Real or virtual, focal length

In summary, real focal length is the distance between the lens and point of image formation, while virtual focal length is the distance between the lens and point of perceived image formation. Focal length directly affects the field of view, with shorter focal lengths capturing wider scenes and longer focal lengths narrowing the field of view. There is no standard focal length for different types of photography, and the best focal length to use depends on the subject and desired composition. Focal length can also impact image distortion, with wider angles producing more distortion and longer focal lengths minimizing it. The focal length of a lens can be changed through zoom adjustments or interchangeable lenses.
  • #1
mike2007
46
0
A positive lens has a focal length of 12cm. An object is located a distance of 3 cm from the lens.
How far is the lens from the image?
Is the image real or virtual, erect or inverted?

My attempt
f = +12cm
o = +3cm
i =?
1/o + 1/I = 1/f
1/i = 1/f – 1/o
= 1/12cm – 1/3cm
= 1/12 – 4/12
= - (3/12)
i = -4cm on the same side of the object.

Since the object lies in within the focal point, the image is virtual and erect.
 
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  • #2
Always draw the ray diagram before trying to do the maths.
 
  • #3
Looks good to me.
 

1. What is the difference between real and virtual focal length?

The real focal length refers to the distance between the lens and the point where the image is formed on the film or sensor. The virtual focal length, on the other hand, is the distance between the lens and the point where the image would appear to be formed if the light rays were extended backward.

2. How does focal length affect the field of view?

Focal length directly affects the field of view, or the amount of the scene that is captured in the image. A shorter focal length results in a wider field of view, while a longer focal length narrows the field of view.

3. Is there a standard focal length for different types of photography?

No, there is no standard focal length for different types of photography. The best focal length to use depends on the specific subject and the desired composition of the image.

4. How does focal length affect image distortion?

Focal length can affect image distortion in certain situations. Wide-angle lenses with shorter focal lengths tend to produce more distortion, while longer focal lengths can minimize distortion. However, the position and distance of the subject in relation to the camera also play a role in image distortion.

5. Can you change the focal length of a lens?

Yes, the focal length of a lens can be changed by adjusting the zoom or using interchangeable lenses. Some lenses have a fixed focal length, while others allow for a range of focal lengths to be selected.

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