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12-28-2010, 05:54 AM   #1
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Lens Newbie

I received a Pentax K-R for Christmas and for the past 3 days, I've been taking pictures none stop. I had a Fuji P&S that I used in manual mode frequently, which is why I decided to make the jump to a DSLR. Although I am not new to manual settings, I dont know the first thing about lenses. Can someone point me to a tutorial or even better a nice photography book on the subject? I am really interested in baby/children photography. I also have an upcoming trip to Italy and Paris and I don't want to miss a thing. Can someone also recommend a lens for both situations?

12-28-2010, 08:37 AM   #2
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Since you are taking photos your lovely new camera obviously came with a lens, almost certainly the 18-55mm kit lens which isn't a bad bit of glass. And, since by your own admission you now nothing about lenses I'd suggest now isn't the time to splash out. The kit lens is pretty versatile within the boundaries of it's focal length and should cover a lot of situation - heck 25 years ago a lot of us had a 35mm SLR camera with a 50mm lens and nothing else! OK, I don't want to revisit the 'I Know My Place' sketch so won't go any further down that avenue!

Suggest you try all the types of photography you can with the current kit, and get the feel of it zoomed in and zoomed out. It's zoom range will probably be less than you are used to.

As to books... It's probably easier and cheaper for you to do some Googling, but you need to put it in the context of shutter speed, aperture, ISO and focal length. There is also the issue of depth of field, and there I can make a recommendation:

Online Depth of Field Calculator
12-28-2010, 08:54 AM   #3
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For your trip, maybe this recent thread is useful.

Further take cats_five's advise. Use the kit-lens and find its limitations for your type/style of shooting. Once you have determined that, it's time to look at other lenses.
12-28-2010, 09:13 AM   #4
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You might want to check out the lens database here to get an idea of the range of stuff available: Pentax Reviews - Pentax Lens Reviews & Pentax Lens Database. As for a concrete suggestion: if you think the kit lens serves you well but could work better in lower light a Tamron 17-50mm 1:2.8 would seem worth checking out. That should suit most travel photos too.

12-28-2010, 09:29 AM   #5
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Understanding Exposure by Peterson is a very good book that covers the basics of photography in simple terms, and will help you understand what the lens specifications really mean, and how they impact your end result.
12-28-2010, 10:11 AM   #6
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QuoteOriginally posted by grainbelt Quote
Understanding Exposure by Peterson is a very good book that covers the basics of photography in simple terms, and will help you understand what the lens specifications really mean, and how they impact your end result.

I second the suggestion to read "Understanding Exposure". Bryan Peterson also has several other good books out. I like "Learning to See Creatively". While creativity is difficult, if not impossible, to teach, this book has some good excercises you can do to help you make more interesting images.
12-28-2010, 11:12 AM   #7
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The Understanding Exposure book also is not specific to DSLRs. You should find some advice that applies to your old camera too.

You can do some experimenting on your own. Zoom in, zoom out, that's easy enough. It should give you a feel for wide-angle (the 18mm end) and telephoto (the other end). The middle, about 30mm, is normal. You can now ignore all discussions of "crop factor". It doesn't matter.

Then there's aperture. It's a set of blades inside the lens that open or close to let in more or less light. At the same time, the aperture setting also affects the image quality greatly. Just changing the aperture setting can turn a boring snapshot into (almost) art.

Aperture numbers look complicated. All you really have to know is, they are a scale, and each time you go up a step on the scale, you cut the amount of light getting to the camera's sensor in half. The steps are f1, f1.4, f2, f2.8, f4, f5.6, f8, f11, f16, f22, and it continues on. The halving or doubling of light allows aperture to work well along with how shutter speed and ISO are measured. On each scale, going up or down one step halves or doubles the light. Also, the low numbers are large apertures ("wide open").

Math part to skip: They are a ratio of the area of the opening (aperture) to the lens's focal length. You'll see something like f3.5, which is supposed to be written f/3.5 but generally isn't. Since it's an area and a ratio, you get the square root of two in there. So f1.4 is really f/1.4142136 or so.

Here are two things affected by the aperture setting:

Depth of Field, or the part of an image that's in focus. At larger apertures, the depth of field shrinks. At smaller apertures, most or all of the image will be in focus. This is an extremely useful way to trick the viewer into seeing a 2D photo as a 3D image. A portrait of a person will look better if the person is in focus, but the background and foreground are softer and less detailed. Landscapes look bette with the opposite effect.

Image Quality. At extremes, lenses are not as good as they are in the middle somewhere. At the largest aperture settings possible, like f3.5 on the kit lens, the lens will have less saturated colors, lower contrast, darker corners (vignetting), and lower resolution. Some of that happens at the smallest aperture setting too. The differences are small enough to escape the casual viewer, but you'll see them clearly with side-by-side comparisons.

Lenses also are not perfect. Eliminating flaws is expensive and not always desirable. Flaws include distortion or flare.

Most lenses are built with a purpose, a job they do particularily well. But they don't stop working if you use them for something else entirely. The secondary use is often about creativity, breaking a rule but getting a good result.
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