
Contents
-
-
-
-
-
-
-
-
-
-
-
Introduction—the nature of superposition imagery Introduction—the nature of superposition imagery
-
Refracting superposition Refracting superposition
-
Telescopes and lens cylinders Telescopes and lens cylinders
-
Resolution and sensitivity Resolution and sensitivity
-
Eye-glow and the superposition pupil Eye-glow and the superposition pupil
-
Light and dark adaptation Light and dark adaptation
-
Single and double eyes Single and double eyes
-
-
Superposition and afocal apposition: the eyes of butterflies Superposition and afocal apposition: the eyes of butterflies
-
Reflecting superposition Reflecting superposition
-
Parabolic superposition Parabolic superposition
-
Summary Summary
-
-
-
-
Cite
Abstract
Superposition eyes produce real, erect images on a retina separated from the optical elements by a clear zone. In refracting superposition eyes, the optical elements may be lens cylinders or corneal lens/lens cylinder combinations. These act as inverting telescopes. Resolution can be as good as in an apposition eye with similar-sized facets, and the sensitivity is usually much greater than in an apposition eye of the same size. Double eyes, with different resolution in the two parts, occur in both insects and crustaceans. Superposition eyes often exhibit eye glow when they are illuminated from the viewing direction, which results from a reflecting tapetum behind the retina. Butterflies have afocal apposition eyes. This system is closely related to refracting superposition, except that the telescopic elements have a much higher magnification than those of moth superposition eyes. Light enters the rhabdom as a parallel beam, rather than as a focused image as in ordinary apposition eyes. Shrimps, crayfish, and lobsters have superposition eyes in which the optical elements are not lenses but mirrors. The reflecting surfaces are at right angles to the eye surface, and form a square array. Most rays encounter two faces of each square, and this corner-reflector configuration makes it possible for the eye to form an image over a wide field of view. A third mechanism – parabolic superposition – makes use of a lens/mirror combination to form the dog-leg ray path necessary for superposition imagery. This is found in certain crabs.
Sign in
Personal account
- Sign in with email/username & password
- Get email alerts
- Save searches
- Purchase content
- Activate your purchase/trial code
- Add your ORCID iD
Purchase
Our books are available by subscription or purchase to libraries and institutions.
Purchasing informationMonth: | Total Views: |
---|---|
October 2022 | 2 |
November 2022 | 11 |
January 2023 | 2 |
February 2023 | 3 |
March 2023 | 7 |
April 2023 | 9 |
June 2023 | 5 |
July 2023 | 3 |
August 2023 | 2 |
September 2023 | 2 |
October 2023 | 1 |
November 2023 | 7 |
December 2023 | 2 |
January 2024 | 1 |
February 2024 | 8 |
March 2024 | 8 |
April 2024 | 5 |
May 2024 | 3 |
June 2024 | 3 |
July 2024 | 6 |
October 2024 | 3 |
November 2024 | 3 |
December 2024 | 2 |
January 2025 | 5 |
February 2025 | 5 |
March 2025 | 8 |
April 2025 | 6 |
Get help with access
Institutional access
Access to content on Oxford Academic is often provided through institutional subscriptions and purchases. If you are a member of an institution with an active account, you may be able to access content in one of the following ways:
IP based access
Typically, access is provided across an institutional network to a range of IP addresses. This authentication occurs automatically, and it is not possible to sign out of an IP authenticated account.
Sign in through your institution
Choose this option to get remote access when outside your institution. Shibboleth/Open Athens technology is used to provide single sign-on between your institution’s website and Oxford Academic.
If your institution is not listed or you cannot sign in to your institution’s website, please contact your librarian or administrator.
Sign in with a library card
Enter your library card number to sign in. If you cannot sign in, please contact your librarian.
Society Members
Society member access to a journal is achieved in one of the following ways:
Sign in through society site
Many societies offer single sign-on between the society website and Oxford Academic. If you see ‘Sign in through society site’ in the sign in pane within a journal:
If you do not have a society account or have forgotten your username or password, please contact your society.
Sign in using a personal account
Some societies use Oxford Academic personal accounts to provide access to their members. See below.
Personal account
A personal account can be used to get email alerts, save searches, purchase content, and activate subscriptions.
Some societies use Oxford Academic personal accounts to provide access to their members.
Viewing your signed in accounts
Click the account icon in the top right to:
Signed in but can't access content
Oxford Academic is home to a wide variety of products. The institutional subscription may not cover the content that you are trying to access. If you believe you should have access to that content, please contact your librarian.
Institutional account management
For librarians and administrators, your personal account also provides access to institutional account management. Here you will find options to view and activate subscriptions, manage institutional settings and access options, access usage statistics, and more.