|The SD1 has built-in pop-up flash with a guide number of 11. Here it's judged exposure and white balance pretty well.
Perhaps more useful to advanced users is the flash's ability to control Sigma's EF DG Super range of units wirelessly.
The SD1 provides a number of preset colour 'looks' that provide a useful range of options. The default 'Standard' option is rather muted (but accurate); if you want punchier output you can switch to 'Vivid' or 'Landscape' (which offers a slightly warmer rendition). Sigma also provides Monochrome and Sepia modes, but mysteriously doesn't allow you to use them when shooting RAW. Sigma Photo Pro offers the same set of colour options for RAW users, but (rather eccentrically) Monochrome appears only as a White Balance option, and Sepia is completely unavailable.
Specific image quality issues
The SD1's low ISO image quality can be intoxicating, but the camera requires perhaps more than its fair share of care and attention to maximise the quality of its output. Its biggest problems are its slightly twitchy evaluative metering system and unimpressive high ISO image quality.
Metering and highlight clipping
One of the first things we noticed during real-world shooting with the SD1 was a disturbing predisposition towards overexposure. Press play and your images' histograms will often show extensive highlight clipping. Clearly Sigma recognized this as a problem from an early stage, and has progressively tweaked the metering with multiple firmware updates. But the evaluative metering remains strongly-linked to the selected autofocus point, which means that if you focus on a dark area of the scene it will overexpose.
The example below illustrates how the evaluative metering depends on the selected AF point with a contrasty scene, placing the AF point successively lower down the scene. We've shown screenshots from the camera to show both the active AF point and histogram, and the associated exposure clipping warning, alongside the resultant image files.
|Camera screenshots||Resultant exposures|
What's perhaps most notable here is that, in this case, using the center AF point gives about the closest thing you'll get to a 'correct' exposure, with just a little clipping of highlights and good shadow detail. Selecting an AF point in the top row results in underexposure and blocked shadows, whereas selecting one in the bottom row results in considerable highlight clipping (and as this was shot at ISO 100, the lost detail can't all be recovered from the Raw file - click here for a conversion with -2 EV compensation).
Arguably this should be considered a characteristic of the camera rather than a fault - it's the kind of thing that you'll get accustomed to once you've used the camera for while - but given the inherent characteristics of digital capture, we'd generally prefer to see pattern metering protect the highlights a bit better. Naturally, if you prefer to shoot using a more-predictable metering mode such as centre-weighted average, it's not a concern. And if you shoot at ISO 200 or higher, you get an extra stop of highlight data in your Raw files, which negates the problem considerably.
High ISO image quality
While the SD1 is excellent at low ISO - 100 to 400 - above this its image quality quickly deteriorates, and by ISO 1600 it has serious problems, with unsightly purple-and-green colour blotches in the shadows making many images practically unusable. This is also where the look of the camera's JPEG and Raw images diverges most substantially, as if Sigma isn't even sure about the best way to handle the files.
The example below was shot at ISO 1600, a point at which we'd expect any modern APS-C (or Micro Four Thirds) camera to be entirely comfortable. But the SD1 is seriously struggling. The JPEG and Raw + SPP output attempts to deal with the image noise in somewhat different ways, but neither is truly successful.
|ISO 1600, camera JPEG||ISO 1600, Raw + SPP 'to taste'|
|100% crop||100% crop|
|50% crop||50% crop|
The row of 100% crops reveals a significant difference in processing - the JPEG shows all sorts of problems, with low saturation, colour bleeding from the tower to the sky, and large 'grains' of noise. The Raw file handles colour better, and has much finer noise grain in evenly-toned areas, but SPP's noise reduction gives vertical streaking that emanates from from all of the (many) vertical features in this image. The lower row of 50% crops reveals the low-frequency green and purple chroma blotching that seriously bedevils the SD1's high ISO output - the JPEGs appear to reduce saturation to make this less visible, but without much success.
As is often the case, the SD1's high ISO problems are accentuated under artificial light sources, which tend to be prevalent in low-light situations. The camera's also not helped by Sigma Photo Pro's noise reduction algorithms, which don't work terribly well and can leave strange artefacts of their own (such as the vertical streaking seen in the example above, that's more obvious if you download the full-size picture). Overall we'd have to say that the SD1 should be considered a low ISO camera only, as any other current APS-C or Micro Four Thirds camera will do a better job at high sensitivities.