MINOX 8x11 DOF

-- martin tai (martin.tai@capcanada.com), December 21, 1998

Answers

Depth of field theory and DOF scale was Leica invention.

Early Leica lens had no DOF scale.

DOF scale appeared on Leica Elmar lens probably around 1934.

The first Riga Minox(1938) has already DOF scale and } mark.

Hyperfocal focusing was a later development probably from the early 50s.

Many Zeiss Ikon cameras of that period has a red marked dstance on focusing scale and a red marked aperture. For example a Zeiss Ikon Contessa camera of early 50s has a red marked F8 and red marked 20 feet-- set aperture at F8, focus at 20 feet and shoot, objects between 10 feet to infinity will be sharp.

Minox GT-X/GTS 35mm series camera has a "green line" snapshot setting, this is the same idea as Zeiss Ikon cameras.

Riga Minox, Minox II, III has no hyperfocal point. Neither the Minox IIIs made in first model year 1954 has hyperfocal point.

In 1955 Minox IIIs started with a red dot hyperfocal point between 6 feet and infinity.

Examine a Minox focusing dial. There is a dot between 6 feet and infinity ( or between 2 meter and infinity on metric Minox ) The distance indicated by the dot is the hyperfocal distance of focuisng MInox A/B/C/LX/TLX/CLX. The hyperfocal distance H on these Minox camera is 12 feet or 4 meter. This is a good general purpose snap shot setting, when you set you Minox lens at this hyperfocal distance, object from 6 feet ( or 2 meter ) to infinty will be sharp up to 5 x 7 " enlargement.

The DOF of Minox A/B/C/LX/TLX was designed with a coc (circle of confusion ) of 1/60mm, such that 5x7" enlargement from uncropped 8x11mm negatives is sharp when viewed at 10" with corrected eyes( ie, wearing eye glasses if necessary , but NO LOUP ). This is essential, as uncropped Minox negative when enlarged to 5x7" and viewed at 10" distance reproduces the exact retina image as if viewing the real scene when the picture was taken. In other word, for Minox negatives, 5x7" viewed at 10" is not only sharp, but also has the correct perspective.

-- martin tai (martin.tai@capcanada.com), January 08, 1999.

Hyperfocal distance

Hyperfocal distance of a lens is the starting point for depth of field calculations.

Hyperfocal distance of lens is usually represented by H.

H is a function of focal length, circle of confusion and aperture of lens. H is given by the following formula H = f + f*f/(N*coc ); where f= focal length, N = fstop number, and coc is circle of confusion.

Many people thing coc is a mysterious number, coming from nowhere.

Minox camera's depth of field (and hyperfocal distance ) is based on a coc of 1/60mm. Why 1/60 mm; because it is derived from that the fact that human eyes can resolve a spot no smaller then 1/4 mm on a print 10" away from eyes; If on a 5x 7" print, the smallest spot resolved by naked eyes is 1/4; and 5x7" represent a 15x enlargment, then obviously the smallest spot on Minox neagtives will be 1/15 of 1/4, that is 1/60mm.

Subsitude f =15mm, N =3.5 and coc = 1/60 you will get approxiately 4 meters or 12 feet.

It is not necessary to calculate hyperfocal distance to high accuracy, because, you see, the choice of circle of confusion is entirely up to you. If you want a larger or smaller size print you may choose a smaller or larger circle of confusion.

For instance, if you choose 8x10" size enlargement, the required coc wil be 1/100 mm, and the hyperfocal distance will be 6.6 meter or 22 feet.

For 11x 14", you need another different set of values

Hyperfocal Series

Hyperfocal distance H has one interesting property: H/0, H/1 , H/2, H/3, H/4.....H/n... forms a HYPERFOCAL SERIES.

When the lens is focus at H/0, ie, infinity, depth of field is from H/0 to H/1; when lens is focus at H, depth of field is (H/0, H/2, that is infinity to half of H ), and so on.

HYPERFOCAL DISTANCE OF MINOX EC.

Minox EC has a F5.6 lens, the stated depth of field is from 1 meter to infinity.

From this we conclude that its hyperfocal distance is 2 meters or 6 feet.

The corresponding circle of confusion for such a value of hyerfocal distance for 15mm/f5.6 lens is 0.022mm or 1/45 mm. That corresponds to enlargement size of 3.5x 5"

One can have Minox EC lens custom adjusted to focus at a hyerfocal distance of 4 meter( for example by DAG ), and change the depth of field from 2 meter to infinity.

This corresponds to a circle of confusion of 0.01 mm, and enlargement of 8x10"

MINOX MX DEPTH OF FIELD TABLE

Focal length : 15mm

Aperture F4.8

HYPER FOCAL DISTANCE = 3 meter/10 ft

MINOX MX DEPTH OF FIELD TABLE

MINOX MX DEPTH OF FIELD TABLE
FOCUS AT	NEAR LIMIT	FAR LIMIT
1 M	0.75 M	1.50 M
1.5 M	1 M	3
2 M	1.2 M	6 M
3 M	1.50 M	INFINITY
3 feet	2.3 ft	4.3 ft
4 ft	3 feet	6.7 ft
5 ft	3.3 ft	10 ft
10 ft	5 ft	Infinity

In general if lens is focus at H/n, depth of field is H/(n+1) to H/(n-1).

-- martin tai (martin.tai@capcanada.com), January 08, 1999.

-- martin tai (martin.tai@capcanada.com), January 08, 1999.

-- martin tai (martin.tai@capcanada.com), January 08, 1999.

-- martin tai (martin.tai@capcanada.com), January 09, 1999.

-- martin tai (martin.tai@capcanada.com), February 02, 1999.

-- martin tai (martin.tai@capcanada.com), February 11, 1999.