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Deciphering the Camera Jargon – Part 1 (Sensors and Megapixels)

When you’re going to buy your first DSLR, it’s so easy to get lost within the technical terms. Without knowing what they mean, it’s difficult to make a choice. Even when you read reviews online, they often don’t make any sense if you don’t know what they are talking about. In an effort to explain some of these terms that tend to appear over and over again, I’ve decided to write a series of posts. I’m going to publish this in several parts to keep each post relatively short. It’s near impossible to explain one term without relying on other terms as they are inter-connected with one another. So if you run into something unfamiliar here, it’s very likely that it will be covered in a future post.

DSLR

This goes without saying but I thought I’d add this here anyway. DSLR stands for Digital Single Lens Reflex. The reflex mechanism is the main difference between a DSLR and a compact digital camera. The light travels through the lens and hits a mirror, which reflects it to the view finder through either a pentamirror or a pentaprism. When you click the shutter button, the mirror flips up, allowing the light to hit the image sensor. The term “single lens” here can be a bit confusing because DSLRs use many different lenses. However, the term refers to the fact that the light travels to both the viewfinder and the image sensor via a single lens as opposed to having a different lens for the viewfinder.

Full Frame vs Crop Sensor

Different Sensor Sizes. Image courtesy - Wikipedia

Different Sensor Sizes. Image courtesy – Wikipedia

In photography, we use the 35mm standard film SLR camera as the reference point. Of course the digital cameras don’t use film but instead full frame cameras have an image sensor with the same dimensions as the 35mm film, which is 36mm x 24mm. Now, why on earth is this called 35mm if the width of the film is actually 36mm? It’s because it actually refers to the full height of the film which is 35mm, including those tiny little holes on the sides. And if you think this is bad enough, it is also called the 135 photographic film format. Why? Because Mr Kodak said so and ain’t nobody’s messing with him. All in all, any DSLR with a 36mm x 24mm image sensor is considered a full frame DSLR. But there are so many different sizes of sensors out there. Technically speaking, a crop sensor is anything smaller than a full frame. But we don’t hear people referring to their pocket cameras as crop sensors even though the image sensor in those cameras are significantly smaller than full frame sensors. This language is mainly used to describe DSLRs.

The size of the image sensor is directly related to the effective focal length of a lens. What is the effective focal length you ask? The advertised focal length of a lens is always in terms of a full frame camera because it is our reference point. But if you put that same lens on a crop sensor body, the lens does not behave the same way it does on a full frame body. Since the crop sensor bodies only capture a portion of the image a full frame body would, it narrows the viewing angle and thus it has a magnifying (zoom) effect. While there are so many crop sensors out in the market, there are several popular ones. Canon APS-C (22.3mm x 14.8mm), Nikon DX, Pentax K, Sony (23.6mm x 15.6mm), Canon APS-H (27.9mm x 18.6mm), Olympus and Panasonic Four Thirds System (17.3mm x 13.0mm). There’s an awesome table in Wikipedia which includes all these numbers and the associated crop factor. Crop factor, or the focal length multiplier, as the name suggests is the factor by which you multiply your focal length to get the effective focal length (full frame equivalent focal length). For instance, the Canon APS-C system has a crop factor of 1.6 which means if you put a 50mm lens on a Canon APS-C body, you have to multiply 50mm by 1.6 to get the effective focal length. 50mm x 1.6 = 80mm and therefore this 50mm lens would behave like an 80mm lens on a full frame body. Thus the effective focal length of a 50mm lens on a Canon APS-C body is 80mm. As you might have already guessed, the full frame sensors have a crop factor of 1.0 just for book keeping purposes. Now that I mentioned APS-C, it stands for Advanced Photo System type C (Classic), in which the sensor size is approximately 60% of the size of a full frame sensor. APS-H stands for  Advanced Photo System type H (High Definition), in which the sensor size is approximately 75% of the size of a full frame sensor. There’s also an APS-P (Panoramic) albeit not very common.

So it all comes down to choices again. Which one is best for you? Well, that I cannot tell. What I can do is to tell you some advantages and disadvantages of each system. I’m going to limit this comparison to full frames and classic crop sensors because they are the most popular out there.

Full Frame Advantages

  • Improved dynamic range and better low light performance leads to higher quality pictures (larger pixels compared to a crop sensor with the same megapixel count).
  • Lenses behave the way they are supposed to. Although this is not a huge advantage due to the large range of available lenses.
  • Easier to achieve a shallower depth of field. If you keep all the other factors the same and shoot the same scene using a full frame and a crop sensor camera, the full frame camera will have a shallower depth of field. The sensor size is a factor determining the depth of field. This is why it’s near impossible to achieve a shallow depth of field with your point and shoot camera despite the fact that it has a f/1.8 lens.
  • Brighter view finder. Comes in very handy when focusing manually.
  • Larger field of view. If you use a 14mm lens on a full frame, you would capture a wider view than using a crop sensor body. Especially useful in landscape and architecture photography.

Full Frame Disadvantages

  • Expensive. That large sensor is sure going to cost you a lot more.
  • Generally heavier and bulkier than crop sensor bodies.
  • Shallower depth of field. I wouldn’t say it’s difficult to achieve a deep depth of field with a full frame because that would be a lie. There are many ways around this. But like I mentioned before, if you use the same settings, a crop sensor body will give you a greater depth of field. There are many occasions where you would want a deeper depth of field.
  • To fully exploit the advantage of a full frame camera, you need those expensive lenses. Mind you, I’m talking about the image quality here, not the photographic quality.
  • Higher quality pictures mean bigger file sizes. But this is hardly a problem now that storage options are dime a dozen.

 Crop Sensor Advantages

  • Cheaper. Most of the entry-level and mid-level DSLRs are crop sensor cameras. They are more affordable than those expensive full frame bodies. This was a reason why photography opened up for so many people, including me. Heck, I still can’t afford a full frame camera.
  • Light weight and less bulky.
  • Extra reach. While crop sensor bodies have a disadvantage on the wide end, they have an advantage on the tele end. This comes very handy especially in wild life, bird, sports photography due to the focal length multiplier. Crop sensor bodies magnifies the subject like I mentioned before.
  • Smaller file size.
  • Specially designed lens series. Canon has EF-S lenses and Nikon has their DX lenses specially designed for their crop sensor bodies. These lenses tend to be cheaper than their full frame counterparts while delivering amazing results at the same time. Crop sensor bodies can also use the lenses you put on a full frame (Canon EF and Nikon FX) but the reverse is not true. The full frame bodies cannot use EF-S or DX lenses. So there’s a wide variety of lenses available for crop sensor bodies.
  • Vignetting and soft focus at the edges are less likely due to the cropped field of view.

Crop Sensor Disadvantages

  • Well this section should be pretty obvious by now after you read everything else I said. So I will refrain from stating the obvious.

It should be pointed out that over the years camera manufacturers have closed the gap between full frame cameras and crop sensor cameras. For instance, there are specially designed lenses to battle the wide angle problem in crop sensor bodies now. Both systems deliver amazing results. There are good enough reasons to pick either one. While most professionals stick to high end full frame cameras, there’s a good amount of professionals who still prefer crop sensor bodies and they are in no way inferior. It’s just a personal choice and depends on what kind of work you do with your camera. For photography enthusiasts like myself, it makes much more sense to use a cheaper crop sensor system because I don’t earn any money from my camera. 99% of the time, each system would deliver similar results. But sometimes you have to push your camera to its limits and then the advantages one system offer over the other becomes important. A professional bird photographer would have to use a $20,000 system to get the results just because anything less wouldn’t deliver exactly what he needs. If you’re still unsure what you need, I suggest that you rent out some equipment and try it out for yourself. If you’re just starting out photography, I would suggest you just get an entry to mid level camera and some decent lenses. But that’s just me.

Megapixels

Where do I even begin? I think in the digital camera world, megapixels have the highest number of myths associated with it. I’ll try to keep it short. The smallest element of a picture is called a pixel (PICture ELement –> pixel, get it?). I’m not gonna go into sub-pixels because it’s not very relevant here. Just so you know, there is something called sub-pixel as well. If you zoom in on a picture, you’ll start seeing individual pixels. Remember the late 90s and early 2000s when digital cameras were gaining popularity? I’m sure you’ve heard a conversation somewhere along the lines of “hey, my camera is 3 megapixels. how many megapixels does yours have?” “five” “woah!”

Now, let us back up here for a moment. Does the number of megapixels really matter? Not really! Let me put it this way. Imagine a 2 cm x 2 cm square (note: most DSLR image sensors have an aspect ratio of 3 : 2 but for the sake of this argument, we’ll consider a square). This square has an area of 4 cm2. If we are to fill this square with 1 cm2 little squares, we need 4 of those. We’ll call each of these 1 cm2 squares a pixel. However, if we are to fill this 4 cm2 square with 0.25 cm2 little squares, we’re going to need 16 of those. Now imagine that the bigger square is the image sensor. This is exactly what happens when they cram in more pixels into the same sized sensor. Simply the size of a pixel goes down. Mega stands for 1 million (106). So a 10 megapixel camera has 10 million pixels. So why does the size of a pixel matter? Larger pixels have more light gathering capabilities, which means at a given time interval, the larger pixel will collect more light compared to a smaller pixel. This results in less noise (little grainy stuff you see when you take a picture, especially under low light. See ISO) and sharper, more detailed images. Hence, what determines the image quality of a camera is not its pixel count but the size of a pixel. This is one of the distinguishing factors between DSLRs and compact digital cameras (and one of the reasons why DSLRs are expensive) because DSLRs have larger image sensors and thus larger pixels when comparing the same number of megapixels.

So why all the hype? It’s one big marketing strategy! The megapixel count was used by camera manufacturers as a primary way of competing with other brands. Don’t you love it when a salesman keeps exaggerating this? If they feel like you don’t know what pixels are, almost always they are going to push this. Sometimes they just don’t have any idea what it actually does either. Once I was on the phone with AT&T and I wanted to get an upgrade. When I asked about different phones, he kept coming back to the number of megapixels. I told him I’m looking for a phone, not a camera. Funny how that works.

Does the number of megapixels matter at all? Very little. If you want to crop out an image and still print it big, a higher pixel count would come in handy. This leads to another discussion on print resolutions. I promise I’ll keep it short this time. Two terms keep popping up. PPI (Pixels Per Inch) and DPI (Dots Per Inch). These are two different terms, although some people use them interchangeably. This page explains the difference in great detail. I promised I’d keep this short 🙂 Anyway, back to the matter at hand, a 15 megapixel camera will allow you to print 10 x 15 images at 300ppi without artificially enlarging (using algorithms) the image. If you want larger prints, you simply reduce the ppi and when you do, it appears pixelated, you know like when you really zoom in on a picture. However, it doesn’t really matter because the larger your print is, greater the normal viewing distance. For instance, you’re not going to make a print 2 meters tall and stand right next to it. You step back. This is how large bill boards work. They are printed at very low resolutions but since you’re viewing them from a greater distance, you don’t notice the pixelation. Of course, if you stand very close, it would look horrible but then you don’t see the bigger picture, do you?

I think I’ve covered most of the important facts about megapixels. Now repeat after me, “I’m not going to be fooled by megapixel count again!”

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