When we published the Sony A900 Full-Frame: Hands-On Preview several weeks ago, the excitement about the world's highest resolution full-frame DSLR was evident in every photography forum you could find on the web. It was not as if the new Sony flagship model was a surprise, because the specifications had been detailed in broad strokes in the year since Sony announced the development of a 24.6MP 24x36mm full-frame sensor. The launch just filled in the blanks with details and answered questions like whether Sony could get their body Image Stabilization to work on a full-frame. The answer was yes they could.

Just as quickly everyone began wondering whether that huge 24.6MP sensor would be any good at low-light high ISO photography, which had risen to the full-frame forefront with the Nikon D3 and D700. The Nikon's are half the 24.6 MP resolution, but with a standard range to ISO 6400 and extensions to a staggering 25600. Everyone wondered whether the Sony A900 could compete with Nikon's full-frame, designed for "available darkness" as some liked to tease.

Fortunately, it was not a long wait until we could buy a Sony A900, and with a production model in hand some of the questions can begin to be explored. It has already been clearly established in every review that the Sony A900 is the highest resolution full-frame that you can buy - even out-resolving the $8000 Canon 1DS Mark III with a 21.6MP sensor. That resolution performance is amazing when you consider the 24.6MP Sony A900 is just $3000, and it gives studio photographers a new choice - since they normally work in the A900 sweet range, which is broadly acknowledged to be ISO 100-800.

What is not as clear is how suitable the Sony A900 is for action photographers. The A900 features dual Sony BIONZ processors and it features a real 5 FPS speed, which most consider remarkably fast for a full-frame DSLR with 24.6MP resolution. The A900 also features the first body-integrated IS system in a full-frame camera. Sony SteadyShot is said to be capable of improving hand-held shooting by 2 to 4 stops depending on the lens. Most important is that SteadyShot is available and works with any lens that you mount on the Sony A900. This is particularly important in very large aperture lenses, which are often prohibitively expensive for optical OS since such huge elements have to be compensated.

With 5 FPS burst speed and always available IS, the A900 on the surface appears a good choice for action and sports. However, a sensor that is too noisy at high ISO could limit the usefulness of the A900 in action shooting.

That is the reason for these tests - to look more closely at noise of the A900 sensor. Noise will be compared to the Nikon D700 and Canon 5D, which are the only full-frame DSLRs you can currently buy other than the A900. Canon has announced the 5D Mark II but that camera is not yet shipping and is not expected in the market until late November.

With the announcement of the A900 Sony also announced an update to firmware Version 4 for the 12.3MP Sony A700 that incorporates all they learned in developing the A900. Our final noise comparison will be the Sony A700 to the full-frame A900.

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.

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.

Sony A900 vs. Nikon D700

Before we begin our noise comparisons we asked the question, "How do you actually compare a 12MP full-frame sensor to a 24.6MP full-frame sensor?" This question is important since the same image shot with the A900 from the same position with the same lens will contain twice as many pixels in a given picture area than an image shot with a 12MP sensor. This was a moot point when image resolution went from 8 to 10MP or 10 to 12MP, but the Sony sensor is double the resolution of competing full-frame cameras and the question becomes more important.

Any who have printed large images from a digital file will immediately understand our question. It is very clear that a larger noisy image when printed smaller often looks like it has very low noise. This is why we often say noise would be good enough for small prints but not for big enlargements. The noise becomes more apparent as the image size is increased.

Our tests didn't land on either side of this issue. Instead the decision was made to provide both same pixel size crops and 0.5x crops; the latter represent the same area of the image as the 12mp cameras in each capture. The same pixel crops are 150x250 actual pixels captured from both images. The 0.5x crops are twice the number of pixels in a 212x353 capture that has been adjusted from the standard 350dpi to 248dpi so the crop you are viewing is approximately the same size as the crop from the 12MP camera. That is the reason for the two crops for the Sony A900. The regular view is a pixel-level 150x250 crop, while the 0.5x is a double the pixels crop adjusted for the same image area as the 12MP crop. We will leave it to you to decide which is the more relevant of the two crops for the A900.

ISO Comparison - Sony A900 vs. Nikon D700 vs. Sony A900 0.5x
ISO	Sony A900	Nikon D700	0.5x Sony A900
100
200
400
800
1600
3200
6400
12800
25600
Click on any of the above image crops for the full image. Note: Full size images are between 3.2MB and 10.4MB!

The Nikon D700, which was introduced just a couple of months ago, uses the same full frame sensor used by Nikon in the $5000 D3. The incredibly wide ISO sensitivity range to an expanded 25600 is also maintained, but the price has been reduced to just below $3000. The Nikon D700 also features one of the fastest burst rates in the full-frame class at 5 FPS, and that can be extended to 8 FPS with the battery grip powered by the Nikon Pro battery or six AA cells.

Looking at the 0.5x samples for the A900 it is hard to escape the fact that looking at noise alone the Nikon D700 is about two stops better than the A900 in high ISO performance. The D700 ISO 6400 output is very similar in noise to the A900 at ISO 1600. Similarly, the A900 ISO 3200 and 6400 compare to the D700 ISO 12800 and 25600. Noise is only part of the A900 story, however. If you look closely at the amount of detail in the A900 crops and pixel peep the full images, you will see the A900 captures more detail than the D700 - even at high ISOs when noise begins to intrude in the A900 images.

The high ISO performance of the Nikon D700/D3 sensor, as everyone already knows, is without equal. That should not come as a surprise since the pixel density of the Sony A900 is double the Nikon D700. On the other hand, nothing currently on the market really comes close to the resolution and detail captured by the A900 sensor. Those who thought 24.6MP would make little difference are just wrong, as the increase in captured detail is very clear.

Sony A900 Full Frame vs. Canon 5D

The Canon 5D was the first "popular" priced full-frame DSLR introduced at the $3500 price for body only about three years ago. It is interesting that during the last couple of months Nikon and now Sony also offer $3000 or less full-frame cameras. The Canon 5D features a 12.8MP sensor, which is about half the resolution of the Sony A900 24.6MP sensor.

Again, the Canon 5D is compared to both same pixel size crops, and 0.5x crops which represent the same area of the image in each capture. The same pixel crops are 150x250 actual pixels captured from both images. The 0.5x crops are twice the number of pixels in a 212x353 capture that has been adjusted from the standard 350dpi to 248dpi so the crop you are viewing is approximately the same size as the crop from the 12.8MP camera.

ISO Comparison - Sony A900 vs. Canon 5D vs. Sony A900 0.5x
ISO	Sony A900	Canon 5D	0.5x Sony A900
100
200
400
800
1600
3200
6400
Click on any of the above image crops for the full image. Note: Full size images are between 4.1MB and 10.4MB!

It is very interesting that the Canon 5D internal processing is just as sharp at ISO 100-400 as the Sony A900. Beginning at ISO 800, however, you can clearly see that noise is being minimized by increasingly softening the image. By ISO 3200 the difference between noise-reduction approaches of the Sony and Canon are very obvious. The A900 output is sharper and much higher resolution. It also extends to ISO 6400 where the three year old Canon 5D stops at ISO 3200. However, in fairness the noise or grain on the A900 is so obtrusive at ISO 6400 that it hardly matters, except for small prints.

It should be clear by now that the A900 shows three distinct noise ranges in these tests. At ISO 100-400 nothing comes close to the combination of the incredible detail combined with low noise. ISO 800-1600 output is also excellent, though noise is certainly starting to impact the captured image. We would not hesitate to shoot anything up to ISO 1600. However, at ISO 3200 and 6400 noise has become a problem. Those settings are good for capturing something when you have no choice as the resolution detail is still pretty amazing, but noise is degrading the image to the point where images are only useful for smaller prints.

The announced (but not yet shipping) Canon 5D Mark II will be a very interesting camera to compare to the Sony A900 when it finally starts shipping in late November. A more detailed comparison of the Sony A900, Canon 5D Mark II, and Nikon D700/D3 is planned when the Canon full-frame update is available.

Sony A900 Full Frame vs. Sony A700 APS-C

The Sony A700 uses the same 12.3MP sensor featured in the Nikon D300, but it was not as well received as the D300 when it was introduced. The main complaint was the poor quality of Sony's built-in JPEG processing and the fact that noise reduction (NR) could not be turned off in RAW mode. Sony has addressed the early criticisms with several firmware upgrades that have finally culminated in firmware Version 4 which was released at the same time as the A900. With firmware v4 the Sony JPEG processing is finally competitive with other top cameras, noise algorithms are more competitive, and you can finally adjust or turn off NR in both RAW and JPEG modes. Many consider output of the Sony A700 with v4 firmware finally to be competitive with the well-regarded Nikon D300.

Since high ISO noise is now much better controlled in JPEG mode on the v4 A700, it should be interesting to compare noise over the range of ISO adjustments to the Sony A900 full-frame. Even though the A700 is an APS-C size sensor, resolution at 12.3MP is about the same as the Nikon D700 and the Canon 5D. The actual view of a 150x250 pixel crop will be about the same as the Nikon D700 or Canon 5D.

Once again, we compare the Sony A700 to both same pixel size crops, and 0.5x crops that represent the same area of the image in each capture. The same pixel crops are 150x250 actual pixels captured from both images. The 0.5x crops are TWICE the number of pixels in a 212x353 capture which has been adjusted from the standard 350dpi to 248dpi so the crop you are viewing is approximately the same size as the crop from the 12.3MP camera.

ISO Comparison - Sony A900 vs. Sony A700 vs. Sony A900 0.5x
ISO	Sony A900	Sony A700	0.5x Sony A900
100
200
400
800
1600
3200
6400
Click on any of the above image crops for the full image. Note: Full size images are between 6.6MB and 11.4MB!

The resolution of the A900 sensor is astounding, but there is no escaping that it is also an inherently noisy sensor at high ISO. This is especially evident in comparing the A900 noise tests to the 12.3MP APS-C sensor used in the year old A700. This is the same sensor used in the Nikon D300 (and the new Nikon D90), and our A700 test shots were with a camera using the latest v4 firmware.

If we pixel peep the ISO 1600 output of the A900 is about as noisy as the ISO 6400 output of the A700, which came as quite a surprise. Since sensor density is a bit lower on the 24.6MP A900 than the 12.3 MP A700 this was not expected. If the comparison is made to 0.5x A900 crops the noise advantage for the A700 is still more than a stop. The only conclusion is that the A900 sensor is inherently noisier than the latest refinements of the A700, or that Sony can lower noise in the A900 further with firmware/software updates. It is also interesting that the Sony A900 tungsten color balance is much warmer than the tungsten balance of the A700.

Please do not misunderstand these conclusions in looking at pixel-level crops from JPEG test images. There could be other variables at play. However, Sony has trumpeted the v4 firmware for the A700 as incorporating all they learned in developing the A900. That leads to the assumption that processing should be very similar between these two Sony cameras. Provided that is the case the A900 sensor is noisier at high ISO values than the A700 sensor by at least one stop once the resolution differences are accounted for and two stops in pixel peeping.

If you look closely at the A900 images, there is also no escaping the incredible detail captured with the 24.6 MP sensor. Even with increased noise at higher ISO the captured detail is stunning.

Looking Forward

The Sony A900 is a truly revolutionary camera. As the highest resolution full-frame DSLR you can currently buy it distinguishes itself with astonishing resolution. As discussed in our preview it is also the first full-frame with body-integrated Image Stabilization (add 2 to 4 stops to hand held shooting) and the viewfinder is the best, brightest, sharpest that we have ever seen in a DSLR - or perhaps in any camera.

It is important to keep those huge pluses in perspective because image noise at extended ISOs, while just one factor in the total image quality equation, is definitely not a strength of the A900. Compared to the Nikon D700, noise in the A900 is about two stops worse. That means the D700 at ISO 6400 exhibits about the same noise as the A900 at ISO 1600. In the case of the D700 that applies to both the actual pixel comparisons as well as the double pixel samples downsized to reflect the same image view in both crops. Despite the huge noise advantage, the D700 outputs nothing near the resolution and detail of the A900, which should not come as a surprise.

The Canon 5D is now three years old, but noise control is still about a stop or two better than the A900. However, we noticed for the first time how much Canon softens images at higher ISOs in an effort to control noise. Looking at the pixel level, high ISO Canon images are extremely soft at higher ISO settings, though they are quite sharp in the lower ISOs most sites use in evaluating the 5D output. Taken in total the A900 is again a clear leader in detail compared to the 5D. The 5D has perhaps a one stop advantage in noise when the A900 and 5D are equalized for sharpness.

Finally we come to the biggest surprise of all, which is our comparison of the A900 noise to the APS-C sensor in the A700. This is the same sensor used in the Nikon D300 and the most recent Nikon D90. When the A700 was first released, some in the press trashed it because of its heavy-handed noise reduction techniques. Sony has worked hard to answer those complaints, and most users were pleased with the v3 firmware fixes. With the release of the A900 Sony also released a v4 firmware for the A700, which allows complete disabling of NR plus a range of adjustments in noise reduction. V4 incorporates in the A700 all Sony had learned in developing the A900.

With sensor density of the A900 less than the A900 (2.9 vs. 3.3) we really thought the A900 would shine compared to the A700. In fact the A700 is about two stops better in noise control looking at actual pixel crops and one to two stops better looking at crops equalized for image view (A900 down-sampled to equivalent 12MP). This performance difference is a complete surprise and it is either good news or bad news depending on your perspective. The bad news version is that the A900 sensor is inherently a high-noise sensor and the high ISO noise performance is as good as we will see. The good news version is that the A900 was just released and, like the A700, Sony will continue to improve the noise performance in future firmware/software releases. We certainly saw that in the A700, but we did have the Nikon D300 as the constant reminder of what that sensor was capable of.

Our hands-on test of the A900 reveals a mixed bag of performance. At Lower ISOs, 100-400, nothing on the market comes close to the Sony. A little is given up at 800-1600 and if that were as bad as it got the A900 would be something of a Holy Grail. However, noise at ISO 3200 and 6400 are truly not competitive. High detail is still there but it is seriously marred by high noise. In the end our expectation is that professionals will stick to ISO 100-400 for the highest resolution shots you can get from a camera in this class. Action shooters and the rest of us will also be happy with ISO 800 and 1600. However, dial in above ISO 1600 only if you will be happy with stunning detail in smaller prints.

The last page contains a few sample images taken in the couple of weeks the Sony A900 has been in the office. As always, we chose the images to show both the strengths and weaknesses of the camera we are testing. The A900 is capable of capturing amazing detail and if you do a lot of pixel-peeping on these images you will see exactly what we mean. There are also a couple of shots that show the potential impact of poor noise performance at higher ISO, which is not always as bad as it sounds.

The Sony A900 will likely be long remembered for its record-setting resolution and its utility as a camera that is a true working tool instead of an amalgam of gadgets. The stunning 100% viewfinder is one example of that, but so is the logical and simple control that is a part of every aspect of the A900. It is not without its flaws but in total the A900 is definitely greater than the sum of its parts or any one area of measured performance.

Samples

Click on any image below to bring up the full Sony A900 24.6MP image complete with EXIF data. Note that image sizes range from 5.1MB to 10.7MB.

The sample images should make it very clear that 24.6MP is capable of capturing an astounding amount of information. This resolution also demands the absolute best in lenses and any fault, no matter how minor, will clearly be an issue in high-resolution images captured with the A900.