As I have alluded to in a burst of recent posts, I am planning to generate a small database of lenses for use on the Fujifilm GFX series. Here's my chance for an introduction to give my rationale and to lay the foundation of this endeavor. I'd like to break this down into three "Y's." Let's begin with a personal "why": I'm choosing to use Sigma lenses to obtain focal lengths and apertures not currently offered in the GF lens lineup. Fujifilm's lineup is sparse at best, and apertures wider than ƒ/2 aren't represented. It's not that I'm a bokeh whore; it's that I need more light gathering for astrophotography and Fujifilm's widest lens, a 23mm, has a maximum aperture of ƒ/4 and that's just not going to work without a star tracker due to the sensor's 51MP resolution. I'm hoping to print a few of these so what counts for "sharp" on the web doesn't work at 20" print sizes. Other benefits: 35mm lenses are much cheaper, especially used prices, and these lenses mostly have direct focusing units unlike the "fly by wire" systems used on Fujifilm lenses. The GFX system just isn't mature enough to have grown both a complete lens lineup or a diverse used lens market.