Canon (2003), Extension Tube EF12 II/EF25 II Instructions. Canon Inc., Tokyo. • Comes with the 12 mm and 25 mm lens extension tubes and lists the maximum magnification for a number of Canon lenses with and without extension tubes. [Accuracy]

Kenko (2012), Auto Extension Tube Set Directions for Use. Kenko Tokina Co., Ltd., Tokyo.

Leica (2013a), Leica Summilux-M 35 mm f/1.4 ASPH Technical Data. Leica Camera AG, Solms. [Accuracy]

Leica (2013b), Leica Summilux-M 50 mm f/1.4 ASPH Technical Data. Leica Camera AG, Solms. [Accuracy]

Merklinger, Harold M. (1992), Depth of Field Revisited.. Dartmouth, Nova Scotia. • A short version of a series of papers which first appeared in Shutterbug in 1991-1992. The author wonders why he hardly ever gets satisfactory sharpness using the hyperfocal distance, and shows why another focusing strategy gives better results. [Infinity Focus]

Merklinger, Harold M. (2002), The INs and OUTs of FOCUS: An Alternative Way to Estimate Depth-of-Field and Sharpness in the Photographic Image. Internet Edition, Dartmouth, Nova Scotia. • Long version with all details. [Infinity Focus]

Nasse, Hubert H. (2011), Planar—The history and features of one of photography's most important high performance lenses. Carl Zeiss, Oberkochen, page 5. [Aperture]

Wegner, Gunther (2017), Diana lernt fotografieren. Verlag, Ahrensburg.

Zeiss (1997a), Depth of field—An insider’s look behind the scenes. Camera Lens News No. 1, Carl Zeiss, Oberkochen, page 3.

Zeiss (1997b), Resolution of camera lenses: Where are the limits—and why? Camera Lens News No. 2, Carl Zeiss, Oberkochen, pages 2-3. • Limitations of resolution due to diffraction, depth of field, film, and motion.

Zeiss (2015), Zeiss Milvus 1.4/85 Technical Specifications. Carl Zeiss AG, Oberkochen. [Accuracy]