How small can you see?

For most people, the closest comfortable viewing distance, termed the near distance for distinct vision is approximately 25cm (10in). A comfortable viewing distance is also one at which the angle of view is approximately 60°; at a distance of 25 cm, this corresponds to about 30cm, approximately the diagonal of an 8×10 inch (25 x 20cm) image.

Circle of confusion diameter limit (“CoC”) is defined as the largest blur circle that will still be perceived by the human eye as a point when viewed at a distance of 25cm. At this distance, a person with good vision can usually distinguish an image resolution of 5 line pairs per millimeter (lp/mm), equivalent to a CoC of 0.2mm in the final image. In this case, a circle is indistinguishable from a point if it is of ~0.03mm (1/850in) diameter or less on the print.
[Note: if an 8x10 inch original image is contact printed, there is no enlargement, and the CoC for the original image is the same as that in the final image. However, if the long dimension of a 35mm image is enlarged to approximately 25 m (10 inches), the enlargement is approximately 7 times. The CoC for the original image is 0.2mm/7, or 0.029mm.]

Resolution lp/mm (1000:1) / Grain RMS
Fuji Reala 100 -- 140 / <4
Fuji Superia 100 -- 125 / 4
Fuji Superia 200 -- 125 / 4
Fuji Pro 400H (NPH) -- 125 / 4
Fuji Astia 100F -- 140 / 7
Fuji Velvia 50 -- 160 / 9
Fuji Velvia 100 -- 160 / 8
Fuji Velvia 100F -- 160 / 8
Fuji Provia 100F -- 140 / 8
Fuji new Sensia 100 -- 140 / 8
Ektachrome 100vs -- 100 / 11
Ektachrome 100 -- 100 / 11
Ektachrome 200 -- 125 / 12
EliteChrome EC 100 -- 100 / 11
EliteChrome 200 -- 125 / 12

Diffraction limit of lenses
At 50% contrast between detail and background, the resolution power is limited by the diffraction limit. The diffraction limit (lp/mm), by approximation, is given by 1000/n where n is the aperture. For example, the value of an f/8 macro lenses is 1000/8 = 125 lp/mm. With the criterion for resolution of 5 lp/mm of above, the largest enlargement factor will be 125/5 = 25.

With modern films and lenses we can enlarge the image 20 - 25x of the original, i.e. in the size of 29 x 19 - 36 x 24 in.

Hyperfocal Distance
The nearest distance of acceptable sharpness = 0.5H; furthest distance = infinity.
The hyperfocal distance of a lens is calculated by

H = F² / (30 x f), where

the value is calculated using a "circle of least confusion" of 0.03mm and
F = focal length (mm), e.g. 28mm wide-angle lenses
f = aperture f/ stop value, e.g. at f/16

Sunny f/16 Rule
Films are designed to give correct exposure with the sun high in the sky (e.g. on a bright day in the northern hemisphere) when the lenses aperture is set to f/16 and the shutter speed at 1/ISO rating. You can fine tune / check the camera's meter by adjusting the offsets of f/16 when the speed is at 1/ISO. For example, for ISO 100 film, f/16 +/- 1/3 at 1/100.


Reference:
Diffuse RMS (root mean square) measures the size of dye clouds, or grain as it was called with black & white film. RMS is simply a measurement of the variability in density using a densitometer trace across an area of even tone. Film with RMS 5 is twice as grainy as film with RMS 4. Resolution is lower in dark (low-contrast) areas than in bright (high-contrast) areas, so is measured at 1.6:1 and 1000:1 contrast levels, specified in line pairs per millimeter (lp/mm); double this number to get dots per millimeter. Sharpness is measured by MTF (modulation transfer function) at different values of lp/mm; numbers show where MTF crosses below 100%.