![Focal length, the simplest and most important number of them all!](https://images.squarespace-cdn.com/content/v1/5882f245db29d6b295c2b5a8/1516300691777-QKDLK6SKBC4WS0ZSEUBT/Cameracrosssection.jpg)
Focal length, the simplest and most important number of them all!
In a world where we are familiar with camera lenses that comprise numerous aspherical elements glazed with Super Spectra coatings, one can be forgiven for asking precisely what focal length is.
![Crop Factor Basics](https://images.squarespace-cdn.com/content/v1/5882f245db29d6b295c2b5a8/1501151601200-MEDBNJXBIJR7R57TFCIN/banner.jpg)
Crop Factor Basics
The first thing to know in the pursuit of crop factor enlightenment is that the entire system is based, rather arbitrarily, on the old 35 mm film standard. I say “arbitrarily” because a crop factor is simply a ratio, one that can just as easily be calculated using an 8" × 10" large-format camera or the tiny iPhone 7 camera as a reference.