Canon 350D + EF 28-105 lens = actually 45-160?

Discussion in 'Digital Photography' started by Steve, Mar 6, 2006.

  1. Steve

    Steve Guest

    I have a Canon 350D with the standard bundled kit lens. I may get
    another lens, like the Canon EF 28-105 F3.5-4.5 II USM. But I ran
    across some confusing comments. I know that digital cameras have a
    different size (smaller?) image sensor (than 35mm film) and that if you
    mix and match lenses it changes things. "I did extensive research and
    finally decided on the 28-105 canon. This equates to 45-160 which is
    good walking around range." and "It is sad that canon has absolutely NO
    cost effective lens equivalent of the ubiquitous 28-105 for a DSLR."

    Are these comments (full quotes below) due to the smaller image sensor
    on digital cameras?
    Is the Canon EF 28-105 F3.5-4.5 (II) USM actually not a digital lens,
    that is, it was designed originally for 35mm film cameras?
    Is that why the guy says "28-105 equates to 45-160"? Does this imply
    that the F3.5-4.5 should also be recalculated?
    Is the kit lens a "digital lens" i.e. its focal length and aperture
    numbers don't need any recalculation?
    Are Canon and everyone planning to move the camera bodies to new 35mm
    sized digital sensors, so they figure there's no reason to re-design
    the lenses, in anticipation of that?
    If I stick this lens on a 350D (= Rebel XT), do I end up "using just
    the middle of the lens", and iisn't there some downside to that?


    Here are the 2 comments that got me scratching my head:

    "First off I don't own an 18-55. I've been using the first and the
    second iteration of this lens, the ones which came along with the 300D
    and 350D. From all the photos I've shot with these lenses, they are
    both worse than almost all other lenses I've used, except for
    (possibly) the canon 28-90 kit lens which comes along with the film SLR

    When I compare this lens with the canon 20-35 and 28-105, the 18-55 is
    much worse wide open, and doesn't get any better even at f/8. I am
    quite surprised at this performance, by f/8 most lenses are pretty darn
    good, and the copy of the 28-105/3.5-4.5USM I have gives the 28-70L a
    good run for the money at f/8 between 40-70mm.

    It is sad that canon has absolutely NO cost effective lens equivalent
    of the ubiquitous 28-105 for a DSLR. The 17-85IS is not something I'd
    get, given that it's an EF-S lens, and at that price. The 18-55 is
    something I'd not even consider. The alternatives are a very expensive
    17-40L or an even more expensive 16-35L. Nikon has a very good 17-55
    AF-S ED lens which does a great job.

    Come on Canon, it's been years with 1.6x DSLR's, we don't have a single
    decent mid range zoom. What are they thinking?

    -- Vincent J M, May 26, 2005

    "This is a great lens. I bought the digital rebel kit recently and soon
    'outgrew' the efs 18-55 kit lens. It is particularly soft at large
    apertures and makes it totally unsuitable for indoor handheld
    photography. I decided to go for 35 mm lenses rather than 'digital'
    format lenses as an upgrade to the kit lens. They are lower in price
    (relatively) and you also only see the center of the lens where the
    picture quality is the best. The Quantaray 28-200 (this is actualy a
    tamron) was the first lens I considered. i returned it after just 2
    photos. it was much worse than the kit lens. Then I did extensive
    research and finally decided on the 28-105 canon. This equates to
    45-160 which is good walking around range. Also fro outdoor wide angle
    landscapes, the kit lens good enough stopped down. I got the lens today
    from adorama and the indoor test photos are GREAT and show fine detail.
    The shallow DOF in macro mode is also nice. The kit lens is no
    comparison to this lens. I would highly recommend this to new
    enthusiast dslr (like Drebel)users on a tight budget but also crave for
    more from their digital rebel. All in all a wonderful lens. And did I
    say the build quality is great too not to mention the ghostly silent
    lightening fast focussing?
    Steve, Mar 6, 2006
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  2. The "digital" lenses do not need to be recalculated as they are specked
    out at their true focal length, not their equivalent full frame size. Just
    to be sure, you should compare the angular width not the focal length. Also
    keep in mind that Canon uses several different sizes sensors not just two.
    Joseph Meehan, Mar 6, 2006
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  3. Steve

    Tesco News Guest


    The specified Focal Lengths for lenses are accurate, whatever size of Film
    or Sensor they are going to be used with.

    A 18 mm lens is a 18 mm lens always and can not be anything except a 18 mm

    When that lens is used on a DSLR it is a moderate Wide Angle. When it is
    used on a 35mm Film or a "Full Frame Digital" Camera it is an Extreme Wide
    Angle. If it could be fitted to a Med. Format Camera it would be a Fisheye.
    (Assuming it could cover that big frame).

    The only thing that varies is the Frame Size of the Camera, and that has an
    effect on the amount of the subject which will be included in the image, at
    any given Camera / Subject distance.

    Hence the use of the Phrase "Crop Factor", and its associated "Multiplier"

    Roy G
    Tesco News, Mar 6, 2006
  4. Steve

    bfisher Guest

    I'm confused. What do you mean "lenses do not need to be recalculated"?
    Focal length is focal length, but unless the camera has full-frame
    sensor (Canon 30D), you have to recalculate, because almost all of us
    think in terms of 35mm (film frame) dimensions. A 21mm lens is almost
    an extreme wide angle on a 35mm, but it's equivalent to 33mm on, say, a
    350D, and a 42mm on an Olympus. And the 35mm standard is handy, because
    we all know what sort of lens we're talking about.
    bfisher, Mar 7, 2006
  5. Steve

    Steve Guest

    Hmmm... so is it accurate to say that,

    35mm film camera bodies have a 35mm "sensor" (i.e. the film)
    DSLR's have 25mm sensors (?) (some newer ones have 35mm sensors?)
    The "crop factor" "multiplier" is 1.6.

    e.g. if I bought a 28mm F3.5 "prime" lens, it would give me just that
    on a 35mm film body.
    but if I fit it to my 350D DSLR, it would actually crop rather a lot of
    the image,
    and behave as though it were a 45mm lens on a body with a 35mm sensor.
    In other words, the outer edges would go outside the sensor edges,
    resulting in cropping.
    And by extension, in that situation, I'm only using the inner parts of
    the lens glass.
    It seems to me that this would mean I'm losing some light then, and as
    such there
    should also be a "multiplier" for a change to the effective F stop??
    Or is it merely that I'm just carrying around extra glass and weight,
    compared to
    a lens that was designed to focus straight onto a DSLR 25mm sensor?
    Should I then get an adapter (adding another lens, and more weight) to
    get around this?
    And... the stock kit lens... its also quoted in the same old 35mm
    metrics and subject
    to cropping alike?
    Steve, Mar 7, 2006
  6. Steve

    Steve Guest

    I see that the 30D, and I suppose the 20D, have a "22.5 x 15.0 mm CMOS
    Steve, Mar 7, 2006
  7. Steve

    Steve Guest

    Let me put it another way. My wife says that a 90mm prime lens is the
    bees knees for portrait photography. So if we had a 20D, we'd get a
    85mm prime lens and enjoy great boket.

    But since we have a 350D, the 50mm lens, after the multiplier or
    cropping effect, is about 80mm. So is this the right equivalent lens to
    use for portraits?

    You can see my confusion, what I'm trying to understand is the actual
    differences between using an 85mm prime on a 20D with its big CMOS 35mm
    equivalent image sensor, and on a DSLR. I can see that I can get the
    equivalent angles, but is there any loss in F stop or depth of field?
    It seems to me that of course if I put an 85mm prime on a DSLR I'd only
    use the center of the lens, get a lot of cropping, and pay for and
    carry around extra glass that never projects onto the sensor. That in
    effect I'd have a 136mm lens.

    I put a 50mm prime on a 350D, do I have a 100% equivalent situation to
    an 85mm prime on the 20D?
    Steve, Mar 7, 2006
  8. Steve

    Tesco News Guest


    You are correct, only part of the image gathered by the lens will fall on
    the sensor.

    The size of the sensor determines the so called "Multiplier", which is
    really only of use to people who still think in terms of the sort of image
    produced by various focal length lenses on 35mm cameras.

    All parts of the lens surface contribute to producing all parts of the
    image, but very generally speaking the central part of most images has the
    better quality.

    The maximum F number for any lens is determined by a calculation which does
    not involve the sensor size. Therefore it does not change, and the amount
    of light falling on the sensor is still determined by the specified F

    Lenses for 35mm cameras tend to be bulkier and heavier than the same Focal
    Length lenses designed for Digitals.

    No, do not think about lens adaptors, just learn what sort of image a
    particular Focal length of lens will produce on a Digital.

    No, the Kit lens is not quoted in "Old 35mm Metrics" it is quoted in its
    actual focal length. The Focal Length of a lens is not dependant on the
    Sensor size, it only depends on the physical construction of the lens.

    A "17 to 55mm" Zoom lens is a "17 to 55mm" Zoom lens no matter what camera,
    or none, it is mounted on.

    Roy G
    Tesco News, Mar 7, 2006
  9. Steve

    Tesco News Guest

    Hi again.

    You really are getting your knickers in a right twist about this.

    Roughly speaking a 50mm on a DSLR will give a similar image as a 80mm on a
    35mm Camera.

    The 20D is a DSLR and has a similar sensor size to the Rebels. Crop factor
    of 1.6. I know that and I am a long time Nikon user. (Nikons have a crop
    factor of 1.5)

    The F numbers on the lenses apply irrespective of the Sensor or Film size.

    The advantage of the bulkier and heavier 35mm lenses, is that they will work
    on Full Frame cameras, but the smaller lighter lenses designed for Digital

    Roy G
    Tesco News, Mar 7, 2006
  10. Steve

    Skip M Guest

    Ok, you have one problem here, the 20D has the same size sensor as the 350D.
    It's the 5D and 1Ds mkII that have 35mm sized sensors. In that context, you
    would get the same composition, standing the same distance from your
    subject, on an image with a 50mm on a 350D or 20D that you would, roughly,
    with an 85mm lens on a 5D. Actually it would be the same as an 80mm lens,
    but, hey, who's picky? BUT! You run into other problems, like distortion
    if you're too close to your subject, since it really is a 50mm lens, not an
    BTW, the new 30D has the same sensor as the 20D, too.
    Skip M, Mar 7, 2006
  11. Since you've got both, why not try it: shoot the same portrait at 50 on a
    20D and 80 on the 5D from the same too close subject distance, print both at
    the same size, and tell us how they differ?

    David J. Littleboy
    Tokyo, Japan
    David J. Littleboy, Mar 7, 2006
  12. I mean the values listed for the lens are for that lens and do not
    represent a recalculated value equivalent for a sensor size smaller than a
    standard 35mm. Just looking at that one section, I would be confusing, I
    could have worded it more carefully.
    Joseph Meehan, Mar 7, 2006
  13. Steve

    Paul J Gans Guest

    I don't believe that the 20D has a full frame sensor. I think
    that it is the same size as your 350D.

    Perhaps this will help. Imagine that your 350D takes
    pictures on 35mm film. And then it (1) automatically
    masks out the outer portions of the image and (2) then
    blows up what is left to fill the 35mm frame.

    The final image on the 350D is 8 megapixels. If the 35mm
    camera was digital at say 8 megapixels too, and had the
    same lens as the 350D, then the final image in step (2)
    above would have *more* detail than the 35mm camera's
    image --- but would include a smaller field of view.

    In your case the lenses will not be the same. but
    the final image would be essentially identical from the
    two cameras.

    The crop factor is a function of the sensor, the "film"
    so to speak. The lens is the lens. It has a focal
    length, an f stop, and a circle of illumination.

    The circle of illumination has to be enough to cover
    the sensor or you will see vignetting -- the falloff
    of light as you go away from the center of the image.

    And remember, a 35mm film camera has an enormous crop
    factor relative to an 8x10 view camera.... Seriously.

    ---- Paul J. Gans
    Paul J Gans, Mar 7, 2006
  14. Steve

    Steve Guest

    So when I use a traditional 35mm lens on my 350D (or apparently on a
    20D or 30D maybe I was wrong, and they have the same size image
    sensor), I should multiply the focal length by 1.6... and also the
    F-stop? I mean lets say I'm talking to my grandpa who never had a
    digital camera, or reading a 10 or 20 year old book about photography,
    that says, use an 85mm lens with an F-stop of 1.4, I need to convert to
    the equivalent on my 350D.

    So the EF 28-105 F3.5-4.5 II USM, I should think of it as a 45-160 F
    5.6-7.2, when used on the 350D or most DSLR's so far. The reason my
    knickers are in a twist is I thought it was a good thing to have a
    lower f-stop (range) on a zoom lens and that people routinely pay
    hundreds of dollars extra for that. And if I have to multiply also the
    F-stop by 1.6 I am throwing that out the window. So maybe I can add a
    conversion lens so that all the glass is used and none of it gets
    wasted by being cropped off the edges of the digital sensor.
    Steve, Mar 7, 2006
  15. Steve

    Joe Petolino Guest

    In a word, yes.

    I think all the "helpful" answers so far have only served to confuse the
    issue. This isn't rocket science, just simple geometry. With a smaller
    sensor, you need a smaller lens to take the same picture. That's all.

    We've all been using 35mm film cameras for so long that when someone says
    "50mm lens" we immediately know what that means in terms of field of
    view in the photographs it takes (it's about 40 degrees from side to
    side, if I did my arithmetic correctly). When someone tells you "this
    31mm lens on your 350D is the equivalent of a 50mm lens on a film SLR"
    they mean just that: with this lens, the camera will capture an image
    that spans 40 degrees horizontally, just like a film SLR would with a
    50mm lens. For the 350D, multiply the focal length by 1.6, and you'll
    know which lens you'd need to take the same picture on 35mm film.
    No. The f-stop is just the ratio of focal length to aperture diameter,
    and it's independent of how big the film/sensor is. It's an
    indication of how much light is reaching the sensor. f2.8 on a 50mm
    lens and f2.8 on a 31mm lens both let the same amount of light through
    (ignoring any differences in the transparency of the glass in the lenses).
    No, the f-stop stays the same. An 85mm lens at f1.4 on a film camera
    using ISO 400 film would capture the same image as a 53mm lens at f1.4
    on a 350D set at ISO 400.
    No, think of it as 45mm-168mm f3.5-f4.5.
    No, the 1.6 scale factor applies only to the focal length, not the f-stop.
    You may now untwist your knickers.

    Joe Petolino, Mar 7, 2006
  16. Steve

    Steve Guest

    Joe, finally you have cleared the muddy waters for me. Only remaining
    question is, what is the best way to fit out this camera beyond the
    stock kit lens. Should I get the Canon EF 28-105 F3.5-4.5 (II) USM and
    just use it as a 45mm-168mm f3.5-f4.5? Or should I get a straight up
    28-105 zoom that is designed for the smaller digital sensor from the
    git go (though apparently Canon over the last 6 or 8 years has not got
    around to making one)? Or should I fit an adapter onto the 28-105
    mentioned above... would many benefits accrue from doing that (sounds
    like it only gets heavier and costs more to go this route)? And...
    similar questions for a portrait lens... maybe I'll just get that $70
    50mm and go to town.
    Steve, Mar 7, 2006
  17. Gisle Hannemyr, Mar 7, 2006
  18. First - swap the 20D for a 5D. The 5D has a sensor the same
    size as 35mm film. And the crop factor for the 350D is 1.6,
    50mm x 1.6 = 80mm.

    So, if you put a 50mm fixed focal length on a 350D, do you have a
    100% equivalent situation to an 80mm fixed focal length on the 5D?

    Not 100%.

    The parameters photographers are most interested in, the field of
    view or perspective, will be 100% equivalent. The f-stop will be
    100% equivalent.

    But the depth of field will behave slightly different. As long as
    we are talking about DSLR cameras - the difference is quite small
    but you'll need to open up around 1 1/3 more on a 350D to
    achieve a similar DOF as you would with film/5D: See also:
    Gisle Hannemyr, Mar 7, 2006
  19. That sound like a good choice if that rather awkward range of focal
    lenghts is really waht you want.
    Well, just be aware that a "designed for digital" EF-S 28-105 F3.5-4.5
    would still behave like a 45mm-168mm f3.5-f4.5 on your camera.
    And probably never will. This is not a "popular" focal length range
    for APS-C sized sensor. Canon's closest digital "equivalent" of the
    popular 28-105mm is their "made for digital" EF-S 17-85mm f/4-5.6 USM
    IS - which gives you the same FOV as a 28- 136mm would give on

    If you want a general "walking around lens" that goes from wide angle
    to tele the EF-S 17-85 mm f/4-5.6 (or the EF-S 17-55 f/2.8 IS if you
    can afford it and can wait until May) is the lens to get.
    Forget this one. Such an adapter introduces extra elements in
    the optical path that degrades performance.
    Gisle Hannemyr, Mar 7, 2006
  20. Steve

    Colin D Guest

    *All* lenses are 'speced out' or marked with their true focal length, or
    range if a zoom.

    The confusion comes about because the smaller sensor gives a narrower
    field of view than does a full-frame 35mm. It's the same as cropping a
    full-frame shot to the digital sensor dimensions, resulting in a
    narrower view. The '35mm equivalent' focal length is meant to give an
    idea of the effective field of view for the smaller sensor, i.e. a 28mm
    lens on a 1.6-crop digital sensor gives the same field of view as does a
    45mm lens on a full-frame. Of course, the image is smaller (linearly)
    by the same factor, 1.6.

    My choice of lens for my Canon is the 17-85mm IS USM, an excellent lens
    for the job. It equates to a 28-135mm on a full frame, having a 5:1
    zoom range.

    Colin D.
    Colin D, Mar 7, 2006
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