Do attachments that block the AF-assist light force you to focus manually?

Question

I'm thinking of getting a cheap macro ring light (something like the Bolt VM-160).

At the moment, when I shoot close-up shots, the AF-assist light comes on to help the auto-focus mechanism.

It seems clear that many attachments, like this ring light, will block the AF-assist light. Is the expectation that one must disable the AF-assist light (in those contexts where it would have been used) and instead focus manually?

The camera is a Nikon D3100. Can the camera "communicate" via the flash shoe, telling the flash to illuminate the scene for auto-focus purposes? Is there a protocol between camera and flash that allows it to say "flash properly" or "illuminate for AF" etc?

Answer 1

Autofocus systems need a certain minimal amount of light to operate. It doesn't matter what the source of that light is as long as the light is present at the time the camera attempts to autofocus.

The light you've linked is a continuous light source. That is, it provides light continuously before, during, and after the photo is taken. Even in its self-described "flash mode", it's operating as a continuous light for approximately one-half second.

If you need AF assist using light from the ring you will need to switch the ring light to the mode that leaves the light on continuously so the light will be on before you fully depress the shutter button.

You could also use any other light source that is shining on your subject to illuminate it. Flashlights can come in handy for this. Many who do very long exposure photography in the dark with subjects too far from the camera for the camera's AF Assist light to reach it with sufficient intensity (if the camera even has one) will use a flashlight to AF or manually focus, then hold focus and turn off the flashlight before beginning the exposure.

As long as the intensity of the continuous ring light is sufficient at the distance you're using it the camera's AF system will be able to use it to focus. The ring light should be much brighter than the camera's AF Assist lamp, even at the lowest intensity setting. Of course that also assumes your target has sufficient contrast running in a direction that the camera's AF points can use, the same as would be the case even in daylight conditions.

If you try to use the "flash mode" the light won't come on until you fully press the shutter button and the exposure has already begun. Since it's not a TTL flash it will not be able to sense when the shutter button is half pressed and turn the light on at that point.

Even if:

• You have the camera set to not release the shutter until AF is confirmed
  AND
• The camera can confirm focus and take the photo in the one-half second window the light is turned on

it won't provide AF assist since the light depends on the flash sync signal from the camera's hot shoe to tell it to turn on. The camera won't send the flash sync signal until focus has been confirmed and the first curtain of the shutter is fully open. Even shooting in Live View the camera won't send the flash sync signal until after focus is confirmed.

If you have the camera set to release the shutter without confirming AF by the time the light comes on in response to the sync signal the image is already being exposed and the AF system is not active any more.

Answer 2

With the ring light turned on, there may be sufficient light that the AF assist light is not needed.

A shoe mounted LED panel would avoid potential conflict. An off camera light would as well. Or a light on a flash bracket.

In the end lighting is mostly a matter of trying things and seeing how they work. Nobody who has been at it a while only owns one light.

Answer 3

A ring light can just be turned on for focusing. This ring light has both flash and continuous light modes. How much use this will be depends on your subject matter. If you are photographing stuff like insects and spiders, it is not feasible to use the same brightness for photographing and focusing since the brightness for achieving short exposure times will stress out your subjects and make them scurry away when used over extended amounts of time. So you'd want to use low-intensity light ("modeling light") for focusing and flash mode for actual photograph-taking.

Does the device offer this in a convenient manner? Would you need to fiddle with stuff like "focus lock" and switch modes?

In contrast, for stuff like product photography, there is nothing wrong (except for battery usage) with just keeping the light at the desired strength for both focusing and photography, assuming that the photography brightness is supported for more than momentaneous use.