A&P Please OT SLR crew, school me in lens information

Discussion in 'Lifestyle' started by BlackWRX02, Jan 31, 2005.

  1. BlackWRX02

    BlackWRX02 OTs Cingular Guru

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    I need to know about lens

    I have a very basic understanding of aperture and DOF, but I see a lot of lens listed as 50-80mm, f.whatever or something to that nature
    can someone enlighten me as to what exactly each part of that means?

    Looking into getting a better camera and want to be exactly sure of the lens that comes with it, and what to buy in the future.

    Most of my shooting right now will be either dusk or very fast action (going to the U.S. Gran Prix again this year), but I'd like to have the ability to shoot stuff around town as well, as I'm going to get into photography more I hope. Also do a lot of car/automotive still shots

    What types of lens are idea for different settings, etc?
     
  2. hash browns

    hash browns lolcathlon champion OT Supporter

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    This is probably easiest to figure out by example.

    Example:
    17-35mm f/2.8-4

    This lens is a zoom, with its widest focal length being 17mm, and its longest focal length being 35mm.

    The widest aperture it can have is variable and changes with focal length. At the widest focal length, 17mm, the largest aperture it can be opened to is f/2.8. (Remember that apertures size is just a ratio based on focal length, and f/2.8 is a larger aperture than f/4).

    Somewhere in its focal length, when you 'zoom-in', the widest aperture it can have shrinks to f/4. More expensive lenses have a constant aperture all the way.


    Example:
    50mm f/1.8

    This lens has a fixed focal length, meaning it's always a 50mm. People call these fixed-focal length lenses 'primes'. Its widest aperture is f/1.8. Primes tend to be easier to build than zooms, and often a prime with a wide aperture is a good way to go.



    More stuff about lenses will depend upon manufacturer, yadda :mb: :mb:
     
  3. BlackWRX02

    BlackWRX02 OTs Cingular Guru

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    cool, thanks for the info.
    In the example you gave, it says
    17-35mm f/2.8-4

    whats the -4 after f/2.8 ? (probably a stupid question :uh: )
     
  4. hash browns

    hash browns lolcathlon champion OT Supporter

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    For that example, the f/xxx thing refers to the widest aperture.

    f/2.8-4 means the lens has a variable 'widest aperture' which changes with its focal length.

    At it widest, 17mm, you can have f/2.8. And somewhere in the range, and definitely by 35mm, the maximum aperture size becomes f/4.

    A constant aperture zoom covering the same focal length range would be a 17-35mm f/2.8. It probably costs twice as much :mamoru:
     
  5. BlackWRX02

    BlackWRX02 OTs Cingular Guru

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    Ok wasn't sure if that was 2.8 through 4 or what. Thanks for clearing that up :bigthumb:
     
  6. Jcolman

    Jcolman OT Supporter

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    In a practical sense, it means that your going to lose a full stop of light when you zoom from 17-35. This isn't a big deal when you shoot in daylight but it could hamper you in low light situations. That's why a constant aperature lens is more desirable.

    If you were to compare two lenses of the same focal length, but one had a widest aperature of say f/2.8 and the other had a widest aperature of f/4, the one with the f/2.8 aperature would most likely be the more expensive lens. Also, the longer the lens (focal length) the smaller the aperature is likely to be.
     
  7. hash browns

    hash browns lolcathlon champion OT Supporter

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    Yup.

    Lenses in the so-called "normal range" for 35mm cameras fit somewhere between 35mm to 70mm or so. Lenses at the 35mm end are mild wide-angles, and lenses near 70mm are mild telephotos.

    Wide-angle or telephoto lenses with large apertures, ie: f/2.8 tend to be quite large, and quite expensive as they are optically, more complicated in design.
     
  8. Scream_Phoenix

    Scream_Phoenix Handsome Boy Model

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    how much more light does one stop let in? like how much brighter is a picture taken at 2 than one at 3, ceteris paribus.

    is there a rule of thumb on how many stops will make up the difference between ISO 100 and ISO 200?
     
  9. hash browns

    hash browns lolcathlon champion OT Supporter

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    The stops are logarithmic.

    From one full-stop to another, ie: from f/4 to f/2.8, there is twice as much light.

    ISO/ASA is the same.

    Doubling the ISO number is a stop difference, and twice as much light, or twice as much sensitivity.

    ISO50, ISO100, ISO200, ISO400, ISO800, ISO1600

    There are full stop differences between each of these sensitivities.

    Shutter speed controls the exposure duration and works the same way.

    Halving a shutter speed (aka: exposing for twice as long), doubles the amount of light -- It is a one stop difference.

    1/250sec, 1/500sec, 1/1000sec

    There are full stop differences between each of these shutter speeds.
     
  10. Scream_Phoenix

    Scream_Phoenix Handsome Boy Model

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    so one full stop for aperture is 1.2, and every time you move down one stop twice as much light enters?

    we should turn this thread in to a FAQ/noobie thread and sticky it :o
     
  11. hash browns

    hash browns lolcathlon champion OT Supporter

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    Mmm, the difference between full stops is going to be twice as much light, or half as much light -- It just depends on which way you're looking.

    Generally, these are the stops considered:

    f/1.4, f/2.0, f/2.8, f/4, f/5.6, f/8, f/11, f/16, f/22, etc.

    Going between any two adjacent stops is a full stop's difference in light.

    So, other things equal, going an aperture setting of f/4 to f/2.8 is doubling the amount of light, or increasing the light contribution to the exposure by one stop -- Remember, f/2.8 is bigger than f/4.

    The great thing about manual controls is, you can adjust each of the parameters that contribute to exposure independantly.

    Shutter Speed + Aperture Size + ISO / Film Sensitivity = Exposure

    So if I went from f/4 to f/2.8 -and- changed my shutter speed from 1/250sec to 1/500sec, keeping ISO equal, the net exposure would have remained the same.
     
  12. Scream_Phoenix

    Scream_Phoenix Handsome Boy Model

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    ok, i see. so when a lens has a minimum of 2.8. thats as wide as it get... can you decrease all the way up through all the other stops, f/5.6, f/8, f/11, f/16, f/22 etc until the aperture ring is closed? or do some lenses only have certain stops available
     
  13. hash browns

    hash browns lolcathlon champion OT Supporter

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    Technically, if a lens is specified as being.. say: 200mm f/2.8, it means it has a maximum aperture size of f/2.8.

    Yup, you can stop down to those smaller apertures, up to a point.

    For example, the lens I'm holding right now is a 50mm f/1.8, and it is capable of stopping down to a minimum size of f/22. Generall, it's maximum aperture size that most people are concerned with.

    And yes, there are partial stops, half-stops etc, in between the stops on that scale.
     
  14. Scream_Phoenix

    Scream_Phoenix Handsome Boy Model

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    thanks for the info :cool:
     
  15. BlackWRX02

    BlackWRX02 OTs Cingular Guru

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    wow keep it coming!
     
  16. MelloBoy

    MelloBoy New Member

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    if you're dealing with a digital camera, any aperture smaller than f/16 or f/22 (i forget which) is useless due to sensor limitations i believe.

    most point and shoot digital cameras have an aperture range of f/2.8-f/8 or so, and i have a feeling as you zoom in on something, the max aperture decreases...not constant like a higher quality lens. unfortunately this can't be changed unless the mfg decides to do something about it. The reason they haven't is, invariably, if you switch to a constant aperture throughout the entire zoom range, you end up with a much larger and much heavier lens, and the typical consumer would not want that.

    that said, you may want to go with a used or new low end digital SLR with a lens that has a large aperture and decent zoom range. i'll add more after meeting
     
  17. mojito

    mojito New Member

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    Look at the Panasonic FZ series, they have a 12x optical zoom with IS and a aperature of 2.8, but look at the size and cost associated with the lens. Its a gretr lens, but its huge and you're paying for it.
     
  18. kuno

    kuno .... OT Supporter

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    Would increasing the ISO setting of a digital camera attribute to the "graininess" of the image if taken in low light situations-sounds weird? If so what's the best thing to do? Increase the apature setting to it's max and play with the ISO setting?
     
  19. MelloBoy

    MelloBoy New Member

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    1. for static shots use the lowest ISO settings possible (mine goes to ISO100 and goes all the way up to ISO3200) which will reduce the graininess.
    2. open up aperture a bit
    3. decrease shutter speed

    2 and 3 will increase the amount of light that the sensor will pickup.

    if you open the aperture up, you will end up with a shallow depth of field. set your ISO to the lowest setting and play around with shutter speed/aperture

    good luck
     
  20. FryingPan

    FryingPan Certified Thread Killer

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    This is true. The lens absolutely dominates the camera, but the tradeoff is well worth it.

    [​IMG]

    My FZ20 with the filter adapter lens hood and polarizer.

    I really enjoy this camera, but I'm already wanting more :hs:
     
  21. FryingPan

    FryingPan Certified Thread Killer

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    Absolutely. Mopst digital cameras (with exception to most DSLRs and the like) produce lots of noise at ISO200 and up mainly due to the limitations of their CCD's. Low light situations are best tackled with a longer exposure and large aperature and a ISO less than 200 with most digital cameras.
     
  22. BlackWRX02

    BlackWRX02 OTs Cingular Guru

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    so I'm wondering....


    Looking at some kits and one comes with the following:
    - 18-55mm f/3.5-5.6 Zoom Lens
    - 70-300mm f/4-5.6 AF Lens
    - 28-80mm f3.5-5.6 HF Lens

    Little confused about the last one. Why include the 28-80mm in this? The first two would cover whatever the third is able to do, correct? Also whats the HF stand for :confused:
     
  23. tenplanescrashing

    tenplanescrashing Active Member

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    if i was looking for two lenses, i'd choose the first two. i'd rather have a wider angle lens then a good zoom than one that takes up the mid range. Though I use a 28-300 and think it works fine for my job.
     
  24. WiLL

    WiLL Active Member

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    Sigma uses HF for Helical Focus. That means when you are focusing, the front of the lens does not turn. And I believe that on long range lenses like 70-300, the quality wont be as good as having 2 lenses that cover that range.

    But someone correct me if I am wrong, I am still learning and saving for a dslr myself.
     

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