A lens of large focal length and large aperture is best suited as an objective of an astronomical telescope si

Question

A lens of large focal length and large aperture is best suited as an objective of an astronomical telescope since:

Accepted Answer

1. **Light Gathering Power:** The objective lens needs to collect light from distant, often faint, objects. The light-gathering power is directly proportional to the area of the objective lens ($Area \propto 	ext{Aperture}^2$). A larger aperture ensures a brighter image, improving visibility.
2. **Resolving Power:** The ability of a telescope to distinguish distinct details is called its resolving power, given by the formula $RP = \frac{D}{1.22\lambda}$, where $D$ is the aperture (diameter) of the objective. A larger aperture ($D$) results in higher resolution.
3. **Image Quality:** Since a large aperture improves both brightness (visibility) and resolution, it directly contributes to the overall quality of the image.
4. **Focal Length:** A large focal length ($f_o$) is required for high magnifying power, as magnification $m = f_o/f_e$. Thus, large focal length and large aperture are ideal characteristics.

Step-by-Step Solution

Practice All PHYSICS Questions