Digital SLRs - What are the benifits?

Discussion in 'Photography' started by Nick C, Jan 3, 2006.

  1. Nick C

    Nick C Guest

    Hi all,

    I am new to this group so please forgive me if this is a daft question. I
    have a decent digital camera (Pentax Optio 555 - 5MP). I chose it because it
    has a good selection of manual features (like an SLR).

    It seems limited in the focal-range department though. I can set Aperture
    Priority and select the largest aperture size, but there is not a huge
    amount of difference with the minimum setting. What I am after is that sharp
    focus forground, but fuzzy background that is good for portraits. Would a
    digital SLR give me more flexibility in this area? Looking at the specs of
    some digital SLRs I see things lik F2.4-F7.5 which seems similar to my
    current compact.

    I'm confused.
    Nick C, Jan 3, 2006
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  2. Nick C

    dj_nme Guest

    The actual focal length (FL) that you compact digicam uses means that
    even wide open (at f1:2.4 ?), the depth of field (DoF) is very great.
    Usualy the widest aperture is at the shortest FL.
    For a 2/3" sensor digicam, the wide end might state something like "35mm
    FL 135 equivalent" but the true FL will be around 8.5mm
    An f1:2.4 aperture at 8.5mm FL (the "35mm FL" setting on your compact)
    has a diameter of about 3.54mm, where that same sized aperture hole on a
    35mm lens on a full-frame 135 film camera would give it an aperture
    setting of about f1:9.89
    The 35mm FL lens at f1:9.89 would have a DoF from about 1m to infinity.
    I'll bet that at the wide end of the zoom on your compact digicam has
    pretty much the same DoF at f1:2.4 that the full-frame lens has at f1:9.89

    What I'm getting at is that for the same FoV, a larger sensor size uses
    a much longer focal length and when set to the same f-stop setting will
    have a much shallower DoF.
    That is why DSLR cameras are able to "isolate" the subject focus-wise
    and create the blurry background.
    dj_nme, Jan 3, 2006
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  3. Nick C

    Nick C Guest

    I appreciate that advice - thankyou. Am I then correct in thinking that the
    aperture size range is not really meaningfuol without the sensor size? If
    this is the case, what can I look for when choosing a DSLR to get that
    blurry backfround

    thanks again
    Nick C, Jan 3, 2006
  4. Nick C

    dj_nme Guest

    That's pretty much it.

    The shorter true focal length of a compact digicam gives it a huge DoF
    compared to a SLR or rangefinder digicam that has a lens with the same FoV.
    There are ways to minimise the DoF with a digi compact.
    Using "macro" mode and getting very close to the subject; also zooming
    right in and using the widest aperture setting.
    dj_nme, Jan 3, 2006
  5. Nick C

    Brando Guest

    It still won't satisfy you though! You are were I was two years ago and I
    know the feeling. You want that DSLR, don't you? ;o) You sound turned on by
    blurry backgrounds. Well, that's the first sign that someone is in the
    market for a new DSLR. Stop messing about with the Optio and get yourself a
    REAL camera...'like the Canon Eos 300D or 10D, or 350D, or Nikon D70. You
    will not regret it and the thrill of owning a new DSLR is something else!
    You won't even have to ask questions about DoF as you'll see the answer as
    soon as you look through that lurvly, wide-angle lens you'll be buying. ;o)

    You've got the bug!
    Brando, Jan 3, 2006
  6. Nick C

    dj_nme Guest

    If you like the Optio, then you will absolutely love the *ist-DS2.
    It comes with the benefit of being able to use hundreds of Pentax K and
    M42 lenses; that while they might be cheap, are some of the best glass
    ever to be attached to a camera body.
    Especialy the SMC lenses.
    Another good feature is that many new Pentax lenses actualy have an
    aperture ring, so that you can have full manual control, without
    requiring a button and jog wheel combo to change the aperture.
    A very good thing are Tamron Adaptall lenses, because they can be used
    with all of the manual focus cameras (with the correct mount attached)
    and all the Pentax bodies (mf and af), but the Canon EOS adapter is only
    slightly more numerous than hen's teeth (and very expensive due to rarity).
    dj_nme, Jan 3, 2006
  7. No you're not -- you *do* want a DSLR, and you know it; you
    really know it :)

    Though I'm not satisfied with dj_nme's explanation (I do not
    believe his analysis is correct), you *do* get a lot more
    flexibility with DSLRs (in the Depth-of-field and in many
    other areas); you also get a *true depth-of-field* preview,
    so that you'll see *exactly* how the blurry background is
    going to come out (in the Nikon D70, there's a little button
    below the lens that sets the aperture to the setting you're
    going to shoot with, and so you see the actual photograph
    through the viewfinder).

    Additional benefits include the fact that a DSLR shoots
    *instantly* (I'm not sure if recent P&S digicams have
    improved, but all the P&S that I've seen take about a
    second or two from the moment that you press the shutter
    to the moment it actually takes the photograph).

    Plus, you get higher customizability for your camera: you
    get the camera, and then you get to choose where to put your
    money in terms of lenses, filters, etc. If you want a truly
    top-quality wide-angle lens, you go for it -- when you decide
    to upgrade the camera (2, 3, 5 years down the road), you keep
    the investment you did in lenses and accesories.

    The list goes on and on and on...

    Go for it... Go for it and never look back!

    Carlos Moreno, Jan 3, 2006
  8. Nick C

    Doug Kanter Guest

    You've gotten good explanations so far, with regard to how aperture affects
    depth of field. But, there's one more advantage to DSLRs - you can get real
    lenses for them. This is important for photographing certain subjects. An
    analogy from film SLRs: Most come with what's called a "normal" lens, which
    theoretically duplicates the human field of vision, sort of kinda. Typical
    focal length is 50mm. However, for portrait work, you get better results
    using a short telephoto lens, in the 85mm to 135mm range. Those longer
    lenses have less depth of field, throwing the background out of focus.

    The lens sizes I've mentioned are based on 35mm film cameras. I'm not
    well-versed in whether interchangeable lenses for digital cameras are sold
    in these configurations - someone else can clear this up. But, the basic
    idea is the same.
    Doug Kanter, Jan 3, 2006
  9. Nick C

    dj_nme Guest

    Almost all of the lenses that can be used on DSLR cameras can also be
    used on 135 film bodies as well.
    The only exceptions are the Pentax Limited lenses, Canon EF-S lenses and
    Nikon DX lenses.
    Both the Nikon DX and Pentax Limited lenses will fit, but not fill the
    frame (vignette) of their respective 135 film SLR cameras.
    The Canon EF-S lenses will interfere with the mirror in their full-frame
    DSLR and 135 film SLR EOS cameras, there may be a horrible "crack" noise
    if you force it on as the mirror is broken by the protruding rear element.
    dj_nme, Jan 3, 2006
  10. dj_nme pretty much discussed this aspect.

    The answer to this is definitely a "yes", as that is the exact
    difference between a point and shoot camera and an SLR.

    Lets expand on this just a little, with some added detail.

    "Built into the Optio 555 is a 5x, 7.8-39mm SMC Pentax lens,
    the equivalent of a 37.5-187.5mm lens on a 35mm
    camera. Maximum aperture ranges from f/2.8 to f/4.6..."

    That's what I found in a web review of the Optio 555. The numbers
    are slightly different than you have (which dj_nme worked with), but
    that really doesn't make any difference.

    Which is to say, it has the fabulously *large* depth of field
    expected from a "wide angle" lense; and what you want is the
    relatively narrow depth of field expected from a telephoto
    lense. Your camera was optimized for snapshots, street
    photography, landscapes, grab shots, ... but not for a portrait
    with an out of focus background!

    The shallow depth of field being what you want here.

    Well, that is a giant leap from what was said! What wasn't
    mentioned is that regardless of the sensor size, either a longer
    lense or a larger aperture (or a combination of both) is
    required for the shallower depth of field. The only
    relationship this has to a SLR (digital or film, and regardless
    of the sensor or film size) is that a variety of lenses are
    available, hence with a SLR you can plonk down your money and
    get a lense that provides the characteristics you want.
    Before doing that, experiment with what your camera can do, and
    see if you are satisfied with the results. If not, then go
    looking for a different camera (which I suspect you will).

    Set the camera aperture priority and take a few images with the
    lense zoomed all the way in each direction. Set up a test which
    has a continuous range in the background of at least the range
    in your concept of a "portrait", and use the widest aperture.

    The least depth of field will be zoomed to the longest focal
    length, and the most will be with the shortest. Certainly with
    a maximum aperture of f/4.6 on a 39mm lense you are not going to
    get nearly as narrow a depth of field that would normally be
    used for portraits. If what you do get is acceptable, that's
    the setup you'll want to use for portraits.

    Otherwise, look for a portrait lense and a DSLR to match. (Note
    the order of significance... :) Focal lengths between 60mm and
    150mm are commonly used. My favorite is the Nikkor 85mm f/1.8
    AFD, one of the best portrait lenses ever made.

    The characteristics of a great portrait lense are being
    very sharp even at wide apertures, a long enough focal length
    and wide enough useful aperture to control depth of field,
    and finally the shape and brightness characteristics of out
    of focus highlights.

    A lot of commentary on portrait lenses might lead one to thing
    that "soft" is good, but you can soften up a sharp lense and you
    can't sharpen up a soft one. The point is that a soft lense
    can only be used for portraits, and has limited flexibility even
    for that. A sharp lense is far more useful.

    Also it does very little good to have an f/1.0 to f/2.0 maximum
    aperture if the lense is so soft or lacking in contrast at those
    apertures that it is necessary to stop down to f4.0! Think of
    the two in balance, because a soft 50mm f/1.4 is not as good for
    portraits as a sharp 90mm f/2.8.

    Focal length and aperture are what buys a narrow depth of field,
    but the quality of that out of focus background is another
    issue! You can buy an inexpensive zoom lense that may indeed be
    a bit too soft at 80-120mm when wide open, but at 200mm and
    stopped down a stop or two it might still provide the narrow
    depth of field you want. But that inexpensive lense will have
    harsh looking out of focus objects (distinct, bright, rough
    edges). The shape, number, and size of blades in the diaphragm,
    as well as the optical design, affect the "quality" of out of
    focus objects.

    Here is an in depth discussion of the topic.

    The significant point is that there's a lot more to it than
    just getting an out of focus background! (Sometimes the trick
    is to have one eye sharp, the other eye soft, and the entire
    background just smoothly defocussed. That's a trick not just
    any lense can do for you.)
    Floyd Davidson, Jan 3, 2006
  11. Nick C

    Chris Down Guest

    When I asked about an Adaptall mount to put my old Tamron glass from my
    Pentax MeSuper bodies onto my new Canon DSLR I was told straight that there
    is no mount available for the current Canon bodies.. so no more numerous
    than hen's teeth.
    Chris Down, Jan 4, 2006
  12. Nick C

    dj_nme Guest

    I have heard about an EOS Adaptall mount, but I've never seen one "in
    the wild" so to speak.
    Maybe it was the switch to the EOS mount, that is basicaly electric
    everything with no mechanical stop-down lever in the camera that makes
    an Adaptall EOS mount kind of pointless, as the Adaptall lenses all have
    a mechanical aperture.
    dj_nme, Jan 4, 2006
  13. Nick C

    Chris Down Guest

    That was pretty much how I saw it, all mechanical manual lenses attached to
    a fully automatic electronic body. Never going to be a real solution.
    With hindsight I am happy that I could not use the old glass as I have now
    discovered the Canon L series which is an order of magnitude better than the
    Tamron lenses from the early/mid 80s.
    Chris Down, Jan 4, 2006
  14. Actually, the important thing is that almost all lenses that can be used
    on a film camera can also be used on DSLR cameras.

    Carlos Moreno, Jan 5, 2006
  15. Nick C

    Doug Kanter Guest

    I love simple answers. :)
    Doug Kanter, Jan 5, 2006
  16. Nick C

    bloke Guest

    The guts of it are that you need a wide aperture but the
    blowout focus
    effect (called 'bokeh') is attenuated by several other
    things: 1) As our
    man here mantioned sensor size. A full frame sensor will
    produce the
    effect better. FF sensors are expensive. Canon's 5D has one
    at about
    $3500 US, luckily sensor size is only a small one of many
    things that
    attenuate or add to the effect. 2) Focal length, the longer
    the lense,
    at any given range, the more pronounced the effect 3)
    distance, the
    closer the subject the more pronounced the effect. try
    setting your
    pentax to macro (if it has it) open the aperture up (low F
    number) you
    will get somewhere closer to where you want to be. 4) high
    lenses which allow you to shoot at wide apertures such as
    f2.8 or better
    and have good contrast so that the edge of your subject is
    properly 5 Aperture blade number. I use Canon L-series
    lense, thet have
    8 - blade apertures, and while this does not add to the
    improves the quality of the bokeh.
    bloke, Jan 14, 2006
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