The shortest wavelengths occur in the:red end of the spectrumblue end of the spectrummiddle of the spectrum The light-gathering capacity of a telescope is dependent upon the:magnificationfocal lengthsize of human irisarea of aperture

The shortest visible wavelength is the last color you can see

at the blue end of the spectrum.

The light-gathering capacity of a telescope depends on the area

of the main lens in the front, or the main mirror in the back.

That's also the area of the opening of the tube, called the 'aperture'.