Circular Fisheye vs Rectilinear Fisheye

[Bob]

Which lens will generally produce a better (detail with less distortion) when stitched with PTGui: a circular fisheye or a rectilenear fisheye? Thanks. Bob

[sc...@highton.com]

Bob,

I think there's some confusion on terminology here.  There's no such thing as a rectilinear fisheye lens.

There are two kinds of fisheye lenses; true (or circular) fisheye – where the entire 180° (or more) image circle is included within the sensor or film frame area, and full-frame (diagonal) fisheye – where the image circle projection is larger so it completely fills the sensor or film frame area.  This means its field of view is 180° along the diagonal of the image frame, but less than that along the horizontal and vertical directions.  Essentially, these parts of the full image circle are cropped off by the edges of the camera sensor/film frame.  Fisheye lenses project what are commonly called a "fisheye distortion," where straight lines outside of the center of the frame are rendered as curved lines.  They generally capture significantly wider fields of view than "corrected" rectilinear lenses.

A rectilinear lens is one where the optics have been designed to project a "corrected" image onto the sensor so that straight lines in the scene (such as walls, doors, windows, etc.) appear straight, rather than curving as they do with fisheye projections.  Rectilinear lens fields of view are generally significantly less (narrower) than what fisheye lenses can capture.

There are tradeoffs between using either type, and your decision will depend on a variety of factors.

In panoramic VR capture, where you are stitching multiple images together to form a complete 360° view, using a fisheye lens means you can capture the scene with fewer shots.  Each shot captures a larger (wider) field of view.  Using a rectilinear lens requires more shots to record that same 360° view, but provides greater detail.  Many VR photographers find using a full-frame fisheye lens is a good compromise.

For example, I shoot 90% of my panoramic VR work (360°x180° fields of view) with a 16mm Nikkor full-frame fisheye lens on a full frame D850 or D800 camera.  I can do it with the camera in vertical orientation by capturing six shots around the horizon (60° pan increments) plus zenith (upward) and nadir (downward) views.  Alternately, I can do  the same capture with a bit more overlap between shots by tilting the camera up 30° and shooting 6 images (every 60° panning), and then tilting it down 30° and shooting 6 more.  Both of these will provide a stitched equirectangular image at between 20,000x10,000 and 22,000x11,000 pixels of resolution – adequate for fairly high resolution presentations and wall-sized printing.

Of course, there's more to "better detail" than higher resolution.  Lens quality makes a big difference, and lens performance (i.e. how well it mitigates lens flare, its color rendition, its edge vs. center sharpness, etc.) is key.

Also, you don't mention whether you're just wanting to use your photographs just for panorama stitching, or whether you want them to serve as stand-alone single images.  That will usually make a difference in which type of lens you choose.

You'll also want to consider your computer's processing power and storage capabilities, as higher resolutions and more source images can tax both of these significantly.

Regards,

Scott Highton

Author, Virtual Reality Photography

Web:  https://www.vrphotography.com