Tone lenses

Cold Springs Station, Nevada, 1999. 2008 Steve Anchell. Ilford HP5+ developed in Edwal s FG-7 for 12 minutes at 70F/21C. The smooth tones of the fine grain effect are enhanced by the use of a medium format negative. Photo made with Mamiya RZ67 with a 65 mm f/4 lens. 

If you decide to make your own ND films the problem to watch out for, next to dust, is that the illumination might not be even at the position of exposure. Clean the enlarging lens and carefully scrutinize the results on film in order to identify any irregularities or fell-off in tone. Of course, it is more common to obtain irregular densities via uneven development than from uneven illumination. 

The ciliary muscle is innervated by the parasympathetic nerve, and acts to decrease the tone on the supporting muscle fibers of the lens, and thus increases the accommodative power of the eye. Acetylcholine and its congeners constrict the ciliary muscle fibers, and atropine and related compounds paralyze the ciliary muscle. 

Halftone (tone)—the image is broken down into a series of cells or dots by a screening process, using 40-300 per linear inch, giving a series from coarse to fine screen. (Look at the coarser process used in newsprint through an 8-10x magnification hand lens.)... 

G.D. Kymionis, M.A. Grentzelos, A.E. Karavitaki, P. Zotta, S.H. Yoo, LG. PaUikaris, Combined comeal collagen cross-Unking and posterior chamber tone implantable collamer lens implantation for keratoconus. Ophthalmic Surg. Lasers Imaging 42 (2011) e22-e25. 

Figure 5. Resolution, (a) Optical image of a standard specimen having patterns for measuring resolution (i.e., resolution chart) for the scanning acoustic microscope in C-scan mode using a tone-burst wave (b) acoustic image. The acoustic lens is focused onto the surface of the resolution chart. The acoustic lens is operated at a frequency of 1.0 GHz.

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