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  1. #1
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    Stoopid Noob Question about aperatures

    I pulled the trigger on a Nikon D50 the other day, and while I'm waiting for it to come, I've been snooping around looking for lens recommendations. While reading reviews, I keep seeing reference to "open all the way" and "closed up a bit" on fixed aperature, prime lenses.

    So, dumb question: Is a fixed aperature lens like a Nikkor 50mm f1.8 not "open all the way" all the time? Or what exactly is being referred to?

    Thanks in advance. Learning very much from this website, and for every question I get answers for, I end up with 10 more questions.

    Rod

  2. #2
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    The Nikon 50mm F1.8 isn't actually a fixed aperture lens. In fact, there are very few true fixed aperture lenses besides cadiotropic-type (mirror) lenses.

    The Nikon 50MM has an aperture range of F1.8-F22. Normally you don't shoot a prime lens "wide open" (at maximum aperture) unless the conditions you're in absolutely demand it, since probably 90% of wide primes benefit optically from a slightly smaller aperture. This is especially prevalent of the lower cost 50MM primes from Nikon and Canon - very good optically for the price, but they really start to shine at F2.0-F2.4 or so.

  3. #3
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    The number listed is the max aperture not a fixed aperture. So f/1.8 is wide open, but that lens is still capable of stopping down to something like f/22. Lenses that have aperture listing like f/4-5.6 are variable max aperture. This is only for zoom lenses. At the short end of the focal range the max aperture is f/4 and at the long end of the focal range the max aperture is f/5.6
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  4. #4
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    A wide open aperture, ie the smallest number the lens can do = the smallest DOF, and the least amount of light required.

    Example, shooting portraits usually uses lower numbers, so that the background is out of focus and blurry. Shooting indoors also uses a lower number because of the small amount of light available.

    A large number, ie stopped down, will give you a large DOF, but will require alot of light.

    DOF = Depth of field.
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  5. #5
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    Quote Originally Posted by TheWengler View Post
    So f/1.8 is wide open, but that lens is still capable of stopping down to something like f/22. Lenses that have aperture listing like f/4-5.6 are variable max aperture. This is only for zoom lenses. At the short end of the focal range the max aperture is f/4 and at the long end of the focal range the max aperture is f/5.6
    Ah, thank you much. Now I can continue my hunt for a macro lens and a prime. The D50 I bought comes with a Nikkor 28-80mm f3.3-f5.6 G AF and a Nikkor 70-300mm f4-f5.6 G AF. I'm given to understand that the 28-80 is a pretty fair lens, however the 70-300 gets soft at 200. I'm concerned about being able to isolate the subject with the f3.3, so I'm snooping for a good prime as my first purchase.

    So is there a decent beginners guide around that would explain that sort of thing? Or a decent book to buy? I've been reading like mad for a couple months, however there doesn't appear to be a good "one stop shopping" website or book.
    Last edited by DiamondSCattleCo; 05-17-2009 at 05:17 AM.

  6. #6
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    Understanding Exposure, Bryan Peterson. read that with your camera handy. most importantly practice and experiment. good luck and enjoy your new camera.
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  7. #7
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    Here's another detail to throw out there for ya... depth of field is enhanced at longer focal lengths, e.g. your 70-300mm will isolate the subject rather well @ 300mm, especially at f/5.6, which will be the maximum (largest) aperture you'll be able to use with that lens at full zoom.
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  8. #8
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    Quote Originally Posted by DiamondSCattleCo View Post
    So is there a decent beginners guide around that would explain that sort of thing? Or a decent book to buy?
    Understanding Exposure has already been mentioned but I also highly recommend Thom Hogans D50 ebook. Not only will it explain all the things the user manual doesn't but it also gives you plenty of general photographic tips.

  9. #9
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    Quote Originally Posted by fionndruinne View Post
    Here's another detail to throw out there for ya... depth of field is enhanced at longer focal lengths, e.g. your 70-300mm will isolate the subject rather well @ 300mm, especially at f/5.6, which will be the maximum (largest) aperture you'll be able to use with that lens at full zoom.
    Depth of field doesn't actually change with focal length it just seems like it decreases with longer focal lengths because you're usually using the longer focal length to make the subject fill the frame. If instead you just moved closer, perspective would change but the in-focus depth would be identical.
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  10. #10
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    Depth of Field (DOF) is comprised of three (four) variables, not just one or two:
    1. Aperture
    2. Focal Length
    3. Distance to subject (center of focus - COF)
    4. Sensor size (minute issue, usually)


    When you move in on a subject, with the same aperture selected and same focal length of the lens, you are changing the center of focus (COF), when you refocus to get the subject. That changes the DOF ... you get something different.

    Please consult with the online DOF Calculator (<- Click on this link) to inspect how these variables and their impact on your photography.
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