[EDIT]: the formula on page 4 of the book below does not seem to have a frequency parameter ...
Also, they seem to consider that objects worth looking at are at infinity, which is why there is a well-defined focal distance from the sun.
What seems to involve frequency is that the gain of the lens varies (same book, page 9).
http://erewhon.superkuh.com/library/Space/Spacecraft/Deep%20...
[EDIT]: the formula on page 4 of the book below does not seem to have a frequency parameter ...
Also, they seem to consider that objects worth looking at are at infinity, which is why there is a well-defined focal distance from the sun.
What seems to involve frequency is that the gain of the lens varies (same book, page 9).
http://erewhon.superkuh.com/library/Space/Spacecraft/Deep%20...