Damage from radiation can be impacted by several things: Time, Distance, and Shielding. The longer you spend next to a radiation source, the more damage you can get from the exposure. Likewise, distance. The farther you are away from a source, the less radiation can impact you. And lastly is shielding. Depending on the type of radiation, different shielding can be applied. Think of shielding as something that will block the radiation. Using a lightbulb as an example: The more time you spend in the room with a lightbulb, the more light hits your body. Light is the radiation in this case. If you are farther away, less of the light hits you. All the light is coming from a distinct point and radiating outward. Up close, many of the light rays radiating outward will hit you. Farther away, because of the angle in which they are being ejected from the bulb, some will hit you but some will go over, under, or around you. And if you turn on a light and then step behind a wall, all of the direct light is shielded so you are protected from it.
In the case of the starlight, the radiation is extremely far away so very few actual rays are making their way to Earth. Magnifying them doesn’t significantly increase the damage from the rays because they are so few. Additionally, our atmosphere adds quite a bit of shielding for us. I personally wouldn’t worry about damaging your eyes looking at stars with or without a telescope.