Does reciprocity failure (Schwarzschild effect) exist in digital photography?

Question

In analog photography (film) there was an effect called "Schwartschild effect", or Reciprocity failure when making long exposures (usually more than few seconds).

Some film brands created compensation tables for their films; for instance, you would need to double the time after 4 seconds, meaning if the meter says f/5.6 at 5 seconds you have to expose 10 seconds at the same aperture to get the film correctly exposed.

1. Does that effect exist in digital photography?

2. If yes - does the exposure metering automatically compensate for it? (meaning with the above example the exposure time will be automatically adjusted to 10 seconds).

Answer 1

Essentially, no - digital sensors are pretty much linear in that if you double the number of photons hitting it, you get double the output. They're obviously not perfectly linear, but they're close enough you don't need to worry about it.

Answer 2

No, the effect does not exist.

However, long exposures in digital have their own host of problems:

• Sensor overheating. This used to be a bigger problem, but with the advent of video DSLRs this has mostly disappeared.
• Hot pixels. Some sensors just don't like staying "active" and will internally leak and produce a single color hot pixel. Cameras and software such as Lightroom will automatically remove them, but in very long exposures or night-sky shots, they do not.

Answer 3

I think the concern here is about what happens as an end result to the user. With reciprocity failure with long exposures on film we used to see shifts in colour balances, with Ektachromes and the shift to magenta and pale yellows with Fujichromes. There will be large artefacts too. I found almost predictable reciprocity failures when we push processed beyond 3 stops — especially in larger formats of 8x10in film sheets shot on Sinars.

So rather than what the technical process would be, it will be relevant to understand the end result. I found artefacts with Canon images shot for above 60 secs, more in the 5D Mark 2, much less in the 5D Mark 4's, probably because of the wider dynamic range. The medium format H6D 100C has a far wider dynamic range and will not see the reciprocity failure we experience. So basically digital offers us a far greater possibilities of success than film can do. Again, if the photons is sufficient. In other words, long exposures means sufficient photons, and therefore reciprocity failures of the colour casts I spoke of earlier will not manifest.

The larger digital backs as opposed to the DSLRs have amazing brightness ranges and are a delight to work with as the need for post editing with layered selection or even HDRs are not needed. A more realistic feel nearing film quality is experienced today.