Why less than 24mm?

After realizing I wanted a wide angle lens, I started researching prime glass since they seemed to offer great values. My general knowledge (and quick reading) told me anything 35mm and less is considered, to some degree, as wide.

The labeled Wide Angle AF Nikkor 35mm f/2.0D Autofocus Lens was looking like a possible choice until I started reading the reviews, indicating that it wasn't that wide on a digital camera. Huh? Why?

Now this applies to most Digital SLRs, not just Nikon. The SLR cameras we know have a sensor that "reads" the image seen through the lens. The old film cameras of multiple decades have a sensor to record the exposure on the film, and the new digital cameras have a sensor to capture the image onto a storage card (i.e. SD, Compact Flash). The thing is that these sensors are actually different sizes (in most cases). The old 35mm or full-frame (full-format) cameras have a bigger sensor than most of the new Digital SLRs. Yes, there are a few DSLRs that have that same size sensor, but they are usually top-of-the-line and expensive.

In Nikon world, you'll see the old "traditional" sensor size referred to as FX, while the newer smaller sensor size is identified as DX. Now, lenses that were generally used with full-frame traditional sensor cameras are generally compatible with DX cameras, but there is a trade-off. Due to the difference in the size of the sensor, the smaller version sees less through the glass than the traditional size. There is a "crop-factor" depending on the size of the sensor, for Nikon DX it is about 1.5x and for Canon DSLRs, it is 1.6x.

So what does that mean with the 35mm prime lens I thought would be a good deal? It means that on my Nikon D50, that 35mm lens is really acting like a 52.5mm lens, not really wide at all. To be even close to the general definition of "wide" on a digital camera, I need to have my focal length less than 24mm since 24mm * 1.5 = 36mm.

Here's a quick table that helps show what is actually wide:

Wide: 24-35mm (FX or 35mm camera) vs. 16-24mm (DX camera)
Super-wide: 16-23mm (FX or 35mm camera) vs. 11-15mm (DX camera) ... "super-wide" is also known as "ultra wide".

In a nutshell, for your DSLR, look at the range of 10-24mm whether that be in zooms or primes for your wide glass. Below 10mm, today, it is more likely you're working with a fish-eye lens, which (while wide) is different than wide-angle lenses. My Tokina 11-16mm is the perfect mini-zoom for me to take a deep dive into the wide-angle world. What lens do you have? Or what glass are you looking to add to your collection?