2
\$\begingroup\$

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?

\$\endgroup\$
4
  • \$\begingroup\$ The camera is a Nikon D3100. Are you saying the camera can "communicates" 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? Sorry for complete beginner questions. \$\endgroup\$ Jun 27, 2021 at 13:28
  • \$\begingroup\$ I don't know about Nikon systems, but on my Canon camera and flash the flash (buit-in or external) will emit short flashes to help focus if the subject is too dark. \$\endgroup\$
    – xenoid
    Jun 27, 2021 at 14:13
  • 1
    \$\begingroup\$ @xenoid Only TTL flashes compatible with the camera they're connected to will do the AF assist thing. This is not a TTL flash. In fact, it's not even a flash. It's a continuous LED light. \$\endgroup\$
    – Michael C
    Jun 27, 2021 at 16:23
  • 1
    \$\begingroup\$ Well, I've discovered something new - TTL - thanks @MichaelC. I've been looking at the TTL protocols that Nikon and others use. I had thought that the camera could basically just tell the flash to flash but I now see much more is possible if the flash supports the camera manufacturer's TTL protocol. \$\endgroup\$ Jun 28, 2021 at 10:08

3 Answers 3

3
\$\begingroup\$

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.

\$\endgroup\$
3
  • \$\begingroup\$ Thank you for such a detailed answer. The ring flash, I mentioned, was perhaps a bad example (as you point out, it can provide continuous light). I was also interested in the more general case for any attachment that blocks the AF-assist. And you've covered that too. \$\endgroup\$ Jun 28, 2021 at 10:14
  • 1
    \$\begingroup\$ I thought there might be a tighter coupling between AF-assist light and the AF system, e.g. if you can see the scene without the light and then have fine-grained control of the AF-assist light then you could start deducing things about the scene based on how much light comes back to the camera. But it seems clear, from what you say, that the AF-assist is just an additional light source that can be replaced by the light from other sources. \$\endgroup\$ Jun 28, 2021 at 10:16
  • 1
    \$\begingroup\$ @GeorgeHawkins Yep, that's pretty much all the flash assist light is. Some of them, mostly the ones built into TTL flashes, project a grid of vertical and horizontal lines which can give the camera some contrast if the subject is a smooth, uniform surface without much contrast. But one could make a mask (possibly combined with a cheap Fresnel lens) for a flash light that does a similar thing. \$\endgroup\$
    – Michael C
    Jun 28, 2021 at 20:32
1
\$\begingroup\$

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.

\$\endgroup\$
0
\$\begingroup\$

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.

\$\endgroup\$
3
  • \$\begingroup\$ If you read the description at the listing, you'll see this really just a continuous LED light that has the ability to turn on for one-half second based on the hot shoe's sync signal. It's really not a flash at all. It's more or less only a modeling light. It can also turn on only the right side or only the left side in addition to turning on the full circle continuously. It has four power levels, but doesn't specify how much difference there is between each one. \$\endgroup\$
    – Michael C
    Jun 28, 2021 at 20:36
  • \$\begingroup\$ @MichaelC Well, sure it isn't a flash. But even LED lights can offer bright illumination modes triggered by a flash foot. Half a second does not make an awful lot of sense (it will blind you after exposure is long over for sensible usage) particularly since the flash foot only fires after autofocusing is already complete. So the device's design choices are a bit of a head scratcher to me. \$\endgroup\$
    – user98068
    Jun 28, 2021 at 21:00
  • \$\begingroup\$ As I point out in detail in my answer, a non TTL flash (or LED light connected to the camera via only the single ISO hot shoe pin and ground) has no way to be turned on via the hot shoe until after the first shutter curtain (either mechanical of electronic) is open and the sync signal is sent to the hot shoe. So it can't be used to assist with AF when set to the half-second mode. AF has to be completed before the shutter begins to open or it doesn't happen at all. \$\endgroup\$
    – Michael C
    Jun 28, 2021 at 21:17

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.