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

In an astronomical telescope the objective lens serves two crucial roles: it must collect as much light as possible from faint celestial objects, and it must form a sharp, high‑resolution image that can be magnified by the eyepiece.

**1. Light‑gathering power** – The amount of light a lens can collect is proportional to the area of its aperture. The area is $A=\pi \left(D/2\right)2^{}$, where D is the diameter of the objective. A larger aperture therefore delivers a brighter image and makes faint stars and galaxies visible.

**2. Image quality and visibility** – With more light reaching the focal plane, the contrast of fine details improves. This enhances the overall quality of the image and makes subtle features easier to discern.

**3. Resolution** – The diffraction limit of a circular aperture is given by $\theta =\frac{\mathrm{1.22\; \lambda }}{D}$. Increasing D (the aperture) reduces the smallest angular separation θ that can be resolved, i.e., the telescope achieves better resolving power.

**4. Large focal length** – A long focal length produces a larger image scale on the detector or eyepiece, which reduces off‑axis aberrations and allows finer detail to be examined after magnification.

Because a large aperture simultaneously boosts light‑gathering ability, improves image quality and visibility, and provides superior resolution, the statement that “All of the above” is true.