Why are "digital" lenses so "slow"

Discussion in 'Digital Photography' started by Dustbunny, Dec 29, 2004.

  1. Dustbunny

    Dustbunny Guest

    Another quick question for this great group. I'm looking at the Canon
    20D and can't quite understand why most of the lenses in the 28-80
    range all seem to have a pretty slow aperature. At least compared to
    my old FD lenses. I understand about the lens factor as it relates to
    focal length, but does something similar happen for f-stop?

    Many thanks
    Dustbunny, Dec 29, 2004
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  2. Dustbunny

    Wilt W Guest

    <<why most of the lenses in the 28-80
    range all seem to have a pretty slow aperature... but does something similar
    happen for f-stop?>>

    Manufacturers know that most people buying digital cameras are amateurs who
    cannot appreciate the photographic value (vs. cost) of lenses with large
    maximum f/stop. There are plenty of offerings with f/2.8 though, and at
    relatively affordable prices, and that's not exactly slow!

    Wilt W, Dec 29, 2004
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  3. It's not a matter of "digital" or not, it's a matter of there being a market
    for cheap slow consumer zooms, so the manufacturers produce cheap slow
    consumer zooms. This market appeared long before dSLRs.
    You should be able to find equivalent lenses for every single one of the FD
    lenses in an EF mount. Fast primes are still available. (Actually, the
    50/1.0 was discontinued, but my understading is that it was increadibly
    expensive and poor optically.)

    Design, manufacturing, materials, and coating technologies have improved a
    lot since the FD days, and those improvements have largely gone into cheap
    slow consumer zooms.

    With the success of the Tamron 28-75/2.8 zoom, Sigma has been releasing new
    f/2.8 zooms at a phenomenal rate of late, so there are more choices in the
    affordable fast zoom range. As of last March, the Tamron 28-75/2.8 zoom was
    (by far) the best rated consumer zoom that covers that range, but people are
    saying nice things about some of the new Sigmas. (There's a Japanese book
    issued every March that reviews every 35mm AF lens in production, although
    they dropped the reviews of the primes in 2004, which indicates that the
    market is shiftimg away from primes. Heck, I bought 4 lenses this year, and
    only one was a prime, whereas I had never purchased a zoom before 2004.)
    Nope. Of course, there is the fact that dSLRs do better at ISO 400 and 800
    than film does, so slower lenses aren't quite so painful on a dSLR.

    David J. Littleboy
    Tokyo, Japan
    David J. Littleboy, Dec 29, 2004
  4. They don't have to be. I'm looking at getting a Nikon Digital body
    and one of the lenses I'll put on it is the f1.4 50mm Nikkor. It just
    depends on your price point.


    "The National Rifle Association has been in support of
    workable, enforceable gun control legislation since its
    very inception in 1871."

    NRA Executive Vice President Franklin L. Orth
    NRA's American Rifleman Magazine, March 1968, P. 22
    John A. Stovall, Dec 29, 2004
  5. Dustbunny

    Jim Townsend Guest

    You must be referring to Canon's midrange zooms.. I actually hadn't
    noticed it before, but you are correct, the only 'fast' midrange zoom
    is the EF 24-70 f/2.8

    I guess 'good', 'fast' and 'zoom' isn't an easy thing to do..
    The 24-70 f/2.8 is pretty fast, but It's probably the most expensive
    of the lot.

    If you want fast, go to a fixed focal length lens.. There you'll find
    a decent selection of lenses in the f/1.x range. But of
    course, don't forget the prime rule of optics... fast = $$$
    Jim Townsend, Dec 29, 2004
  6. Dustbunny

    [BnH] Guest

    Can you get grainless ISO 1600 shots with your old FD mount cams ? :)
    You do need DoF .. but not that desperately .. as f/1.4 was only used in
    very poor lit condition.
    [ tho I dun mind having a 300mm f/1.4 :) ]
    + there is Photoshop ?

    [BnH], Dec 29, 2004
  7. Dustbunny

    PhotoMan Guest

    Unless you need the shallow DOF of an ƒ 1.4 or ƒ2.
    PhotoMan, Dec 29, 2004
  8. Dustbunny

    Skip M Guest

    You mean besides the EF mount 24-70 f2.8?
    There weren't many zoom lenses in the f2.8 range back in the FD range days,
    either. The FD mount 35-70 was a 2.8-3.5, true, but the 28-50 was a 3.5.
    The fastest "new" FD (bayonet mount as opposed to breech lock) was the 25-70
    f2.8-3.5, but the 28-85 was an f4. My Kiron 28-80 was a 3.5, as was my
    dad's Vivitar Series 1 and my wife's Sigma. The Canon EF mount 28-105 is a
    f3.5-4.5, which matches the FD mount 35-105 f3.5-4.5.
    If you're talking about third party mfrs, Tamron, Tokina and Sigma all have
    current 24/28-70/80 lenses in the f2.8 range, some designed specifically for
    digital cameras.
    The digital crop doesn't affect aperture in anyway.
    Skip M, Dec 29, 2004
  9. Dustbunny

    Skip M Guest

    That's a rather broad statement, with all of the pros going to digital
    output. There are no fewer EF mount zoom lenses available at f2.8 than
    there were with the FD mount, check:
    In fact, there are more. There were no single aperture f2.8 lenses in that
    range, at least listed on the Canon site.
    Skip M, Dec 29, 2004
  10. Dustbunny

    Eric Gill Guest

    <shrug> Then you must use f/1.4 or f/2.

    There is no real shortage of lenses in that range, all primes. The Canon 85
    f/1.2 is particularly spectacular, for example, though it focuses *really

    I'm pretty happy with the wide range of f/2.8 zooms, and they are beginning
    to become very affordable.
    Eric Gill, Dec 29, 2004
  11. Dustbunny

    Eric Gill Guest

    Right. Pick any two of the above.

    What is most annoying of the mid-zooms is not so much the speed but the
    fact that it changes through the zoom, making exposure compensation
    neccesary and slowing down your response time.
    Yep. Fortunately, both Sigma and Tamron make real alternatives now, staring
    in the $350 range.

    Eric Gill, Dec 29, 2004
  12. Or faster shutter speed to stop subject motion. Even in informal snapshot
    portraits, subject motion's a nastier problem than camera shake. (Note that
    I didn't really intend to defend the slow cheap consumer zooms: just to
    point out that they're not as much of a disaster as one might think.)

    But the experience here is that the radically shallow DOF at f/2.0 and wider
    is radically overvalued. Sure, the fraction-of-a-mm DOF portrait is a cool
    effect, but it gets old after a while. And as long as one picks a not too
    busy background, almost any f-stop will provide some amount of blurring as
    long as one's subject is less than 25 or so times the (35mm equiv.) focal
    length away.

    According to


    (which overestimates the DOF in my experience: the 0.025 mm CoC (0.016 for
    dSLRs) is a bit excessive if one is looking at a dSLR image (or 4000 dpi
    film scan) at 100% on the screen: a 6MP dSLR has a 0.0075mm pixel pitch,
    which is probably smeared to 0.011 mm by the AA filter.)

    the DOF of an 85mm portrait lens at 6 feet at f/8 is +/- 0.3 feet. That's
    for 35mm, so you'd have to open up to f/5.6 with 1.6x digital at 55mm. But
    that's not enough to get a whole head in focus, and that would be assuming
    perfect placement of the plane of focus.

    At 10 feet, with f/5.6 on a 1.6x dSLR, at f = 75mm (120mm equiv.), DOF is
    +/- 0.4 feet. Still barely a head's worth of DOF.

    David J. Littleboy
    Tokyo, Japan
    David J. Littleboy, Dec 29, 2004
  13. Dustbunny

    Mark² Guest

    Ever hear of a Canon 24-70 2.8 L?
    Mark², Dec 29, 2004
  14. Dustbunny

    stauffer Guest

    This is not unique to digitals. Look at most of the low to medium
    priced film point&shoot cameras- lenses have about same range (in
    relative focal lengths) as P&S digitals.
    stauffer, Dec 29, 2004
  15. Dustbunny

    Jeremy Guest

    One reason that motivates manufacturers to release less-than-top-shelf
    lenses is that the digital photographer can often compensate for some lens
    deficiencies during post-shoot editing.

    The lens is not as critical a component for many digital applications as it
    was for film shots.

    As Wal-Mart has demonstrated, the lowest-priced items will nearly always be
    Jeremy, Dec 29, 2004
  16. Already pointed out by others: not true.
    Manufacturers have long provided a range of quality and apertures.
    Nothing to do with digital.
    Not true for many photographers. And, for some, going digital has caused
    them to upgrade their lens choices as they can better see the
    shortcomings of the lesser quality lenses.
    John McWilliams, Dec 29, 2004
  17. Dustbunny

    dave6134 Guest

    Apparent DOF is so easily controlled in a wide varity of image editors
    that one can now concentrate on using the sharpest lens openings and
    blur background/foreground as required.

    Those big f0.95 and f1.0 lenses all date back to the days of kodak
    supper X ASA 100, pushed all the way to 250. They were not sharp but
    they at least captured something in "black cat in a coal bin"

    East Engelwood
    dave6134, Dec 29, 2004
  18. See my other note. But to reiterate, even with a 1.6x camera, the background
    is blurred quite nicely by a portrait lens or anything longer at almost any
    f stop. DOF goes down with the square of the focal length, so while wide
    angle lenses have gobs of DOF, it doesn't take much beyond normal to get
    into painfully narrow DOF.
    I was knocked out when I tried some shots with the 50/1.4 at f/1.4 at ISO
    1600 with the Drebel. Even at handholdable speeds it's amazingly sensitive.
    A fast lens leverages the usable high ISOs into something seriously neat.

    David J. Littleboy
    Tokyo, Japan
    David J. Littleboy, Dec 29, 2004
  19. They are not slow. All reasonable priced good zoom
    lenses for SLR cameras are slow. It has nothing to do
    with digital cameras.

    I say - buy a 50/1.4 for your camera and you have a nice
    and fast "portrait" lens for a reasonable amount of money.

    Roland Karlsson, Dec 29, 2004
  20. Dustbunny

    Dustbunny Guest

    Well to provide perspective, I was hoping to find a fast lens for
    indoor ambient light shooting in clubs. I was also thinking that
    having IS in a low light environment like this would be helpful. But
    it seems the best I'd be able to do is a fast fixed lens with no IS,
    or a slower lens with IS.

    Anyway, thanks for all the good viewpoints.
    Dustbunny, Dec 30, 2004
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