Question

When do (object distance) is very large, what does the thin lens equation predict for the value of 1/f?

Similarly, when do (object distance) is very small and less, what does the thin lens equation predict for the value of 1/f?
Please explain your answer properly, especially for the first question. Thank you

Answer 1

1 / f = 1 / o + 1 / i

1 / image distance + 1 / object distance = 1 focal length

If the object distance is large the image will be at about the focal length

The value of 1 / f is fixed for any one particular lense

As the object distance decreases the image must increase

The above equation can also be written as

o i / (i + o) = f or i / (i / o + 1) = f

If for instance o was very large the image would be at the focal length