When selecting a dslr lens, what maximum aperture do I need?
For beginner, one important must know before selecting an aperture. You have to know that number of aperture (or aperture value, f) and the size of aperture is inverse. The aperture value normally show as “f/5.6″, or “f-5.6″, or sometimes like “1 : 5.6″.
As smaller aperture number, as wider aperture size.
As larger aperture number, as narrower aperture size.
So, now is the question: What maximum aperture do I need?
1. Depends on the object speed
If an object is moving very fast, I need a very fast shutter speed to take its picture (may be 1/2000 second or 1/4000 second). But, do you realize that, as faster shutter speed, as darker picture. Why? Because faster shutter speed allow less light to in. So, may be I can set the aperture wider to balance this situation, because wider aperture allow more light in.
2. Depends on the lighting condition
If you want to take a picture in a low light environment (such as indoor) without flash, there has two ways to get the light that it needs. First method is adjust your shutter speed (open it for long period, may be take 2 seconds to 5 seconds). Second method is open your aperture as wider as possibble.
3. Depends on the depth of field (DOF)
As some example picture I show on previous post, wider aperture will decrease the depth of field (means make the background become more blurry). So, if you want to focus more on the object you want to capture, and reduce the impact of the busy background, you may need wider aperture.
As the maximum aperture is wider, as the cost of dslr lens more expensive. What lens you choose is still depends on your personal demand. Choose it properly, don’t pay more for the thing that you do not really need.
Below is the sample chart source from http://www.digital-slr-guide.com/
| Lighting | Max Aperture | Rationale |
| Indoors | f/1.4 – f/2.8 | If you want to take photos indoors without a flash, you need to get a lens with a very wide maximum aperture to let in plenty of light |
| Overcast | f/2.8 – f/3.5 | Overcast days are especially challenging for sports photographers, who need to use fast shutter speeds to freeze motion |
| Shade | f/3.5 – f/5.6 | Shade is not as dim as a cloudy day and you have a bit more leeway when it comes to the maximum aperture |
| Daylight | Any | In broad daylight it really doesn’t matter what the max aperture of the lens is – you probably won’t be using it because it lets in too much light and over-exposes the image |
Thank you for writing this. A good complement to your thoughts from the YC panel at the Seattle Tech Startups meeting a few weeks ago. I’ll definitely keep this bookmarked to check back on when I decide to apply.