How can I reduce perspective distortion in close-up top-down photos of small objects?

Question

I’m photographing small laboratory subjects about 60 mm across, and I need them to fill the frame for maximum spatial resolution. Right now I’m using a Nikon Nikkor Z MC 105mm f/2.8 VR S at roughly 30 cm working distance.

The problem is that in these close-up images, vertical features don’t look truly top-down: the inner sides of cylinders or edges become visible, while the outer edges are obscured. For my scientific use, I need the image to look much closer to an orthographic/top-down view.

Is the best fix simply to move the camera farther away and use a longer focal length to keep the same framing? Are there other practical options, such as attachments or optical setups, that would help reduce this effect?

user70370 · Accepted Answer

Yes, increasing the distance is the most practical solution.

You can use your existing lens from any distance to determine at what point the perspective is suitably overhead/parallel. You would simply need to zoom in during image review. I.e. all lenses record the same perspective from the same distance; the same your eyes see. And focal length simply crops and magnifies that perspective... really no different than doing so after the image is taken (if there is enough image resolution to allow it).

Once you find the right distance, then you can use that to determine the right focal length to fill the sensor (4x dist = 4x FL). You will also want to choose a lens with minimal optical distortion (barrel/pincushion) and probably one with flat field focus (more important at shorter distances, and more common in macro lenses).

How can I reduce perspective distortion in close-up top-down photos of small objects?

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