GUIDE TO: How Lenses Work

Discussion in 'Photographic Discussions' started by Beast95, Mar 3, 2012.

  1. Beast95

    Beast95 TPF Noob!

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    First Note: I didn't know what forum to put such a guide in, but i figured that this would help a lot of people understand their cameras a little bit better.

    Science Experiment:
    To try to explain lenses.

    1. Take your lens. I suggest using something around 20-50mm, but any should work. Be very careful, but take all of the lens caps off of it.
    ---DO NOT: Do anything stupid. I am not responsible if you accidentally drop your lens....

    2. Turn on a very bright ceiling light. Set a sheet of white paper on the surface directly below it (id say at least a few feet away)

    3. Put the lens in between the ceiling light and the paper. Move it up and down until an image of the light forms on the sheet of white paper.

    4. This is what the camera sensor see's. It picks up the light that would have landed on the white paper. The lens bends light so that the light reflecting off of an object is all refracted equally and parallel. This is the reason that lenses work. Without a lens, the light reflecting off of an object is scattered everywhere and therefor cannot form a very nice image.

    5. This is proved by removing the lens from between the light and the paper. There is no image that is formed.


    Explanation:

    Lenses align the light. I will get into some complicated physics here, you may skip this if you aren't interested in the science explanation. It isn't important.
    ---The light hits the glass, which light travels through slower than in air. Different rays of light hit the lens in different places. Simplified, this makes the light that is closest to the center refract slightly sooner than the rest. It is for this reason that the light bends. Each of the lenses in what we consider a "camera lens" does this. The light is all angled towards a center point called the "focal point". The sensor is lined exactly where this focal point is. This is where all of the light is in perfect focus because all of the diagonally aligned light is fixed on that exact point.
    ---If this doesn't make sense, don't worry.


    It is for this reason that the light is all aligned in parallel that you can block parts of it. With the lens between the paper and the light, if you put your finger near the side of the lens toward the light, you will see the image of your finger on the paper. It blocks the light that is going in that direction.
    ---You might be able to see color too...


    Focusing:

    The camera lens moves some of the lenses that make it up farther apart or closer together so that the focal point changes and so that the light can be in focus from different places at different times.

    Final Words:
    If you understand this mostly to this point, I hope that I helped explain lenses and how they work.

    THANK YOU for reading! If you guys want any more information added in here, please just let me know! I will read all of your responses and try to help answer all questions. Best of luck to you all!


    Aperture is harder to explain; I'll add that in here at a latter time perhaps :)


     
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  2. KmH

    KmH In memoriam Supporting Member

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    Then how is it that the top, bottom, left, and right side of the image frame can all be in focus at the same time?
     
  3. Beast95

    Beast95 TPF Noob!

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    This "center point" is actually a smaller sized, proportional image; relative to what kind of lens that you use. This "point" will be different sizes depending on the type of lens, but it is known as the Focal Point because it is the distance (1 dimensional point) from the lens that the entire image is in focus.

    Think of it like this:

    [​IMG]
    NOTE: The final image will be upside down....

    I dont know if that helps, but I'm hoping it does
     
    Last edited: Mar 3, 2012
  4. 480sparky

    480sparky Chief Free Electron Relocator Supporting Member

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    Your "Final Image" is upside-down.
     
  5. cgipson1

    cgipson1 TPF Noob!

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    I think you are copying my visual aid instructional style.... and that's grounds for a lawsuit! lol! :p You even made your "light" the same color I use... you are toast, buddy! ;) LMAO!
     
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  6. Beast95

    Beast95 TPF Noob!

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    Tried to keep it simple. And I'm on my laptop that doesnt have photoshop so i made this in MS Paint in 2 minutes, and i dont know how to flip it upside down anyways hahaha. Oh well.

    That, my friend, is COMPLETE coincidence :eek: hahaha.. i tried to do it differently actually because i didnt want you to think i was BUT theres no other way to do it in MS Paint lol. our secret >.>
     
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  7. Helen B

    Helen B TPF Noob!

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    There are some weird statements up there - you seem to be a little confused. Where did you get these ideas from?

    Do you know that many, many lenses do not focus by moving 'some of the lenses that make it up farther apart or closer together so that the focal point changes and so that the light can be in focus from different places at different times' but by moving the entire lens as a unit? That is probably the easiest situation to describe.
     
  8. Beast95

    Beast95 TPF Noob!

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    That would probably be easier to describe, but to the best of my knowledge, the higher end camera lenses especially have about 7 or 8 glass pieces to them (or more), and all of the glass won't move. Correct me if I'm wrong though.
     

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