Sony SLT Alpha A55 In-depth Review
Sweep Panorama and 3D Sweep Panorama
With NEX Firmware version 2 Sony introduced the world to 3D sweep panorama mode, which finds its way into the A55 and A33. This feature essentially creates a stereo pair of panoramic JPEGs which can be played back on Sony's 3D Bravia TVs. The camera records both a conventional panoramic JPEG, and alongside it an 'MPO' file (Multi-Picture Object - sometimes known as 'Multi-Picture Format', proposed as a standard 3D file format in 2009 by CIPA) containing the stereoscopic image pair that's precisely double in size. If you have a Bravia television or other compatible viewing device, you can download a .MPO file from the link given below.
In 3D mode you gain an additional 16:9 option in the Image Size menu, alongside Normal and Wide settings with similar aspect ratios as before; all three produce images that are 1080 pixels high to match HD TVs. You get the same limited exposure controls as before, but the camera will only allow you to pan left-right (or vice versa). The image sizes created are as follows:
1920 x 1080 (2Mp)
4912 x 1080 (5Mp, 4.5:1)
7152 x 1080 (7.3 Mp, 6.6:1)
|Sweep Panorama ('Normal'/'Left', 8192 x 1856 px, 16-105mm lens)|
|3D Sweep Panorama ('Normal'/'Left', 8192 x 1856 px, 16-105mm lens)
click here to download .MPO file
Conventional Sweep Panorama mode in the A55 works in exactly the same way as it does in the NEX-3 and NEX-3. You can read our conclusions on the relevant section of the NEX-3/5 review here.
In Auto+ mode, - a new feature in the Sony Alpha range - the A55 analyzes the scene and if necessary applies Auto HDR as well as other multi-shot options like Hand Held Twilight and Multi-shot NR. It means the multi-shot modes are now available regardless of whether you have any interest in learning what HDR is or when it could be applied.
The SLT Alpha A55 offers Sony's 'Auto HDR' feature, which takes three shots of the same scene at different exposures, then combines them to produce a single image that incorporates a larger range of tones than would be possible from a single exposure.
The A55 takes three images - one of the 'correct' exposure plus one over-exposed image to capture shadow detail and one underexposed image for highlight detail would otherwise be missing. The breadth of the exposure gap between these three shots can either be chosen automatically by the camera or set manually. Here, we've shown you four images, spanning 'off' to +6EV HDR effect.
|Off (no DRO or HDR)||Auto HDR +2EV|
|Auto HDR +4EV||Auto HDR +6EV|
We like Auto HDR - it enables users to easily capture high-contrast scenes without losing all the highlight and shadow detail. The results can be slightly flat and low contrast (an inevitable result of trying to squeeze greater tonal range into an image), but this can be rectified with a bit of a 'curves' tweak if you like - which you couldn't do with a conventional image if the highlight or shadow information had never been captured.
Understandably, because the end result is a composite of three exposures, there can be ghosting effects where subjects have moved between the three exposures, but the system does remarkably well at canceling out movement - you can see in these images that although some figures are a little blurred, other moving elements - a jogger, and boats on the river - appear frozen in a single exposure.
Multi-shot NR is a new mode, which becomes effectively an 'extension' ISO setting available in JPEG capture mode. When set to multi-shot NR, the A55 takes 6 frames in a fast burst, then automatically aligns them to cancel out any camera shake, and blends them together to produce a final image.
|ISO 25,600 (using Multi-Shot NR). Click the magnifying glass for the full size original (opens in a new window).||100% crop of ISO 25,600 (top) and 12,800 (bottom). Click the magnifying glass for the full size original (opens in a new window).|
Because high ISO noise is random, blending multiple images together it is possible to 'cancel out' the worst of it. If you have some time on your hands you can do the same thing in Photoshop, but as you can see here, the A55 does an excellent job. Assuming that your subject is static and your hands don't shake too much, JPEG image quality at ISO 25,600 using multi-shot NR is slightly superior to ISO 12,800.
Much like the HDR and DRO+ modes, when you select the Multi Frame Noise Reduction option from the ISO menu, you can push left and right to select whether to let the camera automatically choose the ISO or specify it yourself.
Highlight clipping / dynamic range
The Sony Alpha SLT A55 has an extremely capable metering system, which helps enormously to avoid clipped highlights, especially in JPEG files. Coupled with the impressively wide dynamic range of the sensor, this means that the A55 is capable of delivering a wide tonal range in most shooting situations. In all of our shooting with the A55, it certainly seems as if the new camera is immune to the frequent overexposure problem which we found in Sony's NEX-3 and NEX-5 (and the Alpha 550).
Overall Image Quality / Specifics
The A55's 16.2MP sensor is capable of excellent results. Right up to its maximum 'standard' ISO setting of ISO 12,800 the A55 delivers detailed, useable JPEGs, which - coupled with effective metering - make the A55 a very agreeable companion in a range of different shooting situations. The A55 also has a very wide dynamic range in JPEG mode of almost 9EV which means that assuming metering is accurate, highlight clipping is not a problem in all but the most challenging of scenes.
The A55's .ARW RAW files are a better starting point for anyone interested in getting the absolute best out of the 16MP CMOS sensor, but the A55's JPEGs are certainly good enough for most purposes. At any rate, there is not the gulf in image quality between JPEG and RAW files from the A55 that we have seen with some previous low-end and midrange Alpha DSLRs.
Since we published the first version of this review in late August, there has been some discussion on our forums and elsewhere of the risk of a so-called 'ghosting' effect caused by the presence of the semi-transmissive mirror in the A55's light path. This takes the form of a vertically displaced ghost image around highlight areas, and is caused by a tiny portion of the light which passes through the mirror being reflected off the inner surface of the mirror and back onto the sensor.
Where we'd expect ghosting to be apparent are images which contain very small specular highlights, such as distant streetlamps in a night scene, or reflections from a shiny object which are - again - very small in the frame. Examples are shown below.
|In this image, ghosting is clearly visible at 100% along the edge of the wall of a distant building, but in another area of the shot, where logically we would also expect to see the effect, it is invisible against a brighter background.|
As these examples show, if you go looking for ghosting in images shot with the A55, you might find it, in some pictures. The areas to watch out for small, very bright (to the point of being either clipped or almost clipped) highlight areas against a dark background.
We shot hundreds of frames with two samples of the A55 and the A33 in 'real world' environments, and after examining them all pragmatically as well as critically, we're confident that Sony has controlled this issue very well. Even in images where the effect is noticeable on extremely close inspection, it is largely of academic interest only. After exhaustive studio testing, we estimate that when ghosting is visible, it is roughly 8EV darker than subject brightness - or approximately 1/200th. In practical terms, the abberrations created by mounting a poor quality lens on the front of the A55 are likely to have a more noticeable effect on image quality than ghosting.
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