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Thread: Lens identification

  1. #1

    Default Lens identification

    HI All,

    I am new to this forum and also to photography. Did some Film based SLR photography and am trying to move to DSLR. I was scouting to some information and was trying to understnad the concepts. I came across this new way (it may not be new, but i am not aware of it) of lens marking. I can relate to the lens convention of denoting the zoom factor as 35mm to 70mm or 28mm to 200mm etc. But lately with the DSLR i see that the lens range for zoom are marked as 18 - 70mm etc. What does this?

    Are the lens more wide angle than b4.
    I think they are not, is there a multipication factor that needs to be multiplied to convert the zoom range to the traditional convention.

    Would appreciate if someone cud throw some light on this topic will help me understand this aspect of photography much better.

    THanks in Advance for the clarification and knowledge provided to this novice.

    Regards
    Sameer[/list]

  2. #2
    Senior Member Kit's Avatar
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    The smaller the number, the wider the lens. If you use these lenses on DSLRs with smaller sensors, you need to add it the "multiplying" factor to the focal length of any lenses. Such factors vary from model to model; brand to brand, ranging from 1.3x to 2x.

  3. #3

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    Quote Originally Posted by sameer_Sh65
    HI All,

    I came across this new way (it may not be new, but i am not aware of it) of lens marking. I can relate to the lens convention of denoting the zoom factor as 35mm to 70mm or 28mm to 200mm etc. But lately with the DSLR i see that the lens range for zoom are marked as 18 - 70mm etc. What does this?

    Are the lens more wide angle than b4.
    I think they are not, is there a multipication factor that needs to be multiplied to convert the zoom range to the traditional convention.[/list]
    Zoom lens means having a variable focal length, be it 35-70, 18-70, 12-24 or 17-35 it is still call a zoom lens

    Yes, you are ritz, you do need to multiple to have the equilivant 35mm film view. In DSLR there is a cropping factor, I make a bold guess tat you are looking at the D70 with the 18-70dx. all nikon DSLR have a crop factor of 1.5 .i.e a 18-70 len mounted on a nikon DSLR would have a view like if it is a 27-105mm lens. (do take note at 18mm end ,it is still having a distortion of18 mm , it is a crop factor not a focal length multipler). And to add to tat, the 18-70 dx , the dx means it for DSLR camera, and would not work fully on your film camera.
    The cause of the crop factor is due to the smaller CCD size compare to the 35mm format.

    Help it helps, cheers.

  4. #4

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    Quote Originally Posted by Jus_a_Nick
    Zoom lens means having a variable focal length, be it 35-70, 18-70, 12-24 or 17-35 it is still call a zoom lens

    Yes, you are ritz, you do need to multiple to have the equilivant 35mm film view. In DSLR there is a cropping factor, I make a bold guess tat you are looking at the D70 with the 18-70dx. all nikon DSLR have a crop factor of 1.5 .i.e a 18-70 len mounted on a nikon DSLR would have a view like if it is a 27-105mm lens. (do take note at 18mm end ,it is still having a distortion of18 mm , it is a crop factor not a focal length multipler). And to add to tat, the 18-70 dx , the dx means it for DSLR camera, and would not work fully on your film camera.
    The cause of the crop factor is due to the smaller CCD size compare to the 35mm format.

    Help it helps, cheers.

    THanks for the explanation it really does help. Regarding the Crop factor is this mentioned in the Specs of a Camera or is it a unsaid norm.

    Thanks Again.
    Sameer

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    It will be mentioned in the specs somewhere.

    Yes you keep the characteristics, including the distortion, of the actual focal length, say 18mm, but don't forget that you're only using the middle portion of the frame and as a result distortion effects are less anyway. Comparing full frame and smaller frames at "equivalent" focal lengths, you need to look really, really hard to find differences between the straight 30mm and the multiplied 20mm lens.

  6. #6

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    Quote Originally Posted by Jed
    It will be mentioned in the specs somewhere.

    Yes you keep the characteristics, including the distortion, of the actual focal length, say 18mm, but don't forget that you're only using the middle portion of the frame and as a result distortion effects are less anyway. Comparing full frame and smaller frames at "equivalent" focal lengths, you need to look really, really hard to find differences between the straight 30mm and the multiplied 20mm lens.
    Thanx very much everyone for your answers and clarification

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    Do all DSLRs have this distortion?
    If so, why?
    No wonder the kit lens with Canon 300D is 18-55mm. I was grumbling a bit about that part.
    This morning, I realised that all the pictures I took with that 300D was a little bigger than what I saw in the viewfinder. That really screwed up my framing. Any ways to right it?

    thanks in advance!

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    I believe the 300D VF has a 95% coverage, so if you want exactly part of a shot you're taking, it's only 95% you're seeing, there's another 5% you're not seeing. Which will be added in left right up down when the shot is taken.

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    *grumble, makes more notes in her notebook about the cons of DSLRs*

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    Quote Originally Posted by Poledra
    *grumble, makes more notes in her notebook about the cons of DSLRs*
    This is not limited only to DSLRs. Most SLRs do not have 100% VF other than the flagships.

  11. #11
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    Serious?
    Hmmm... Guess I haven't been observant enough. Thanks for telling me so I wouldn't sound so much like a bimbo (what's new?).
    *erases her last entry on her notebook*

  12. #12
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    poledra, did the camera price dip below S$1K already?

    /me runs away from Poledra + UL

  13. #13
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    Quote Originally Posted by sehsuan
    poledra, did the camera price dip below S$1K already?

    /me runs away from Poledra + UL
    Nope. I wish it would, though.
    Every minute I spend with that 300D, I think I won't get married because that camera takes the place of a husband.
    Kidding.

    I'm gonna appear in CT again. Soon. Billy Teo has a motive for lending me that 300D.

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