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Technical Data

Optical Surface Quality
(Scratch/Dig)

 

 

 


Optical Surface Quality

Scratch / Dig

Measuring Optical Surface Quality can be an easily misunderstood concept.

While the industry continues to use & reference MIL-O-13830's numerical / quantitative listing of scratches / digs through an optical comparator, a more "proper" way is to compare to a set of standards, measuring the reflectivity of the surface under the naked eye.

Sinclair uses Edmund Optics standards, but provides the MIL-O-13830 information as a reference.

Scratch Dig Standards

Reference Article on Optical Quality Measurement at Edmund Optics

Sinclair provides the traditional MIL-O-13830 table as a reference, but it is important to remember it is the reflectivity that is important, and the numbers are reference only in the case of scratches.

Optical Surface Quality per MIL-O-13830
Scratch
or Dig #
Maximum
Scratch Width
Maximum
Dig or Bubble Dia
Dig or Bubble
Separation Distance
.
inch
mm
inch
mm
inch
mm
120
.0047
.12
.0473

1.20

.787
20
80
.0031
.08
.0315
.80
.787
20
60
.0024
.06
.0236
.60
.787
20
50
.0020
.05
.0196
.50
.787
20
40
.0016
.04
.0158
.40
.787
20
30
.0012
.03
.0118
.30
.787
20
20
.0008
.02
.0079
.20
.787
20
15
.0006
.015
.0059
.15
.787
20
10
.0004
.01
.0039
.10
.040
1
05
.0002
.005
.0020
.05
.040
1
03
.00012
.003
.0012
.03
.040
1

MIL-O-13830 Reference Definitions:
• A Scratch is any marking or tearing of the glass surface.
• A Sleek Scratch is a hairline scratch.
• A Crush or Rub Scratch is a surface scratch or a series of small scratches.
• A Dig is a small rough spot on the glass surface, similar to pits in appearance. A bubble is considered a dig.

MIL-O-13830 Reference Procedure:
Optical Surface Quality is to be specified by a number such as 60/40. The first digits relate to the maximum width allowance of a scratch as measured in microns. The next digits indicate the maximum diameter allowance for a dig, in hundredths of a millimeter. As can be seen in the table above, a 60/40 callout would permit a scratch width of .0024 inches, and a dig diameter of .0158 inches. The size of the defect is to be measured through the use of an optical comparator.

If you have any further questions on Scratch / Dig callouts or Optical Surface Quality as they apply to Sinclair's products, please contact us.

 


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