Ok, this question is an important one to answer for a couple reasons. This question pops up a lot and needs to be answered honestly. I hate seeing people buy a camera that they don’t enjoy. I also know that marketing hype muddies the water and causes people to become confused. Let’s deal with the confusion and help you decide on if you want to start off with a full frame sensor.
First, what do we mean with “full frame” and “cropped” sensor? Cropped is usually a dirty word, it means, less than the whole. On the surface then you would never want anything cropped because you are being robbed of part of the sensor size right? The answer to this goes back to film. “Full frame” is defined by the film it replaced. In this case it was 35mm film. In film when one refers to 35mm they are referring to a film size of 35mm or 1.4 inch wide by 24mm or 0.9 inch tall. When we refer to a “Cropped” sensor we are referring usually to APS-C format or size. Cropped sensors are possible because pixels can be crammed into a smaller space than full frame. You may be wondering how a “Cropped” sensor in one camera specs has a higher number of pixels than a full frame, and even from this diagram how different companies can claim to have the same sized sensor yet they are different sizes. All you need to know is that a cropped sensor preserves the ratio of 35mm and thus you will rarely notice a difference when comparing images between a camera that is full frame or not.
So what are the advantages of using a cropped sensor? Well there are a few very good ones. Camera lens glass for high end lenses is very expensive. Imagine a small pane of it being thousands of dollars. The glass must be completely void of any imperfections that will create distortion to light over the entire size of the image. The glass must also be of a special composition that will not refract light at different angles over the spectrum. This is called chromatic aberration and is very bad for photos. With a smaller sensor you can get by with smaller pieces of glass in the lens and save money. This means that lenses for a cropped sensor camera will be significantly cheaper than those for a full frame.
But what advantages do full-frame cameras offer? You will find yourself paying out the nose for good lenses for your full frame camera because manufacturing costs are higher. As discussed previously the manufacture of the lenses cost more. There is however a matter of market demand as well. Full frame cameras are usually bought by professionals for professional work, so the lenses are made to a higher standard all around in most cases. In the case of Canon, their professional lenses are usually made with a metal body to make the lens more rugged, and the tolerances are usually higher meaning that a 50mm from the pro line will marginally outperform one from the regular line. Full frame cameras also have a more gentle bokeh since the light has more space to blend. Being able to control for a more gentle depth of field can be very important in some situations, however it can be meaningless in many others.
Full frame cameras may not have a higher number of pixels than a cropped sensor, you may be wondering why this is. What is going on here is that a full frame camera has bigger pixels than a cropped camera. This can mean that a full frame camera will gather significantly more light with each pixel and thus will have much better low light performance. The ISO numbers a full frame camera can become insanely high. What disadvantages do full frame cameras have? Well for one their cost, they are much more expensive than cropped cameras. The lenses are mentioned previously are also very high compared to a lens for a cropped camera.
Now we know the differences, and now we can answer the question. Most of the time one should buy a DSLR camera with an APS-C sensor as their first camera. The lower cost being the most important factor. However, there are reasons why a full frame camera might be a good choice. One disadvantage might be that full frame DSLRs are really big and heavy, and getting more bulky and heavy with every generation. The bottom line being that neither sensor type is better than the other. Each sensor type will shine in different areas.
One important note is that if you buy a cropped camera first, and collect a bunch of lenses for it, you will not be able to mount those lenses to your full-frame camera if you upgrade. This is important to note because your glass is more important to consider than your camera body.
You need to think about what you plan to do with your first DSLR camera. I don’t mean just the sort of shots you will be taking, but what kind of environments you will be taking your photos in and what sort of capabilities you will need. Choosing any camera over another is going to require a compromise somewhere. So the compromises you choose will possibly not work for the next person. So ask yourself what reason you have for wanting to own a DSLR. It used to be that the only choice for DSLR was full frame, but those days are long gone. Now even mirrorless cameras might be a good choice instead of a DSLR all together. Mirrorless cameras are approaching the image quality of pro DSLRs at a fast pace yet can fit in your pocket.
Ask yourself why you need the DSLR in the first place. Why would a full-frame camera do what you want to do better than one with an APS-C, or even a mirrorless? If you can’t answer this question, you need to reevaluate your motivations for buying such a camera. It could be that a full frame camera just “looks” like what you want because it fits your preconception that a good camera must be bulky and heavy and built like a tank. When you remove your preconceptions about what makes a good camera and look at specs relevant to your needs, you will be much better prepared to buy your first camera, I hope it’s a DSLR, but I hope more that you choose a camera that can give you what you want from it.