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So recently I got a 90mm macro lens, installed a focus bracketing app onto my camera and let it run. Unfortunately, turned out that this lens has focus breathing which means the actual zoom level in each frame is slightly off.

How can I tell before purchase if a lens has focus breathing? (This was a Sony FE 90mm, in case you're curious.)

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  1. Get s few paralel lines (at least 5) with equal distance between them printed on a sheet of paper. You can also find test grid photos online.

[edit] Try for example 7 lines with 1cm between each 2 of them. Thickness of lines ..let's say 2mm would work great. You can also use a simple ruler.

  1. Position the paper and the camera so you see through the viewfinder the paralel lines horisontally. The angle on which you watch should be somewhere below 35 degrees or so. Or in other terms, the angle between the sheet of paper and the imaginary axes centered with all your lens glass elements.

  2. Test the focus several times on a single line, without modifying the camera position or lens zoom. If for the same position of camera and same zoom, your lens focuses differently, you might have focus breathing.

Also, keep in mind the focus is dependent of course on what is in front of camera. There might be better examples of test grids online, that put the camera and lens to a better test.

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