Reviewing the exposure meter constant: improving the exposure equation

Michael G. Prais

doi:10.1117/12.844933

18 January 2010 Reviewing the exposure meter constant: improving the exposure equation

Michael G. Prais

Proceedings Volume 7537, Digital Photography VI; 75370X (2010) https://doi.org/10.1117/12.844933
Event: IS&T/SPIE Electronic Imaging, 2010, San Jose, California, United States

Abstract

A careful mathematical analysis of the meaning of variables and equations used in standards for exposure meters and the determination of sensitivities S demonstrates that standards and authors of many photographic texts have erred in interpretations and applications of the common exposure equation. This article concludes that it is inappropriate to use the exposure meter constant K_s as an exposure meter calibration constant because it is essentially a label for a product of characteristics of the photosensitive array employed (the reference exposure H_o = Hsp/_S and the midtone shift M = H_mid/H_sp). It also concludes that the sensitivity and the common exposure equation ultimately depend on the midtone photosensitive exposure target H_mid. This midtone exposure equation can be generalized by including a shift to a arbitrary (non-midtone) photosensitive exposure target in its derivation. This more general exposure equation includes the exposure compensation and eliminates the need for exposure indices. Analysis of the exposure equation for incidentlight exposure meters shows that these meters avoid the vagaries of the current scene by calculating exposure for a potentially very different standard scene and often can be, in effect, less accurate in exposure calculations than reflectedlight exposure meters.

Citation Download Citation

Michael G. Prais "Reviewing the exposure meter constant: improving the exposure equation", Proc. SPIE 7537, Digital Photography VI, 75370X (18 January 2010); https://doi.org/10.1117/12.844933

ACCESS THE FULL ARTICLE

INSTITUTIONAL
Select your institution to access the SPIE Digital Library.

SELECT YOUR INSTITUTION

PERSONAL
Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.

PERSONAL SIGN IN

No SPIE Account? Create one

PURCHASE THIS CONTENT

SUBSCRIBE TO DIGITAL LIBRARY

50 downloads per 1-year subscription

Members: $195

Non-members: $335 ADD TO CART

25 downloads per 1 - year subscription

Members: $145

Non-members: $250 ADD TO CART

PURCHASE SINGLE ARTICLE

Includes PDF, HTML & Video, when available

Members: $17.00

Non-members: $21.00 ADD TO CART

PROCEEDINGS
10 PAGES

DOWNLOAD PAPER SAVE TO MY LIBRARY

GET CITATION

RIGHTS & PERMISSIONS

Get copyright permission Get copyright permission on Copyright Marketplace

KEYWORDS

Cameras

Photography

Calibration

Holmium

Photosensitizer targeting

Standards development

Camera shutters

Show All Keywords

Keywords/Phrases

Search In:

Publication Years