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I was with my family at a seaside, late and in darkness. My nephew and niece were playing in the water and running around, and I wanted to take picture of them, but my autofocusing system was taking too long to focus. By the time the autofocus system focused on my nephew, they were already gone. I also had my flash on, so that I could freeze there motion.

Is there any way I could take a picture of them while they are playing in the dark?

Would it works to set up manual focus with broad depth of field? For instance, at 50mm, f/16, 10 feet, i get about 9 feet of depth of field.

I have a Nikon D7200 with the 18-140mm kit lens.

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  • \$\begingroup\$ Possible duplicate of How does one focus for landscape photos in very dark conditions?, although that is landscape-oriented. \$\endgroup\$
    – mattdm
    Commented Nov 2, 2015 at 17:37
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    \$\begingroup\$ It's quite a bit different with landscape, where IR focus assist is not usually effective at the distances needed. For informal portraits the distances are usually less and often within the range of the flash's focus assist. \$\endgroup\$
    – Michael C
    Commented Nov 2, 2015 at 18:43
  • \$\begingroup\$ @MichaelClark Agreed, although that may also be the case in the seaside scenario described. \$\endgroup\$
    – mattdm
    Commented Nov 2, 2015 at 18:45
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    \$\begingroup\$ If his subjects were within the effective range of the D7200's built in flash with a GN of only 12 meters, one might assume they were a little closer than the other question addresses. \$\endgroup\$
    – Michael C
    Commented Nov 2, 2015 at 19:02

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Your camera needs more light to focus. There are a few ways to add light in your situation:

  • Use a lens with a wider maximum aperture. Remember that metering and AF are done with the lens wide open. It isn't stopped down to the set aperture until the instant before the shutter opens. A fast 50mm f/1.8 lens is the probably the most budget conscious choice.

  • Use a flash (or wireless flash transmitter) that has an IR focus assist lamp. Although their effective range is somewhat limited, they can be effective when used at typical casual portrait distances.

  • Use a directional external light source such as a flashlight/hand torch to illuminate your subjects for focusing. With small children an assistant that can follow them with the beam of the light might come in very handy!

Additionally, most cameras' AF systems have center focus points that are more sensitive and more accurate with wide aperture lenses in low light. Manually selecting the center focus point may help increase the speed at which your existing lens can focus in marginal conditions.

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  • \$\begingroup\$ i am struggling with autofocus, will IR focus lamp solve that problem, one more question, a while back i was doing the same think but with a street lamp and i was quite far away, i took about 12 long exposure photo, in all of them i saw a red dot, i think what was made by my camera for autofoucs, i can manually use that system in this scenario. \$\endgroup\$
    – Iori
    Commented Nov 3, 2015 at 15:05
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    \$\begingroup\$ IR focus assist will help when used properly. The flash must be aimed so that the grid emitted by the IR lamp is projected within the focus point you have selected. The subject must also be within the range of the particular IR assist lamp. The inverse square rule applies to IR assist the same way it applies to flash: twice the distance means one-fourth the field intensity. Just as a more powerful flash has a further reach, a more powerful IR assist lamp will have greater range. \$\endgroup\$
    – Michael C
    Commented Nov 3, 2015 at 20:39
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Autofocus requires a minimum amount of light/contrast.

Get a lens with a larger f/ rating (i.e., f/1.4 instead of f/3.5.) This lets in more light and your camera will able to focus in darker conditions.

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Personally, I'd probably go higher for your aperture and take a longer exposure with manual focus.

That being said, you are dealing with kids and they tend to wiggle, but try to see if you can set them up for a pose (be their favorite uncle or aunt and get them ice cream for holding still).

You could always bump up the ISO to 800 or 1600, but I don't think the noise would be acceptable.

If you're on a beach and they are playing in the sand, then you might just have some real fun and build a fire behind and to the side, so you have a nice orange glow to contrast against the blue night sky.

Eventually, you will get good enough to do manual focusing and all of this will be moot.

@icor103 also has a good point of having a faster lens. Using a 1.8 or something that fast will allow in more light; however, you loose depth of field. That may be fine if you can get enough light to the sensor to autofocus.

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    \$\begingroup\$ The problem with a narrower aperture is that motion blur caused by the longer shutter speed becomes worse than missed focus in marginal light. \$\endgroup\$
    – Michael C
    Commented Nov 2, 2015 at 19:07
  • \$\begingroup\$ @MichaelClark That is a problem, especially with kids. \$\endgroup\$
    – SailorCire
    Commented Nov 3, 2015 at 14:41
  • \$\begingroup\$ The D7200 can handle ISO 1600 rather well. It is not you older cousin's D40X! Also, the faster lens allows more light in for focusing, which is done before the lens is stopped down the instant before the shutter opens. Even if all lenses are set at f/8, an f/1.4 lens will let in 4 times as much light for focusing as an f/2.8 lens will, and 16x more than an f/5.6 lens. \$\endgroup\$
    – Michael C
    Commented Nov 3, 2015 at 20:45
  • \$\begingroup\$ @MichaelClark I took me a second to realize what you are making with your second point. You're right! The lens won't stop down until the actual picture is being taken. We aren't in the bad old days where your aperture is always stopped down. \$\endgroup\$
    – SailorCire
    Commented Nov 6, 2015 at 16:44
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You can set your lens for 'hyperfocal distance'. That is, the distance at which all objects will be in focus. I'm not sure about your lens, but the older, non-digital lenses had coloured reference marks on them corresponding to the f-stop. You set your lens to let the infinity mark fall on one edge of the partitular f-stops range, and the other mark at the 'nearer' range will indicate the 'closest' distance that is in range. The higher the f-stop the deeper the depth of field and the more powerful the need for your strobe.

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