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Foundations of Photography: Lenses

with Ben Long

Video: Maintenance

Your lens is where your image making begins, which means it's also where a lot of problems can start. Fortunately, many of these problems can be prevented with some simple lens maintenance. In general, a lens is a very sturdy device that can withstand a fair amount reasonable abuse, unless it's an especially cheap plastic-y model. One way to really reduce the chances of that kind of abuse is to carry your camera properly. This is particularly true when you're carrying your camera with a long lens on it. I see this all the time. People walking around with their lens hanging like this.
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Watch the Online Video Course Foundations of Photography: Lenses
2h 32m Beginner Feb 11, 2011

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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.

Topics include:
  • Understanding field of view and camera position
  • Depth of field and lens choice
  • How to choose a lens
  • Examining lens features
  • Using specialized lenses such as fisheye and tilt/shift lenses
  • Focusing techniques
  • Using filters
  • Camera maintenance
Ben Long


Your lens is where your image making begins, which means it's also where a lot of problems can start. Fortunately, many of these problems can be prevented with some simple lens maintenance. In general, a lens is a very sturdy device that can withstand a fair amount reasonable abuse, unless it's an especially cheap plastic-y model. One way to really reduce the chances of that kind of abuse is to carry your camera properly. This is particularly true when you're carrying your camera with a long lens on it. I see this all the time. People walking around with their lens hanging like this.

The problem is, you're going to bump it into something. It's also not that comfortable, because with the lens hanging off this way, it's pulling on my shoulder in different ways. It's flopping around more, the center of gravity is all along. So a very simple fix for this, which is, take it off of your shoulder, turn it around, and put it back on. Now the lens is not hanging around out here, and it's much more stable. It's tucked into the small of my back, and it tends to just stay there as I move around. If I want to hike or climb or something like that, I can make it even more stable by putting it over my shoulder and keeping it there.

Now I can be pretty mobile this way and it's not going to move around. So this is particularly true with long lenses that carrying it this way is going to make the camera much more stable and greatly reduce your chances of smashing the lens into something. For the most part, your only maintenance concern with your lens over the long haul is just keeping it clean. Because as we mentioned before, if your lens gets dirty that can transfer to the image sensor in your camera, and that can cause real problems with your images. So, keeping your lens clean is pretty easy.

First of all, we never ever, ever take compressed air, a can of compressed air, and use it on our lenses or on our camera because compressed air has a liquid propellant inside it. If you don't have the can perfectly leveled, some of that liquid propellant can spray out and it's really sticky. So instead, we use blower brushes for, or blower bulbs or blower brushes, for cleaning our lenses. So, I can just blow of the front of the lens. Typically, before I go out shooting with my kit of lenses, if I'm going to go for a while, I take them out of the bag and I clean them.

I'm not so worried about the front of the lens, because any dust or things on here, the lens is just going to focus past. But if this is dirty and I'm putting it in my bag, I'm just transferring lens into the bag. It's this end that is the potential problem area, because this is the end that goes into the camera. If dust gets in here, I'm translating it or transferring it directly into the camera body where it could get on the lens. So to clean it, again, I go for a blower bulb. You can get these at any photo store. Hold the lens upside down, so that I've got gravity working on my favorite. I'm just going to blast some air up there, hoping that I'm dislodging any little particles and things that are in there.

Of course, lot of those, you can actually just see with the naked eye. So if you blow on it a bunch and you can't get those off, get a blower brush, which again is available at any photo store. This is going to be a something like this, only smaller, and it's going to have a brush bristles on the end, and you can actually brush it off. Use a brush designed for cleaning lenses. Don't think that you can get a paintbrush, or a makeup brush, or something like that, and clean off your lens. No matter how clean that brush may look, what you don't know is how abrasive the individual bristles and hairs on the brush may be.

A brush designed specifically for cleaning optical equipment is the only thing you want to take near your lens. Now as I mentioned earlier, it is possible for dust to get inside the sensor chamber of your camera and get on your sensor. You'll know this has happened when you look at an image and there is a little smudge or a smear. Sometimes they're completely opaque, sometimes it's just a little shadow that appears. You're usually only going to see it an area that's kind of flat color like a sky, because another area might be too busy. So if you think you've got sensor dust, one, the first way to test is look at some other images and see if you see the same problem in the same area.

After that, it's time to get a little more serious about your dust testing and so you can take some test pictures to see if you've got a dust problem. Put a kind of not such a telephoto lens, a more walk-around lens on your camera. Go outside, point it at the sky, switch the lens to manual focus, and defocus the lens. Go into aperture priority mode and set to a small aperture and take a picture, because this is going to give you basically just a blurry shot of bright sky. We want it be an empty sky.

If it's the middle of winter where you are and you can't go outside because it's too cold or the sky is not empty, a blank wall will do, preferably a white wall. Take a picture, move it into your computer, see if you can see spots. If you do, then you got a sensor dust problem and it's time to start thinking about cleaning. There are couples of ways to go for cleaning. First of all, most SLRs these days, and bear in mind with sensor dust, we don't really worry about that with a point-and-shoot camera, because you can't take the lenses off. Most SLRs these days have built-in cleaning mechanisms and you may have seen this when you turn the camera on.

When I power it up, it gives me a message that says Sensor cleaning. What it's actually doing is there is in front of the sensor a clear glass plate that it shakes and so any dirt on there gets hopefully shaken off and falls down the bottom of the camera where there is a little pad of something sticky and it gathers there. You can set your camera to do its sensor cleaning cycle at power up and power down, either or, or you can set it to do both. If you are the type of person who walks around with your camera off and you like to be able to just switch it on, have it boot up really quickly so you can start shooting, you might want to set it so that it doesn't clean the sensor at power up.

That will make it come up to speed a little bit faster. The same menu where you choose those options, there is probably an option to clean now. You pick that, and it'll shake its little glass plate, and try and dust off the sensor dust. So if you see that you have a dust problem, first thing to do is if your camera has a cleaning mode go in and activate it. That'll shake the thing around. You can then go do another test picture and see if you still have a dust problem. If that doesn't work, you have a couple options. You can send the camera into the manufacturer and have it cleaned. Most SLR makers have a page on their website you can go to and they give you very easy explicit directions for sensor cleaning, how to send it in, and they're usually very speedy about that.

It kind of depends on where you are, how far the camera has to go to a service center that can clean it. That is the safest, most thorough way to get your sensor cleaned and very often not only will they clean the sensor, but clean up some of the other bits of your camera. So if you got dust in the viewfinder, or sometimes even dirt in the LCD up here, they can clean that stuff off. If you're in hurry, if you need the sensor clean now because you've got a shoot or you just don't want to be without your camera, you can try to clean the sensor yourself. Now I do this a lot. I clean my own sensor. I've never had any problems. Either I've just been lucky, or I don't know.

But you can damage the sensor when you're cleaning it. So the first thing is if you are not real comfortable with hand-eye coordination and using tools, don't do it yourself. Second thing is get the right supplies for cleaning your sensor. You do not want to use anything other than gear designed for sensor cleaning when you're working on inside of your camera. Now here is how it works when it comes time to clean your sensor. The first thing is you take the lens off, because you got to get to the sensor. If we look in here, we can see this is the mirror chamber.

Here is the mirror. This is what bounces light up into the pentaprism that goes out to the viewfinder. I can tell the camera to flip that up, that mirror up, so that I can clean the sensor. I do that in the same menu where I pull up the sensor cleaning mechanism. If your camera doesn't have a control to do this, but it has a mirror lockup feature, which a lot of cameras have because that allows you to lock the mirror up to reduce vibration during long exposures, that will work just as well. You want to be sure your battery is charged or the camera is running off of the wall power, because we're going to be working inside here.

We're going to have tools in there. We don't want the power to die and the mirror to come down in the middle of that because it could damage the mirror. So I'm going to tell it to flip the mirror up now, and it's asking me if I'm really sure that I want to do this and I am really sure. So there it goes and now we're actually looking at the sensor. That's where all the magic happens inside the camera. It's right there. Now the good news is, as I said before, there is a clear glass plate in front of it. I am never actually going to be touching the sensor. So my next step is to figure out where the dust is.

Now if I had done a shot before like I said of the sky or a wall, I could look at that and try and zero in where it might be. Remember that it is going to be the mirror image. Or I can use a special tool. I have here a sensor loop. This is made by a company called VisibleDust. is where their stuff is located. They are a company that has been around for years, designing material specifically for cleaning fine optical equipment. Microscopes, telescopes, all that kind of stuff. They really know their stuff. They know how to build tools that are not going to damage your camera.

I really recommend VisibleDust. So they make this sensor loop tool thing, which is cool. I can put it on here, and it's lit on the inside. There are little light bulbs inside. So I can put it here. Now when I put my face over to look at my sensor, because there are those lights in there, I can still see. One thing that's tricky is when you look at the sensors, you can see here it's got this weird moire holographic quality to it. Your eye is going to look deep into that. It's going to focus past the surface of the sensor, because of that kind of optical illusion thing that is going on there.

So it can take a while to learn to focus your eye on the surface where the dust is. This particular sensor is actually clean. It doesn't have any dust in it, but I'm going to step through the cleaning stuff anyway, but what you're seeing here is a very clean sensor. We'll see if it stays that way, because then I'm just sitting here with the camera open like this. So, there are three types of dust. There are simple particles that sit on the surface of the sensor. There are bits of moisture that can get on the sensor. Those kind of leave stains. Or you can get a bit of moisture that then attracts a particle, and that's just really bad news.

So we've got multiple ways, kind of stages we go through for cleaning. The first thing is we go back to our blower brush. So again, I'm going to turn the camera upside down to get gravity working with me. I am taking this and I'm actually going inside the sensor chamber. Here I'm being very careful not to touch the sensor or the mirror, which is now up above, and I'm just blasting away. If I had seen a bit of dust in there, I would be trying to aim specifically at that dust, hoping to dislodge it. So I do that and now I would do another test.

I would either take the sensor loop and look at it again or I would go outside and shoot another picture. Come back in. If the dust is still there, I might try blowing it again. I might try zeroing in on the bad spot again. Do another test, come back in. If it's still there, it's time to go to the next tool and the kind of next more invasive step, which is a brush. Again, just as with cleaning your lenses, you don't want to use just any brush. You want to use a brush designed specifically for sensor cleaning. Think about how small this sensor is right there. You can see it.

It's a very small rectangle. In this case, it's got millions of pixels on it, which means an individual pixel is much smaller than the diameter of a single brush bristle. So, one tiny little brush size scratch in front of the sensor could really mess things up. So I want to be sure that I'm using a brush that's designed for sensor cleaning. This brush is, and it's very cool, the bristles I know are safe to be rubbing on that glass plate in front of my sensor and it's got batteries in it and a button on the side. When I push the button, it does this.

So the idea here is not that I put it on the sensor and spin it around. What's going on here with the spinning is one, I'm hopefully through centrifugal force flinging any dust that was there before off of the brush. But also I'm charging the brush with a static charge. So now when I go in and start brushing it on my sensor, in addition to the brush dislodging dust, hopefully the static charge is kind of sucking it up. I bring it out here. I clean off the dust. Maybe I do that a couple of more times. Then I do another test. Again, either with my loop or by going outside and taking a test picture.

If that still doesn't work, then I might kind of at Defcon 5. I'm not panicking yet, but I'm going to the really kind of distasteful next stage. This is a swab designed specifically for cleaning a sensor. It's kind of like a big Q-tip, but not abrasive at all. There is a special cleaning fluid I can put on here. I do that and then I rub it on the sensor and it just-- you are thinking this is my $1500 SLR, and I am smearing a liquid on the image sensors, is it really a good idea? Anyway, then you turn it over and you dry it off and you go to check again.

This is the part that's really distasteful that you hope that you don't have to do. Again, after each time I would take my loop or go to a test shot and make sure that I had actually tackled the dust problem. When I am all done cleaning, I turn the power on the camera off and the mirror comes back down. So now I want to get lens on as quickly as possible, because having just gotten rid of the dust, I don't want it coming back. Before I do that though, I might want to take a look at these, the contacts on my lens. There are these little contacts here and they match up with these contacts inside the camera body.

This is how the lens communicates with the camera, all the automatic features on the lens. Autofocus, image stabilization, the control of the aperture, that information is all send through these from the camera into the lens. If these get dirty, I might find my lens behaving a little bit strangely. It might be that autofocus doesn't work every time I try, or image stabilization doesn't turn on, or just in general the lens acts a little flaky. If you're having some lens problems, first thing to do is take the lens off, clean the contacts. That can just be a Q-Tip or even the end of your shirt and just wipe it off.

We don't use the end of our shirt of course for cleaning the lens. Wipe that off. Put it back on. See if it fixes it. If it doesn't, then your lens is probably broken, and it's time for it to go into the factory. Now these are sturdy machines. They can go through a lot and withstand a lot of wear and tear and a lot of foul weather and a lot of the abuse, and still take great images. But even just a little bit of dust can get in there and though it won't necessarily ruin an image, it will certainty make you have a lot more image editing to do.

With just a little bit prevention, making sure that the camera end of your lenses stays clean, making sure that you're careful when you change lenses, you can keep that from happening. So, basic maintenance is very simple. For more advanced maintenance, check the web site of your camera vendor. They'll have places where you can go, web site pages you can go to, to easily figure out how to send your camera. If you do decide to take sensor cleaning into your own hands, sells everything that you need.

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