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Thread: Lenses and Zoom?

  1. #1
    Member Davidtodd85's Avatar
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    Lenses and Zoom?

    Hi All,

    This might sound like a stupid question but i will ask anyway.....
    So... with my current digital compact i have 16X optical zoom.
    How do you know how much an SLR lens will zoom? As i would like to use this as a comparison when buying lenses for my DSLR when the time comes.

    Thanks guys.

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    Administrator ricktas's Avatar
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    Interesting question. With a DSLR (or any other removable lens) system, the use of MM is the guide to the zoomability of the lens. Let's start with the good old 50mm lens. In the days of 35mm film and now with full frame sensor DSLR, the 50mm lens was what people referred to as being the same as the human eye. So basically if you looked through a camera with a 50mm lens attached, everything would look the same as what you saw with your naked eye (size and distance wise). So understanding that concept can be a start to understanding DSLR lenses. However just a point to note, the 50mm lens was not entirely accurate as being exact to what a human standing beside it saw, it was very close, but from memory, I think for full accuracy it had to be something like 52mm.

    So from knowing that 50mm is approximately equal to what the human eye can see, you know now that anything less than 50mm could be called 'wider' and anything over 50mm could be called zoomed (based on your point and shoot). So take a Sigma 10-20mm lens, this is classed as a Wide Angle lens, cause it is a long way below 50mm. A wide angle lens allows a lot more of the scene to be fitted into your shot (than a 50mm one), and results in a 'wider' view. Conversely, a zoom lens, say a 100mm lens will effectively give you a closer look at the action, but will also remove a lot of the peripheral scene that you would have seen with the 50mm lens.

    Choosing the right lenses is really just a matter of knowing what Genre you shoot and what lenses suit that Genre. For example, no use trying to shoot a game of rugby, where you want to get the expressions and interactions between individual players with a wide-angle lens, you need a decent lens length (200mm or more..more preferably) to get your results. No use going to shoot that wonderful sunrise over the lake with a 300mm lens, if you want to get the small jetty and the sides of the lake in your shot, for that you need a wide angle lens.

    As for your 16x zoom we cannot tell you exactly what the comparable DSLR lens is without knowing the actual lens length. Your camera might have a 28mm lens with a 16x zoom, and the 16x relates to a multiplication factor based on knowing the 28mm information, along with the size of your sensor. I think the use of 16x zoom etc is really mostly a marketing ploy, as it doesn't really tell you the whole story, without knowing the lens length and sensor size, it is just used to attract the punters in the store. Oh look this one has 20x zoom and that one has only 15x..etc
    Last edited by ricktas; 31-05-2011 at 10:37am.
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    To calculate the "zoom" of an SLR lens, divide the maximum focal length by the minimum focal length. a 70-200mm telephoto lens has about 2.9x "zoom". A 16-240mm "superzoom" lens has 15x zoom.

    However, it is a bit of a poor way to compare P&S and DSLR cameras. You don't buy a DSLR (or most DSLR lenses) for its big zoom range; you buy one for its improved image quality and creative options.

    ---- EDIT ----

    Rick's post is sort of correct (that the "zoom" on P&S cameras is mostly marketing spin); basically what I've indicated above is how the "zoom" is calculated on point-and-shoot cameras. They don't take into account the amount of zoom based on normal perspective, they just take the maximum effective focal length and divide it by the minimum. That's how they get such massive numbers like "16x zoom" - if this figure were based on a 50mm "normal" perspective, a P&S compact would have a whopping 800mm zoom. Sadly, that's not the case. Ever.
    Last edited by ElectricImages; 31-05-2011 at 10:41am.
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    Member markjaffa's Avatar
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    EDIT

    Beaten to the punch, but going to leave it anyway.

    You will be disappointed!

    With a full frame DSLR, 50-70mm(commonly reported as 50mm, many people suggest it is more towards 70mm) is approx WYSIWYG - same magnification as your eye - but not the same field of view(FOV). You need a much wider lens to get the same FOV.

    On a cropped body, its 30-45mm(for a 1.6 body). So a 200mm lens on a FF body will have a magnification of 4X. But you still cant compare this number to the 16X optical zoom on your P+S. These cameras generally have a tiny sensor(in relation to FF), and are very wide at the bottom end(large FOV). So it MIGHT take 4 or 6 of your 16X to get to your eyes magnififcation - the other 10 or 12X are going PAST your eyes capability.

    I dont doubt that your P+S camera will be able zoom in more than most kit lens. And probably wider than most too. Where a DLR wins, is the image size. It enables you to crop your images down - isolating the element of the photo you are interested in - effectively making it larger within the finished image. Having a longer lens would remove the need to crop so much - if at all. Depending on our interest, wider may be more important to you. The only way to get wide is buy a wider lens - or walk backward!

    Most P+S dont have the resolution to crop down very far. Being able to swap lens to have the perfect one attached(if you have unlimited dollars ) for the shot you are trying to get removes the need for compromising - which is what P+S manufacturers must have had to do, when designing their cameras.

    Another spec that may be more important to you is actually the FOV of the lens - how many degrees of the scene are visible - through the lens. Magnification is NOT the only point that you need to compare IMO.
    Last edited by markjaffa; 31-05-2011 at 11:02am. Reason: Beaten to the punch!
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    Terms like "16X optical zoom" are arguably a marketing tool rather than really worth while info and then mainly relevant to compacts or point and shoot's. The differentiation made with compact cameras re "digital" vs "optical zoom" is only relevant to compacts or point and shoot's as DSLR's don't have digital zooms at all.

    You won't really ever hear people comparing SLR or DSLR lenses based on the zoom factor. TBH, I also think this is a poor criteria as a factor in lens selection. It's not impossible to build lenses with massive zoom factors (some third part lens makers do this for SLR/DSLR's) but lens makers tend not to so that better performing lenses can be made (but there are exceptions). Lenses with great zoom factors normally have to compromise some where in their design, often in their light gathering ability so are often very slow. I would personally prefer to have 2 lenses to cover a wider range (but that perform very well) rather than a single lens which underforms in some respect.

    JJ

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    Please tell us your Camera Model Number.
    Then we can see the specs & adjust this to what you would get in DSLR terms.
    Col

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    I have a Panasonic TZ20.

    I understand that the zooms on a compact are totally different, I am just trying to guage sizes in my head and also try to understand what lenses do what...... I'm getting a fair idea so far but almost to the stage where i need to go and try them to see what i would like (my friend is madly into his D90 and knows a fair bit, will have to annoy him i think)

    Thanks for all the comments, much appreciated!

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    Arch-Σigmoid Ausphotography Regular ameerat42's Avatar
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    David.
    It appears that you still harbour some confusion about zoom lenses, compacts, and such. This can happen to anyone for something new, although the info presented so far is fairly accurate, if a little generous in its scope.

    Getting back to facts you started with...
    Yes, your Panasonic DMC-TZ20 has an optical zoom range of 16X. (Forget about any digital zoom for now.) I looked here for its specifications on the Panasonic site and it tells you quite a bit about the camera.
    Its actual lens zoom range is, as quoted
    Focal Length f=4.3-68.8mm
    That means the lens has a focal length of 4.3mm at its widest, and 68.8mm at its longest focus.
    Dividing them, longest/widest, or 68.8/4.3 ≡ 16X zoom range.

    Now the sensor size in that camera is stated as "1/2.33 inch". That means it is pretty small compared to a full 35mm frame.
    Often, manufacturers (and almost everyone else) will compare the focal lengths of lenses to a 35mm camera frame. It is supposed to give a "standardised" comparison between different cameras which will have different sensor sizes. (You may have heard of APS-C, 1/1.7 inch, "Full-Frame" or FF, Nikon DX, etc.)

    So, for your camera, the equivalent zoom range compared to a 35mm camera is quoted as (I won't explain why here as it may muddy things):
    Focal Length f=4.3-68.8mm (24-384mm in 35mm equiv.)
    (29-464mm in 35mm equiv. in movie recording)
    You can see that if you do the sums, 384/24 ≡ 16X zoom range.

    Basically, it is done by upscaling the sensor size to that of a 35mm camera frame. OK, for your Movie mode, a slightly different measure is taken of the sensor, but it is still 16X.

    Up to here is about the gist of what you first asked. I hope it hasn't just confused the issue more for you.
    ***
    Two other issues were raised in the replies above.
    1. What is considered to be a "standard" view through a camera that approximates the human eye view.
    2. How to compare a focal length ranges between different cameras.

    If you like, ask about these once you've got the basics down fairly pat.

    Cheers, and now go and annoy your friend.
    Am.
    CC, Image editing OK.

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    Thanks Am, that is spot on
    Hi David
    So the bottom line is your Panasonic DMC-TZ20 with 16x zoom is equivalent in terms to 35mm DSLR language to 24mm - 384mm lens.
    Col

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    Ok...... so i had a squiz at the mother in law's D60 last night (she has the VR 55-200) and then had a look on digital camera warehoure to try and figure out what size lenses do what and i think i've got a pretty good grasp on what they all do at each size.
    Thanks so much for all the help guys, i feel like i now have a lot better understanding of what the sizes mean!

    Cheers.

  11. #11
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    16 x what?

    The reason for compacts having a large zoom range is you can't change lenses.
    With a DSLR you can get away with a few primes (as heard in Hardly Normal, "how much zoom does this 50mm lens have" ) and have no zoom at all.

    Remember: You can zoom with your feet.

    What really matters is focal length and the size of your sensor (crop factor) in the context of what you are shooting.

    Eg: Landscapes 10-20 mm is good.
    Birding ... 300 to 500 or more.
    Sports maybe 300
    Portraits 70-100mm
    And so on
    regards, Kym Gallery Honest & Direct Constructive Critique Appreciated! ©
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