My hope is that by reading this article you will come away with better understanding about some of the differences between full frame (FF) and cropped sensor cameras (APS-C). Many of the topics I will cover are very complex and quite frankly often the subject of heated debate. Some are questions that should be left to physicists rather than photographers, or better yet, someone with a strong background in both. For such topics that are under such high scrutiny my humble article should read more as an opinion piece than a statement of hard fact. At the very least, by the end, you should have a better idea of what questions still need to be answered before you; one, buy your first digital camera, or two, decide to make that jump from cropped sensor to full frame.

Full Frame and Crop Defined:

Full frame with regard to cameras refers to a camera with a sensor size matching that of a 35mm piece of film.  More specifically a sensor measuring roughly 36mm by 24mm. Full frame with regard to a lens means a lens that is designed to project an image circle that will cover a full frame sized sensor at a specific distance.  When considering cropped sensor cameras things get just a little more confusing.  Any sensor smaller than FF can technically be called “cropped”.  The two most common  cropped sensor sizes are APS-C and micro four thirds.  APS-C size is based on a long since gone film size called Advanced Photo Systems Classic, hence APS-C.  What you really need to know is that APS-C is basically the same aspect ratio, but about half the surface area of FF.  Micro four thirds (MFT) is 4:3 ratio and about one-quarter the surface area of FF.  

Price:

This is the most simple and easy to understand topic with regard to this comparison. As a general rule of thumb full frame systems are more expensive. This includes both the bodies and the lenses.  There are definitely exceptions to this rule, especially with regard to lenses but the vast majority of the time this price variance holds true.  To date I can’t think of a single full frame digital camera that retails for less than $1,999.95. It is also very rare to find a cropped sensor camera that exceeds $2,000.  In essence that $2,000 is pretty much a divider between Full Frame and Crop Sensor camera prices. The line dividing Full Frame and Crop Sensor lenses is not quite so well-defined but it does follow the same general trend.  So why the price difference? The simple answer is that Full Frame sensors are obviously larger and comes with a higher production cost. Further most companies tend to market their full frame bodies and lenses to a “Pro” consumer base.  This means that as a general rule FF equipment is paired with more high-end features.

Crop Factor:  35mm Equivalency

This is generally the point where all hell breaks loose and people start scratching their heads. First of all, why do we even have a crop factor?  It’s simply a way to develop a common reference point so that we can more easily achieve the same result if we shoot with both systems or know someone using the opposite system.  So if your friend is getting great results using their 50mm lens on their full frame body but your shooting on a crop body, crop factor is a fast and easy way to figure out what lens or focal length you need to get those same results as your friend.  If you were to grab a 35mm lens given the 1.5x crop factor (35mm x 1.5) you would achieve a 52.5mm focal length ie. very close to that of your friend.  Below is a visual representation of the field of view change between FF and crop.

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Megapixels & Light Gathering:

All else being equal a larger sensor size will lend itself to greater light gathering ability and thus better high ISO performance.  Likewise more megapixels results in smaller photosites and lower light gathering ability and worse high ISO performance.  For the purpose of this comparison it boils down to FF sensors having an advantage over cropped with regard to high ISO performance.  This advantage becomes less and less relevant as advances in sensor technology makes high ISO noise less of a factor.

The Depth of Field Confusion:

Read enough about full frame vs. cropped sensor cameras or ask enough sales people, and you will no doubt find someone who will tell you that shooting full frame is more conducive to shallow depth of field work. The truth in this statement is largely up to the point of view of the photographer. In fact, the very definition of depth of field usually includes some sort of reference to “acceptably sharp,” which is already open to interpretation.  Worse yet you may hear mention of the phrase, “circles of confusion,” which, as it turns out, are very aptly named. Factors such as subsequent enlarging, either for printing or digital pixel peeping, also come into play to further complicate the topic. However, when considering only the original capture, if you were to take a photo with a standard 50mm lens, for example, at a given aperture on a full frame camera; then take the exact same shot with the same lens on a crop camera, assuming all other factors being equal, you will find that the depth of field is also identical. In short, the image produced at a fixed distance from the rear element of a given lens does not change based on what sensor is receiving it.

So where does the confusion come from? Most likely it comes from the fact that if you were to adjust your position relative to the subject, in order to get the same field of view, with the same focal length lens, you would have to back away from your subject using a cropped sensor camera relative to a full frame. This change in position relative to the subject, for various reasons, results in an increase in depth of field. I find that the best way to come to terms with these changes is to simply download a depth of field calculator on your phone and start plugging in numbers.

Magnification:

Perhaps the most often uttered “advantage” for APS-C cameras beyond price, is the crop factor itself. You will always hear people say that crop sensor cameras are great for bird photographers who want a little more distance out of their lenses without the big price tag. People will often be told if they simply put their 300mm lens on a cropped sensor camera then “poof” they have the equivalent of a 450mm on a full frame. Sounds great right? The question is; what exactly does “equivalent” mean? In most cases the result is probably not quite what one would expect or hope for. The truth is using the crop factor of an APS-C camera to get more range out of a lens is doing nothing more than chopping the sides off an image that would have come from a full frame camera… sort of.

Any lens regardless if fitted on an APS-C camera or full frame camera is designed to focus an image in a single plane at given distance from its rear element. As I stated earlier this distance does not change based on the camera to which it’s mounted. Therefore, when you are using a standard 35mm lens on an APS-C sensor camera you’re allowing the outer edges of the projected light to go passed the edges of the sensor. The portion that does hit the sensor produces the exact same image as it would have on the corresponding portion of a full frame sensor. So all else being equal, namely pixel size and density you are not getting any magnification using a cropped sensor camera. This is why the name cropped sensor is so appropriate.

There are however some advantages to using a cropped sensor camera in a situation when you know using a full frame you will later need to crop your image because you did not have a lens of adequate focal length.
For example, retaining full sensor resolution:
If both full frame and crop sensors are 24 megapixels, then cropping the full frame image to the crop sensor frame would end up being ~12 megapixels; while if shot directly on a crop sensor would retain the full 24 megapixels.

All else being equal, your camera should more accurately focus and meter a shot with regard to your subject since you’re shooting your desired field of view rather than one wider. One might also argue that composing your shot will also be easier since you will not have to mentally adjust for the extra material around the edges; material that you later intend to crop out. Further, the viewfinders of many cameras have internal grids or overlays to assist you in composing your shot. Such overlays would be essentially useless if you are working with a composition that you intend to crop in post. 

Crossing Lenses & Bodies:

I saved the most complicated and highly debated topic for last so buckle up.  Let’s start slow and simple. What happens when you put a crop lens on a FF body? One of two things will happen; your image will have drastic vignetting due to the small image circle being projected onto your larger sensor, or your body will switch into “crop mode” activating only a small APS-C sized portion of your FF sensor.  This will allow you to avoid having to crop out large black areas on the edges of your photo but it will also reduce your effective megapixels by just over half, ie a 24mp full frame sensor in crop mode renders a 12mp cropped size image.

Now for the really confusing part.  What happens when you put a FF lens on a crop sensor body?  Let’s start with the good news. Basically any lens starts to lose some quality as you get out toward the edges. The image it projects starts to lose light causing vignetting and the image becomes a little softer.  Since a crop sensor will not even “see” that edges of the image circle than you are essentially cutting off the lower quality areas. This should result in less vignetting and better center to edge sharpness. Essentially your only using the heart, or highest quality part of the lens.

There is however a much less talked about, negative effect of putting a FF lens on a crop body.  You will reduce the maximum resolution your can capture. Though you don’t generally think of lenses as having “resolution” they absolutely do.  Any lens has a maximum resolving power and this maximum is based on the entire image circle. When you only capture the center portion of a lens’ image circle you naturally sacrifice some of that resolution. Obviously if your camera has a 24mp sensor you are still ending up with a 24mp image no matter what lens you use, but your effective or theoretical maximum resolution is reduced.  This is why there will always be a balance between megapixels of a sensor and resolving power of lenses; as one grows so must the other or there is no benefit. 

Conclusion:

The vast majority of articles such as this will give their recommendations as to who a specific format is for. My personal view is that the topic is too complex, with too many variables, the largest variable being the person themselves. I could not presume to make such a blanket recommendation without having a discussion with the individual. I have a hard time making the decision for myself so how could I do so for someone else. My best advice is to do your best to understand the variables I have touched on here before you decide what is best for your budget and style of shooting.  Full disclosure, for several years now I’ve always owned both systems and used each for various purposes.

 

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