Picking out the right camera lens can feel a bit confusing, especially when you see terms like DX and FX. Many new photographers wonder what the difference is and how it affects their pictures. Don’t worry, it’s not as tricky as it sounds!
We’re going to break down the dx vs fx lens topic in a way that makes perfect sense. Get ready to see how these lenses work and how to choose the best one for your shots.
What Does DX vs FX Mean for Lenses?
When you’re looking at camera lenses, you’ll often see the terms DX and FX. These terms are specific to Nikon cameras, but the concepts apply to other brands too, often with different letterings (like Canon’s EF vs EF-S). Essentially, DX and FX refer to the size of the image sensor in your camera.
This sensor size is what determines whether a lens is designed for a smaller or a larger sensor. Understanding this difference is key to getting the best quality out of your camera and lenses.
Understanding Image Sensor Sizes
Think of your camera’s image sensor like a digital film. It’s the part that captures the light and turns it into the photo you see. The size of this sensor matters because it affects how much of the image projected by the lens actually gets recorded.
This, in turn, influences the field of view you get with a particular lens.
DX Format Cameras (APS-C)
DX cameras have a smaller image sensor compared to FX cameras. These are often found in entry-level and mid-range DSLR cameras. Because the sensor is smaller, it only captures the central portion of the image that a lens projects.
This “crop” effect means that a lens designed for a larger sensor will appear to have a longer focal length on a DX camera. For example, a 50mm lens on a DX camera might behave like a 75mm lens on a full-frame camera. This is known as a crop factor, typically around 1.5x for Nikon DX sensors.
FX Format Cameras (Full-Frame)
FX cameras, on the other hand, feature a larger image sensor, roughly the same size as a 35mm film frame. This is often referred to as a full-frame sensor. Because the sensor is larger, it captures the entire image projected by the lens.
This means that a lens designed for an FX sensor will provide its true focal length on an FX camera. Full-frame cameras are typically found in higher-end professional and enthusiast models.
DX Lenses on FX Cameras and Vice Versa
Now, let’s talk about what happens when you mix and match lenses and cameras. It’s not always a perfect fit, and sometimes it works, but with limitations.
Using DX Lenses on FX Cameras
You can generally mount a DX lens on an FX camera. However, most FX cameras have an automatic crop mode enabled when a DX lens is detected. The camera will essentially use only the central portion of its larger FX sensor, acting like a DX camera.
This means you lose a lot of the resolution from your FX sensor because only a smaller area is being used. The image might look like it was taken with a higher focal length, similar to the crop factor effect you’d see on a DX camera.
Some photographers might choose to do this if they need a specific focal length that’s only available as a DX lens or if they are on a budget. However, it’s important to be aware that you’re not getting the full benefit of your FX camera’s sensor capabilities in terms of image quality and resolution. The image circle projected by the DX lens is simply not large enough to cover the entire FX sensor.
Using FX Lenses on DX Cameras
This is usually a more straightforward and often preferred combination. When you put an FX lens on a DX camera, the lens projects a larger image circle than what the smaller DX sensor needs. The DX camera will capture the central portion of this larger image circle.
This means you get the full field of view that the FX lens is designed to provide for a full-frame camera, without any cropping or loss of resolution due to the lens itself. Essentially, the FX lens behaves as it’s supposed to, and the DX camera simply records a portion of its projected image.
The advantage here is that you’re using a lens that’s built for higher quality and a wider projection, which the DX camera can fully utilize without any image degradation from the lens-camera interaction. You’ll get the true focal length of the lens, just like you would on an FX camera, because the DX sensor is small enough to be fully covered by the center of the FX lens’s image circle.
Key Differences and Their Impact
The core difference between DX and FX lenses boils down to the size of the image circle they project and, consequently, the sensor size they are designed for.
Image Circle Size
FX lenses are designed to project a large image circle that can cover a full-frame sensor. DX lenses project a smaller image circle, just enough to cover the smaller DX sensor. This difference is fundamental.
Field of View (Crop Factor)
On a DX camera, a DX lens will give you a field of view that is effectively narrower due to the crop factor. An FX lens on a DX camera will also provide a narrower field of view compared to what it would on an FX camera, but it will give you the true focal length of the lens, not amplified by a crop factor from the lens itself. The “crop factor” on a DX camera means that a given focal length will appear more zoomed in than it would on a full-frame camera.
Image Quality and Resolution
When you use a DX lens on an FX camera in crop mode, you’re essentially using fewer pixels from your camera’s sensor, leading to a lower resolution image. This can impact the fine detail and ability to enlarge prints. FX lenses, designed for full-frame sensors, are generally built to a higher standard of optical quality, which can also translate to better sharpness and fewer distortions, even when used on a DX camera.
Weight and Size
DX lenses are typically smaller, lighter, and less expensive than their FX counterparts. This is because they are designed to cover a smaller sensor area. FX lenses, needing to cover a larger area and often built for professional use, tend to be larger, heavier, and more costly.
Choosing the Right Lens for Your Camera
Deciding between a DX and FX lens depends primarily on the type of camera you own and your photography goals.
For DX Camera Owners
If you have a DX camera, you have two main options:
- DX Lenses: These are specifically designed for your camera. They will be more affordable, smaller, and lighter. You’ll get the expected field of view for your DX camera system, taking into account the crop factor.
- FX Lenses: You can use FX lenses on your DX camera.
They will provide excellent image quality and the true focal length of the lens. However, they might be larger and more expensive than necessary for your current camera body.
Generally, starting with DX lenses is a good economical and practical choice for DX camera owners. As you advance, you might consider investing in FX lenses that you can use later if you upgrade to an FX camera.
For FX Camera Owners
If you have an FX camera, the best choice for maximum image quality and utilizing your sensor’s capabilities is almost always an FX lens.
- FX Lenses: These lenses are designed to cover the entire full-frame sensor, giving you the full field of view and the highest possible resolution and optical performance from your camera.
- DX Lenses: While usable in crop mode, this severely limits the resolution of your FX camera. It’s usually only a temporary solution or for specific scenarios where space or weight is a critical concern and ultimate image quality isn’t paramount.
For FX camera users who want the best results, investing in FX lenses is the way to go.
Compatibility Chart
Here’s a simple way to visualize lens compatibility:
| Lens Type | DX Camera | FX Camera |
|---|---|---|
| DX Lens | Compatible (designed for) | Compatible (in crop mode, reduced resolution) |
| FX Lens | Compatible (provides true focal length, smaller image circle used) | Compatible (designed for) |
When to Use Which
Let’s look at some scenarios:
- Beginner Photographer with a DX Camera: Start with DX lenses. They’re cost-effective and designed for your system.
- Enthusiast with a DX Camera Planning to Upgrade: Consider buying FX lenses that you can carry over to a future FX body.
- Professional Photographer with an FX Camera: Always use FX lenses for the best performance and image quality.
- Occasional DX Lens Use on FX Camera: If you have a specific DX lens you love or need for a particular situation and image quality isn’t critical, it can be used, but be aware of the resolution loss.
The “Focal Length Multiplier” Explained
This is a term often heard when discussing DX versus FX. On a DX camera, the effective focal length of a lens is multiplied by the camera’s crop factor (usually 1.5x for Nikon). This means a 35mm lens on a DX camera behaves like a 52.5mm lens on an FX camera in terms of its field of view.
DX lenses are designed with this in mind, so a 35mm DX lens gives you that “52.5mm equivalent” field of view on a DX body. FX lenses on DX bodies also experience this crop, so a 35mm FX lens on a DX body will also give you the 52.5mm equivalent field of view, but the lens itself is still projecting a larger image circle.
Pros and Cons Summary
Here’s a quick look at the advantages and disadvantages:
DX Lenses
- Pros: More affordable, lighter, smaller, optimized for DX cameras.
- Cons: Image circle is too small for full FX sensor coverage, can result in low resolution if used on FX cameras.
FX Lenses
- Pros: Designed for full-frame sensors, offer the highest image quality, can be used on both DX and FX cameras (with different field of view characteristics on DX).
- Cons: More expensive, larger, and heavier.
Frequently Asked Questions
Question: Can I use any DX lens on an FX camera?
Answer: Yes, you can physically mount most DX lenses on an FX camera. However, the camera will usually automatically switch to a “crop mode” to use only the central portion of the sensor, which reduces the overall resolution of your image. You lose the benefit of the larger FX sensor.
Question: Will an FX lens work on a DX camera?
Answer: Absolutely. An FX lens will work perfectly on a DX camera. The lens projects a larger image circle than the DX sensor needs, so the camera captures the center of that image.
You get the true focal length of the lens, without any cropping due to the lens itself, though the DX camera body will still apply its crop factor.
Question: Do DX lenses have a different image quality than FX lenses?
Answer: Generally, FX lenses are designed for higher optical performance and to cover a larger sensor, often meaning better sharpness, contrast, and fewer distortions. While DX lenses can be excellent, FX lenses are typically considered the premium option.
Question: Is it better to buy DX or FX lenses if I have a DX camera?
Answer: For most beginners with a DX camera, buying DX lenses is more cost-effective and practical. If you plan to upgrade to an FX camera in the near future, investing in FX lenses now can save you money later, as they will work on both camera types.
Question: What happens to the focal length when I put an FX lens on a DX camera?
Answer: The focal length of the FX lens remains its actual focal length. However, because the DX camera sensor is smaller, the field of view will be narrower, similar to having a longer lens. This effect is described by the DX camera’s crop factor (e.g., 1.5x).
Final Thoughts
Understanding the difference between dx vs fx lens is a key step for any photographer using Nikon cameras or systems with similar sensor sizes. It’s all about matching the lens’s projection size to your camera’s sensor. For DX cameras, DX lenses offer an efficient and affordable way to shoot, while FX lenses provide flexibility and are a smart investment if you plan to move to a full-frame system.
For FX cameras, sticking with FX lenses ensures you’re getting the most out of your high-resolution sensor and enjoying the full optical capabilities of your lens. Don’t let the technical terms intimidate you; think of it as choosing the right tool for the job. Experiment with what you have, and you’ll quickly get a feel for how different lenses perform on your specific camera.
