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.
25
votes
3answers
6k views

Why isn't this portrait taken at f/29 sharp?

I am confused as to why this picture is not sharp. This is a portrait shot at F/29 ISO100 1/250 with a 17-85mm lens focused at 38mm. The subject distance was 1.2M. My DOF app tells me that my DOF ...
18
votes
6answers
15k views

Why is depth of field affected by focal length?

As the focal length decreases, the depth of field increases as well. Why is this? I'm not so much interested in a physics lesson as I am interested in a simple, down-to-earth explanation.
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 ...
15
votes
4answers
4k views

What is a parfocal lens and how beneficial is it to photography?

I heard someone say that after using a parfocal lens for the first time, they would never switch back. What is a parfocal lens, how is it different from any other lens, and what are the advantages and ...
25
votes
3answers
11k views

How can a 18-55mm lens focus on objects beyond 55mm?

I guess this is a total noob question, but doesn't 18-55mm mean that it can focus only up to 55mm?
13
votes
3answers
16k views

What is the technical difference between focus and zooming?

This may look like a silly question but I don't know what the difference between zooming and focusing is. Zooming in will usually let me have fewer subjects in the scene while zooming out will allow ...
8
votes
2answers
3k views

Is it normal for focal length to change while focusing?

When I change the focus distance on my Pentax 55-300mm lens, the focal length appears to change. More specifically, the lens appears to zoom in as I focus towards the minimum focusing distance. This ...
-1
votes
3answers
2k views

At what distance from the lens will the image be in focus given a subject distance and focal length? [closed]

I've been trying to figure this one out for more than an hour now and I have no idea how to calculate this... You capture a picture of a tree which is standing 3m away from the camera. The focal ...
2
votes
2answers
319 views

How does (auto-/manual-)focus changing work?

I know when I change focal length of a zoom lens the physical length of it is changed. It's understandable: the optical parameters of the lens were changed. But what is going on when (auto-/manual-)...
0
votes
1answer
706 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)?