Intermediate If you use a photo printing service, such as the one offered by your local drugstore, you may occasionally (maybe even frequently) get photos back that don't look the same as they did when you shot them. I don't just mean color and exposure (which can often be wrong when you use a commercial printing service), I mean decapitated heads, scenery that's missing important elements and crops that just look, well, wrong. Why does this happen?
It happens because of your camera's sensor size, and the fact that your commercial printing company didn't print your image with the same aspect ratio as your file. But let's back up a little.
The Moment It Clicks - 17/365 by Flickr user fstoaldo
Before digital cameras became the dominant technology in the photography marketplace, we took pictures on SLR cameras. "SLR" just means "single lens reflex," which refers to the mirror and prism system of a 35mm camera. The DSLR, of course, is the digital variation of that same technology, a "digital single lens reflex."
In those days, we shot photos on film. In order for film to work in all SLR cameras, it had to be a standard size. That way you could use any roll of 35mm film with any SLR camera, because that rectangle on the film where your exposure appeared was always going to be 24mm x 36mm. Ah, simpler times.
And then came digital. Now, manufacturers were no longer married to that 24mm x 36mm standard. In fact they actively rejected it, because producing a camera with a 24mm x 36mm sensor was expensive. Most consumers didn't want to pay that kind of money just to have a camera that would produce 24mm x 36mm image, so manufacturers didn't really offer them to the consumer market. Instead they used a sensor size that was considerably smaller than that, and decidedly non-standard, though 14.9×22.3mm and 15.8×23.6mm are the most common. This family of sizes eventually became known as APS-C format.
To complicate matters further, sensor sizes are often just referred to by "crop factor." DSLRs may be "full frame," which means they have no crop factor, or they may have crop factors ranging from 1.3x to 2x. That basically just means that they produce images that are smaller than their full frame counterparts, by whatever that crop factor is. Some cameras (most DSLRs) will still produce images with the same aspect ratio as a 4x6 image. Other cameras will produce images that don't have the same aspect ratio, and will be cropped when printed to 4x6.
Pros and cons
Full-frame cameras do have certain advantages, and one of them is that they will produce 4x6 images without decapitation or any of the other goodies that go with having to crop an image to a standard photo size. But they have other advantages, too. The quality is better, hands down. They have much better performance at higher ISOs (producing images with less visible grain).
The cons, of course, are that you get a bigger, heavier and more expensive camera. Not everyone wants to spend that kind of cash on a camera, and not everyone wants to be stuck carrying around a heavy camera, either, especially if you're going to be on your feet all day long.
Whether you own a full-frame camera or one with a smaller sensor, you need to be aware of how this impacts the lenses that you'll need to purchase. Not all lenses sold by your camera's manufacturer are necessarily designed for your camera. If you have a full frame camera, for example, and you buy a lens designed for a camera with a smaller frame, you'll have to keep certain factors in mind when using the two together.
Prime Candidates by Flickr user pangalactic gargleblaster and the heart of gold
Let's take Nikon as an example, since it has only two different sensor sizes: full frame (called FX) and 1.5x (called DX). In general, you will want to use FX lenses on Nikon's full frame cameras, and DX lenses on their 1.5x cameras. But you don't have to. You can buy a DX lens and attach it to your FX camera, but you'll get vignetting around the edges because the FX sensor size doesn't match the DX lens. To compensate for this, you can set your FX camera to use a DX crop, but then you end up with reduced resolution because what you're doing is telling the camera to crop out everything outside of that DX area. You also have to be aware of where this area is when you're shooting, so you don't inadvertently put something important into the area that is going to get cut out anyway.
FX lenses, on the other hand, are fully compatible with a DX body.
So what should I choose?
The answer really depends on what kind of shooting you do. A camera with a crop factor gives you more magnification when you're shooting with telephoto lenses, so that's something you may want to consider if you're doing a lot of long-distance shooting. But if you prefer to shoot with wide angle lenses, you may want to choose a full-frame camera, since they often give you better image quality at those smaller mms.
Full-frame cameras are also great for photographers who shoot in low light, since they often have better ISO performance. Keep in mind though that ISO technology gets better all the time, and even some point-and-shoots can keep up with older full-frame digital cameras when it comes to noise-free low light photos.
For the average photographer, though, a camera with a smaller sensor is going to be perfectly adequate. You'll get great detail at long focal distances, and you'll have the added advantage of a lighter, smaller camera that's easier to carry around. For basic lighting situations, you'll get nice images and you'll have most of the same features available as you have on a full-frame camera, without the added expense.
Just remember, though, that crop factor the next time you send your images off to the drugstore for printing. If your camera's sensor size doesn't produce images with the same aspect ratio as a 4x6 image, you may need to request "true digital" prints, but you have to request them--or crop them to that 4x6 size yourself. Either way, it's a tweak you have to take into consideration, or risk decapitating your loved ones.
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