Covert Wide-Angle Lens Adapter

... This is a simple wide-angle camera adapter invented by Steve Hines for covert photography where a picture must be taken through a small opening. The technique provides the benefit of it being inexpensive and likely that a tube can be improvised in the field, used, and discarded without it drawing attention if found. The tube is an afocal adapter and does not depend on a camera's lens being removed to be used, and therefore is usable with any camera or format.

... The wide-angle adapter can be any tube, with a specular interior surface, attached to the front of the camera lens. The camera photographs the direct view (the zero order image) directly through the hole in the tube. The camera sees a reflection of the scene reflected off the interior surface of the tube (the first-order image), as a circular ring around the hole. The camera also photographs the multiple reflections inside the tube. The next image is a larger ring or circular band twice reflected (the second-order image). Alternate circular images, starting with the open-hole, are erect and right reading (zero, second, fourth-order, etc.). Alternate odd-numbered images (first, third, and fifth-order, etc.) are inverted and reversed left-to-right, giving the appearance of being rotated.

... The angle of view is dependent only on the lens coverage and the interior reflectivity and surface quality of the tube. Image quality in the reflected rings is greatly dependent on the internal surface quality. A clear cast acrylic (Plexiglas, etc.) tube, painted black outside, is reflective enough to reflect images 3X - 4X wider than the field of view of the open hole. Wider angle views may require a polished metal tube, or a ground and polished and aluminized optical glass tube. A clear plastic or glass tube, wrapped with black electrical tape to absorb second-surface reflections, can also be used. To preserve image quality, the camera's lens aperture should be stopped down.

... Above is an animation of taking a photograph through a hole in a wall. The lower frame is the camera's image. Initially the field of view is restricted by the size of the hole. When the hollow tubular adapter is placed on the lens, wider parts of the scene can be seen in the reflections inside the tube, shown progressively. Alternate bands of reflections are upside down, and reversed left to right. These reflected rings can be corrected with dedicated camera electronics, or later with a 180° rotation using Photoshop.

... It can sometimes appear as if the wall of the tube is transparent because alternate image rings, starting with the central opening, are visible as if part of the image seen through the open tube, interrupted by alternate odd-numbered (1st, 3rd, etc.) images which will later be rotated 180°.

Increased coverage using Hines' Covert Wide-Angle Adapter

Image order	Image-Diameter increase (Field of View)	Image Area increase = (image dia.)2
"0", zero order (open hole)	1X (reference)	1X (reference)
1st Order (1 reflection, image must be rotated)	3X	9X
2nd Order (2 reflections)	5X	25X
3rd Order (3 reflections, image must be rotated)	7X	49X
4th Order (4 reflections)	9X	81X
Nth Order (this list can be expanded for any number of reflections; however, the image quality falls off with each reflection in the tube)	(this list can be expanded to include any lens angle)	.

Note, all odd-numbered reflections must be rotated.
Even numbered reflections do not require rotation.