How Everything Works
How Everything Works How Everything Works

Question 415

What would happen if a magnifying glass is set at the end of a telescope? How would the stars appear?
You could place the magnifying glass at one of two spots: at the entrance to the telescope or at the eyepiece of the telescope. If you put it at the entrance, it would bend the light before it had a chance to reach the main optic for the telescope. The effect would be to increase the light bending ability of the main optic and reduce the lens's focal length. This change would make it difficult to focus the telescope on distant objects, such as stars. The images of these distant objects would form too close to the main optic and you would have trouble observing them through the telescope's eyepiece. But very nearby objects form real images farther from the main optic. The magnifying glass would help the main optic form real images of very nearby objects. It would act as a close-up lens. That is what close-up lens attachments for cameras or even cheap reading glasses do: they help the camera lens or your eye form an image of very nearby objects. On the other hand, a magnifying glass held over the eyepiece of a telescope would increase the power of the telescope. You would have to adjust the focus of the telescope because the added magnifying glass will reduce the effective focal length of the eyepiece. The new super eyepiece will have to be placed closer to the real image formed by the main optic of the telescope. When it is place properly, it will give you a very highly magnified view of that real image, so you will see a highly magnified view of the stars.

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