What makes a macro lens a macro lens?

Discussion in 'Photography Beginners' Forum' started by MDesigner, Jun 11, 2008.

  1. MDesigner

    MDesigner TPF Noob!

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    I'm a little confused about lenses that are advertised as macro lenses.. even though many lenses DO have the macro symbol printed on them along with a range (e.g. 0.9 feet). What exactly does 0.9 ft mean in this case? Is that the closest you can get to an object before it can't focus on it? What does macro mode on my EOS 40D actually do, from a technical standpoint, and how do I use macro mode in Av or Tv modes? (I'm pretty sure it has something to do with setting a certain focal length)

    I'm looking at a Canon 60mm macro lens, and it says the closest focusing distance is 0.65 feet. Yet my old Nikon Coolpix 8700, far from DSLR, could do macro with a minimum distance of 3-4 inches or so.

    How does this work?
     
  2. asfixiate

    asfixiate TPF Noob!

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    Its the minimum distance you have to be from your subject in order to focus.

    Generally people here use full manual with Macro.

    60mm is good lense by the way.
     
  3. im_trying11

    im_trying11 TPF Noob!

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    i was wondering the same thing i can get so much closer on my coolpix s7c
     
  4. asfixiate

    asfixiate TPF Noob!

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    getting closer meaning zoom in closer or moving the camera closer?

    the .65 means you can literally be .65 feet away from target and take a pic.
     
  5. MDesigner

    MDesigner TPF Noob!

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    What I don't get is, why would this 60mm be called a "macro lens" and a 50mm not be called a macro lens? What is it about the 60mm that allows it to be referred to as a macro lens? And again, 0.65 ft doesn't sound too impressive to be honest... that's 7.8 inches away from your subject.

    Also, another question: depending on what lens you get.. let's say your lens has a range such as 18-55mm. Which focal length do you need to be at to achieve that shortest shot distance?
     
  6. asfixiate

    asfixiate TPF Noob!

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    why isn't 7.8 inches away not impressive? You need to get closer than that?

    the below will resemble difference between macro and my zoom lense.

    The minimum focus of my zoom lense is 14.6 feet.
     
  7. Socrates

    Socrates TPF Noob!

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    The bottom line is the size of the image on the film/sensor.

    There is a bit of disagreement regarding the correct definition. Purists maintain that a true macro will focus close enough to the subject so that the image of the subject on the film/sensor will be the same as the physical size of the subject. A picture of your thumbnail will cover half a 35mm frame and won't fit in a DX-sized frame!

    I have a (now discontinued) Nikon 28-85 zoom with "macro" capability in the 50-85 range. I can get the image to be one-half of the physical size of the subject and that's fine for my purposes.
     
  8. chris

    chris TPF Noob!

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    A macro lens should be able to give 1:1 reproduction (ie lifesize) of the subject on the sensor or film in the camera. Sometimes this is achieved by using an extension tube. The best macro lenses (usually primes) are built to give their best performance at short subject distances and often have minimum apertures that are significantly smaller than for normal lenses.
     
  9. Helen B

    Helen B TPF Noob!

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    The convention for focus markings on interchangeable lenses is that the distance is measured from the image plane, not from the front of the lens. At 1:1 magnification (the limit of that Canon 60 mm lens when used on its own) the 'working distance' is less than 4 inches. That's the distance from the front of the lens to the object in focus. The distance from the image plane to the object in focus is 0.65 feet (7.8 inches).

    As already mentioned, it is better to look at the maximum magnification that the lens can achieve, rather than the closest distance it can focus, because you may be dealing with lenses of different focal lengths etc.

    Macro lenses are optimized for macro work - ie their optical formula is designed for the macro range. General purpose zoom lenses may be able to focus closely, but their image quality may not be very good.

    Best,
    Helen
     
  10. julie32

    julie32 TPF Noob!

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    Back to one of the original questions here. If I have a 28-135 F2.8 lens and I want to shoot macro why can't I just zoom to 100 mm like the 100 mm macro lens and it be the same thing? Is it the glass that's actually different? Please explain why someone would want a 60mm versus a 100mm prime macro?
    Thanks
     
  11. Socrates

    Socrates TPF Noob!

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    Be reminded that the desired end result is the size of the image relative to the actual physical size of the subject. (Read my previous post as well as the ones that followed from Chris and Helen B.) The focal lengths and focusing distances are nothing more than the means to achieve that end. There is nothing in your descriptions of lens choices that tells me the ratio of the image size to the actual subject size. Give me that information and you'll be able to answer the question yourself.

    One thing that will not shout out to you is the possibility that a 100mm prime and a zoom set to 100mm will give the same size image. Then, you need to drop down to the next decision factor - which one produces better quality images? Almost without exception, the winner in that category will be the prime.
     
  12. JimmyO

    JimmyO TPF Noob!

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    Becuase it can focus closer at that length... thus more magnification.
     

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