Autofocus Is Not Working On My Nikon D5100

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Mark (New Jersey, USA) asked: I have a Nikon D5100 and recently bought a Nikon 70-300mm f/4-5.6G lens with AF but it is not auto-focusing. Am I missing some settings or something is wrong with my camera or the lens?

Hello Mark! Nikon's Autofocus system works by utilizing the motor (to move the lens elements) either inside the lens or inside the camera body. Unfortunately, neither your camera body nor the lens is equipped with such motor. Your lens might be capable of autofocus but the lens elements should be driven by some mechanism to "autofocus" and that is what missing in your combination. In short, the minimum requirement for Autofocus to work is, either the lens or the camera body has to have a focus motor. Lets discuss both of these scenarios one by one.

First scenario: Lens is AF and the camera body has a built-in motor for Autofocus.

The lens you bought is AF lens which stands for Autofocus but it will only autofocus if your camera has a built-in motor inside the camera body. All full frame (FX body) Nikon DSLRs as well as some high end crop sensor (DX body) DSLRs have a built-in AF motor which drives the Autofocus system. Among Nikon DX format (also known as APS-C image sensor format) bodies, D90 and all D7000 series come with the built-in motor inside the camera body but D60, D3000 series and D5000 series do not come with the motor. In case of such consumer DSLRs that do not come with the built-in focus motor, they need to use an AF-S or AF-P Nikkor lens to get the full Autofocus capabilities from the lens itself which we will discuss in our second scenario.

When you attach an AF lens with the camera that has a built-in motor in it, the mechanical coupling between the camera body and the lens is formed by utilizing the screw in the motor and the several pins on the lens (which is connected to the focus ring). When you try to autofocus by pressing the shutter release button half way down, camera uses multiple focus sensors to determine which part of the subject is in focus and which part is not and turns the motor accordingly to adjust the focus. These AF lenses come with their own CPU which gives the focal length, aperture setting and other information to the camera CPU which allows the camera to adjust TTL (Through The Lens) Metering for different shooting modes.

Nikon D810 Focusing Modes (Click the picture above to read my initial experience with Nikon D810)

If you want to manually focus while using an AF lens, you have to switch the lever on the camera body (box 1 in the picture above) from AF to M which then disengage the mechanical coupling between the motor and the lens so that you can freely move the lens focusing ring to adjust the focus. In this situation, camera still gets the TTL Metering and different shooting modes data through the lens CPU.

Tip : The DSLR camera bodies that feature a focus motor can use both AF and AF-S or AF-P lenses for Autofocus.

Second scenario: Lens is AF-S or AF-P and the camera body doesn't have a built-in motor for Autofocus.

Nikon's another type of Autofocus lens is called AF-S lens (not to be confused with AF-S focusing mode) which has an Autofocus motor built inside the lens. Those Nikkor AF-S lenses feature Nikon's Silent Wave Motor (SWM) which converts "traveling waves" into rotational energy to focus the optics, according to the Nikon. This enables high-speed auto-focusing extremely accurate and super quiet. You can use Nikon’s AF-S lens with any current Nikon’s camera body whether the body has a focus motor or not, because the lens itself has a built-in focusing motor which controls the focusing function based on the information it gets from the camera’s focusing sensors.

Nikon's third type of Autofocus lens is AF-P lens which uses a “Pulse” motor or “Stepping” Autofocus motor making it even quieter and smoother to autofocus than AF-S lens. According to Nikon, AF-P lenses are ideal when shooting video with a DSLR camera. Some of the Nikon's newer AF-P lenses let you set certain settings from the camera's menu system (VR, AF/MF for example) but on older model lenses, you still have to switch those modes on the lens barrel itself like you do on AF-S lenses. Sometimes, even if your camera supports newer AF-P lenses, you might need to upgrade the camera firmware to be able to set lens’ parameters from the camera menu.

Since the lower end Nikon DSLRs such as D3000 and D5000 series do not have the focus motor built-in, if you want to manually focus using AF-S or AF-P lens, you have to switch the focus mode on the lens barrel from A or M/A to M (box 2 in the picture above) and then rotate the focusing ring on the lens. Since there is no mechanical coupling between the camera body and the lens for Autofocus, most of the higher end lenses let you focus manually in M/A (or A/M in some lenses - works same as M/A but manual focus is less sensitive than M/A) mode as well. The reason behind making such consumer level Digital SLRs without a built-in focus motor is to reduce the size and the weight of the camera for portability.

Conclusion: If you prefer to use Autofocus feature, either you have to upgrade your camera body or the lens if you can't afford upgrading both at the same time. If you want to keep the same body and upgrade your lens and feel comfortable shooting with 70-300mm, you can go with either AF-S or AF-P version of 70-300mm which might be little more expensive than your current lens but you get the VR feature as a bonus. And when you upgrade your body to FX format later, the lens is compatible with the newer body as well.

If upgrading either is not an option at the moment, you can continue using your existing combo and manually focus the lens using the focus ring on the lens barrel. While shooting manually, the green dot, which is visible in the lower left corner of the viewfinder, will confirm that your subject is in focus. When you want to focus, rotate the focus ring on the lens barrel and when it lights up green, the subject is in focus.

I hope this blog helps you to make your decision. Thank you for the question and keep shooting!

How To Tell My Camera To Focus On Particular Area?

This post is a part of our Q&A section. If you want to submit your question, please use the form in the Contact page.

Lita (Manila, Philippines) asked :  When I am taking pictures of wildlife, I use Autofocus (AF) most of the time for obvious reasons. And most of the time when I try to frame and focus the animal, trees and branches get focused instead of the main subject. How can I force my Nikon D90 to focus on particular area?

Lita, if you do not want camera taking the control of the focus, short and quick answer is to manually focus the subject. When you manually focus using the focusing ring on the lens barrel, you can select the area to be in focus whether it would be in the middle of the frame or at any other focus point. But we all know that focusing manually is not a practical solution specially when you are shooting wildlife and that is the reason our DSLRs come with the autofocus option to quickly focus your subject. And autofocus works perfectly in most of the situations but sometimes you may encounter the problem you have described in your question. When you are using the Manual Focus mode, you can take over the control of the focusing system but the good news is that, your camera Nikon D90, may have a solution for the AF users as well.

When you are shooting in Autofocus mode and want to take the control of the focusing system, you need to change the Autofocus option inside the Custom Setting Menu (CSM). By default, Nikon D90 selects the focus point automatically based on the information it gets through the lens and that was the reason, sometimes, you were encountering the focusing issue. And the reason is, your camera can not differentiate between the subject and the object inside the frame. To change that default setting, press the MENU button on the back of your camera and go to the CSM menu (Pencil Icon). Then choose the first option (a Autofocus) and select the Single Point. When you select the autofocus point to a single point, you can now select the focus point by using the Thumb Pad (Multi-selector button) on the back of your camera and lock the focus point wherever you want by using the AF Selector Lock lever next to the LCD screen. This guarantees that the camera is focusing on your intended subject because you've told it in advance which of the 11 AF points to use for the focusing.

Note: If you want to lock the focus point into one spot, please make sure that the lever next to the LCD screen is switched to the L (Locked) position after you select the preferred focus point, otherwise, you might inadvertently select a different AF point by bumping into the thumb pad. The lock switch was designed to prevent such accidental change of the focus point and works really well. Your camera locks the focal point in L position of the lever switch and allows you to change focus point when the lever is set to the Unlocked (Single DOT) position.