Difference between revisions of Chromatic Aberration

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 [[File:Chromatic aberration lens diagram.svg|Chromatic aberration lens diagram]]
-= Duochrome test =
+== Duochrome test ==
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-The chromatic aberration expected during a normal eye exam is about a half diopter difference between red and green.  This can be a handy test to dial in a final prescription by looking at text on red and green backgrounds and seeing which is clearer.  For a standard [[Prescription]], if the green side is clearer, a quarter diopter of sphere is added, if the red side is clearer, a quarter diopter is removed.  If the optometrist is trying to introduce a small amount of [[Myopic defocus]] he/she wants the red side clear.
+The chromatic aberration expected during a normal eye exam is about a half diopter difference between red and green.  This can be a handy test to dial in a final prescription by looking at text on red and green backgrounds and seeing which is clearer.
 <youtube>WP6eeoyB9go</youtube>
-= External Sources =
+== External Sources ==
 * [[Wikipedia:Chromatic aberration]]
 * [[Wikipedia:Duochrome test]]
+== Lens Material ==
+Different materials have different [https://en.wikipedia.org/wiki/Abbe_number Abbe numbers]. Materials with higher values are better, since they tend to have less chromatic aberration.
+Here are some typical values:<ref>https://www.allentownoptical.com/abbe-value-interpretation/</ref>
+{| class="wikitable sortable"
+!Material
+!Index
+!Abbe Value
+|-
+|Crown Glass
+|1.523
+|59
+|-
+|High Index Glass
+|1.60
+|42
+|-
+|High Index Glass
+|1.70
+|39
+|-
+|Plastic CR-39
+|1.49
+|58
+|-
+|Mid Index Plastic
+|1.54
+|47
+|-
+|Mid Index Plastic
+|1.56
+|36
+|-
+|High Index Plastic
+|1.60
+|36
+|-
+|High Index Plastic
+|1.66
+|32
+|-
+|Trivex
+|1.53
+|43
+|-
+|Polycarbonate
+|1.58
+|30
+|-
+|MR-174
+|1.74
+|32
+|}
+[[File:Lens materials and optical quality chart.png|Lens materials and optical quality chart]]
+[https://community.endmyopia.org/t/lens-materials-and-optical-quality-chart/4415 chart created by steadicat]
+=== Tradeoff Between Chromatic Aberration vs Distortion ===
+When choosing lens index, remember to take into account overall distortion at the edges of the lens.  Too much overall distortion may make it difficult to view the edges of the lenses.
+[https://endmyopia.org/need-high-index-lenses/ EndMyopia: Do You Need High Index Lenses?]
+The following vendor articles may be of interest:
+* [https://www.zennioptical.com/glasses-lenses Zenni]
+* [https://www.eyebuydirect.com/prescription-lens/lens-index EyeBuyDirect]
+* [https://www.selectspecs.com/guides/lenses/single-vision/ SelectSpecs]
+* [https://www.framesbuy.com/trends/lens-index/ FramesBuy]
+Anecdotally from the forums, -3 is a balanced cutoff range for CR-39 where one can take advantage of higher abbe and competitive cost, without experiencing too much distortion at lens edges. Outside of that range, consider higher index lenses to minimize distortion.
 ==References==