DoF Equivalency - DoF calculation Experts

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jamesev

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Jamesev
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If you have say a focal length (FL) 400mm f2.8 and a 1.4 tele (1 stop f loss) if you put the tele on it will make it a 560 f4.

As DoF is a function of focal length and f number (amongst other things) if the other things are kept constant does the DoF stay the same

ie

400mm f2.8 focused at 30 m
560mm f4 focused at 30m

is the DoF the same or are f an FL not linear in the DoF calculation?
 
I think they both change exponentially.

If you change your aperture by 1 full stop you will halve or double the dof depending on whether you open or close the aperture.

If you double the length of the the lens you will reduce the dof by 4 times if you half the length of the lens you will increase it by 4 times.

In the example you have given the dof wouldn't be the same.
 
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