How long should a good image keep your attention?
You go to galleries and some people look at an image for two seconds or less and move on. You feel you should spend more time with an image, but you notice that some images you "get" in the first glance, may even really like them, yet don't offer a whole lot more when you stick around for a few minutes.
Truth is good images vary dramatically in their "staying power". Take for example an image that is all about shapes of colour - there are only three - the background and two shapes one red and the other yellow - and that's basically it - they might be cars or a sign or building, doesn't really matter. It's not difficult to "get" the image very quickly. It may affect you profoundly, yet doesn't require further reading.
An analogy would be a good joke. You read it in two seconds, you may continue to occasionally chuckle as you remember it for a long time after. On the other hand, a novel by a great writer may have you pausing with each sentence to revel in the language, description and feeling. it would appear that the length of the text doesn't relate well to the impact. So it is with photographs. You can have the bold graphic described above or you might have a sophisticated image with not only basic shapes but textures and contrasts and alignments and harmonies which might take you many minutes to appreciate - and in fact may require "rereading" to get the full meaning.
The latter image isn't necessarily better than the first, just different, just as the one liner is different from the novel. Perhaps a better analogy would be a joke and a poem, both with the same number of words, the one having it's impact complete and instant, the other containing subtleties and levels, nuances and depths. The immediate impact of the joke is certainly the more powerful, yet one might keep going back to the poem, re reading it, thinking about the words, their pace and sequence, their meaning and relationships.
Neither the poem or the joke is better, just different. Why shouldn't two photographs be just as different?
Yeh, but what does that mean when I'm out photographing?
Well, quite a lot. If you want the equivalent of the joke, then you need a bold, simple image that grabs you. If on the other hand you want poetry, you'd better be thinking in terms of mutliple levels, more than just pretty or dramatic, you want to offer the big details that grab the viewer but small details that keep them looking. There's the plot, the sub plots, the details and the designs within designs.