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DX vs FX Crop Sensor

DX vs FX Crop Sensor

DX vs FX Crop Sensor

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Which is right for you

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To baseline the discussion we will consider a comparison between two similar MegaPixel sensor cameras, one being a DX (23.5 mm x 15.6 mm) and the other an FX sensor (35.9 mm x 23.9 mm), the DX & FX having the very similar number of pixel resolution - so, is there a difference?

Right off the bat you notice the size difference as illustrated in the diagram, yellow portion represents our camera sensor, the DX sits well within the larger FX sensor, this matters to some degree throughout this article. When I say sensor size I am speaking about the physical size, so let us dig into dx versus fx cameras.

Sensor Size and Image Quality: This is basically an urban legend. Sensor size matters to some degree for several reasons but is not necessarily a big factor in everyday use.  What drives image quality? Consider two sensors both having 24MP.  Sensor (1 is DX), to cram 24 million of light gathering diodes onto a fixed size sensor each light-gathering diode has to be of a certain size. So DX sensors as compared to the FX sensors will in most situations have smaller light gathering diodes. On FX sensors there is more room for the larger light gathering diodes which can be can larger. Larger diodes normally have better light sensitivity and dynamic capabilities – as a general statement. In most everyday use for posting photos on websites, or producing regular-sized prints you will be hard-pressed to notice ANY real difference between DX & FX image quality, otherwise, pros would not use crop sensor cameras along with their pro bodies. Where things begin to become more noticeable is when we drive the cameras into higher ISOs & more difficult lighting situations, then try to produce very large prints or 100% closeups. Why do smaller sensors begin to show noise at comparable ISOs/shooting situations? 

Factor in the “Engine” of the Camera: Everyone knows newer software and hardware normally makes images look better, as the technology of the camera progresses so does the ability of the processor to deal with “noise & artifacts” more quickly, and more efficiently, camera manufacturers also work hard to optimize algorithms that help produce better images. Camera sensor technology also improves over time. What most of us are starting to see is the gap shrink between sensor size when used within the “normal”  casual range or use, because we have newer faster “camera processors" and sensors, both Canon and Nikon take turns leapfrogging each other.  Electronics have a lot to do with the image quality, as light-gathering diodes are more closely packed onto smaller sensors so increases the electrical “noise” and the ISO goes up and the light goes down.   Back in the day, medium format cameras produced better images than 35mm, the ratio of negative to print size; today we are dealing with electronics and variations of sensor sizes coupled with the density of diodes on the sensors. So, that larger sensor can have larger diodes and usually edges out in performance once you move into higher ISOs, and while newer camera processors make smaller sensors perform better they also make larger sensors perform better.. Win-Win for everyone. So nowadays, you see DX cameras produce quality on par with FX especially if the FX is running older software/hardware. Just consider the Nikon D500 which has received excellent reviews for image quality.  So, why even worry about DX VS FX? read on.

What about the CROP Factor:  The funny thing is, if you never use an FX camera and only use DX cameras, chances are you don’t even know the difference exists. It becomes noticeable when switching between "systems". Example: If you are an FX user and love using that wide 24mm on your FX camera you know generally what Field of View (FOV) you will get based on our experience with that focal length of the lens.  But if you change systems to a DX and slap that 24mm on your DX camera body the FOV changes because the sensor is smaller – hence the term crop factor.  In this situation the 24mm will look more like a 35mm, 36mm to be exact, this is not a bad thing just something to remember, requiring you to make this consideration when shooting DX.

 DX Camera with 400mm 1.5 Crop FX Camera  with 600mm 
Nikon 400mm on DX Body
Nikon 600mm on Full Frame Body
Compre the two images - notice how close the 400 looks to a 600 when the 400mm lens is mounted on a DX camera body?
This is the benefit of DX for wildlife and bird photography


Why is this? In the simplest terms possible – the image being projected from the rear lens element will exceed the boundaries of a DX sensor. The sensor will be capturing the central-most portion of the image projection, giving your final image a larger footprint on your sensor - which causes the image to fill the sensor.  An FX lens on an FX camera will project the image to the edge of the sensor capturing the entire image projection from the lens. See the illustration. This gives the impression of magnification on the DX sensor while the FX will show the entire image on the sensor, not a portion of it. To get the same effect with an FX you would need to zoom in 1.5 to fill the sensor more.  Homework example: Draw a 1-inch square and a 2-inch square, now drop a penny on the 1-inch square and slide it over to the 2-inch square. Compared to the 1-inch square the edges of the penny will overlap on the 1 inch, while the 2 inches will include the entire penny, and if processed this digitally, Abe's head would appear larger on the smaller sensor, because a portion fills up more space than on the 2-inch square.

So what is the difference between FX and DX lens: Not much really at least for Nikon, at the end of the day, both serve the same purpose when used with the intended camera system.  DX lenses are engineered for DX cameras body, are normally smaller, lighter Cheaper :)  as compared to the larger FX lenses (larger glass=more weight & cost).  In most situations FX lenses work perfectly fine on DX cameras, while all DX lens may not work properly on an FX camera body due to the image projection from the rear DX lens element was not designed for FX sensors, thus you may have dark/black corners when using some DX lens on FX cameras, Tamron 11-20mm (DX) is a good example, this lens is designed for DX cameras, the lens will not fully cover the FX sensor until you zoom out to 16mm and beyond, it works fine at 16mm and beyond but not at the wide end. Nikon solves this on some FX camera bodies by placing the camera in DX mode when you attach the DX lens.  Yes, you can use the FX lenses on DX bodies, most all Nikon lense are compatible.

Depth of Field: Something else we must mention when speaking about crop sensors and lenses like the crop the DX also influences the depth of field (DOF). More compressed on DX, this issue might be less of a concern for most folks. As an example using a 35mm will have a DOF more like a 50mm. Unless you concentrate on DOF as a primary objective in your photographic compositions, it will be not too much of a concern.

Does the crop factor work for me or against me:  Both. Let’s take the positive first. If you like a longer lens and have a passion for outdoor wildlife, bird, and sports photography – you are in luck. DX cameras help get you closer. That cheaper 300mm f/4 will become a 450mm on a DX, then slap on a 1.4 TC and you’re out to 630mm 5.6 FOV - perfect for wildlife shooting.

On the downside: if you like the wide side of things, the wide-angle lens also has the same crop factor, to go wide you need a really wide lens. But don’t fret, the DX market has it covered, just need to be aware of the 1.5 crops when shopping for the wide lens.  Nikon recently releases an 8-15 fisheye that works on both an FX and DX. 

Why can’t I just buy an FX camera and set it to CROP mode when I need it: Good news is, you can! Many newer FX cameras offer a CROP mode in-camera.  The side story to this is: consider both camera examples above as having 24mp sensors. When you set the FX camera to internal 1.5 crop mode you lose some of that wonderful 24 MP resolution & your optical view (what you see) has not changed from full-frame FX mode, you may see a rectangular boundary box as you peer through the camera, but trust me, you sometimes forget you are shooting in crop mode, and anything outside the bounding box will be lost and in the heat of the moment, oops. While DX cameras will retain the full (sensor megapixel) 24mp for this discussion, and your optical view will remain constant, IMHO it is best to use DX for situations needing longer lens vice an FX camera in crop mode, but it is doable with an FX.

You never answered the question, what should I get a DX or FX: Today, I don’t have a high argument one way or the other. My first digital camera was an Olympus 3mp camera costing $900.00, expensive at the time and I thought I would never need another camera, the sensor of the Olympus was smaller than a DX sensor and I was happy with that until I got my hands on a Nikon D70 and started using my older film lens on the D70 camera. Remembering back, those first FX cameras were very expensive and the camera companies were in a race of the MegaPixels more than anything.

The fact is, nowadays you could be completely happy with either format.

If I were to do it all again, I would have skipped the Olympus and started with an FX DSLR then purchased a DX body, with lenses being primarily made up of FX since they work on the DX camera, the only exception to this is a couple of DX lens for lightweight travel – sometimes you just want to travel without the hassle of added weight. By the way, I have a CX sensor camera (even smaller than DX) @ 2.7 crop, and I enjoy using it, and at times astounds me with the speed of focus and the quality of images it produces for such a small sensor camera.  This is exactly my setup today I use my FX, DX and my CX alongside each other, without worries of which is better - each has benefits.

One final: Nikon is the only Camera company that most cleanly supports the use of Nikkor lenses on their FX - DX - CX camera bodies.  I can use my 600mm on my FX, my DX outright, and my little CX with the FT-1 adapter.

Finally, I would not worry too much about which is a better platform - Sadly, it seems the FX line has much better camera bodies and lens selection, Nikon D500 is the closest DX body to date that rivals everything before it.  

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John Montfort · 5/18/2016 5:29:20 PM

I very much enjoyed your article on DX vs. FX and as I own lenses and camera bodies in both formats (all Nikon), I thought I would add my experiences.

(1) In regard to lenses for DX, there are many who lament the lack of choices from Nikon. However, there are quite a number of advantages of using FX lenses on DX bodies that I have personally experienced. Though great optically in the center area, many FX lenses have issues in the corners, such as astigmatism, vignetting, general softness, CA, distortion etc. All of these problems are minimized when used on a DX format camera. I will take just one lens of Nikon, the 80-400mm f4.5-5.6 VR as an example. This lens suffers a bit in the corners as well as having the usual vignetting when used wide open. On a DX camera these shortcomings are mostly eliminated, with the added benefit of having a longer reach. (120-600mm 35mm equivalent)

(2) A few DX lenses are actually superior to their FX cousins. One such lens is the new DX 16-80mm F2.8/4. Compare this lens on a D7200 to the 24-120mmF4 on a D750 and you will discover the DX to be sharper, much lighter, and at the wide end, 1 stop brighter.

(3) If you are having to attach teleconverters to your lenses for that extra reach, then DX is a no brainer. It is better to get that extra reach with the DX format rather than having that extra glass on your best telephoto lens. Not only are you slightly compromising the optical path but you are loosing at least one stop of light. That loss often caused focus problems as well as loss of aperture control over a wide range.

I use my DX (I now own the D500) as my travel camera body and my wildlife camera. My FX D800 is best suited for exceptional landscape photography, and my D750 to the larger animals in the world of nature. Although FX does give a one stop or better improvement in low light, that only holds if the lens does not require a teleconverter.

I personally think that DX may come back as a roaring Lion. Just as the big advantage Medium format had over FX has dwindled over the years, so has the advantages of FX over DX. If Nikon did one thing right, it was to make their lenses work on virtually all of their better camera bodies.

TrueToad · 5/19/2016 1:59:17 PM

John, Thanks for taking time to write up such great insightful thoughts and provide your experience to the community. Well received by me and the many more who shall visit. Open honest two-way sharing is pivotal for continued growth - Thank You, I grew a bit today!

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