How do you read a lens?

Discussion in 'Photography Beginners' Forum' started by TwoRails, Nov 22, 2008.

  1. TwoRails

    TwoRails TPF Noob!

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    If this isn't a newbe question, I don't know what is. What do all the markings mean on a lens? For example, what the heck are the bell-shaped symbols in the shot below? Why is there an "R" in there? And how do they relate to the other numbers?

    TIA

    TR :)

    [​IMG]
     
  2. Helen B

    Helen B TPF Noob!

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    The sideways 8, or 'lazy eight' is the infinity symbol - a far distance.

    The R is the infrared focus mark. Most lenses do not focus all wavelengths at the same place. This is less important when you are using a wide range of wavelengths than it is when using only infrared - so the manufacturer provides a focus mark representative of near infrared radiation.

    The bell shapes are depth of field (DoF) markings. They give you an idea of what will appear to be in focus at different apertures (f-numbers: 8, 16, 22 in this case - maybe that will need explanation next). The bell shape is because of the varying focal length being represented to the right (90-50-28) - there's less DoF at greater focal lengths at the same focus distance. You have to imagine lines going up from the bell shape to the distance scale on the ring above.

    Best,
    Helen
     
  3. TwoRails

    TwoRails TPF Noob!

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    To the rescue again! Thanks Helen. OK, I imagine the "N" on the distance scale stands for "Near?" I kinda figured it was a distance related scale but going from 3' to 6' to infinity threw me off as I'd figured there be more markings. (Believe it or not, I do have a decent grasp of f-numbers: the larger = more DoF and the smaller = less DoF :) )
     
  4. Helen B

    Helen B TPF Noob!

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    I'm not familiar with that lens, but the focus scale is very compressed - hence the jump from 6' to infinity. The N? There's a switch to the left: 'Normal: Macro at 90' could that have something to do with it? Can you only go from 'Macro at 90' back to 'Normal' when the lens is focused past the N or something? Or is the N simply to mark the change from magnification to distance? Can you only go to 'Macro at 90' at the 90 setting - I guess?

    Best,
    Helen
     
  5. TwoRails

    TwoRails TPF Noob!

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    You're right again: I just played with it and the 'N' has to stand for 'Normal." I can switch to Macro at 90 with the distance scale in any position, but I just discovered I can not switch back to Normal unless the distance scale is a 'N' or more (toward infinity).

    I also just discovered that I don't know what the macro settings are. I had *assumed* that the larger the number, say 1:3 versus 1:2 would make things appear bigger, but it's just the opposite!?! I just turned to 1:2.3 and focused by moving the camera back and forth and the image in the viewfinder is a lot larger than doing the same at 1:3.5.

    If I remember right, n:n is a ratio, so I'm now thinking that 1:2 = 1/2 and 1:3 = 1/3, so 1/2 of something is larger than a 1/3 of something. That would explain why 1:2 is "bigger" than 1:3, but I'm unclear as to what it is referring to, exactly, meaning 1:2 is 1/2 of what? I'm not explaining it right so I'll try this: is it 1/2 of the object at the closest distance that will fill the viewfinder? It certainly has to be distance related...
     
  6. tirediron

    tirediron Watch the Birdy! Staff Member Supporting Member

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    I'm curious, what lens is this?

    With respect to your last question, in fact, this isn't a true macro lens. A true macro lens will do 1:1 reproductions. The best this will provide is 1:2, or 1/2 full size. What that means is that the greatest magnification that can be acheived is that which will produce the object 1/2 size on the sensor or fill plane.

    To put it aother way, if you set the lens up for it's greatest magnification and photograph a ruler, one inch will be recorded as half an inch.
     
  7. Dao

    Dao No longer a newbie, moving up!

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    With the embossed letter "Q" (below the 90), i will guess it maybe

    Quantaray 28-90mm D ... maybe is a nikon mount lens (like Af-D)
     
  8. TwoRails

    TwoRails TPF Noob!

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    Goes to show what I don't know... It's a used setup I recent bought from a friend and the lens caps says "Sigma" so that's what I thought it was, but in looking for a model number I found this on the front where filters mount:

    "Quantaray for NiKon AF 28 - 90mm 1:3.5-5.6 Macro"

    In that area it doesn't have the 'D' like it does on the barrel. I *assume* 'D' is for digital?

    ~~~~~~~~~~~~~~

    Not sure why I'm not seeing the ruler thing. I just took a pic of a ruler at 1:2 and as close as I can get. The image shows just over two inches width. In 'normal' mode focusing as close as I can get, I can see approximately 4" (didn't take a pic of this one). I assume, then, that at 1:1, if I could with the same lens, I would then see only aprox. 1" of ruler.

    Wouldn't that make it lens specific? By that I mean if I switched to a lens that could show only 8" of ruler in normal mode, and at 1:2 macro mode you would then see 4" of ruler, yes? If so, then I would understand that the "magnification factor" is in relationship to what a particular lens produces in 'normal' mode.
     
  9. Helen B

    Helen B TPF Noob!

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    No, it's purely the relation between reality and the size of the image on the film or sensor, that's all. You need to know how big your film or sensor is. What camera do you have?

    If you can see 2" of ruler and the image of that is 1" on the film or sensor then you have a 1:2 relation.

    Best,
    Helen

    PS D is Nikon-speak for distance - the lens tells the camera where it is focused. See this link for an explanation of all the Nikon lens letters. I don't know whether or not that is what it means on a Quantaray lens, however.
     
  10. TwoRails

    TwoRails TPF Noob!

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    I have a few cameras. More than I have brains to use, that's for sure. (Hopefully "you all" will change that! :)) The used unit I just picked up a couple of months ago is a D70 which came with the lens above plus a Sigma lens. The only numbers I could find on that is: "Sigma 70-300mmD 1:4 - 5.6"

    I also have a Sony 707 (love that one!) and then a Sony H9 (a great P&N, too). Then, a little over a year ago, my BetterHalf said I could get a "real" camera for Christmas and I picked up a Olympus E-510 in a two lens kit. Still learning all the knobs and controls on that one as well as the D70. The lens shot above was with the 510.

    PS: I looked a some of your shots in your links. Good stuff. The shot with the 3 Webers brought a smile to my face as I BBQed Thanksgiving turkeys on mine for about 12 years straight. That's sure good eating! If you've never tried it, you might want to as it really is good.
     

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