23 - drafting manual - optical parts

7/30/2019 23 - Drafting Manual - Optical Parts

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DRAFTING MANUALSection K23

Optical Parts Page 1Update 38 March 1991*

1.0 General

Unlike other physical objects, optical parts havetypically been a part of some other assembly orproduct, i.e., a microscope, a telescope, a camera, a

measuring device, etc. Thus, the drawing practicesfor such optical parts have been considered to beproduct peculiar; unlike the universe of otherproducts usually identified within the engineering

and manufacturing fields. However, highly special-ized optical parts are appearing in increasing num-bers within many other products used in industry.Some examples are alignment measuring instru-ments, leveling devices, optical tools, industrialphotographic products, projection devices (com-parators), and document reproduction machines.

1.1 The manufacturer of optical parts applies con-

siderable judgement and expertise above and be-yond the stated requirements of the related drawingor specification in producing the part. Unless suchparts are described precisely as intended, it may notbe possible to produce the optical parts as accu-rately as required. The purpose of this section,therefore, is to provide guidance and general prac-tices for the design definition of the required opticsand related documentation. The manufacturingcomplexities of optics in general place severelimitations on the kind and amount of design infor-mation that can be provided without placing undueconstraints on the optics manufacturer. In recogni-

tion of this fact, the guidelines in this section shouldenable an OEM (original equipment manufacturer),which includes optics in its designs, to acquire thenecessary optical parts with confidence.

2.0 References

American National Standards Institute (ANSI)Standard Optical Parts Y14.18-1986

American National Standards Institute (ANSI)

Standard Dimensioning & Tolerancing, 1982

MIL-STD-34 General Requirements for OpticalElements and Optical Systems

3.0 DefinitionsThe following figures provide a graphical overvieof the commonly used abbreviations to definevarious characteristics of some of the more comm

lens types. These abbreviations are not inclusiveand cover only a limited number of lens designs.See Figure 1 for definitions of abbreviations used Figures 2,3 &4.

3.1 Apertures

3.1.1 Clear ApertureThe clear aperture is the portion of element surfacfilled with the image-forming beam.

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3.1.2 Mount ApertureThe mount aperture is the mechanically toleranceportion of the element surface. Unless otherwisestated, the mount aperture is the same as the clearaperture.

3.1.3 Coating ApertureUnless otherwise stated, the coating aperture is thesame as the mount aperture.

3.1.4 Wedge ElementA wedge element may be a window, filter, reticle,

or other element depending on its specification andfunction. Aside from the mechanical features ofsize, the optical deviation should be provided andtolerance to a specified wavelength of light (Figure5).

Figure 5. Wedge Element

right angle prisms with appropriate interferencecoating on the hypotenuse surface (Figure 6).

3.1.6 ReticlesReticles are centering or aiming markings usuallyetched on a piano element. (Figure 7).

3.1.5 PrismA right angle prism is an element generally used to

achieve a 90bend in the light path. A variation of

this is a prism cube constructed by cementing two

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3.1.7 Windows Filters, Flat MirrorsWindows, filters, and flat mirrors are similar to

single lens elements. They differ from each otherprincipally by materials and applied coatings.

4.0 Specifying Requirements for Optical Parts

4.1 Conventional Practices

In general, the conventional practices describedelsewhere in this manual are also applicable todrawings of optical parts, assemblies, and opticalsystems.

4.2 Dimensioning PracticesDimensions and tolerances for optical parts shouldbe expressed in metric. The bilateral method ofTolerancing is preferred.

4.2.1 Mechanical Tolerances

The mechanical tolerance should indicate theallowable departure from the specified dimensionsinsofar as it affects size but not irregularity toler-ances of geometric shape. See Par. 4.2.2. Themechanical tolerance should be specified in thesame units of measure as the dimension to which itis applied.

4.2.1.1 Control of Chamfers/Bevels/Chips

In addition to normal tolerances, it is frequentlynecessary to apply tolerances to chamfers anddispersion of chips. When such tolerances arespecified, Figure 8 provides some acceptable prac-tices. Chamfers and dispersion chip size may becalled out on the detailed part or in the title block ofthe drawing. Since glass characteristics frequentlyresult in chipping throughout the manufacturingcycle, it may be desirable to specify on the drawing

an acceptable level of such chipping. A note may beused for this purpose, such as: Edge chips shall notexceed 15% of the total perimeter or be larger than0.5 max. width.



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4.2.2 Irregularity Tolerance

The irregularity tolerance specifies the allowabledeviation from the geometric shape. Such deviationis expressed in fringes, also called birefringes, eachof which is equivalent to 10 microinches. The

deviation applies to the entire surface unless other-wise noted. Where necessary the wavelength of thetest light used should also be specified.

4.2.3 Mechanical Surface Characteristics

Machined surface characteristics are normallyspecified in the same values as for other mechanicalmachined surfaces described elsewhere in thismanual,

4.3 Optical Surfaces

4.3.1 Spherical Optical Surfaces

Spherical optical surfaces should be dimensioned inthe form of a radius with both a mechanical toler-ance and an irregularity tolerance per Par. 4.2.2.

4.3.2 Flat Optical SurfacesFlat optical surfaces should be dimensioned as in

Figure 5. Irregularity tolerances should be ex-

pressed in fringes.

4.3.3 Aspheric SurfacesAspheric optical surfaces are dimensioned byindicating the algebraic equation of the curve of the

surface as a defined deviation from that surface.Surface coordinates may also be used for thispurpose. Tolerances should be specified and theaxis of the aspheric contour clearly defined.

4.3.4 Parabolic Surfaces

Parabolic surfaces are dimensioned by showing the

orientation of the axis and the location of the foci.

See Figure 9.

4.3.5 Hyperbolic and Elliptical Surfaces

Hyperbolic and elliptical surfaces should be dimen-sioned by delineating the orientation of the majoraxis and the semi-major and semi-minor diameters.

4.4 Pictorial and Descriptive Representations ofOptical Parts

4.4.1 Single Lens

A single lens is depicted by a sectional view as inFigure 10. Hidden lines are omitted in simpleconfigurations; however, complex configurationsare described using as many views as may be neces-sary. Glass hatching is optional.

4.4.2 PrismsAs many views as may be necessary should be usedto describe a prism (Figure 6).

4.4.3 Cemented Elements

When cemented elements are required, an assemblydrawing should be prepared in accordance withFigure 11. The optical parts are listed in the form ofa generic parts list. However, the elements may belisted and described in a parts list format above thetitle block or on a separate parts list that is refer-



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enced on the drawing. Suggested parts list formsand arrangements are described elsewhere in thismanual.

4.4.4 Piano ElementsA piano element may be a window, filter, reticle, or

other element not previously described. Some piano

elements are defined in the following paragraphs.

4.4.4.1 WedgesWedges are drawn as shown in Figure 5. In additto the thickness, the optical deviation should alsoprovided and tolerance at a specified wavelength

of light.

4.4.4.2 ReticlesDrawings for reticles should contain as many vie

as may be required to present all the necessarydetails. Reticle markings should be shown on the

drawing and be fully portrayed and dimensioned.

Enlarged views of the markings may be used if

necessary. It is usually necessary to specify certa

processes such as etchings and pattern deposit fo

manufacturing control of the item. Additional no

required for proper control of the reticle marking

are shown in Figure 7.

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4.4.4.3 Windows and FiltersWindows and filters are described in Figure 12.

Where a special orientation of an element is re-

quired, as in the case of a polarizing filter or beam

splitter window, the required orientation should be

stated in the field of the drawing note describing the

orientation and permissible deviation limits.

4.4.4.4 Flat MirrorsFlat mirrors are drawn in a manner similar to that

shown in Figure 5 except that specifications may be

different.

4.4.4.5 Coatings, Cementing, and Sealing

Surfaces applied to a specification should referencethe document and point of application. If a specifi-cation is nonexistent, then the necessary informa-tion such as coating material, method of application,thickness, light characteristics, color, etc., should beprovided. If the thickness of the coating is to be

expressed in wavelengths, the color or wavelengthof the test light should be specified.

4.4.4.6 Notes on FiguresThe notes shown on the various figures in thissection are intended for reference only. They mayor may not be applicable to the lens described in thefigures. Moreover, they may be placed on thedrawing in a manner consistent with the internal

practices of the originator of the drawing.4.5 Orientation

4.5.1 Optical System DrawingsOptical system drawings should be oriented so thatthe light is assumed to enter from the left side of thedrawing. The same practice should be observed foroptical elements and components (Figure 13).

4.5.2 Complex Optical SystemsThe optical elements and components of complex

systems should be displayed as they appear on thesystem drawing except that they may be rotatedclockwise to bring the optical axis horizontal on the

drawing. If the light does not enter from the left, theappropriate direction should be indicated by arrows

along the optical axis (Figure 14).

5.0 Selected Optical FormulasFollowing are some of the more common formulasfrequently used. Five variables, U, V, D, M, and Fdefine the system in the first order analysis. See

Figure 15. Each of the following three pairs ofvariations fixes the system, U & V, D &M, or M &F. Select the pair most important to the application

at hand.


Figure 12. Filter Element


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5.1 Lens PairsThe following formulas may be used to combinelenses in pairs to obtain focal lengths other thanthose in a catalog. In this manner on ecan demon-

strate principles much more easily and economic-ally than by fabricating special focal lengths for

prototypes

Where: FC = focal length of combinationF1 = focal length of first lensF2 = focal length of second lens

d = distance between principle planes ofthe two lenses

The above are first order relationships and as such

are only approximations. They are sufficientlyaccurate, however, for the majority of situations.The degree of sophistication required to make thetransition from thin lens to thick lens analysis is

beyond the scope of this section.

5.2 Glass PlatesWhen glass plates, filters, or prisms are introducedinto a converging beam of light, the focus shift musbe taken into consideration. The focus shift iscomputed as follows:

Where: N1 = index of the medium surrounding theglass plate (usually air: N1 = 1.0)

N2 = index of the glass platet = thickness of the glass plate

by rule of thumb then, the image if further from thelens by t/3 when flat plate is inserted in the b



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5.3 Relative Aperature = F NumberThe f number of a lens is defined by the ratio of the

effective focal length of the lens divided by thediameter of clear aperature of the lens. It is a meas-

ure of the amount of illumination that can passthrough the lens. It is expressed as

Where: N.A = numerical aperature

Where; n = index of refraction of the mediumbetween the object and objective (of

a microscope) usually air (n = 1.0)

=the half angle of the cone of lightentering the objective

5.4 DiopterThe diopter is the unit of power of the lens that is

most used in the opthalmic branch of the optical

industry. It is defines as the reciprocal of the lens

focal length stated in meters. It is computer as

follows:

5.4.1 Surface Diopter - DSThis is the quantity measured with diopter gauges.

The measurement can be converted to the surface

radius as follows:

Where: N = index of the glass

R= radius in mmDS = surface diopter

5.4.2 Prism DiopterA prism diopter power of1.0 indicates a beamdeviation of 1Omm at a distance of 1 meter

1 prism diopter = 0.573 beam deviation

Millidiopter

5.5 Effective Focal Length - EFL

This is defined as the second focal point withparallel incident light.

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