As I have a Canon 7D the smallest Fstop I can use is f5.6. My eyes are not good enough for manual focus. The 70-300L is a lovely lens, but it is just not long enough at times.

There are two lenses I can afford, the 100-400L & the 400L f5.6. Both are very old and due to be replaced.

When I look at something over 400mm the price is well above my budget.

So my question is why the big jump in price? Is it because the lens elements are so large? Why is there no 500mm f5.6?

Is some learned person who can help to answer my question?


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