The practical decision guide: DX or FX?

DX or FX? APS or full-frame sensor? There are many articles and videos which explain the differences between the two formats. But a simple decision guide for users is missing. No problem, it just happens that I’m too lazy to write and qualify a whole bunch of scientific essays anyway – so I’ll just focus on putting together this simple, straight-forward guide to help users decide between DX and FX.

(Speaking of which, Cambridge In Colour is an excellent resource for anyone looking to learn everything about the basic topics in photography and some simple physics behind them.)

Obviously there are other camera brands which offer APS and full-frame formats. As different camera systems have different characteristics, I will only focus on Nikon’s DX(APS) and FX(full-frame) in this article. Readers can make intelligent correlations to other camera brands, but please note that subtle differences will be present.

Let us get into the guide right away. Consider the following questions.

(1) Do you need very shallow depth-of-field?
(2) Do you need to shoot fast action indoors or in low light?
(3) Do you need very high megapixel output?
(4) Do you need specific lenses which are only available on FX?
(A) Are you a beginner?
(B) Do you feel you have a financial obligation to not spend too much money on camera gear at the moment?

If your answers to (1)-(4) are “no”. Go for DX. If you answer “yes” to any of (1)-(4), go for FX. The exception rules are (A) and (B). If you answer “yes” to either (A) or (B), ignore (1)-(4) and go for DX. Let me explain the reasons.

(A) The beginners

If you are starting out or feel you are still in a beginner’s shoes, go DX. In this stage you are supposed to be experimenting with different shooting styles, photography genres and focal lengths. You may end up spending too much on gear that you eventually realise you don’t need when your photography preferences start taking shape after 2-3 years of shooting. DX provides a much more economical path of starting out and experimenting. You can spend the money you save on courses and trips that actually enable you to practice and take more pictures. Go DX.

(A) Financial considerations

This one is simple. You should never spend too much on hobbies that are beyond your financial condition. If you intend photography to be your means of livelihood, you can still start with DX, then upgrade to FX later when your business and financial conditions allow it.

Having gone through the DX exception rules, let us dig into the FX conditions from (1)-(3).

(1) Depth-of-field

For the same camera-to-subject distance, achieving the same scene composition always requires a shorter focal length on DX compared to FX. The practical end-result is that the same aperture value on FX always delivers a more shallow DOF, and the difference is slightly more than a stop.

Here is a practical illustration. If you create a composition of a subject 2 meters away with a 60mm FX lens at f/2.8, an equivalent DX setup will have to be 40mm f/2.0 to achieve a similar composition and depth of field. (If you count millimeters, the FX setup still delivers a more shallow DOF.)

This means that in real-life usage, you are more likely to get images with a more shallow DOF with FX as opposed to FX. This benefits users who prefer to isolate their subjects from the background as much as possible.

But wait, this works the other way too. A practical example: 20mm DX at f/5.6 will have slightly more DOF than 30mm FX at f/8 framing the image!

Amateurs think that having more shallow DOF is automatically better. This is false. Not everyone needs shallow DOF. What is the point of f/1.4 shallow DOF if your photography style requires you to keep as much as your scene in focus? There are many photographers who need shallow DOF. But there are also many photographers who actually do not need it. If you are sure you want it, go FX.

(2) High shutter speed in low-light

There are a lot of test charts and pictures comparing high ISO performances out there. In real life, the only times when the high ISO performance difference between DX and FX matters is when you need to shoot at high shutter speeds in low light. In an indoor sports venue, even during daytime with natural light coming through windows, the ISO can climb to extremely high values at 1/1000s shutter speed. Go FX if low-light high-speed pictures are what you do.

(3) High-MP demands

Do you need high MP? They don’t make pictures look better. A lousy picture at higher resolution is just a high-resolution lousy picture. Depending on your political affiliation, a higher resolution picture of Donald Trump, Hillary Clinton or Vladimir Putin won’t make any of them look better to you. 😛

I printed a 24-inch picture with 24MP. No one looks at it closer than from a distance of 1.5 feet away. Another guy I know made a wall-sized wallpaper with 16MP to decorate a corporate office. People consume images on mobile phones measured in centimeters. Apple made billboards with 8MP.

You need more high-MP output when commercial clients tell you they need it. In general, you will gravitate to higher MP when you can qualify they bring a quantifiable advantage to your business.

FX has more space to accommodate high MP. So go FX if you need it.

(4) FX lens needs

There is no secret that Nikon produces a larger variety of FX lenses compared to DX lenses. They want users to spend more money on bigger, faster, higher-resolution FX. So there may be an FX lens out there where there is no DX equivalent. If you really need such FX lenses, your only choice is to go DX. Yup, Nikon wins in their evil plan to make users pay more. Curses!

Conclusion

So should you pick DX or FX? Hopefully this guide is helpful. I started with Sony APS-C, then upgraded to Nikon FX in 2013 for the high ISO advantages of a full-frame camera. However by the end of 2017, my shooting style has grown to favour deeper DOF. In addition, DX has advanced far enough that ISO 3200 has become usable for my needs with sufficient post-processing. In fact, I regain the high ISO advantage I lost from FX to DX because I can get deeper DOF with a larger f-stop in DX!

Honestly, quit listening to people who insist that bigger and better (and expensive!) are the only way to build an effective set of tools. That’s like nincompoops who believe that getting an expensive golden pen makes you a better writer. Examine what you really need and make your investments worthwhile. If you really need FX, go for it! If DX is all you need, get it and save yourself a lot of cash and weight, then spend those savings on more constructive stuff such as lighting tools, training, a new tripod, a gift for a loved one, etc. Endless possibilities here!
-WY

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