MIL-STD-150A 军用标准更新通知 - CSDN文库

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MLSTB-I SOA

--\

12 May 19s9

mum cleti opening cl the surface which is

actually u;ed in forming an image

in any

part of th( field:The mount aperture at each

surface sk d] be at least as large as the clear

aperture :

n order that vignetting will not

exceed the computed value. The clear aper-

ture is ust,ally circular and specified by its

diameter. ;t is sometimes referred to as the

free aperw re.

&2JiRe, u~ctiaperture.s The relative aper-

ture shall .}edefinedas the ratio of the EFL

to thediameter of the effective aperture. The

SVITIUOJ for relative aperture Sha]i be A“j

Ioiiowed

by a numerical value. it IS~vritten

as a iraction, for exampie, f/2 signities that

Lhediameter [~t’theeffective aperture is one-

half the focal length. For an object at an

infinitedistan.e, thedenominator of therela-

tive aperture ,md the second member, N, of

the aperture r.kio are identical, provided-the

image is formed in air and the imageryobeys

the sine condition.

32.5.1 ~-?wnJbw,6The f.number ~ha]] ~

definedas the denominator in the expression

for the rel:itive aperture. Thus, if the rela-

‘; ve aperture is f/2, the f-number is 2.

3.2.6 T-a‘op and T-nwnber.7 The T-stop is

referred to as the aperture of a lens cali-

brated photometrically and assigned a T-

number, ,rhich is the f-number of a circular

opening in a fictitious lens having 100 per-

cent tram: uittan- andwhich gives the -e

central image illuminance as the actual lens

at the specified stop opening. Hence, for a

lens with a circular aperture, the

f-number

T-niiixber = ---

(8)

Vt

.-. —.

Wher?t is th~transmittance. For a lens with

.tr eflect+.ve::nerture ,>”any shape and area

A, the corresponding formula is:

f

T-number = —

r

w

— ,1)

2

At

The transmittance of thelens shall be defined

as the ratio of the transmitted light flux to

the incident light flux. The symbol for the

T-stop shall be T followed by a space and a

numerical value —

for example, T 2. The

numeral 2 r+:presentsthe T-numher. (F r

test procedure, see 5.L2.1O.)

3.2.6.1 Area weightdd average T-wtt .... ,

The T-number ~s defined in 3.2.6 is a c, i, -

parative measure of illuminanceon the ax:.

of a lens.Since theilluminanceusuallyvarie=

over the field,a need may exist for determin.

ing T-numbers for

OfT axia] im4ge ~in~ ~~

computing an average T-number. In accord-

ance with the basic photometric relation-

ships involved, the general detlnition of T-

number is given as

1

I

(5)

Since, in accordance with this definition,

l—

–d

=B = TO

d

Eti

2

d

.——

T,

%

= T,

(6)

E, “

In these expressions, T, is the T-number for

an image point in a zone i, To is the axial

T-number, B is the object luminance, E. is

the illuminance on the axis, and E, is the

average illuminancefor the zone. Compatible

units should be used for quantities B, EO,

and El. when the illuminance is averaged

over the field, weighting the average by the

area cifthe circular zone in which the iMni-

nance is determined,and this average is sub-

stituted ior El in equation (6), the resulting

T-numkr i~ called the area weighted aver-

age T-number, or AWAT. For cmcular zones

which extend beyond the ~undaries of the

SUptwaks Page s d 12 May1959

5

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