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Which is Better a Full-Frame or DX Sensor?
©Darrell Young
 

I ask you to consider a slightly different point of view in this article. Sometimes I can get worked up, and even rant and rave a bit over the subjects I'm interested in. Maybe I'm like you in that respect, maybe not. In this article, I am trying to hold a more even technical path, with less hyperbole. I ask, please, that you read this carefully, and think about it afterwards.

Instead of looking at the APS sized (DX) sensor as some sort of compromised "crop" of a so-called Full-Frame (FF) camera, I hope you'll consider a different way of looking at things. Let's cover some basics first, then consider an alternate reality.

One Lens - Three Formats

If one uses a 50mm lens and the same subject is at the same distance from the camera, the subject size projected on the sensor or film will be exactly the same on any camera, no matter what its format.

The APS sized (DX) sensor is, technically, a "crop" of the 35mm Full-Frame (FF). However, with digital imaging, that crop provides a full-sized image that exceeds 35mm film in quality. Who cares if it's a crop. The resulting image from a 10 or 12 MP Nikon is better than 35mm in quality.

The difference is not best described as a "crop factor," it is a format or image frame-size difference. The crop factor words were invented to make it easy to explain to people how slightly different the formats are. Think about it, though, do we call a 35mm frame a crop factor of a 6x7cm medium format frame? No! But it's exactly the same thing!

If we used the same reasoning, a medium format is a crop factor of a large format camera. A 5x7 view camera is a crop factor of a 8x10 view camera. A 35mm half-frame is a crop factor of a 35mm full-frame. That's not the way we think, uh, except with FF vs. DX sensors?

The only reason a DX sensor is considered a crop factor of a so-called full-frame sensor, based on 35mm, is because a clever marketing guy, hoping to sell you something, invented the term! It's all about the format not the crop.

I chose a 50mm lens for this example because they are generally available for most all camera formats. Study the illustration below and see if you understand what I mean (frame sizes are approximate):


On a medium format camera a 50mm is a wide angle lens, on a 35mm film camera it's a normal lens, and on a DX camera is a slight telephoto. The subject stays the same size, but the format is different. That's all the "crop factor" really is - a difference in format!

Medium Format vs. 35mm vs. DX

A DX sensor is a different format from 35mm and medium format. However, the 12 megapixel DX sensor exceeds 35mm film and approaches or equals medium format in quality. A six megapixel camera at least equals 35mm out to 11x14, but may not be as good at 16x20 or larger. Use as many megapixels as you can afford, up to the maximum size of the image you will normally print. Why go larger and deal with storing the bigger files on your computer's hard drive?

Full-Frame 12 Megapixel vs. DX 12 Megapixel

If one uses a so-called Full Frame (FF) digital camera with 12 megapixels, and DX sized sensor with the same 12 megapixel resolution, the 1.5x DX sensor has the effect of a 50% telephoto, since the resolutions are the same but the subject is occupying more of the 12 megapixel area in the DX format. See below for a visual reference:

I admit that this is a somewhat strange way to view things. However, the projected image from a 50mm lens on a 12 megapixel FF sensor covers a smaller area of those same 12 megapixels than the 50mm image on a DX sensor. The image on the DX sensor is covering more pixels, making it a potentially larger image. (that's why it's like magnification) See how the FF sensor in Figure 4A is wasting megapixels because the same lens is slightly wider in angle of view and projects an image that only covers part of the sensor. To reverse the thought, you'd have to use a 600mm lens on a FF sensor to cover the 12 megapixel frame like a 400mm lens on a DX sensor.

Notice how the same lens projection on a DX sensor in Figure 4A has more of the sensor covered than the FF sensor. Both of the sensors are 12 megapixels, but the FF sensor is using less of its capacity to produce the image, so it is a smaller image. That means that the DX sensor produces a larger image with the same lens. Voila, you have a telephoto effect that is real.

Study both images above, then think about this for a bit. You'll see what I mean.

Full-Frame 16 Megapixel vs. DX 12 Megapixel

Finally, let's compare a FF sensor at 16 megapixels, with a DX sensor at 12 megapixels. In this case the 1.5x factor is a true crop, and resolution loss. The 1.5x crop factor is providing an image of lesser quality - or is it? I have seen several comparisons between a competitor's 16+ megapixel camera and a Nikon® D2X/D2Xs at 12 megapixels, and in each case, other than in noise, the Nikon outresolved the competitor and provided a better looking image. The D2X/D2Xs has a smaller “Pixel-Pitch” and can resolve finer detail in distant objects. (90 lp/mm vs. 60 lp/mm)

So, I honestly do not understand what makes some get so excited. The quality of the image is the important thing, not the size of the sensor. The DX sized sensor is every bit as capable as a 35mm-based full-frame sensor.

How Many Megapixels Do You Need?

Megapixels do not matter as much as many people think. You would have to double the resolution of the sensor to really make a difference. So, a FF 24 megapixel sensor would soundly trounce a 12 megapixel sensor, since it would not have the resolution for larger enlargements. But, between a 6 megapixel and 8 megapixel sensor there is little difference. Same with a 10 to 12, or 12 to 16. Not enough resolution difference except for the largest of enlargements.

Why do you think that the latest cameras coming out are not massive jumps in megapixel ratings over the previous cameras? The simple reason is that we do not need many more megapixels than we currently get with our digital cameras. What will you gain if you can make an image as big as a billboard when you will never print an image bigger than, say, 16x20 inches? Nothing much! How many of us already have one or more hard drives overflowing with large images. Do we really want bigger image files to speed up that process? Especially when a D2X/D2Xs' files will cover a double page magazine spread (double-truck) with no difficulty. Who needs it?

Look at the old standard of 35mm as an example. That format has been around for a long time and was quite successful. Why? It provided just enough image quality to make a nice big print. If one wanted a gigantic print, one could always use medium or large format.

So, if a DX sized sensor equals or exceed 35mm film, why worry about getting even more megapixels. If a so-called full-frame digital sensor can only provide a marginal difference in quality, but costs a lot more to make, who needs them! They have known light-falloff (vignetting) issues with 35mm lenses, anyway. DX sensors are using only the sweet spot of 35mm lenses, the center, not the edges, so they provide superior quality images even with older 35mm lenses.

Nikon and even major competitors have been intelligent in making almost all their cameras with APS sized (DX) sensors, so far. At the time this article was written, there were only two small-bodied cameras that have full-frame sensors, and they provide no big resolution benefit to the user. Their cost is significantly higher compared to their DX-sensor cousins. Their primary benefit is a reduction in noise, and older wide-angle lenses still performing like they did on the now mostly obsolete 35mm platform.

What About the Wide-Angle Problem?

I simply do not agree that the full-frame sensor is necessary, even though most of us wouldn't mind owning one. I like the apparent increase in the focal length of horribly expensive telephoto lenses with the DX sized sensors.

A few years ago, when DX sensors were first released, there were not many good wide-angle lenses to overcome the 1.5x format difference. So, a 24mm lens acted like a 36mm lens. Many people were upset, and the cry for FF sensors started, and hasn't let up yet.

The perceived wide-angle situation is now a completely moot point, since I can buy a 10-20mm Sigma, or 12-24mm Nikkor or Tokina. Here's a sample from my pro-level Sigma 10-20mm EX at 10mm (15mm 1.5x factor equivalent):

Which Sensor is Better, a DX or a FF?

Which is better? In my humble opinion (cough, cough) neither of them are better. They are too close in performance to really make a difference. Each has good points, each has bad points. Since DX sensors are much cheaper to manufacture, and give comparable quality, I'm sure that most all camera manufacturers will continue to pump them out. Do you want to pay 50% more for your camera just to get a bigness factor that makes only a marginal difference? Some will shout a resounding YES! Others ... NO WAY !

As technology develops and FF sensors can be created that do not have the problems of today's sensors, I am quite confident that Nikon will reward us with the best FF ever made, or even one that is closer to FF than today's 1.5x format difference. Time will tell! Maybe sooner than any of us expect, from all the fever pitched Nikon FF or almost FF conjecture and rumors.

Is There a Real Benefit to the 1.5x Crop Factor?

The fact that there's an apparent reach or "crop," allows us to use our long lenses more efficiently. Remember, the crop is only a crop when compared to a so-called full-frame sensor. The DX sensor has a giant 12 megapixel crop on my Nikon D2X/D2Xs, and even my tiny little Nikon D40 (ain't it cute) has a six-megapixel crop. That's quite a sizable crop!

Most of us will do just fine with our efficient and less expensive DX (APS) sensors! We'll even relish the benefit of the 1.5x crop factor providing us greater real or apparent reach with our expensive telephotos, such as shown in the bird image below, with my vibration reduction AF Nikkor 80-400mm lens at 400mm (600mm 1.5x factor equivalent):

This image shows no comparison shot, since I didn't take one. The point is that there is no need for a FF sensor just to get frame filling images. In fact, my 400mm filled this frame quite nicely, even though some will consider this a crop. This is the equivalent field of view of a 600mm lens, as you and I have read in countless articles, and are experiencing in person.

I suppose I could bend a little and say, “hey, it isn't really magnifying like a 600mm lens, since a real 600mm lens on my camera would look more like a 900mm field of view.” However, the way the image looks with a 400mm lens is the same as with a 600mm on a FF sensor. My camera has sufficient megapixels to make huge images with my DX sensor. What difference does it really make? Very little!

Another Lens Factor to Consider!

The smaller DX sensor requires a significantly smaller circle of light to fully cover the edges of the rectangular area of the sensor. That means something very important! Lenses can be made in smaller sizes and less expensively compared to 35mm lenses. That is a very important lens factor, and one of my favorites!

Using a DX sensor, the camera manufacturers can create new lenses that perform as well as lenses costing significantly more money. The glass does not have to be as big around, since the required image circle is smaller. You save money on your camera and your lenses. That seems pretty smart business to me! Plus, you can keep right on using your older 35mm lenses for years to come.

Digital Darrell's Conclusions on the Matter

The technology world is constantly changing. Rumors are flying around the Net about a Sony 1.1x (compared to 1.5x) sensor in the 18.7 MP range. I found that rumor on at least 3 sites. Will they come true? We'll see.

However, in the meantime, and for most of us, a DX sensor will work just fine. When Nikon does release a camera with a FF sensor, it will surely cost more than a DX-based camera, all things being equal. If one is willing to pay the difference, then have at it. On the other hand, once the buying frenzy on cameras such as the D3X begins, hundreds of thousands of D2X/D2Xs and D2H/D2Hs cameras will enter the market instantly. The price will drop like crazy. Want to buy a good used D2X for $1500.00 USD? Maybe you won't have to wait too long?

I've toned down the rhetoric, in this article, compared to my other one on FF. However, I am a firmly entrenched DX user. I like the smaller, lighter lenses it allows, and I find that the image quality is simply superb from a DX sensor. Why do I need anything else, since my 35mm lenses all work fine, too?

Nikon Acquisition Syndrome (NAS) is a terrible force. When a FF is released, I may fall in with the slobbering pack. But, in my heart, I'll always leave room for a nice DX sensor. Won't you?

Whichever format you chose, DX or FF, the important thing is that you ...

Keep on capturing time...

   
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