Guide to Choosing a Lens: From Macro to Astrophotography [Archive]

Suhit Gupta

01-17-2007, 03:00 PM

<img src="http://www.digitalmediathoughts.com/images/canon_lenses.jpg" /> Product Category: SLR Camera lenses (specifically Canon lenses) Manufacturer: <a href="http://www.canonusa.com">Canon USA</a> Where to Buy: <a href="http://astore.amazon.com/digitalmediathoughts-20/103-9581613-5121420?%5Fencoding=UTF8&node=14">Amazon.com Affiliate Store</a> Price: Varies from lens to lens System Requirements: SLR Camera Specifications: Depends on the lens Should:<li>Know your application; <li>Know the various parameters in a lens; <li>Know your budget.Should not:<li>Rush into buying a lens; <li>Buy a lens that looks or sounds cool but you might not use it because it is too heavy or delicate.Summary: I wanted this article to serve as a guide to someone in the market for a lens for their SLR camera, or if they were just getting a camera body and didn't know which lens to get. I am writing this article on lenses instead of one on how to pick a camera because I believe, quite strongly, that it is the lens that makes or breaks the photo. Obviously, there the camera, the settings, the lighting, the sensor are all important, but I feel that the lens is the focal point. I got into the SLR photography market about two years ago and I feel like I have learned a lot. Honestly, I wish there had existed a short and succinct article like the one I am going to write here to give advice on what lens to get because honestly, it is the lens that is the most important piece of hardware equipment in your setup. BTW, this article is focused on Canon cameras an lenses, however I will be discussing extremely basic concepts so they apply to all products. Read on for the full article!<!> <PAGEBREAK> What I bought... Before I start this article, I wanted to tell you what lenses I own and the chronology of how I bought them. This might help point out some of my reasoning for buying the lenses that I have. This, by no stretch of the imagination, makes me an expert, but it will show you one set of lenses that have worked for a consumer/prosumer. I bought a Canon EOS 10D over two years ago and since I had spent all my money on the camera, so my budget for a lens was tiny. I still wanted to have options when taking photographs so I purchased a couple of lenses. Of course, given my small budget, I decided to go cheap (big mistake!). I got - <li><a href="http://consumer.usa.canon.com/ir/controller?act=ModelDetailAct&fcategoryid=149&modelid=7335">EF 28-80mm f/3.5-5.6 II</a>; <img src="http://www.digitalmediathoughts.com/images/lens1.jpg" /> I bought this as my first general purpose lense and boy, have I used it a lot. I realized early on that it was a cheap lens, it was loose and felt very mcuh like toy plastic when using it but it was my only option for some time and it served me very well as a workhorse. The AF system is relatively fast on this lens and the fact that it is a < $100 lens makes it a decent purchase if you really cannot afford a more expensive lens. <li><a href="http://consumer.usa.canon.com/ir/controller?act=ModelDetailAct&fcategoryid=152&modelid=7306">EF 50mm f/1.8 II</a>; <img src="http://www.digitalmediathoughts.com/images/lens2.jpg" /> This is a very good and inexpensive 50mm lens. It is small, and light (turns out that it is Canon's lightest EF lens of all at a mere 4.6 oz. (130g)) which makes this a perfect companion for when I want to travel and know I will be taking shots that don't really require much zooming.After a year, I bought two more lenses - <li><a href="http://consumer.usa.canon.com/ir/controller?act=ModelDetailAct&fcategoryid=150&modelid=7342">EF 75-300mm f/4-5.6 IS USM</a>; <img src="http://www.digitalmediathoughts.com/images/lens3.jpg" /> I was extremely happy when I bought this lens. This is a great lens at sports events as it is not so heavy that it makes taking photographs uncomfortable. It has Image Stabilization built in which makes it consume battery a little faster when I have the IS turned on. The Auto Focus on the lens is extremely fast but when the IS is turned on, it can be a little slow. Overall, at 300mm and with IS and AF turned on, it is an incredible lens and the price to performance ratio is very good. <li><a href="http://consumer.usa.canon.com/ir/controller?act=ModelDetailAct&fcategoryid=149&modelid=7336">EF 24-85mm f/3.5-4.5 USM</a>; <img src="http://www.digitalmediathoughts.com/images/lens4.jpg" /> This lens was my 28-80mm lens replacement and I am extremely happy with it. It has a very smooth feel and it take some very good photographs. My one minor complaint about it is that at 85mm, a setting that I do end up using often enough, some of my photos have a bit of motion blur and Image Stabilization would have been wonderful. However, this is my basic all purpose lens so I can see not having IS.Finally, due to my love of astronomy, I bought a telescope. However, my passion for photography was still strong and it greatly influenced the telescopes I purchased. <li><a href="http://www.meade.com/etx_premier/index.html">Meade ETX-90PE Maksutov-Cassegrain f/13.8 1250mm</a> <img src="http://www.digitalmediathoughts.com/images/etxPremier.jpg" /> <PAGEBREAK> Understanding The Lens There are several concepts that you need to understand before you can go and buy a lens. I encountered this problem especially when I was about to buy a telescope for some astrophotography.<li>ISO - A camera's ISO function sets the light sensitivity of the camera's image sensor (this is similar to the speed rating of FILM). ISO settings are often rated at 100, 200, or 400 but go as high as 800, 1600, and even 3200 on some advanced models. A lower ISO setting is used when capturing overly bright scenes, since it reduces the light sensitivy of the image sensor. But realize that the higher the ISO setting in a photograph, the granier the image. <li>White Balance - Our own eyes are an amazing judge of colors because we can (from what I understand) judge colors based on, among other things, comparison to the color white and we can judge white based on temperatures. Cameras need to do the same thing, however they need a reference point to what white is. So cameras have settings for allow the user the specify the dominant light in the space where the picture is being taken so that the colors in the image a appropriately callibrated. <li>Aperture - The lens you will be buying is simply a device that will take light from the world (at least the direction in which it is pointing) and pass it along to the camera. The aperture of the camera is the "entrance" that controls the amount of light that is let into the camera. <li>Auto-focus - This is a feature that a lot of people mistake to be a function of the camera but it is actually a function of the lens, even though it is the camera that controls/activates it. Lenses have a zoom function and a focus function. For a given focus, there is a correct focus value that will produce an optimal image. Most cameras will have Auto-Focus (AF) points that will be used to auto-focus an camera. When taking a picture, the camera will try and focus as many AF points as it can. In fact, if you keep trying to tell the camera to auto-focus, it wil usually try and cycle the focus setting to focus on a different combination of AF points so as to give you the option of picking the setting you would like to shoot with. <li>Image Stabilization - This is another setting in the lens. Most lenses are just a bunch of pieces of glass, where you can control the distance between the various pieces of glass (i.e. move them along the X axis of the lens) in order to zoom and focus the image. However, some lenses (usually much more expensive) have some gyroscopes built in that further control the pieces of glass in the lens along the Y and Z axes. Since most photos are taken by people holding cameras in their hands and since there is always some jitter when we hold or cameras, no matter how steady we think our hands are, the photographs we take can be blurry. The blur is even more pronounced when we take photos of action shots or are in moving vehicles. Image Stabilization gyroscopes are built to counter that motion and provide a stability to the components within the lens, regardless of the motion outside. <li>Focal length - The definition of focal length is the distance from the lens to focal point, i.e. the distance from the center of a lens or the surface of a mirror to the point at which light passing through the lens or which is reflected from the mirror is focused. A system with a shorter focal length has greater optical power than one with a longer focal length. <li>Focal Ratio - The focal ratio is the relationship between the aperture and focal length. The focal ratio is defined as the focal length divided by the aperture. For example, a refractor with a focal length of 800mm and an aperture of 100mm has a focal ratio of 800/100 = 8 or f/8. The focal ration gives the relative "speed" of the optical system. This is important for recording extended objects . A faster focal ratio will record an image faster (with a shorter exposure). <li>Other Attributes - Of course, there are a number of other features a swell. Optical quality is just as important as the above mentioned items. You can have a gigantic aperture and if the optical quality of the lens is not good, the light won't be very well focused, and the images produced won't be very good. Weight and cost of the lens are also important criteria. If either of them are too high, well, you know the rest. <PAGEBREAK> Understanding The Application Now that you have understand the various concepts in a lens, a quick word about the application. There are a very large number of scenarios for which you can buy lenses. Since lenses are expensive, it is always good to understand the most typical kind of scenario that you will be photographing in, so you can optimize on a few, but the right, set of features from above. <li>General - Having a general "do-it-all" lens is a fantastic idea. Usually a good general lens is a 28-80mm lens that basically covers the 35mm within its range and gives about a 3x zoom. I have found that adding image stabilization (unless you have money to throw around) is not really necessary for this kind of lens. Usually, your standard camera lens will be perfect for portrait shots. <li>Panoramic/Wide Angle - If you feel that you will be doing a lot of outdoors landscape photography, ISO is probably not as important as Aperture, Zoom and Focal Length. What you are looking for is more of a wide angle lens. Wide angle lenses give sweeping perspective and better depth of field and reproduction than a standard camera lens. They’re best for covering large subject areas. expanding the apparent distance between the foreground and background, they provide a unique perspective. Their exceptional compactness allows for greater mobility. They have a focal length on the lower side of the standard lens, i.e. around 24mm. <li>Macro - If you’re interested in extreme close-up photography, consider a macro camera lens that allows for extremely sharp focusing at short distances. Macro lenses can uncover detail that would be impossible to detect by the eye and give new perspective to extremely minute subjects such as insects or the petals of a small flower. These lenses usually have a very low focal ratio (around f/2.8 ) and range from 50mm to around 200mm. <li>Tilt Shift - You may think this is a weird category but I list think of this as the sky scraper category. With most lenses, when taking a photo of large vertical (or horizontal) objects with lots of straight lines, you may have noticed that in order to fit the entire object into the image, you take the photograph at a steep angle, which causes all the vertical lines to appear at slant as if they were going to a vanishing point. A tilt shift lens helps with this with shift movements that correct the trapezoidal effect seen in pictures taken of tall objects, so as not to distort the subject. <li>Ultra Wide Angle and Fisheye - The wide angle allows you to bring more area into focus and provides greater depth of field. The images from such lenses usually end up giving you an image where things up close and in the center of the image appear large large and items at the periphery of the image are smaller. The image also appears rounded and bent around the center. A typical focal length rangest between 16-30mm. <li>Telephoto and Astrophotography - As opposed to the wide-angle camera lens, the telephoto camera lens is a narrow angle lens. It appears to narrow the image, which is important when you are not able to get close to your subject. You will find that these lenses and telescopes have very high focal lengths. The longer focal lengths effectively compress the distance between the subject and camera to capture the details and the feeling of a far-off scene. If you are into astrophotography, usually you would want to concentrate on the focal length and aperture. But if you want to do the same in a strongly lit city like New York, you can buy something with a small aperture (since you want to capture less light in any case), and get something with a better focus system. A good telephoto lens is at least 300mm. You head into the super telephoto range at around 500mm to 600mm. Telescopes are usually in the thousands of millimeters in order to focus in on celestial bodies. As you can see, there are many different types of lenses and each category in itself has a very large number of options. So understanding your own scenarios and applications is very important. Cost vs. Quality My very first DSLR body itself had set me back so much in my budget that I ended up buying a couple of very cheap lenses. And while cheap lenses will certainly get the job done, you have to realize that there is a difference between the cheap and expensive lenses. There is not only a difference between the durability of the lens and the body that the lenses are housed in, but also the quality of the glass; and I have also found a difference with the speed at which the cheaper lenses get dirty vs. the more expensive ones. The cheaper ones also feel cheap when taking photos -- what I mean is that the wheels on which the inner pieces rotate when zooming and focussing feel light and loose vs. the more expensive lenses feel tighter, smoother and give better control, especially when the changes I want to make are very slight. If you have a choice between buying two cheap lenses vs. one expensive lens, I would say that you should spend the extra money to buy the one better lens and then save up for the extra few months to get the next one. The reason for this is that you will definitely end up wanting a better lens at some point in the future, and you would rather save your money and use it wisely in the first place than realize that you wanted some of your money. The resale value on lenses (especially the cheap ones) is extremely low so hoping to upgrade after having sold your first set usually doesn't work out as one hopes. Conclusions Lenses are expensive, but I think it is worth waiting for a bit and getting a better lens if you can. The lenses I would still buy are a good macro lens and a wide angle lens. And of course, it would be great to play with a tilt-shift lens at some point. I hope the above article gives some of you some assistance when you are out buying your new lens. Suhit Gupta is a Contributing Editor for Digital Media Thoughts. He is a fan of all things digital media and photography related and when he is not reading or watching movies, he is out with his telescope pursuing his passion for astronomy. He lives in Redmond, WA, USA though yearns to be back in New York City.