1506. Why does P5 put a short time limit on combining exposures?

There are two reasons for imposing a short time limit, one philosophical and one practical.

1. For philosophical reasons: “one moment” is one of the 9 characteristics that every TTG-qualified photograph must have, and neither common definition of “moment” would accommodate combining exposures that were taken with a generous amount of time between them.

2. For practical reasons: having “no time limit” would lead to unacceptable combinations of exposures (“I returned to this national park a year later and the scene had hardly changed at all, so I combined an exposure I made last year with an exposure I took this year”).

Every TTG photograph — including those made by combining exposures — must look like a single-exposure, undoctored photograph. (See also FAQs #1401–1403.)

The longer the combined-exposure time limit...

. . . the more likely that changes in the scene between exposures will produce a result that requires making changes that are not* on TTG’s Allowable Changes list to make the image look like a single-exposure, undoctored photograph.

*Any changes not on that list disqualify an image from P2 and from TTG