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Depth of field of extension tube vs dedicated macro

Started 7 months ago | Questions thread
JamesMorgan Junior Member • Posts: 36
Re: Yes, and no

I recently bought a close up filter to use with my Oly 75-300 so am also experimenting with DoF with close up photography.  No doubt it is challenging and with DoF of around 1mm, I am often using focus bracketing in an attempt to find one photograph correctly focused.

As others have pointed out DoF is a function of the magnification of the image - it doesn't matter how you get there, whether with a macro lens, an extender, a close-up filter, a telephoto lens etc.

However, my understanding of post-processing cropping is that whilst this does reduce DoF, it does so in a linear manner rather than according to a square rule if increasing lens focal length.  So, for example, if I increase focal length from 150mm to 300mm, DoF reduces to a quarter, however, if I crop the 150mm image to achieve the same field of view DoF only reduces by around a half.   This can be useful to extract the maximum possible DoF if you don't mind losing a few pixels.

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