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Thread: Understanding Lenses

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    Understanding Lenses

    Hi,
    I am currently new to the world of photography but am loving it. Something I am finding hard to understand is lenses. I am currently completing an assignment and have to be able to apply different size lenses to different scenarios. This is hard as I do not fully understand how to apply different size lenses to there best suited uses. Does anyone have any information or suggestions that could help??? Thanks

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    jiro's Avatar
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    Re: Understanding Lenses

    You could try clicking the "Photography Tutorials" button on top of this page if you want. Most of the Mods prepared these materials for us newbies. Welcome to CiC, by the way.

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    Re: Understanding Lenses

    Hi Steph and welcome to CiC.

    How long is a piece of string? This is a very broad question and the answer is you can use any lens for any purposes but different focal length lens will change the perspective of the image.

    The human eye has a field of view (i.e. your lateral vision) around 43 degrees and so the 50 mm lens has become the common lens for normal perspective (everything in relative proportion as to how you would see it in the real world).

    Anything longer than that i.e. 70mm + begins to compress perspective. If you had two people standing in front of you and one was 10 feet away and another behind the first at 30 feet away and the nearest person is just 5 feet from you then the gap between them would appear large. If you know moved back 200 feet and looked again the gap would look much smaller. Nothing has changed except the camera to subject distance but the perspective (the relative distance between subjects) looks closer.

    Anything less than 35mm is considered wide angle and has the opposite effect to longer lenses and pushes perspective out.

    Having said that most digital cameras have sensors smaller than a full frame 35 mm film SLR and the normal is around two thirds to size (1.5 times drop factor) so on these smaller lenses a 35 mm lens approximates the normal field of view (akin to a 50mm lens on a full frame camera).

    As I mentioned that all lenses can be used for any job and combined with focal length perspective and aperture control for depth of field changes you start to build up a large armoury of skills to present your image.

    On lens that is often used in portraiture is a 105mm that slightly compresses the perspective (i.e. facial features) to enhance portraits.

    I am sure others here will have other views but that is the great part about photography.

    I do hope you stay around and show us some of your work.
    Last edited by Dave Humphries; 31st January 2011 at 10:36 PM. Reason: correct m to mm in focal lengths

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    Re: Understanding Lenses

    Quote Originally Posted by Stephanie View Post
    I am currently new to the world of photography but am loving it. Something I am finding hard to understand is lenses. I am currently completing an assignment and have to be able to apply different size lenses [(my understanding) . . . "Different Focal Length Lenses" . . .] to different scenarios. This is hard as I do not fully understand how to apply different size lenses to [their] best suited uses.

    Practical exercise:

    You need a camera and three or four different Focal Length Lenses or a zoom lens and you determine three of four set FLs on it.

    For example:
    A Canon 500D and a 17 to 85 zoom lens.

    PART A of EXERCISE

    Choose 17mm; 35mm; 50mm; 85mm.
    Choose a Subject – e.g. the muscled torso of a good looking Bloke sitting on a stool
    (i.e. in all these shots you are getting the torso and head of the man – an HALF SHOT )
    Use the Camera in Vertical Orientation (Portrait)
    Frame each of the four shots in your camera so you only get that HALF SHOT of the Subject
    (You will move closer in for the 17mm shot and further back for the 85mm shot)


    PART B of the EXERCISE
    Repeat the four shots, still using the camera in Vertical Format:
    BUT first select 85mm. . .
    Stand at about the distance you were for the 85mm shot in Exercise A, and then step back one big step do you will now have his knees in the HALF SHOT
    Take the 85mm shot and then do not move your position.
    From the same position take the other three shots at 50mm / 35mm and 17mm.
    As you do this there will be more of the background and middle ground which comes into the frame.

    Part C & D
    Are a repeat of A&B but using the camera in Horizontal Orientation (Landscape)

    ***

    You will now have 16 photographs of the same man sitting on a stool – and you will clearly see the elements of: PERSPECTIVE and VIEW (“Field of View”), which I believe is what the assignment is all about.


    I expect that the teacher will want the class to see that:

    1. The Camera’s Position and Viewpoint is chosen to address the Perspective of the Subject in the Scene .

    2. Then the Focal Length of the Lens is chosen to address the Field of View. Or how much of the Subject is “In Shot”


    I also expect that the Teacher would be totally wrapped, if a Student mentioned that using a wide Focal Length Lens close to a Subject for a “Tight Half Shot” (like the 17mm lens in EXERCISE A) there is a likelihood of FORESHORTENING . . .
    Using this word should make the teacher very happy . . .
    As opposed to using words to describe the” funny big nose phenomenon” as “Perspective Distortion” – which it is not.


    Further the exercise could develop to show how (and why):

     A FULL LENGTH SHOT is “better” (meaning “generally more artistically pleasing / more true a rendition) taken with a “Standard Lens” (about 30mm on APS-C camera) and with the camera at Belly Button Height.

     An HALF SHOT is “better” taken with a slight telephoto lens (about 45/50mm on an APS-C camera) and with the camera an height between Breast Bone and Chin Height.

     A TIGHT HEAD SHOT is “better” taken with a mid telephoto lens (about 85mm on APS-C) and with the Camera elevated to Eye Level.

    ***

    Then, after learning all these Rules and Understanding why they are; hopefully the Teacher will encourage you to squeeze guts right out of them, when it is suitable so to do and also give you skills to know how to control the nasties of Foreshortening, whilst still allowing a nice image and a reasonably truthful rendition of the Portrait – and have fun doing it :

    Understanding Lenses
    Love Those Glasses
    5D 24/1.4, Available Light

    WW

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    Re: Understanding Lenses

    Quote Originally Posted by Peter Ryan View Post
    This is a very broad question and the answer is you can use any lens for any purposes but different focal length lens will change the perspective of the image.
    Gidday,

    I don’t want to argue, so please take this as a constructive comment – as it seems to me you know what you are meaning to say but are just using the wrong words to say it.

    The assignment described by the OP is right out many Text Books and is taught as a Practical Assignment in many Courses, especially TAFE type Courses in AUS, and also as part of the Art (Photography) Curriculum in High School, here.

    If this is indeed a Textual and Course Assignment – then one key point the Student is expected to derive from the exercise is that PERSPECTIVE is determined by the CAMERA DISTANCE and the CAMERA VIEWPOINT relative to the Subject and the Subject’s position in the scene.

    PERSPECTIVE is NOT a function of the Focal Length of the LENS.
    The Focal Length of the Lens controls only the Field of View.

    This is a Standard exercise used for TVOCP and Cinematography courses also: the budding camera operator is made to first choose the Camera Viewpoint to set the Perspective and then choose the lens to make “The Shot” (the Field of View).

    WW

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    Re: Understanding Lenses

    Thanks William. One reason I respond to these questions is to tighten up ability to describe photography matters and my use of language around technical issues. I do understand what you say and have noted it for the future. I do have faith in CiC that people like you and Colin will correct me if I get too far off the mark. Thanks.

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    Re: Understanding Lenses

    Quote Originally Posted by William W View Post
    PERSPECTIVE is NOT a function of the Focal Length of the LENS.
    The Focal Length of the Lens controls only the Field of View.
    This is perhaps the most common misperception about lenses. The second most common misperception may be that sensor size changes the focal length of a lens - but this is for another lesson.

    For the OP, perhaps the most valuable lesson is to use a zoom lens, and walk around shooting the same object from the same distance with different focal lengths.

    When this is mastered, shoot the same object from different distances and different focal length, but keeping the same "framing".

    I will not enter into the zoom versus fixed focal length debate, but a zoom lens can teach a new photographer so much in a short period of time.


    Glenn

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    Re: Understanding Lenses

    Quote Originally Posted by Peter Ryan View Post
    . . . tighten up ability to describe photography matters and my use of language around technical issues. I do understand what you say and have noted it for the future.
    Personally I was almost certain that YOU understood what was going on, because you wrote this:

    "If you had two people standing in front of you and one was 10 feet away and another behind the first at 30 feet away and the nearest person is just 5 feet from you then the gap between them would appear large. If you know moved back 200 feet and looked again the gap would look much smaller. Nothing has changed except the camera to subject distance but the perspective (the relative distance between subjects) looks closer."

    And that CHANGE OF CAMERA POSITION describes why the PERSPECTIVE CHANGES, and the ONLY reason for it.

    It was just your colloquial use of the word "Perspective" in other parts of your text was an issue which could have caused confusion - and that confusion is generally rampant because of colloquial word usage when technically correct words are actually required – as you pointed out.

    I think if the OP is doing a structured Photography Course correct and pedantic usage is required . . .

    Thanks for coming back with your reply so quickly and also so professionally.

    WW

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    Re: Understanding Lenses

    Just out of interest William - Where is Sraylya? Not Austalia by any chance.

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    Re: Understanding Lenses

    Quote Originally Posted by Glenn NK View Post
    "For the OP, perhaps the most valuable lesson is to use a zoom lens, and walk around shooting the same object from the same distance with different focal lengths. When this is mastered, shoot the same object from different distances and different focal length, but keeping the same "framing".

    Oh! MAMMY! This just gets better and better. . .


    Stephanie . . . if you are OK up to this point and understand what is going on with Glenn's suggestion and how it is similar to mine . . . and if indeed you do have a teacher whose socks you want to blow off . . .

    Then collect these "Same Framed" pictures, taken at different Focal Lengths (FL) and thus Different Shooting Distances (SD) . . .

    AND make sure you take each "Same Framed" picture AT THE SAME APERTURE . . .

    and then look at the Depth of Field (DoF) of each - or even look up the DoF using one of the many DoF calculators on line.

    Hey Bingo! You are now well on the way to describing and showing in a Practical exercise to your Teacher the Axiom of Depth of Field

    Geez Louise, you'll be the teacher's star Pupil in no time!

    WW

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    Re: Understanding Lenses

    Quote Originally Posted by Peter Ryan View Post
    Just out of interest William - Where is Sraylya? Not Australia by any chance.
    Fair dinkum Mate: you didn't think I was a Kiwi or a Pom did you?

    I am an old (cyber) mate of Colin Southern. We are separated by the Tasman Sea - but we think terribly the same on many matters - We are both poor (in money) but rich (in spirit) because we both have Daughters . . .

    This is a really, REALLY good site.
    The vibe from it is nice and is a credit to Sean and his team of ever so dedicated people - I have come to know a few from my visits here - all wonderful.

    The CiC tutorials are exemplary and I reference them often.

    It is always a pleasure to share, here.

    WW

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    Re: Understanding Lenses

    Quote Originally Posted by William W View Post
    Fair dinkum Mate: you didn't think I was a Kiwi or a Pom did you?
    You're not THAT classy Bill (I can say that 'cause I've got both NZ and British passports! )

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    Re: Understanding Lenses

    geez a bit slow today Colin - that took you nine minutes to respond . . .

    Best to you and yours,

    Bill

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    Re: Understanding Lenses

    Quote Originally Posted by William W View Post
    geez a bit slow today Colin - that took you nine minutes to respond . . .

    Best to you and yours,

    Bill
    I know ... I'm having to work for a living today ...

    ... how sad it that!

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    William W's Avatar
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    Re: Understanding Lenses

    sad, me too, just starting, it's like a million degrees here and I have two outdoor shoots this afternoon . . .

    CU CiC guys and girls round like a record - looking forward to feedback from Stephanie hey!

    Bill Out!

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    Re: Understanding Lenses

    Wish I was on your side of the world. Blizzard warnings, -12 C, 50+ cm of snow expected on top of ice. burrrr. However, maybe the sun will come out tomorrow and I can get a chance to get some shots of ice covered tress, etc.

  17. #17
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    Re: Understanding Lenses

    A quick exercise that is seldom done but, which is very easy to accomplish.

    Shoot any scene with your widest focal length available. It is best if the scene contains subjects at many distances from the camera. Now remain standing in the exact same place and shoot this same scene with the longest focal length you have available. Try to keep the camera in the same place (a tripod is great for this) and your telephoto image should be centered as per the wide angle shot.

    NOW, use a image editing program and crop the wide angle view to equal the telephoto view. Enlarge the cropped portion of the wide angle view to equal the size of the telephoto image.

    You will see that the perspective of the two shots is exactly the same. Of course, the quality of the enlarged portion of the wide angle view will not be good because of noise and probable lack of sharpness (which is why we use longer focal length lenses instead of just cropping the center of a wide angle shot) BUT... the perspective of the two shots will be exactly alike. In fact, except for quality, the two shots will be identical.

    Photographers often talk about focal length impacting perspective, it does not. Only lens to subject distance will impact perspective.

    OTOH: We often choose our focal lengths based on the camera to subject distance. As the old saying goes, "Which came first, the chicken or the egg?" Do we choose our focal length because of the camera to subject distance or do we choose our camera to subject distance because of our focal length? IMO, it is a bit of both. Sometimes we can more easily change our shooting distance but, most often it is easier (and sometimes the only way) to change our focal length.

    This shot using a long focal length appears to compress this Hong Kong street scene. I shot it from the top of a sightseeing bus. There is no way I could have changed my camera to subject distance. The only way I could frame the image the way I wanted was to change my focal length...

    Understanding Lenses

    Of course, there are some occasions when you desire to isolate specific subjects by using a long focal length and a relatively wide aperture (smaller f/number). This will keep your desired subjects in focus and blur the background. The result is that emphasis is placed on the subject and they are separated from the background...

    Understanding Lenses

    And, of course, there are some occasions when the photographer will use a long focal length in order to isolate subjects by eliminating the area around. In effect, by cropping in the camera. Depending on the aperture used (large apertures provide a more narrow depth of field) a secondary benefit to using the longer focal length in these occasions is the reduced depth of field; accentuating the subject even more.

    Understanding Lenses

    I personally enjoy using zoom lenses because of the ability these lenses to allow me to "crop in the camera". I shoot with two 1.6x cameras using a 17-55mm and a 70-200mm lens. These lenses allow me to choose focal lengths which result in images that require minimal post processing cropping. Cropping "in the camera" requiring very little cropping of the sensor's image allows me to use a 1.6x crop camera and get very nearly the same quality (and sometimes better quality) than a person using a full frame sensor and relying on significant post processing cropping to get the final image.

    At the risk of overdoing this post... I like to use a wide angle lens to accentuate interesting details near the camera rather than to just cover a wide area in a landscape shot. In this shot, the lava flow is accentuated and leading lines bring attention to the pinon tree.

    Understanding Lenses
    Last edited by rpcrowe; 1st February 2011 at 03:10 PM.

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    Re: Understanding Lenses

    Nicely summarised Richard with good examples.

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