Help me understand this....

Discussion in 'Photography Beginners' Forum' started by R6_Dude, Feb 5, 2010.

  1. R6_Dude

    R6_Dude TPF Noob!

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    So I've been reading a lot of post (as well as member signatures) and have a question in regards to the reason for purchase of a certain lens.

    Lets keep all F stops constant on these lens I am about to mention.

    For example.....why would one feel it necessary for a 17-40mm when their is already a 18-55 kit lens?

    Or....why would one feel it is necessary for a 28-135 if they already have a 55-250 lens and a 18-55?

    One more....why would a 10-22 be considered rather a 11-16 if there is the option for the 18-55.

    I think you see what I'm getting at. If the focal length over lap each other why get an additional lens?

    Is it simply a convenience factor (although you'll have a ton of lens to carry around)? Are the glass that much better? Will the glass give it a big notable difference.

    Again....VERY noobish question, I was waiting to see if I can find it through search or another noob to ask :lol: but a curious mind asks questions haha.
     
  2. dxqcanada

    dxqcanada Been spending a lot of time on here!

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    That 1mm difference on an APS-C format camera does make a difference.
    Also, you will find that the image/manufacturing quality is better on the 17-xx lenses.

    Image/manufacturing qualty. The focal length is not the factor ... it is the quality of the lens.

    10 or 11mm provides a very wide angle.

    Most photographers sell their 18-55mm and get the 17-40mm lens as a upgrade.

    I have a 28-135mm because it is a high quality lens.
    I would sell my 18-55mm lens, but it is not worth much.
     
  3. Big Mike

    Big Mike I am Big, I am Mike Staff Member Supporting Member

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    You can't really take that out of the equation. Some lenses are better & more desirable because they have a larger maximum aperture. For example, I don't like the 18-55mm 'kit' lenses because their maximum aperture is too small (F3.5-5.6).

    Quality, performance, comfort, prestige, ego etc. The same reasons why someone would buy a BMW over a Hyundai.
    That's a different issue and I think it just comes down to people's budgets when they buy their lenses and convenience. You might only be able to afford a 28-135mm lens to start with...but later, you might buy a 70-200mm lens. There is significant overlap here, but the 70-200mm is a superior lens. But you may not always want to carry a 70-200mm lens around with you, so the 28-135mm might be more appropriate for you needs that day.

    Given an unlimited budget and ideal circumstances...I don't think there would be much overlap.
    For example, my three main lenses for a wedding shoot are a 10-22mm, a 17-50mm and a 70-200mm.
     
  4. chip

    chip TPF Noob!

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    One thing you need to know is some are EF-S lenses designed for 1.6x crop frame cameras and others are EF lenses designed for FF cameras. You have to multiply the focal length by 1.6 when using crop frame bodies.
     
  5. R6_Dude

    R6_Dude TPF Noob!

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    ahhh ic
     
  6. Derrel

    Derrel Mr. Rain Cloud

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    The 17-40 f/4 L is a professional-grade lens from Canon. It focuses well, and has a constant f/stop over its entire range. It offers very good optical performance, and with a front filter on it, it offers L-level weather sealing against moisture and dust ingress. For anybody doing event photography with a non-TTL flash unit, and there are quite a number of those types of old-school professional photographers, the constant aperture is nice, since the lens never changes its effective aperture when it is zoomed out to the longer end, which is different from the 18-55.

    The 18-55, and most especially the first generation, NON-IS and NON-USM focusing model sold in North America is a very poor lens, optically. It has high levels of chromatic aberration, and its images look sub-par compared with Canon's better lenses. That lens was replaced after millions of the original, junky model were sold, by a newer 18-55 with better corner performance and with lower levels of chromatic aberration.

    MOST, but not all, of Canon's 18-55 models are non-USM, meaning a small A/M switch must be moved to manually focus the lens when the lens cannot find the right focus. On every single 17-40 f/4-L, the photographer can grab the focusing ring and override the camera at ANY time, which is a pro-lens feature. In JAPAN, the very first 18-55 lens was a USM model, but North America got a really cheezy, dumbed-down NON-USM version of the 18-55. Japanese camera buyers are as a whole,much more savvy about lenses than North American buyers. I guess in total, there must be four different 18-55 variants that Canon has released over the years for the 18-55.

    Simply put, Canon's 18-55 non-IS, non USM and its IS models are really about as cheap a lens as they can make, with poorer optics than their better lenses, and they are not weather sealed, have an aperture that varies from f/3.5 at 18mm to a very slow f/5.6 at 55mm,and are optically clearly below the pro lenses. They also do NOT cover the image size of larger sensors, so if one hopes to shoot a larger-sensor Canon, the 18-55 is a no-go: it will not even mount on the body, since it is an EF-S mount lens.
     
  7. R6_Dude

    R6_Dude TPF Noob!

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    Thanks Derrel for the reply. Can you give an example on what you mean by a constant f/stop? From a noobs view, as long as I don't change the F/stop manually it'll remain the same?

    Also you mention USM. If a lens was a non-USM (eg tokina 11-16) would you stray away from it?
     
  8. R6_Dude

    R6_Dude TPF Noob!

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    True, I guess if you had both a FF and a crop, you'll need lens that are similar.
     
  9. Big Mike

    Big Mike I am Big, I am Mike Staff Member Supporting Member

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    No you don't.

    The focal length of a lens does not change based on what camera it's on. Or whether is has an 'S' on it's name.

    The 'crop factor' is simply a comparison between the Field of View that you get compared to what you would get when you use a 35mm film camera.

    So if someone doesn't have a 35mm film camera, they don't need to multiple anything or even think about the crop factor.

    If there is a chance that someone might someday upgrade to a 'full frame' digital (or use a 35mm film SLR) then they should be aware that some lenses are only made to work with cameras that have and APS-C sized sensor.
     
  10. Big Mike

    Big Mike I am Big, I am Mike Staff Member Supporting Member

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    Constant maximum aperture.
    For example, the 17-40mm has a maximum aperture of F4 throughout the whole zoom range. Just like a 70-200mm F2.8 has a max aperture of F2.8 at 70mm or 200mm.

    Cheaper lenses don't have a constant max aperture. For example, an 18-55mm kit lens is listed as F3.5-5.6, which means that the max aperture is F3.5 at 18mm but it's only F5.6 when zoomed out to 55mm.
     
  11. R6_Dude

    R6_Dude TPF Noob!

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    I don't have my camera with me right now. But if I understand you correctly, my camera with automaticaly adjust the F if I zoom from 18-55? Even while I am in Av mode?
     
  12. Derrel

    Derrel Mr. Rain Cloud

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    Okay, using an 18-55 lens on a Canon 50D and using a manual-mode flash (Norman 200 or 400, Lumedyne, for example) or a speedlight flash set to non-TTL Automatic mode, which a lot of professionals use--if the lens is set to f/4 at 18mm, as the focal length goes longer, the lens begins to as we say,"Lose aperture," meaning the lens lets in less and less light. By 55mm, not a very long zoom, the lens loses its light admitting ability and it admits only f/5.6. if the flash is set to be correct with an f/4 aperture, then the flash needs to be re-adjusted every time the lens is zoomed out to where it drops below f/4. Basically, a huge PITA,and mistakes and variances in exposure all over the zoom range.

    In other exposure scenarios, like say using M mode, the lens admits varying amounts of light throughout the zoom range, going from f/3.5 and steadily downward--that changes the shutter speed needed. It can spell the difference between getting the correct exposure at 18mm, and the WRONG exposure at 55mm, unless the shooter takes the time to verify settings and re-adjust for the lost light. For people whose income depends on not making mistakes,and having the same,exact equipment capabilities at BOTH ends of the zoom range, and everywhere in between, those people gravitate to what are called "fixed maximum aperture zoom lenses"--which are bigger, heavier, and more capable and costly. Variable maximum aperture lenses can often be made MUCH, much smaller and lighter, and also sold at a lower price point. A case in point: the 70-300 f/4~5.6 lens is much smaller and lighter and less costly than say, Sigma's 100-300mm f/4 EX-HSM lens, which is f/4 all the way from 100 to 300mm.

    A non-USM lens in the 11-16mm category is not so critical as an everyday "event" or general photography lens. The Tokina is built for ultra-wide angle uses, and focusing is not nearly as critical as at, say 55mm. There have been a number of non-USM lenses that are good lenses. Ultra-wide zooms can be focused by scale or by guess and by golly and still have a lot of DOF to cover mistakes. If you want the Tokina, by all means, don't let its AF protocol scare you off.
     

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