I don't make that effect deliberately; I guess it's just the way it is with that camera and my processing workflow.
The D7 is a 5Mpx camera with a fairly small sensor, so a bit noisy. However, unlike other users of the same Sony sensor, Minolta added very little processing in the camera - Sony themselves, by contrast, applied both sharpening of the luminance and exaggeration of the colours to make pictures more "vivid"*. Minolta also preserved the full colour range of the sensor, using a colour space that is much wider than sRGB, and somewhat wider than Adobe's - this makes unprocessed pictures look dull when viewed by people/systems that are not colour-space aware. The 7x zoom lens is superb, and the combination of lens and sensor gives no colour fringing at all, unlike many of the competing cameras. However, the lens (like any fast wide-range zoom - it is the equivalent of 28-200 f/2.8-3.5) has a lot of distortion, including gull-wing distortion at the wide end.
So my workflow starts by running
PTLens to correct the distortion (this program has the characteristics of most lenses programmed in, and reads the EXIF data to adjust the parameters according to the focal length for each shot). I then run an all-in-one enhancement program,
DCE AutoEnhance, that changes the colour space to sRGB and then does a raft of other things (noise reduction, contrast adjustment, sharpening, et al) which can be enabled or disabled individually, and which can be adjusted to different degrees according to the EXIF data (mainly shutter speed, ISO setting, focal length, flash usage). I have this set up so that I like what it does in 90% of cases, and I can treat any others individually if I want (using more sophisticated noise reduction, like
Neat Image, for example).
So, now you know what I do, but it doesn't really tell you what makes that effect (a combination of low colour fringing and modest colour noise reduction is what it comes down to, I suppose).
*
When Sony bought out Minolta's camera division and rebranded their SLRs as Sony alpha, they had the good sense to retain Minolta's trade-mark conservative level of processing rather than changing it to be like their other cameras.