Answer:
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
