Sony is best known as a giant electronics manufacturer making devices across a range of markets, but its camera division is doing especially well. The market for compact point and shoot cameras has fallen, but Sony is doing very well with its professionally-orientated full-frame A7 series and A9 cameras. It also makes a continually expanding range of high-end professional lenses.
‘Alpha’ is the generic brand name used by Sony for its interchangeable lens cameras. This can be confusing because Sony makes cameras in two types – SLT (single lens translucent) and mirrorless models. Both are Alphas, but the Alpha A9 (mirrorless) and Alpha A99 II (SLT) are entirely different cameras with different lens mounts and lens ranges. Sony’s SLTs use Alpha A-mount lenses, while the mirrorless models use E-mount lenses.
The lens mount used by Sony’s Alpha SLT cameras. Because these cameras have a mirror in the body, even though it’s a non-moving one, the rear of the lens is further from the sensor, so Alpha mount lenses are physically different to Sony’s E-mount lens range. You can use Alpha lenses on an E-mount camera with an lens adaptor, but not the other way round.
Aspherical lenses offer better correction for many common lens aberrations than regular spherical lenses. Lenses with a spherical profile are easier to grind into the correct shape, but aspherical lenses have a more complex profile that’s more difficult and more expensive to make. Many modern lenses use moulded aspherical elements instead to get round this. Lenses with aspherical elements in their design command a higher price and generally give better results.
An apochromatic (APO) lens is designed to offer improved correction of chromatic aberration and spherical aberration using specialised materials and combinations of lens elements. It’s a selling point for lenses, though only indicates the lens design used and isn’t really a guarantee of good performance on its own.