This is the next installment in my series of Quick Tips for photographers.

New photographers often get confused about terms like Wider Aperture, smaller F-stop, Stopping Down, and Opening Up. So here is a series of explanations for what some of these terms mean.

The thing is, photographers that know this stuff just know it, and they don’t even have to think about it. When a new person comes onto the scene and they hear terms like Stop Down, Open Up, Fast Glass, and Maximum Aperture, they often have no idea what language is being spoken. It’s really not obvious what any of these terms mean, and it can be very confusing to figure it out unless someone explains it clearly and simply.

Here are some key points to remember:

• A small F-stop means a large aperture.
• A large F-stop means a small aperture.
• Large apertures (small F-stops) let in more light than small apertures, so you can use faster shutter speeds to get the same exposure.
• “Stopping Down” means to use a smaller aperture, which is a higher F-stop.
• “Opening Up” means to use a larger aperture, which is a smaller F-stop.
• “Fast Glass” means using lenses with a very low f-stop (such as f/2.8 or smaller) which let in lots of light. More light means faster shutter speeds, hence the term Fast Glass. Fast glass is good.
• “Maximum Aperture” means the largest aperture, or smallest F-stop, that a lens is capable of. See “Fast Glass” to figure out why this is important.

This can be very hard to remember until you’ve used your camera so much that it just comes natural to you and you don’t even have to think about it. For many people, simply memorizing the table above will be enough to make this all work flawlessly!

More Detail for the Advanced Class

For some people it helps to think about what the numbers mean. If you don’t want to know, just stop right here, and go back and finish memorizing the terms above!

The F-stop is really just a ratio between the size of the lens opening (called the aperture) and the focal length of the lens you are using. The size of the aperture is simply the focal length divided by the F-stop number.

The important part is that no matter what lens you are using, if you divide the focal length by 4, you will get a larger number than if you divide by 16; this means that at f/4 you will have a much larger aperture than at f/16, and therefore the lens will let in much more light at f/4 than at f/16.

For example, if you are using a 100 mm lens:
- At f/4 the size of the aperture is 100/4 = 25 mm
- at f/16 the size of the aperture is 100/16 = 6.25 mm

You can see that the aperture at f/4 is significantly bigger than at f/16, and therefore the lens will let in way more light at a smaller F-stop.

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