No, the sensor of the Nikon D5100 is not a full-frame sensor. It is an APS-C sized sensor, which is smaller than a full-frame sensor. This means that the field of view captured by the sensor is narrower compared to a full-frame sensor, resulting in a crop factor of approximately 1.5x for Nikon DX format cameras like the D5100. **

To determine if your Nikon D5100 is defective, you should first identify the specific issue you are experiencing. If you are facing consistent problems with the camera's performance or functionality that are not resolved by troubleshooting or basic maintenance, it is possible that there may be a defect. In such cases, it is recommended to contact Nikon customer support or take the camera to an authorized service center for further evaluation and potential repair. **

You can sell your Nikon D5100 by listing it on online marketplaces such as eBay, Craigslist, or Facebook Marketplace. Make sure to take high-quality photos of the camera and provide a detailed description of its condition, features, and any accessories included. You can also consider selling it to a camera store or through a camera equipment buy/sell/trade group. Be sure to research the market value of the camera to set a competitive price and be prepared to negotiate with potential buyers. **

The Nikon D5100 can be charged internally by using the camera's USB port to connect it to a power source, such as a computer or a USB wall charger. The camera must be turned off during charging, and it is recommended to use the original Nikon USB cable for optimal charging performance. Additionally, the camera can also be charged using an optional AC adapter that is compatible with the camera's power requirements. **

The Nikon D5100 is suitable for a wide range of lenses, as it features a Nikon F lens mount. This means it is compatible with Nikon's extensive lineup of F-mount lenses, including both DX and FX lenses. The camera is particularly well-suited for portrait, landscape, and general photography, making it a versatile choice for photographers looking to explore different genres. Additionally, the D5100's 16.2-megapixel sensor provides good image quality, allowing for sharp and detailed photos when paired with high-quality lenses. **

Without more specific information or context, it is impossible to definitively determine if the autofocus of the Nikon D5100 is broken. Autofocus issues can be caused by a variety of factors such as settings, lens compatibility, or mechanical problems. It is recommended to troubleshoot the issue by checking settings, trying different lenses, and consulting the camera manual or a professional technician for further assistance. **

Some alternative cameras to the Nikon D5100 include the Canon EOS Rebel T7i, Sony Alpha a6000, and the Fujifilm X-T30. These cameras offer similar features and performance to the D5100, such as interchangeable lenses, high-resolution sensors, and advanced autofocus systems. The Canon EOS Rebel T7i is known for its user-friendly interface and excellent image quality, while the Sony Alpha a6000 is praised for its compact size and fast autofocus. The Fujifilm X-T30 is popular for its retro design and film simulation modes. **

To film with the Nikon D5100, first, make sure you have a fully charged battery and a memory card with enough storage space. Turn on the camera by flipping the power switch to the "on" position. Set the mode dial to the video mode (which looks like a small camera with a film strip). Press the red record button to start recording, and press it again to stop. You can adjust settings like exposure, white balance, and focus to customize your video recording. **