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Many of the creative options available to a photographer hinge on an in-depth understanding of lenses. In Foundations of Photography: Lenses, Ben Long shows how to choose lenses and take full advantage of their creative options. The course covers fundamental concepts that apply to any camera, such as focal length and camera position, and shows how to evaluate and shop for DSLR lenses. The second half of the course focuses on shooting techniques: controlling autofocus, working with different focal lengths, and managing distortion and flare. The course also examines various filters and contains tips on cleaning and maintaining lenses.
By now you should be well acquainted with the idea that different cameras can have different sized sensors. But if you use an SLR with a cropped sensor, that is, one whose sensor is smaller than a piece of 35mm film, then you have some additional lens options. Take a look at this. I have got here a Canon 5D, which has a full frame sensor, and a Canon 7D, which has a cropped sensor with a crop factor of 1.6, just like we were talking about earlier. I have taken the lenses off so that you can see inside to see the mirror chambers.
Now, we haven't talked about SLR anatomy. You can learn about that in the exposure course. But inside this chamber, when I take the lens off, there is mirror that reflects light up into the viewfinder and you can see very easily that the full frame sensor has a much larger mirror than the camera with the crop sensor. That's because the sensor is so much larger that it takes a bigger mirror to cover it up. Now, what you can't see here from this angle is that the mirror in this camera in the 7D, the camera with a crop sensor, the smaller mirror, is actually set a little farther back in the mirror chamber than this camera is.
What that means is I've got more space here in front of the mirror than I do here. Now to understand this next bit, you need to know that if you can get a lens closer to the sensor, you can build a lens that is physically smaller and lighter. So, now take a look at this. I have two lenses here. This lens will fit on either the 5D with the full frame sensor or the 7D with the crop sensor. Now, look at this little bit right here.
That bit that's sticking up. This is what goes into the mirror chamber when the lens is mounted on the camera. Now, I've got another lens here. This lens is specifically for a Canon camera with a crop sensor, like the 7D. And if you look at this bit that's sticking out, the part that goes inside the mirror chamber, you can see there is this extra little bit on top. This lens will not work on the 5D. There's not enough room in the 5D's mirror chamber for this extra little bit. What this means though, the advantage if you have a crop sensor camera, like the 7D or the Rebel or the 10-series Canon camera, is that the back part of the lens can actually be physically closer to the image sensor.
And as I explained earlier, if you can get the lens closer to the sensor, you can make the lens physically smaller. This is a Canon 18mm to 55mm lens. To build an 18 to 55mm lens that would work on the 5D with its full frame sensor would require a bigger, a physically larger lens than this. So, this is one of the advantages of a crop sensor camera, is that lenses can be made smaller and lighter. Now, Canon labels their lenses that are designed specifically for smaller cameras or smaller sensor cameras with an S label.
So, I can see here this is an 18 to 55 EFS. Nikon also makes a line of lenses designed specifically for their crop sensor cameras and those have a DX modifier. Now, you might have another SLR like an Olympus SLR, and there there's no difference because Olympus only makes crop sensor cameras. So, all of their lenses will work on all of their cameras. What this means is if you've got a crop sensor camera and you're going out lens shopping, you want to be sure to remember to look for the lenses that are specifically for crop sensor cameras in addition to the full range of full frame sensor lenses, because the crop sensor lenses are possibly going to be lighter and smaller and less expensive.
Something else you should know with Canon lenses, you may know about L lenses. The L series of lenses is Canon's high-end professional line of lenses. That means expensive. A lot of S lenses are actually L glass, meaning you're doing an L quality lens, but in a small package. Canon has just made the decision that they will not put both an L and S on a lens. So, the crop sensor lenses can be extremely high quality. Both Canon and Nikon make very, very good crop sensor cameras.
They are worth looking at if you have a crop sensor camera, because they are going to be smaller and lighter. The downside is if you ever upgrade to a full frame camera, you are not going to be able to take your lenses with you, but that's what eBay is for. In the meantime, it means your camera bag can be much, much smaller and lighter.
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