Home News Buyers Guide About Advertising
 
 
 
   
Results 1 to 8 of 8
  1. #1
    Join Date
    Jun 2006
    Posts
    34

    Need help understanding zoom and lenses?

    I really do not understand optical zoom. First of all how to you calculate the optical zoom? Do you divide the distance of the lenses? ex 380mm/38mm = 10 times optical zoom? If that is correct why do the telephoto lenses cost so much more when many do zoom any more? I assume I am wrong in the dividing part

    I assume focal length has something to do with this.

    I understand that some lenses have a different purposes, I mostly just do not understand how the zoom is any different on most lenses.

    Also I see and hear the word "noise" with lenses. What is this?

    If someone could clear up the concept of optical zoom and lenses I would be very greatful.

  2. #2
    Join Date
    Jul 2005
    Posts
    6,590
    Focal ranges are referring to facal ranges as we know them from 35mm film photo cameras. With them a 50mm lens is a "normal" lens, 80-135mm is portrait slight tele range, 80 and up is considered tele range, 35 and down considered wide angle.

    A digital compact that touts 36-420mm focal range of course does not actually have a lens with 36-420mm focal range. That would mean that the lens would/could actually extend around 40cm at least, that is over one foot.
    The sensor of these cameras is a LOT smaller than what a 35mm film's size is. That is where the crop factor of the sensor comes in.

    So, with this crop factor they calculate what the actual field of view of the camera/lens is in comparison to the field of view of 35mm camera lenses. And then they come up with the 36-420mm numbers.

    So... what is important to know when you see figures like that, and want to know what they mean, you have to have an understanding of field of view with 35mm full frame, and the different focal lengths.
    To get a better understanding of what those figures mean, play around here:
    http://www.tamroneurope.com/flc.htm

    You can see the field of view on a 35mm full frame SLR and of a digital APS-C size sensor DSLR.

    The "optical zoom range" quoted in the camera marketing does not say anything about what the lens actually shows, it just says what you actually figured out: 380/38 = 10.

    Consider this: a Sigma 50-500 lens has BIG tele range, and no wide angle range.
    A Sigma 18-200 has a medium telerange and a medium wide angle range.

    Yet the "zoom range" of the 50-500 = 10x, the zoom range of the 18-200 = 11x.
    The "10x" and "11x" figures say nothing about what the lens actually will be capable of.

    So it is best to get used to what the milimeters mean, so you can leave the "12x zoom range" blurb for what it is, marketing blah.
    Canon EOS 350D, Tamron SP AF 90mm F/2.8 macro, Sigma 18-50mm F2.8 DC EX, Canon EF 70-200mm f/4 L USM, Tokina AT-X124 Pro 12-24mm F4, Soligor 1.7x C/D4 DG Teleconvertor, Manfrotto 724B tripod, Canon Powershot S30

  3. #3
    Join Date
    Nov 2004
    Posts
    1,807
    Quote Originally Posted by tnelson42345
    Also I see and hear the word "noise" with lenses. What is this?
    noise as in it's loud when auto focusing - a problem on some slr lenses. some lenses have motors that are quiet and fast.

    most all in one cameras are also a bit noisy when zooming
    canon 17-40 L, 70-200 f2.8 L, 400 f5.6 L, 50 f1.4 & f1.8, 1.4x TC, sigma 15 f2.8 fisheye, flash 500 DG Super, kenko extension tubes

    note to self: don't participate in sad, silly threads unless you're looking for sad, silly responses.

    "anti-BS filter" (from andy): http://dcresource.com/forums/showpos...94&postcount=4

  4. #4
    Join Date
    Jun 2006
    Posts
    34
    "The sensor of these cameras is a LOT smaller than what a 35mm film's size is. That is where the crop factor of the sensor comes in. "


    Does this mean you are losing quality as far as megapixels go? Or just are not zooming as much as you are being told?

    Thank you very much for the responses

  5. #5
    Join Date
    Jul 2005
    Posts
    6,590
    No, it means the lens can be a lot smaller, not "420mm" for instance, but giving the equivalent of 420mm on a 35mm film camera with a much smaller lens.

    And yes, smaller sensors give less image quaility due to smaller photo diodes on the sensor.
    Canon EOS 350D, Tamron SP AF 90mm F/2.8 macro, Sigma 18-50mm F2.8 DC EX, Canon EF 70-200mm f/4 L USM, Tokina AT-X124 Pro 12-24mm F4, Soligor 1.7x C/D4 DG Teleconvertor, Manfrotto 724B tripod, Canon Powershot S30

  6. #6
    Join Date
    May 2005
    Location
    Crapville, Australia
    Posts
    5,148
    Quote Originally Posted by tnelson42345
    I really do not understand optical zoom. First of all how to you calculate the optical zoom? Do you divide the distance of the lenses? ex 380mm/38mm = 10 times optical zoom? If that is correct why do the telephoto lenses cost so much more when many do zoom any more? I assume I am wrong in the dividing part

    I assume focal length has something to do with this.

    I understand that some lenses have a different purposes, I mostly just do not understand how the zoom is any different on most lenses.

    Also I see and hear the word "noise" with lenses. What is this?

    If someone could clear up the concept of optical zoom and lenses I would be very greatful.
    Focal length is 'rough and dirty' the length of the lens, it controls the magnification of your subject. With respect to the imager size it also controls the angle of view.

    As Coldy says, a 500mm lens provides ten times magnification as a 50mm lens, hence the '10x' tag.

    Some telephoto lenses offer things that a zoom lens doesn't, such as optical quality, lens-speed, focusing-speed etc - helping to explain why a non-zoom lens is often more expensive than a zoom lens.
    Christian Wright; Dip Phot
    EOS 5D Mark III | EOS 600D | EOS-1V HS
    L: 14/2.8 II | 24/1.4 II | 35/1.4 | 50/1.2 | 85/1.2 II | 135/2 | 180/3.5 Macro | 200/2.8 II | 400/2.8 IS | 16-35/2.8 II | 24-105/4 IS | 70-200/2.8 IS II | 100-400/4.5-5.6 IS
    580EX II | EF 12 II | EF 25 II

  7. #7
    Join Date
    Mar 2006
    Posts
    2,162
    Do they use the "crop factor" at the wide or telephoto side?
    My camera gear Found on e-bay.

  8. #8
    Join Date
    Jul 2004
    Posts
    901
    Quote Originally Posted by BowerR64
    Do they use the "crop factor" at the wide or telephoto side?
    The crop factor is used at all focal lengths of a lens. For example on a 1.5x crop factor camera (APS-C), a 70-200mm lens is equivalent to a 105-300mm lens on a full frame 35mm camera.

    Ray.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •