.0 fps
Number of frames 17 14
Buffer full rate 1.3 fps 1.1 fps
Write complete 9.0 sec 11 sec

As you can see at 3.0 frames per second at all image quality settings the A850 performs exactly as specified. This is two frames per second slower than the A900 but, as you would expect, due to the slower shooting speed the A850 captures more frames in a burst. When shooting in JPEG mode with a fast card you can actually shoot indefinitely (well, we stopped after 400 frames or so).

ISO Sensitivity / Noise levels

ISO equivalence on a digital camera is the ability to increase the sensitivity of the sensor. This works by turning up the "volume" (gain) on the sensor's signal amplifiers (remember the sensor is an analogue device). By amplifying the signal you also amplify the noise which becomes more visible at higher ISO's. Many modern cameras also employ noise reduction and / or sharpness reduction at higher sensitivities.

To measure noise levels we take a sequence of images of a GretagMacBeth ColorChecker chart (controlled artificial daylight lighting). The exposure is matched to the ISO (i.e. ISO 200, 1/200 sec for consistency of exposure between cameras). The image sequence is run through our own proprietary noise measurement tool (version 1.6 in this review). Click here for more information. Room temperature is approximately 22°C (~72°F), simulated daylight lighting.

Sony DSLR-A850 vs. Sony DSLR-A900

To test the Sony A850's image quality we photographed our standard studio scene and the ISO noise test charts. Whilst we could not find any discernible differences in terms of image quality to the A900 in the shots of the studio scene, in our noise test the A850 measured very slightly lower chroma noise levels than the A900 at almost all sensitivities. The difference is marginal but upon close inspection just about visible. See below for the results.

Sony tells us that the DSLR-A850 and A900 imaging pipelines are identical. We processed and inspected RAW files from both cameras and could only find marginal differences. We would therefore attribute these differences in the two cameras' noise reduction to sample and/or environmental variations.

  • Sony DSLR-A850: Sony 24-70mm mm F2.8 lens, Manual exposure, Manual WB,
    Default Parameters (Standard), High ISO NR (Normal - default), JPEG Large / Fine
     
  • Sony DSLR-A900: Sony 85 mm F1.4 lens, Manual exposure, Manual WB,
    Default Parameters (Standard), High ISO NR (Normal - default), JPEG Large / Fine
  Sony DSLR-A850 Sony DSLR-A900
ISO 100
ISO 200
ISO 400
ISO 800
ISO 1600
ISO 3200
ISO 6400

Noise graphs

The graphs below pretty much confirm what we see in the sample crops above. While black and gray luminance noise are (within margin of error) on the same level as the A900, chroma noise is slightly but consistenly lower on the A850.

  Sony DSLR-A850
Chroma
Black
Gray

Indicated ISO sensitivity is on the horizontal axis of this graph, standard deviation of luminosity on the vertical axis.

Below you can see crops from A850 and A900 RAW files that were captured (NR setting 'Normal') and processed using Iridient RAW Developer Version 1.8.6 with all sharpening and NR turned off. Any differences are absolutely marginal and almost certainly down to sample variation.

A850 ISO 3200 A900 ISO 3200
A850 ISO 6400 A900 ISO 6400
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