# How far do I need to extend bellows to achieve particular minimum focal length [duplicate]

If I have a 200mm lens, and want to focus at, say, 450mm from the camera, two questions:

1. can I (do I need to) use bellows to achieve this?
2. is there a formula for how to work out how much extension I need on the bellows to achieve the minimum focal length?
• It's hard to answer this because you are completely confused. A 200mm lens has to do with its focal-length and determines the angle-of-view when mounted on a certain sensor-size. This has nothing to do with focus-distance.
– Itai
Apr 22, 2016 at 3:40
• I understand that. I guess I naively thought that the minimum focal distance would be a function of the lens length. Apr 22, 2016 at 3:56
• Indeed, there is no relation. If you look at the set of 200mm available for DSLRs and mirrorless cameras, you will see the minimum focus-distance varies between 50cm and 190cm.
– Itai
Apr 22, 2016 at 4:00
• Yes but can that distance (190cm for example) be reduced by moving the lens away from the sensor? That's my first question. My second is how far to move it by in order to achieve a particular distance. Apr 22, 2016 at 4:03
• The answers in the supposedly duplicate question seem to assume knowledge of the magnification. Is this calculatable given a working distance? Apr 22, 2016 at 6:41