Linked Questions

5
votes
3answers
5k views

Does focal length change when I adjust the focus? [duplicate]

When I adjust the focus of my camera, in general, does this affect the focal length? I have heard that it does.
15
votes
4answers
17k views

How can a lens with a single focal length focus on more than one plane?

By definition, a prime lens is a fixed lens system with a fixed focal length. Then, simple physics tells us that it should be able to focus only on one plane (at a fixed distance) in front of it. But ...
29
votes
3answers
8k views

Does changing the focal length change focus?

When using manual focus or back focus on D60, I sometimes zoom in the lens, set the focus, and then zoom out. Does changing the focal length (zooming out), also change the focus? In case the answer ...
17
votes
5answers
10k views

How to test actual focal length?

From Matt Grum's comment to my previous question, I learned that manufacturers may casually "round" actual focal length of a lens to some nice number that gets printed on the box and stored into EXIF. ...
3
votes
2answers
9k views

Difference between zoom and focal length? [duplicate]

Until now I thought that focal length is just another way of measuring how much a lens zooms: The higher the number the more it magnifies, the smaller the number the wider the angle and thus the less ...
12
votes
2answers
559 views

Does focus breathing make a lens slower when close focusing?

I've heard that focal length of some lenses will become noticeably longer when focusing to a close distance, an effect called "focus breathing". Since f-number is focal length divided by diameter of ...
1
vote
5answers
641 views

Why are lenses characterized by focal length and not the effective field of view?

In photography, it's the accepted norm to say that if you know the sensor size of your camera and the focal length of your lens, then you know the field of view of your system. However, in optics, it'...
2
votes
1answer
745 views

Supermoon: In focus and Out of focus

In focus moon Tonight I took several pictures of the Super Moon, I am a novice practicing in manual mode. Can someone explain why these photos are drastically different. The out of focus was shot ...
0
votes
1answer
712 views

How can I calculate sensor size (width and height) from focus length, vertical, and horizontal angle of view?

How to calculate sensor size (width/height) when knowing focus length, vertical & horizontal angle view (FOV)?
0
votes
3answers
376 views

What exactly happens when one turns the focus ring on a DSLR while shooting video?

I'm about to buy my first DSLR and I'm trying to understand every single aspect of it. If I've got a prime lenses and I'm shooting a video with f/2.8 aperture, I'm going to have a fixed depth of ...
0
votes
1answer
772 views

How do lenses focus? (and zoom?) [duplicate]

My understanding of focal length is that it is the distance from the lens to the sensor; in my observations: higher focal lengths make for longer lens. Then I started thinking about how a lens ...