3.1 Stabilization, Coatings, and Focusing Motors
Better lenses will often have features like ultra fast focusing motors, fancy lens coatings, or image stabilization. What are these things? Is any of this worth it? In this lesson you will learn all about these features and why you might want to look for them in your next lens!
1.Introduction1 lesson, 02:27
2.How Do Lenses Work?3 lessons, 43:08
3.Special Lens Features1 lesson, 09:35
4.Choosing a Zoom Lens5 lessons, 44:07
5.A Guide to Prime Lenses2 lessons, 26:57
6.Getting Perspective Right in Your Photographs3 lessons, 35:17
7.Conclusion1 lesson, 02:22
3.1 Stabilization, Coatings, and Focusing Motors
Better lenses will often have features, such as, ultra-fast focusing motors, fancy lens coatings, or image stabilization. But, what are all these things? Is any of it actually worth it? In this lesson, you will learn about all of these features, and why you might want to look for them in your next lens. Image stabilization is a fantastic feature to have in a lens. But what exactly is it? Lens based image stabilization or optical image stabilization are techniques used to reduce blurring associated with the motion of a camera during an exposure. The sensors in the lens analyse vibrations and then apply correction via a special stabilizing lens group, that shift the image parallel to the focal plane, motion blur is cancelled, resulting in a sharper image. This allows you to shoot at slower shutter speeds and still get sharp images. Different lens makers have different names for these techniques, such as O.I.S. or optical image stabilization, optical steady shot, SR, which is shake reduction. VC, which is vibration cancellation, VR, vibration reduction, MegaOIS, and Canon just calls this IS, for image stabilization. There's also stabilization that can be done in the camera, but what we're talking about here is done with the lens. Let's take a look at how this helps make sharper images. So let's check out an example of image stabilization in action. Here we're taking a look at a video I shot in my back yard, and I'm shooting handheld at about 18 millimeters with a DLSR. Now what I'm gonna do is switch on image stabilization and hold the camera the exact same way. And check out the dramatic difference in what image stabilization does. Now it doesn't completely eliminate all motion, but it does smooth it out tremendously. Now we're looking at a shot here, I believe this is at about 270 millimeters. And you can see the amount of shake is just incredible. Right? It'd be very difficult to get a shot like this. But as soon as I switch on image stabilization you can see the dramatic effect that it has on the image. Everything is smoothed out, and things are looking much better. Now you'll see some jitters and jumps. From time to time, but that's just the way image stabilization works. So probably where you'll see image stabilization have the most dramatic effect is when you're at a more telephoto range. So this first one here, this image of these two horses on a playground was shot with a 270 millimeter lens. Handheld, I was probably 20 or 25 feet away, the shutter speed is 1/30 of a second. Now, if you're shooting at a focal length of 270 millimeters, handheld on a crop sensor body, that is really slow, because the general rule of photography when you're shooting handheld is you shoot one over your focal length, or your effective focal length. In the 270 millimeter lens on a crop sensor body has the equivalent focal length of a 430 millimeter lens on a full frame camera. So, what that means is the threshold shutter speed which means just probably barely sharp, with good technique would be somewhere around 1/500th of a second. So a little bit faster than what the focal length is, or the effective focal length is. And what I shot this image at is 1/30 of a second. Now you can see from this image here. If we look at a one to one pixel crop, this is not sharp. There's motion blur in this image, but that's because image stabilization was off for this shot. If we look at the next shot, and we look at a one to one pixel crop, what you'll see is that this image is acceptably sharp. Now, it may not be as sharp as if I put it on a tripod, but to my eye, this looks perfectly fine, and perfectly usable, it's a heck of a lot better than the one that I shot right before it with image stabilization off. That one is not usable at all. There's way too much motion blur. And 1/30th of a second is way, way slower than what we should be shooting at to get a sharp shot. And so if we were at 1/500 of a second, half of that would be 1/250 of a second. Okay, so even at 1/250 of a second, it would be very, very difficult, probably impossible to get a still shot using that kind of focal length, hand-held. We cut that in half again, now we're down to 1/125 of a second. Half of that would be 1/60 of a second. So that's three full stops, four stops would be 1/30 of a second. There's no way. You know, even with really great technique you can shoot a still image at 270 millimeters on a crop sensor body at 1/30 of a second, it's just not gonna happen. Let's check out a few other ones here. I did another very similar one here, I shot the side of a garbage can. This one I shot at 1/50 of a second, so if you look at the one to one crop here of this sign, even at 1/50 of a second at the same focal length, you can see there's definite motion blur there. If you look at the next image where I turned image stabilization on, same exact shutter speed, this is what I would call acceptably sharp. I can't see any signs of camera shake in this image, which to me makes it work. Now it's not a great image, because, well, it's the side of a dumpster, but I thought it would be good to look at, because it has some very high contrast. It's a white sign with black lettering on it, which is very easy to see any tiny amounts of motion blur. So,you can see what a dramatic effect this has on your images. Now this won't stop motion, because things on motion are not going to be effected by image stabilization. What will be effected is your own cameras movement, especially when you are shooting handheld shots. Lens coatings are treatments applied to the outer surfaces of lens elements, to reduce reflections. Reflections occur whenever a ray of light moves from one medium to another, such as when light enters a sheet of glass after travelling through air. Some portion of the light is reflected from the surface. Without coatings, each air-to-glass interface would reflect about 4% of the light that reaches it. The reason this becomes important is because lenses are made up of several glass elements. A complex lens without coatings would have as much as 70% of the light absorbed or scattered before it reached the image sensor. Most lenses these days have multicoatings, at the very least, and better lenses will have nanocoatings, which do a better job at reducing reflections. Where you might want to pay attention is when it comes to filters. The cheapest aren't coated at all. Some have a single coating on just one side. The vast majority of even lower priced filters have single coatings on each side. The very best have multi coatings or nano-coatings on both sides. If you're shooting in, let's say, the direction of the sun, and you're using a cheaper filter, you're going to be throwing away a lot of contrast and image quality in your images. So, lens coatings and filter coatings, especially, is something to consider. Finally, let's talk about focusing motors. One of the many acronyms you will see listed on lens models has to do with the focusing motor, you will see SSM for supersonic motor and SAM for smooth autofocus motor in Sony lenses. Tamron uses USD for ultrasonic silent drive and PZD for piezo drive in their lenses. USM stands for ultrasonic motor, and these are found in some Canon lenses. SWM is silent wave motor, and AFS is auto-focus silent, and these are found on Nikon or Nikkor lenses. SDM is Pentax's supersonic drive motor. HSM is Sigma's hypersonic motor, IF stands for internal focusing, and is found on many lenses from many manufacturers. These lenses are constructed so they don't change in length as the lens is focused. It also means that the front lens element doesn't rotate, which can help with the use of some attachments, like a petal shaped lens hood, and polarizing filters. The main point here is to distinguish these fast focusing lenses to the older server style focusing mechanisms. These older focusing motors are easy to spot as they make a good deal of noise and are somewhat slow. [NOISE] You can still find these older style focusing systems used on lenses that are still being made and sold today. Having a lens that focuses super-fast is a fantastic feature when you are shooting moving targets, or anything dynamic. Slow focusing systems will not work for these shooting situations. If you are looking for a lens, having one of these ultra-fast focusing systems is a definite advantage. Now that we've covered the major special features that you will find on lenses, you are ready to move on to the next chapter in this course, where you are going to learn all about zoom lenses.