Sony A900: A Closer Look at 24.6MP Resolution and Noise
by Wesley Fink on October 27, 2008 2:00 AM EST- Posted in
- Digital Camera
Full-Frame and 24.6MP Compared
The A900 is the first Sony to feature a full-frame DSLR. The sensor is approximately the size of a frame of 35mm film, which is 24x36mm, and 24.6MP is the highest resolution currently available in a full-frame camera.
Compared to most digital cameras today where the sensor size is closer to APS-C size, the lenses appearing to be 150% to 200% longer than the specified focal length. Other Sony DSLR cameras, like the A700, feature a 23.5x15.6mm sensor. 24.6MP is also double the sensor resolution of today's prosumer or advanced amateur models, which are generally around 12MP.
In the computer world smaller and smaller traces mean higher density, more transistors, and generally better and faster performance. However, the digital sensor is not a digital device. Instead, it is an analog device that gathers light and turns it into a digital signal. The reverse is true in sensors in that larger sensor size is almost always better, with everything else equal.
As you can see in the chart below, none of the APS-C sensors is even half of the area of a full-frame sensor. With a range of 28.1% to 42.4% of full-frame size, there is clearly a lot more information that can potentially be captured with a full-frame sensor.
| DSLR Sensor Comparison | ||||
| Camera | Effective Sensor Resolution | Sensor Dimensions and Area | % of Full-Frame | Sensor Density (MP/cm2) |
| Olympus E-520/E-3 | 10.0 | 13.5x18 2.43 cm2 |
28.10% | 4.0 |
| Canon XSi | 12.2 | 14.8x22.2 3.28 cm2 |
38.00% | 3.7 |
| Canon 50D | 15.1 | 14.9x22.3 3.32 cm2 |
38.40% | 4.5 |
| Pentax K20D | 14.6 | 15.6x23.4 3.65 cm2 |
42.20% | 4.0 |
| Sony A700, Nikon D300, Nikon D90 | 12.3 | 15x23,5 3.66 cm2 |
42.40% | 3.3 |
| Sony A350 | 14.2 | 15.8x23.6 3.72 cm2 |
42.90% | 3.8 |
| Nikon D700/Nikon D3 | 12.1 | 24x36 8.64 cm2 |
100% | 1.4 |
| Canon 5D | 12.7 | 24x36 8.64 cm2 |
100% | 1.5 |
| Canon 1Ds Mark III | 21.1 | 24x36 8.64 cm2 |
100% | 2.4 |
| Sony A900 | 24.6 | 24x35.9 8.61 cm2 |
100% | 2.9 |
The last column in the chart is the one that tells the story most accurately, however. Here the resolution of the sensor is divided by the sensor area to yield a sensor density. The lower the density, the larger the individual pixel size, and the more info that pixel can gather - all else being equal. There are a few surprises here, such as the Sony A350 being essentially the same density as the Canon XSi, and the new Canon 50D having the highest density of any current DSLR camera.
The last column does put into perspective the true potential of the full-frame sensor and sheds some light on the true meaning of Sony's 24.6MP A900 sensor. At 2.9MP per cm2 the A900 still exhibits a lower density and theoretically better high ISO performance than any current APS-C DSLR. This is very much at odds with the ridiculous claims many on the web are making about Sony going too high in resolution on the A900. In fact, sensor density on the A900 is lower than the 10MP Canon 40D, which is 3.1.
The point is that any issues the Sony may be found to have with noise are not the result of pixels being "too small". All else being equal the high ISO noise should be at least as good as an 8 to 10MP Canon sensor. Where the Sony does suffer is in comparison to sensor density of other full-frame sensors. In that metric the Sony has twice the pixels per cm2 of a Nikon D3/D700 and Canon 5D, and keeping up in high ISO performance with those cameras would be quite a feat.
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LTG - Monday, October 27, 2008 - link
Ok I'll eat a shoe then :).I know it's not unlikely that opinions can be similar looking at the same product (if a car is 0-60 in 30 seconds is any reviewer not going to say it's slow?).
But I just kept getting deja vu while reading it. Maybe they read your preview article.
Thanks for the article in any case, I did read it after all :).
TechLuster - Monday, October 27, 2008 - link
Wesley, I think the ISO 12800 and 25600 crops on page 3 are just repeats of the ISO 6400 crops (they don't seem to match what's in their respective full-size images).JarredWalton - Monday, October 27, 2008 - link
Sorry - that was my error when I put together the HTML code for the tables. Lots of copy/paste in there, and the linked images were correct but had the 6400 thumbnail still. (Had to change 64 to 128 and 256 after pasting.) The correct crops are now in place, which show that ISO 25600 on the D600 is about the same as the 6400 on the A900.Heidfirst - Monday, October 27, 2008 - link
Sony's JPEG engine still isn't the best, you really need to shoot RAW & convert (& again ACR still isn't very good with Sonys).http://www.photoclubalpha.com/2008/10/23/the-alpha...">http://www.photoclubalpha.com/2008/10/23/the-alpha... is worth a read.
twistedlogic - Monday, October 27, 2008 - link
We get your point, no need to triple post. Just playing, :).I really don't see the point of buying a $3000 body and then shooting in JPEG. Unless your doing studio work, newspaper work(overkill), or just snapshots.
I do like its low light capabilities coming close to the D3, I just hate Sony as a company for its lackluster customer service and shady business practices. Competition is good though.
Heidfirst - Monday, October 27, 2008 - link
Sony's JPEG engine still isn't the best, you really need to shoot RAW & convert (& again ACR still isn't very good with Sonys).http://www.photoclubalpha.com/2008/10/23/the-alpha...">http://www.photoclubalpha.com/2008/10/23/the-alpha... is worth a read.
Heidfirst - Monday, October 27, 2008 - link
Sony's JPEG engine still isn't the best, you really need to shoot RAW & convert (& again ACR still isn't very good with Sonys).http://www.photoclubalpha.com/2008/10/23/the-alpha...">http://www.photoclubalpha.com/2008/10/23/the-alpha... is worth a read.
araczynski - Monday, October 27, 2008 - link
is it my untrained eye or were all shots but the 2 ducks just fuzzy as all get go? is that a benefit of an oversensitive camera? or the photographer?Wesley Fink - Monday, October 27, 2008 - link
Please pixel-peep on the large image. The ducks themselves are sharp and a small crop from the larger image. With a full-frame and high resolution the depth of field is shallow and the background and foreground are less sharp in this image.The lens that was used for this photo also looks like it could benefit from a micro-adjust for focus, which is a feature available on the A900.
wheel - Monday, October 27, 2008 - link
Good to see the DSLR camera reviews on AT are slowly getting better :)But, can't you find something more interesting to test other than just the one picture of an SLI logo on a nVidia box? For instance, something that shows fine detail (in addition to flat areas of solid color)