The Flirty Thirty: the Sigma 30 mm f:1.4 DC Art lens
Why not indeed. And there are good mathematical reasons why you should consider this focal length. As mathematics are the food of the photographer let us begin the feast.
The standard focal length of a lens for a 35mm camera used to be stated as 50mm. It also used to be stated that the standard focal length was the diagonal length of the gate in the film plane. Here's where the two statements differed: the diagonal of the 35mm frame is about 43.4 mm. Thus if you were shooting with a 50 mm, 52 mm, or 55 mm said to be standard you were really shooting with a very mild telephoto...
That's enough to disturb some people so we'll pause while they breathe into a paper bag or lie down briefly.
There were some manufacturers - like Voigtländer - who put out good fast lenses close to this focal length - you could still get them a few years ago for the Nikon mounting and they were cracker sharp affairs. And just that bit wider than the 50 mm jobs. In many cases that were considered just perfect for universal use.
Roll on the digital time and the APS-C camera sensor...and the 18 mm x 24 mm sensor size approximating the half-frame of the film era, but not hoiked vertically. ( Separate blog post will be coming on the naming conventions and sales mystique of sensors in the near future. Prepare to be infuriated...). If we apply the mathematics to this sensor that we did to the film gate we get a standard measurement of 30 mm...and we arrive at the subject of this post:
the Sigma 30 mm f:1.4 DC Art lens
It's only for the small frame cameras - the DC defines that - but there are no restrictions after that. It is MEANT to be the standard lens for a small DSLR and to do that job superbly.