An astronomer is using a telescope to observe two distant stars. The stars are marginally resolved when she looks at them through a filter that passes green light near 550 {\rm nm}. Assume that the resolution is not limited by the atmosphere. Which of the following actions would improve the resolution? Part A: Changing the filter to a different wavelength? If so, should she use a shorter or a longer wavelength?
Part B: Using a telescope with an objective lens of the same diameter but a different focal length? If so, should she select a shorter or a longer focal length?
Part C: Using a telescope with an objective lens of the same focal length but a different diameter? If so, should she select a larger or a smaller diameter?
Part D: Using an eyepiece with a different magnification? If so, should she select an eyepiece with more or less magnification?