Autofocus Is Not Working On My Nikon D5100

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.

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!

Should I Get DX Model Or FX Model As My First DSLR?

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.

Andy (Colorado, USA) asked: I want to buy my first DSLR and I am struggling to make a decision on whether to get a DX model or a FX model? Are there any advantages or disadvantages of getting one over another?

Andy, when I bought my first DSLR in 2010, I didn't know anything about the DX models or the FX models. Let alone the details of different models, I didn't even know about the existence of those models. But nowadays, due to many wonderful photography blogs and magazines, we have much more detail information about the different brands of camera, different models and their functionality, which is really a good thing so that the buyers can make an educated decision.

Buying the first DSLR is always exciting and yet very confusing task. We get easily confused on which brand to consider as our first DSLR. Some of your friend might say that the camera they are shooting with, whether it is a Nikon or a Cannon or a Sony or any other brand, is the best brand which makes your brand selection job even tougher. But once you get your mind set on the brand you are getting, next question you will encounter is which model should you get? At the beginning and specially if you are trying photography as a hobby, you might want to get an entry level and relatively cheaper DSLR camera and in that case, decision is relatively easier. But if the budget is not an issue and you are considering photography as a serious hobby and then later turn it into a profession, you might want to get a decent DSLR and that's when our discussion of DX vs FX might come handy.

The first and the most important thing you have to remember while selecting the DX or the FX model is, they differ by their sensor size. The DX models have a smaller sensor or also referred as a APS-C censor which is approximately 24x16mm whereas, the FX models have a larger sensor and also called a full frame (same as 35mm film format) sensor which is 36x24mm. If you are a beginner, DX models might serve you well but if you are looking to upgrade to more "serious" camera, you have to go to full-frame because most of the DX line-up are aimed to let you introduce into the photography world but lacks many pro-level features and specs. But it is also true that with the change of technology and the competition among different brands, DX models are also getting close towards being professional camera if you get the top of the line DX model, Nikon D500 for example. Nikon D500 is the most expensive DX-format DSLR within Nikon brand and it comes with many pro-level features. In fact, many professional photographers have started using this camera as a main or backup camera because of it's light weight and other pro level features.

DX camera bodies are relatively smaller and lightweight than FX bodies and built quality is little bit compromised with the high quality plastic vs aluminum on FX bodies. Usually, DX-format lenses are more compact because the image circle that they need to produce only needs to cover the smaller sensor area compared to that of full frame camera. This makes DX camera bodies an ideal choice if you want to travel with lightweight camera and lenses. Another advantage of DX camera is that you get an extra reach on the lenses because of it's 1.5x crop factor on the sensor. If you use 70-200mm f/2.8 lens on DX bodies, it gives you an effective focal length of 105-300mm but it won't help you to get the shallower depth of field because depth of field depends on "actual" focal length rather than "effective" focal length.

But in FX camera sensor, for any given pixel count, the photo-diodes will be larger than those on a DX sensor and that is the reason FX camera can produce cleaner images when shooting in a low light condition using higher ISO. The latest high megapixels FX camera bodies have an additional advantage of more pixels packed into the sensor to capture more details although it might produce little noisier picture at higher ISO.

In my opinion, which came from my own personal experience, if you are just starting out, you may want to get a decent DX model DSLR so that you can understand how does your camera work and also get to know about the different controls and the features of the camera and then later upgrade it to the FX model. By doing so, you can discover pros and cons of both sides and decide which fits best for your work. Good luck!