Matthiessen's ratio

{{Short description|Type of optic ratio}}

{{For|the electron mobility rule|Matthiessen's rule}}

{{one source |date=March 2024}}

In optics, Matthiessen's ratio is the ratio between the distance from the centre of the lens to the retina, versus the lens radius.{{Cite journal

| issn = 0042-6989

| volume = 39

| issue = 6

| pages = 1071–1078

| last = Shand

| first = J.

|author2=K. B Døving |author3=S. P Collin

| title = Optics of the developing fish eye: comparisons of Matthiessen's ratio and the focal length of the lens in the black bream Acanthopagrus butcheri (Sparidae, Teleostei)

| journal = Vision Research

| year = 1999

| pmid = 10343827

| doi = 10.1016/S0042-6989(98)00215-6

| s2cid = 8525655

| doi-access = free

}}

This is of particular importance in fish, where the value may decrease from as high as 3.6 to 2.3, decreasing the focal ratio of the lens. A higher focal ratio is thought to compensate for the relatively high Matthiessen's ratio brought about by constraints of small eye size during early development. This provides a means for larval fish to focus images from different distances, before the ability to accommodate is gained.