Canon T5i, takes blank pictures after focusing

Question

I've used manual mode with the exact same setting 100's of times taking pictures of the moon. Setting of ISO 100, f/11 at 1/500. Everytime it's come out perfect but tonight it will focus perfectly, but take a completely black picture. All other modes work perfectly. What could be the problem?

Answer 1

You shouldn't be getting a solid black photo at that exposure value, but it will be about 3-4 stops underexposed.

The classic rule for photographing the moon is the "Lunar 11" rule of thumb. It is similar to the "Sunny 16" rule of thumb. When shooting the moon at f/11, one should use a shutter time that is the reciprocal of the ISO. So if you are using f/11 at ISO 100, your shutter time (Tv for time value) should be around 1/100 of a second. If you are using ISO 200 at f/11, you should be using a Tv of 1/200 second. If you open up the aperture to f/8 (one stop more exposure) you should compensate by reducing the Tv to 1/400 (one stop less exposure).

Here's a clear sky view of the moon, along with the planet Jupiter, shot at ISO 200, f/8, 1/125 second. As exposed it is about one and two-thirds stops brighter¹ than the "Lunar 11" rule of thumb, which for ISO 200 and f/8 would indicate a shutter time of 1/400. Exposure reduced 1/3 stop in post (which leaves it at +1.3 stops over the rule of thumb), as well as contrast slightly increased. The lens was tripod mounted and mirror lockup with a wired remote shutter release were used to reduce blur due to camera movement.

_{EOS 7D + Kenko C-AF 2X Teleplus Pro 300 + EF 70-200mm f/2.8 L IS II at 400mm, ISO 200, f/8, 1/125 second}

This shot was exposed four stops brighter than the exposure settings you quoted in the question. If the brightness is reduced 3 stops in post, it looks like this:

If the brightness of your camera's rear LCD screen is turned down too low, it might look like you have a solid black image, but there should be some information in the raw file.

_{¹ The image was exposed brighter to allow the dimmer planet Jupiter to appear in the scene. At the exposure level used the moons of Jupiter are all still too dim to be seen. For a look at how much brighter exposure was used to capture the four brightest moons of Jupiter, please see this answer to Can you photograph the milky way with a full moon out?.}