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.
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.
©2009 Sinclair Manufacturing Company