Above: Giacometti. Credit: HC-B.
The point of candid photographs is this: once a person knows they are about to be photographed their behaviour and facial expression will change. The facial expression in particular will immediately transform into a posed one; the pose decided upon by the subject will likely be drawn from a familiar repertoire ... "quietly confident" ... "open-and-sincere"... "Mr Cool" .... "What ... me?" etc. A candid approach to photo is one in which the photographer is seeking to avoid the crunching banality of pre-selected photo-poses: that's all.
The candid subject does not realize or know that they are being photographed and so has got no reason to pose. The candid photographer is just a photographer who is not really interested in documenting banal poses-to-camera.
The candid photographer is interested in documenting life as it is actually lived, in other words, the candid photographer is interested in subjects who are natural, uninhibited, spontaneous, informal.
That the candid photographer often has to engage with some-or-other subterfuge or disingenuousness to achieve this goal, is just something that goes with the territory--it is unavoidable. Candid work is rooted in (and always has been rooted in) a sort of "noble rudeness" on this account. It is not intrinsically unethical to take a candid photo for artistic reasons, however, it is important to proceed with sensitivity and mindfulness of any intrusion on your subject's privacy (and right to privacy).
Thinking technically, if you bring out a camera and hold it up in the direction of your subject, you are also alerting them to your intention to take a photo--and so curtailing the candid-photo-opportunity. This being the case, one basic and vital tool of the candid photographer is the waist-level finder. Using this format of viewfinding the photographer peers down into their viewfinder and is much less likely to alert their subject to their activity. Some cameras, like the Rolleiflex are built with waist-level finders as standard.
For digital cameras to be used in candid work, it is essential that the viewfinder screen can be flipped-out and angled horizontally (so you are looking down into it). If the screen does not flip out this way it is not suitable for candid work. With DSLRs a waist-level-finder is a specific optional accessory which is expensive-but-needed.
When using a smartphone an angled mirror device is available which clips over the lens thus allowing the photographer to hold the smartphone as if texting or reading from the screen--a great subterfuge!
What to do if someone stops you to question your intention? The intention to take candid photos in the era of international terrorism and avid social-media posting tends to be greeted not with indifference but with righteous indignation. A reaction that is very different from the mood on the streets in the era of Winogrand, Frank, or Cartier-Bresson.
It is important, if you are confronted, to have with you some examples of your candid photography and ideally a printed business card (perhaps with the url of your website on it). Another option is to carry examples of great canonical street photography with you (I used to carry a bunch of postcards of work by Kertesz and Friedlander).
Patiently explaining about candid photography and its rich history to a vexed stranger is all part of the gig. So, be prepared to stop and talk, and not turn-and-run. Doing the latter will likely--and rightly--cause your subject to call security or the Police.
One other way of achieving true fly-on-the-wall candid photos of subjects going about their everyday lives is to become a super-sniper using a long telephoto lens. Telephoto lenses of more than 500mm are the best for this application but are very expensive. One can often be rented-by-the-day from pro-camera equipment companies.
(13 December 2018)