Filters

Discussion in 'Digital Photography' started by Eric Miller, Apr 12, 2004.

  1. Eric Miller

    Eric Miller Guest

    After getting some great info concerning shooting with my Sigma Mirror lens
    without the "normal" filter, I thought I'd follow up with a more focused
    question. I think that my Canon EF 70-200 2.8L IS USM lens will "outresolve"
    the sensor on my 10D. I think this because when I get a shot in good focus,
    the limitation on resolution seems related solely to the number of pixels in
    the resulting image. I also notice that my Sigma Mirror lens has a front
    "element" that seems to have no purpose other than to hold the internal
    optics in place. If I am correct, this is just a piece of clear glass, just
    like my normal filter. If not using the normal filter will have no
    noticeable effect on the resulting image, then, generally speaking, will the
    use of a clear filter on the front of any lens have any noticeable effect?
    In other words, will my Canon EF 70-200 2.8L IS USM lens still outresolve
    the sensor on my 10D with a UV filter on the front for "protection?" I have
    seen a lot of posts about not putting an unnecessary piece of glass in front
    of an expensive lens and yet if the difference can't be picked up by the
    sensor in my camera, why not use a UV or Skylight filter as protection, even
    a cheap one? After all my Sigma lens has two pieces of unnecessary glass in
    the light path (meaning they aren't there for optical purposes).
     
    Eric Miller, Apr 12, 2004
    #1
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  2. Eric Miller

    Don Guest

    "Eric Miller" <ericmilleratcoxdashinternetdotcom> wrote in message
    news:...
    > After getting some great info concerning shooting with my Sigma Mirror

    lens
    > without the "normal" filter, I thought I'd follow up with a more focused
    > question. I think that my Canon EF 70-200 2.8L IS USM lens will

    "outresolve"
    > the sensor on my 10D. I think this because when I get a shot in good

    focus,
    > the limitation on resolution seems related solely to the number of pixels

    in
    > the resulting image. I also notice that my Sigma Mirror lens has a front
    > "element" that seems to have no purpose other than to hold the internal
    > optics in place.


    And keep the bugs out :)

    If I am correct, this is just a piece of clear glass, just
    > like my normal filter. If not using the normal filter will have no
    > noticeable effect on the resulting image, then, generally speaking, will

    the
    > use of a clear filter on the front of any lens have any noticeable effect?
    > In other words, will my Canon EF 70-200 2.8L IS USM lens still outresolve
    > the sensor on my 10D with a UV filter on the front for "protection?" I

    have
    > seen a lot of posts about not putting an unnecessary piece of glass in

    front
    > of an expensive lens and yet if the difference can't be picked up by the
    > sensor in my camera, why not use a UV or Skylight filter as protection,

    even
    > a cheap one? After all my Sigma lens has two pieces of unnecessary glass

    in
    > the light path (meaning they aren't there for optical purposes).
    >

    There are several possible unwanted effects from inserting a filter in the
    image path.

    1. The additional surfaces (at least two, more if it's a gelatin filter in
    glass) cause reflections, even if coated. These may not be a problem, but
    they'll be there in any case. It can be signifcant with cheap, uncoated
    filters.

    2. Also, imperfections on those surfaces (scratches, dust, etc.) cause
    scattering, usually seen as flare. Of course, these "imperfections" might
    otherwise be deposited on the front element of the lens - not good either.
    The obvious advantage of having them on the filter is that the filter is
    much cheaper to replace.

    3. Another effect is to shift the focus slightly for off-axis light. This
    has the effect of slightly un-flattening the field. For the particular case
    of your 70-200 mm lens, the field angle is small enough that it won't be a
    problem, but it usually is measureable on a wide angle lens and can cause
    problems at large apertures if you're working near the diffraction limit.

    4. And, of course, any time you insert extra surfaces in the optical path
    they will cause perterbations in the wavefront if those surfaces are not
    perfectly flat.

    In short, if you buy a good filter, there shouldn't be any problems as long
    as you keep it clean, and replace it when it becomes damaged.

    BTW, my current main camera is digital, but when I was using a film SLR I
    *always* kept a good skylight filter on the lens. My digital (Canon G2)
    doesn't easily accommodate filters, although I do use a polarizer on
    occasion.

    Don
     
    Don, Apr 12, 2004
    #2
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  3. Eric Miller

    Tony Spadaro Guest

    If you get a good quality, multicoated UV filter you will not lose any
    resolution and will be protecting your lens from a lot of crap that can
    lower it's resolution by quite a bit. I've had to throw out a number of
    protective filters over the years but never a lens.
    How much will you lose? About 35 years ago teh oldtimers who hung out at
    the local camera store (wearing their Leicas but probably never actually
    putting any film through them) told me there is nothing more amatureish than
    using a filter to protect the lens. "That filter will destroy all your shots
    sunny boy - you're wasting your time shooting through it."
    I came back the next day with two prints from two shots of the same
    scene, one taken with the filter in place and one with the filter removed. I
    asked them to tell me which shot had been ruined byu the filter. They told
    me with a cheap lens like I had (Pentax top of the line 50mm f1.4 Super
    Takumar -- a legendary lens for sharpness and the sharpest lens I ever
    owned) I wouldn't be able to see the difference. So I said. "Since I won't
    be able to see any difference, I guess I might as well leave the filter on."
    I suggest you do the same - that lens is not a cheap one to replace.

    --
    http://www.chapelhillnoir.com
    home of The Camera-ist's Manifesto
    The Improved Links Pages are at
    http://www.chapelhillnoir.com/links/mlinks00.html
    A sample chapter from my novel "Haight-Ashbury" is at
    http://www.chapelhillnoir.com/writ/hait/hatitl.html
    "Eric Miller" <ericmilleratcoxdashinternetdotcom> wrote in message
    news:...
    > After getting some great info concerning shooting with my Sigma Mirror

    lens
    > without the "normal" filter, I thought I'd follow up with a more focused
    > question. I think that my Canon EF 70-200 2.8L IS USM lens will

    "outresolve"
    > the sensor on my 10D. I think this because when I get a shot in good

    focus,
    > the limitation on resolution seems related solely to the number of pixels

    in
    > the resulting image. I also notice that my Sigma Mirror lens has a front
    > "element" that seems to have no purpose other than to hold the internal
    > optics in place. If I am correct, this is just a piece of clear glass,

    just
    > like my normal filter. If not using the normal filter will have no
    > noticeable effect on the resulting image, then, generally speaking, will

    the
    > use of a clear filter on the front of any lens have any noticeable effect?
    > In other words, will my Canon EF 70-200 2.8L IS USM lens still outresolve
    > the sensor on my 10D with a UV filter on the front for "protection?" I

    have
    > seen a lot of posts about not putting an unnecessary piece of glass in

    front
    > of an expensive lens and yet if the difference can't be picked up by the
    > sensor in my camera, why not use a UV or Skylight filter as protection,

    even
    > a cheap one? After all my Sigma lens has two pieces of unnecessary glass

    in
    > the light path (meaning they aren't there for optical purposes).
    >
    >
     
    Tony Spadaro, Apr 12, 2004
    #3
  4. Eric Miller

    John J Guest

    "Eric Miller" <ericmilleratcoxdashinternetdotcom> wrote in message
    news:...
    > After getting some great info concerning shooting with my Sigma Mirror

    lens
    > without the "normal" filter, I thought I'd follow up with a more focused
    > question. I think that my Canon EF 70-200 2.8L IS USM lens will

    "outresolve"
    > the sensor on my 10D. I think this because when I get a shot in good

    focus,
    > the limitation on resolution seems related solely to the number of pixels

    in
    > the resulting image. I also notice that my Sigma Mirror lens has a front
    > "element" that seems to have no purpose other than to hold the internal
    > optics in place. If I am correct, this is just a piece of clear glass,

    just
    > like my normal filter. If not using the normal filter will have no
    > noticeable effect on the resulting image, then, generally speaking, will

    the
    > use of a clear filter on the front of any lens have any noticeable effect?
    > In other words, will my Canon EF 70-200 2.8L IS USM lens still outresolve
    > the sensor on my 10D with a UV filter on the front for "protection?" I

    have
    > seen a lot of posts about not putting an unnecessary piece of glass in

    front
    > of an expensive lens and yet if the difference can't be picked up by the
    > sensor in my camera, why not use a UV or Skylight filter as protection,

    even
    > a cheap one? After all my Sigma lens has two pieces of unnecessary glass

    in
    > the light path (meaning they aren't there for optical purposes).
    >
    >

    I concur with the 2 previous posts but would just like to add that I often
    avoid using filters simply to reduce the chance of flare (a real problem in
    my line of work) but ALWAYS use filters in dusty/dirty environments or where
    there is any chance of debrit striking the lens element. Filters are cheap
    (B+W and Heliopan excepted), lenses expensive...
    JJ
     
    John J, Apr 12, 2004
    #4
  5. Eric Miller wrote:
    > After getting some great info concerning shooting with my Sigma
    > Mirror lens without the "normal" filter, I thought I'd follow up with
    > a more focused question. I think that my Canon EF 70-200 2.8L IS USM
    > lens will "outresolve" the sensor on my 10D. I think this because
    > when I get a shot in good focus, the limitation on resolution seems
    > related solely to the number of pixels in the resulting image. I also
    > notice that my Sigma Mirror lens has a front "element" that seems to
    > have no purpose other than to hold the internal optics in place. If I
    > am correct, this is just a piece of clear glass, just like my normal
    > filter. If not using the normal filter will have no noticeable effect
    > on the resulting image, then, generally speaking, will the use of a
    > clear filter on the front of any lens have any noticeable effect? In
    > other words, will my Canon EF 70-200 2.8L IS USM lens still
    > outresolve the sensor on my 10D with a UV filter on the front for
    > "protection?" I have seen a lot of posts about not putting an
    > unnecessary piece of glass in front of an expensive lens and yet if
    > the difference can't be picked up by the sensor in my camera, why not
    > use a UV or Skylight filter as protection, even a cheap one? After
    > all my Sigma lens has two pieces of unnecessary glass in the light
    > path (meaning they aren't there for optical purposes).


    You are thinking at least partly right. The filter is not going to make
    much of any real difference. It is a very small situations where even the
    best of equipment will show any noticeable difference.

    However, while it does not happen often you will still be subject to
    some imaging problems with most filters, especially cheap ones because they
    are less well protected from flare and often not or less well coated. This
    will not show up on most lens test. If you use a good lens shade, then this
    is much less of a problem.

    Of course if you use a good lens shade, your less is better protected,
    under most conditions, than by using a filter.

    In short, you are not likely to either hurt or help your photography by
    using a filter.



    --
    Joseph E. Meehan

    26 + 6 = 1 It's Irish Math
     
    Joseph Meehan, Apr 12, 2004
    #5
  6. Eric Miller

    Bob Salomon Guest

    In article <FQvec.20879$>,
    "Joseph Meehan" <> wrote:

    > because they
    > are less well protected from flare and often not or less well coated.


    This is redundant.

    Coatings reduce flare. Uncoated filters have the most flare, period.

    Multicoated (on both sides and with 8 or more coats per side) have the
    least flare.

    You want filters that protect the best from flare? Then buy fully
    multicoated filters.

    Buy filters with no coating on one or more sides you are inviting flare.

    --
    To reply no_ HPMarketing Corp.
     
    Bob Salomon, Apr 12, 2004
    #6
  7. Bob Salomon wrote:
    > In article <FQvec.20879$>,
    > "Joseph Meehan" <> wrote:
    >
    >> because they
    >> are less well protected from flare and often not or less well coated.

    >
    > This is redundant.


    No. The original lens is almost always recessed somewhat from the edge
    of outer most edge. The filter is not.

    >
    > Coatings reduce flare. Uncoated filters have the most flare, period.
    >
    > Multicoated (on both sides and with 8 or more coats per side) have the
    > least flare.
    >
    > You want filters that protect the best from flare? Then buy fully
    > multicoated filters.


    Better yet add a good lens shade, even better both the lens shade and
    proper coatings.

    >
    > Buy filters with no coating on one or more sides you are inviting
    > flare.


    --
    Joseph E. Meehan

    26 + 6 = 1 It's Irish Math
     
    Joseph Meehan, Apr 12, 2004
    #7
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