Question - Different Lenses, Human Eyes??

Question
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What's the difference between different camera lenses?
i.e. 12mm vs 30mm vs a 50mm, etc... etc...
What does the Human Eye usually see?

Answer
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Good question and it's all the more confusing when relating it to full frame sensors.

Ok right off the bat let's get something established. Cropped Sensor equivalent is the Full Frame rating x the cropping factor. So a 18-200mm lens on a full frame camera is really a 27-300mm lens on a dslr body.

That being said, there are three ranges in lenses.

- Ultra wide angle
- General Zoom
- Telephoto

Ultra Wide angle lenses are lenses that are less than 18mm on a dslr and less than 27mm on a full frame camera. Ultra wide angle lenses give you about 105 degrees (sometimes more) viewing angles. They give your shots crazy amounts of barrel distortion but it's like shooting a panoramic shot without taking multiple shots. Keep in mind with wide angle lenses, when shooting a subject, the subject will look further away than they actually are. This is a side effect of the effective focal length of the lens. Basically, wide angles make distance between
your subject and you seem vast.

General Zoom lenses fall in the range of 18-70mm (dSLR) or 27-105mm (Full Frame). These cover some wide and some telephoto. They're the in between lenses and are quite useful for about 85% of your shots.

Telephotos are lenses greater than 70mm (dslr) or 105 mm (Full Frame). These beasts sometimes come with their own stands depending on how much zoom you have (i.e. 500mm). The thing to note about telephotos is that they essentially are magnifying the image. As a result, it will make everything in the photo appear closer to the photographer than it really is... You say Duh? What I mean to say is that, your subject will look close, but anything in the background will also look like it is right behind the subject. I will post up example photos to describe this a bit better. This effect is called perspective compression.

There is one other category of lenses which is mostly for professional photographers or people with lots of money. This category is called prime lenses. These lenses are dedicated focal lengths... i.e. 50mm, 35mm, 85mm, etc... They have no zoom and therefor less moving parts
inside the lens. This means less chromatic abberation and also larger apertures. They are great lenses but they are obviously not as flexible as zoom lenses.

To answer your question directly, a 12mm lens is ultra wide angle lens. It's equivalent to 18mm lens on a dslr. 30mm falls into the general zoom category. 50mm starts falling into the telephoto range. With the above effects of each lens category explained, you can make
your lens choices wisely with the new knowledge.

I can go on and on about lenses, but I'll leave it at that for now. I'll get some shots into the post to describe the perspective compression.

The human eye views about 20-22mm in terms of focal length. We can also perceive 324 Megapixels and we have an incredibly high dynamic range. If someone could use our eyes as cameras, we'd have amazing shots.

Happy Shooting,

Shutter Nirvana