Quality, Affordable Lens with low f-stop

Discussion in 'Canon Lenses' started by 311Photo, Nov 21, 2016.

  1. 311Photo

    311Photo TPF Noob!

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    Hi, friends!
    I've recently been shooting more portraits, trying to get experience in that arena. My problem is that the two lenses I own (I think they are the EF-S 18-55mm f/3.5-5.6 IS Lens and Canon EF-S 55-250mm f/4.0-5.6 IS Telephoto Zoom Lens) that came in the package deal when I bought my camera (Canon EOS Rebel T2i) several years ago do not go below about f/5.0.
    Do I have the wrong settings that are preventing it from going any lower? I see that the aforementioned description states that they do, but I have not been able to achieve that.
    I've been reading that the best f-stop for portraits is 2.5ish. So what lens do I need to invest in for portrait photography that will enable me to accomplish the desired settings?
    Any help you guys could be provided would be much appreciated, as always!



     
  2. tirediron

    tirediron Watch the Birdy! Staff Member Supporting Member

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    Your lenses are variable aperture models, which means that the longer the focal length, the smaller the aperture; at 18mm it's f3.5, but at 55 it's f5.6. If you can't get f3.5, than "zoom in" a bit. As for f2.5 being a portrait aperture? Umm... you probably need to read some other books. While there are certain applications for large apertures/shallow DoF in portrait work, they're the exception and not the norm. I shoot portraits almost exclusively and f8 is my 'go to' aperture. Nothing worse than shooting a great set at f1.8 only to find out that half the model's face is soft due to lack of DoF.
     
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  3. astroNikon

    astroNikon 'ya all Bananas I tell 'ya Supporting Member

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    Normally with Pro zooms such as a 70-200/2.8 or 24-70/2.8 you will have improved image quality due to the glass elements being much higher quality than in your kit zooms. You'll also have the ability of using f/2.8 throughout the entire range of zoom (you'll pay for it too).

    with f/2.5 you're probably thinking a Prime lens, such as a 50mm f/1.8 or 85mm f/1.8.

    Of which using f/2.8 to f/1.8 you can really mess up single person portraits if you don't know what you are doing because of the lack of Depth of Field. Thus recommendations of f/5.6 up to f/8.

    Using a Prime will give you better image quality too as they are generally designed for one focal length. Though of course lack any zoom, foot movement notwithstanding.

    As to any "quality, affordable" lens? I think on Canon you'll have to look at the 50mm/1.8 series of prime lenses. Quality, fast (low aperture numbers such as f/1.8 and f/2.8) and cheap normally don't go together. Except Canon/Nikon makes some affordable 50mm lenses.
     
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  4. KmH

    KmH In memoriam Supporting Member

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    Three things to consider:
    1. F/stops are fractions. The f is the focal length of the lens.
    F/2 is a larger/higher number than f/8 is.
    A lens set to f/2 has a much larger lens opening than a lens set to f/8.

    A 50 mm lens set to f/2 has a 25 mm wide aperture • 50 mm / 2 = 25 mm.
    At f/8 the aperture is only 6.26 mm wide • 50 mm / 8 = 6.25 mm.

    2. Most 'fast' lenses that can be opened wide, say f/1 to f/2.8, benefit a great deal focus sharpness wise by being 'stopped down' a couple of stops.
    The issue is light passing through the more curved outer area of the front lens element often does not get focused in exactly the same place as light through the center of the lens., making the focus 'soft'.

    3. A blurred background is created and controlled by more than just the lens aperture.
    The lens focal length, the point of focus distance, the image sensor size, and how far the background is behind the subject also matter.
    Many new to doing portrait photography have difficulty controlling the very shallow DoF (Depth-of-Field)
    Understanding Depth of Field in Photography

    Like tirediron I made most of my portrait shots at f/8, not f/2.
    My favorite lens for portraits was a 200 mm prime lens.
     
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  5. beagle100

    beagle100 Been spending a lot of time on here!

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    like others have mentioned consider the 50mm 1.8 STM (refurbished $89) or the 85mm 1.8 or 100mm 2.8 for portraits
     
  6. Designer

    Designer Been spending a lot of time on here!

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    Without reading the same article, I have no idea how the writer arrived at this conclusion. IMO, he is either talking about a certain set of circumstances, or he is just plain wrong. While a given lens might have good performance at that aperture, it certainly would not hold true for all lenses.

    Assuming that he is using some lens at around 100mm focal length, mounted on a "crop sensor" camera, at a distance of 8 feet. Using DOF Master, we see that the DOF is 0.18 ft., or 2.16 inches, total. Shooting a person's portrait with the eyes in focus, it becomes unlikely that the tip of the nose and the tops of the ears would be in focus. Not to mention hair, which is most certainly OOF.

    Screen Shot 2016-11-22 at 2.29.22 PM.png

    If such OOF portraits are something you aspire to, then so be it, but I don't know who else would want that.
     
  7. jtran76

    jtran76 TPF Noob!

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    If you can afford it I highly recommend the Sigma F1.8 18-35 wide angle lens. The aperture on the lens is constant meaning no matter what focal length you are shooting at the aperture will remain the same to what ever what you have it set it at.
     
  8. Didereaux

    Didereaux Been spending a lot of time on here!

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    Yeppers, an up close and personal lens. At shooting distance for portraits you get nice big noses, and at the same time you hope they do not fog the lens with their breath! ;)

    If you can only afford (or want) one good all around lens i would highly recommend the Canon 24-105mm L series. It has been around for ages for a reason it is GOOD! and it is versatile. Landscape, macro, prortraits it does them all very well.
     
  9. astroNikon

    astroNikon 'ya all Bananas I tell 'ya Supporting Member

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    Yes generally wider lenses introduce perspective distortion.
    Which if you don't know about it, it bring about big noses, etc. ==> go down to # 3 Perspective Distortion ==> What is Distortion?

    this shows a comparison of various focal lengths on a face ==> http://gizmodo.com/5857279/this-is-how-lenses-beautify-or-uglify-your-pretty-face

    this is why most prefer 80 up to 135mm lenses for portraiture.
     
  10. Gary A.

    Gary A. Been spending a lot of time on here!

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    The 85mm and 100mm are considered to be in the focal length sweet spot for portraits. Both will serve you extremely well in that regard ... about a step up or back difference between those lenses. A problem for the neophyte with the 70-200 F/2.8 is that it is a huge white lens that tends to intimidate the subjects. The Canon 135mm F/2 is on the edge of the focal length sweet spot, but it is one of those magical lenses that the planets were lined up when it was designed ... extremely sharp with a crazy soft bokeh.

    Portraits can be taken with any focal length. But the further away from from the focal length sweet spot the greater photographic skill is required for a pleasing portrait.
     

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