# Optics - Imaging from focal plane

• Wminus
In summary, if an object is placed at the focal length of a lens, the image will be at infinity. The image can be considered as a virtual image at infinity to the left or a real image at infinity to the right, but it does not affect calculations.
Wminus
Hi!

Assume paraxial rays. If I have a lens with a focal length ##f## and I place an object at the focal length to the left of the lens, the image will be at infinity. Correct? But will it be imaged in infinity to the left or right of the lens?

If I am looking into the lens from the right I will see the object as very far away, right? So i guess the image is to the left of the lens?

Thank you for all replies

I suppose you could consider it either way: as a virtual image at infinity to the left (as in your example), or as a real image at infinity to the right. It doesn't make any difference in calculations (e.g. in the thin lens equation), because "-1/∞" and "+1/∞" are both zero.

Wminus

## 1. What is the focal plane in optics?

The focal plane is the plane in which all the light rays coming from a distant object are focused by a lens or a mirror. It is the point of convergence for parallel light rays.

## 2. How does imaging from the focal plane work?

In imaging from the focal plane, light from an object passes through a lens or a series of lenses and gets focused onto the focal plane. This creates an image of the object that is then captured by a detector or film.

## 3. What factors can affect imaging from the focal plane?

The quality of the lens, the distance between the object and the lens, and the wavelength of the light are some of the factors that can affect imaging from the focal plane. Other factors include the presence of aberrations, diffraction, and the size of the aperture.

## 4. What is the difference between imaging from the focal plane and imaging from infinity?

Imaging from the focal plane involves focusing light from a specific object onto the focal plane, while imaging from infinity involves focusing parallel light rays from an object at an infinite distance onto the focal plane. In other words, imaging from infinity is used for distant objects, while imaging from the focal plane is used for closer objects.

## 5. Can imaging from the focal plane be used for all types of imaging?

No, imaging from the focal plane is most commonly used in photography and microscopy. Other types of imaging, such as X-ray imaging, may require different techniques and setups.

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