Lens with fixed focal

Discussion in 'Digital Photography' started by Antonio Martos, Sep 26, 2004.

  1. I posted this at sci.optics, but was directed here.

    I look for a 35mm SLR Nikon mount lenses for a Fuji S2 with a very
    particular requeriment, focal lenght must be constant when focusing at
    least in the 3 meters - infinty range, for arquitectural photography
    (photogrammetry).

    Secondary requeriments are price, auto-focus, luminosity, overall
    quality, and so as usual, I apreciate them, but the key factor is "fixed
    focal lenght".

    A zoom lens could also fit if used only in the wide and tele end
    positions if the focal lenght does not changes when focusing.
    For example, Sigma 5.6 28-200 IF Lens is a good lens, but at 200 position
    the real focal lenght varies from around 165 mm focusing at 10 meters to
    190mm focusing near infinity, you can see how magnification varies when
    focusing. This maybe because its internal focus system, good for others
    but a big problem for me. I purchased this lens and gave me lots of
    problems because this until I noticed and now I almost can't use it.

    On the other side a very cheap Nikon 1.8 50mm lens is my best one for
    this prupouse. The focual lenght varies quite little (around 0.2mm from
    the real 52.7mm) and image quality and luminosity is very good.
    Also works fine Cosina 3.5 19-35mm when used in 19mm position. This one
    has some distortion but that is no problem while the focal lenght doesnt
    vary too much with focus range.

    I was told to look for fixed focal, manual focus, and extension focus
    (Cosina 19 and Nikon 50 are extension focus lenses, I mean, they move
    frontal lens when focusing) but im not sure what lens to order.

    Im thinking in purchasing some vivitar cheap lenses just for trying as
    there is not much money and could worth the while, but Im afraid of
    purchasing quality lenses when then might be useless for me. Price is not
    a problem, but I dont want to spend 2000 Euro in a lens that becomes
    worst (for this) than a 100 Euro one...

    Any recomendation? Any website or catalog where I can check this
    caracteristics or any clue o keyword to look for.
    Antonio Martos, Sep 26, 2004
    #1
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  2. Antonio Martos <> wrote in
    news:Xns9570E51BB4BBDamt@130.133.1.4:

    > I look for a 35mm SLR Nikon mount lenses for a Fuji S2 with a very
    > particular requeriment, focal lenght must be constant when focusing at
    > least in the 3 meters - infinty range, for arquitectural photography
    > (photogrammetry).


    I assume that you mean that the size of the picture does not
    change when you focus.

    Many years ago I also searched for such a lens. Did not find any.

    With a zoom lens you can theoretically compensate by zooming.
    Maybe you can make some meassurements and marks on the lens how
    to compensate.

    You can always use e.g. Panorama Tools to semi-automatically make
    the pictures the same size by scaling them.


    /Roland
    Roland Karlsson, Sep 26, 2004
    #2
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  3. > I assume that you mean that the size of the picture does not
    > change when you focus.


    Oh...ok....I was trying to figure out what he wanted.

    >
    > Many years ago I also searched for such a lens. Did not find any.


    > You can always use e.g. Panorama Tools to semi-automatically make
    > the pictures the same size by scaling them.


    No good way to do this. Hmmmm....a pinhole is all is focus...if sharp enough
    it might be a way to go about it. I have gotten great DOF from digitals as
    the sensor is smaller. Shooting the close-up layer separately from the
    background might work. But, I can imagine that there are technical
    situations where you want to take a photo close focused....and far
    focused....and if the lens changes anything it is messed up.

    No ideas...but are we understanding the problem better?
    Gene Palmiter, Sep 27, 2004
    #3
  4. Antonio Martos

    Lourens Smak Guest

    In article <Xns9570E51BB4BBDamt@130.133.1.4>,
    Antonio Martos <> wrote:

    > I posted this at sci.optics, but was directed here.
    >
    > I look for a 35mm SLR Nikon mount lenses for a Fuji S2 with a very
    > particular requeriment, focal lenght must be constant when focusing at
    > least in the 3 meters - infinty range, for arquitectural photography
    > (photogrammetry).


    > Also works fine Cosina 3.5 19-35mm when used in 19mm position. This one
    > has some distortion but that is no problem while the focal lenght doesnt
    > vary too much with focus range.


    I can hardly believe that distortion isn't a problem for architectural
    photogrammetry, but okay... ;-)

    > Any recomendation? Any website or catalog where I can check this
    > caracteristics or any clue o keyword to look for.


    Have a look at the 70-180mm micro-nikkor, I think this is the only lens
    that will do what you need, it won't change the reproduction-ratio
    (image size) when focusing.

    Lourens
    Lourens Smak, Sep 27, 2004
    #4
  5. Antonio Martos

    [BnH] Guest

    I dun understand anything you typed :p
    but anyway .. try PC Nikon lens
    http://www.mir.com.my/rb/photography/companies/nikon/nikkoresources/PC_Nikkor/
    http://www.naturfotograf.com/28pc.html

    =bob=



    "Antonio Martos" <> wrote in message
    news:Xns9570E51BB4BBDamt@130.133.1.4...
    >I posted this at sci.optics, but was directed here.
    >
    > I look for a 35mm SLR Nikon mount lenses for a Fuji S2 with a very
    > particular requeriment, focal lenght must be constant when focusing at
    > least in the 3 meters - infinty range, for arquitectural photography
    > (photogrammetry).
    [BnH], Sep 27, 2004
    #5
  6. Lourens Smak <> wrote in
    news::

    > I can hardly believe that distortion isn't a problem for architectural
    > photogrammetry, but okay... ;-)


    It is not a problem if distortion is fixed. If so, you can calibrate the
    lens for radial and decentering distortion and using this data for
    calculations or correcting it by postprocessing.
    Every lens has distortion, even metric lenses for aerial photogrammetry
    has some, but a simple rutine mapping of coordinates in the image plane
    can solve that (in fact it is not a problem at all).
    Also perspective is not a problem, I don't need PC lenses.

    >> Any recomendation? Any website or catalog where I can check this
    >> caracteristics or any clue o keyword to look for.

    >
    > Have a look at the 70-180mm micro-nikkor, I think this is the only
    > lens that will do what you need, it won't change the
    > reproduction-ratio (image size) when focusing.


    Seems that this lens is a macro lens... Also seems expensive and has lots
    of groups. I understand that keeping the macro reproduction ratio is not
    the same as keeping focal lenght fix when focusing, but when focal lenght
    changes (zooming) reproduction ratio don't change, oposing to other
    lenses, like the Sigma 28-200 I mentioned, that change their macro ratio
    from 1:4 at 200mm to 1:12 at 28mm. Correct me if I'm wrong.

    The lens is zoom and also seems to focus internaly, what keeps me sceptic
    about being what I need, if not the opposite.

    Maybe I didn't explain well. What I need is a pinhole with a fixed focal
    lenght, but this is very impractical to use. (BTW is there pinhole lenses
    for sale?) I will take photos of buildings, so there uses to be enough
    light and not too much movement, but I can't use tripod for practical
    reasons. Typical focals I use are 19 to 50 mm and a just some few times,
    80 and 200 mm for details.
    The pictures are taken from diferent angles, so distance to the object in
    oblique photos is variable between maybe 20-30 meters range at most so
    depth of field usually is not a key problem.
    I use lock zoom at his wide end to take the first picture and then lock
    focus at a compromise range so all the next pictures that are taken from
    diferent angles are in depth of field range, usually from 10-12 meters to
    infinity.

    This way all photos are taken with exactly the same optical focal length
    and all internal camera parameters are the same, and can be calibrated.
    Nothing moves, so there is no change.

    But sometimes I need to take closer photos, say at 5 meters, and DOF is
    not enough... I can allow for a small change in optics parameters, like
    focal length if I move focus ring a little (never touching zoom) but not
    too much.

    In some lenses focusing causes a minor change in focal length making
    objects grow or reduce at the same time they blur. This is sometimes
    evident at sight, but sometimes hard to see (because the blur).

    I don't need that DOF ranges from 5 metres to infinity in those cases
    although this would be a solution if enough light. But it is enough
    having usual DOF range at 5 meters and a different one at 15 meters if
    focal length does not change when changing focusing.

    I hope this could clear the problem a little. Thank you to all.
    Antonio Martos, Sep 27, 2004
    #6
  7. Antonio Martos <> wrote in
    news:Xns9571A5773C3F6amt@130.133.1.4:

    > Maybe I didn't explain well. What I need is a pinhole with a fixed
    > focal lenght, but this is very impractical to use. (BTW is there
    > pinhole lenses for sale?) I will take photos of buildings, so there
    > uses to be enough light and not too much movement, but I can't use
    > tripod for practical reasons. Typical focals I use are 19 to 50 mm and
    > a just some few times, 80 and 200 mm for details.
    > The pictures are taken from diferent angles, so distance to the object
    > in oblique photos is variable between maybe 20-30 meters range at most
    > so depth of field usually is not a key problem.
    > I use lock zoom at his wide end to take the first picture and then
    > lock focus at a compromise range so all the next pictures that are
    > taken from diferent angles are in depth of field range, usually from
    > 10-12 meters to infinity.
    >
    > This way all photos are taken with exactly the same optical focal
    > length and all internal camera parameters are the same, and can be
    > calibrated. Nothing moves, so there is no change.
    >
    > But sometimes I need to take closer photos, say at 5 meters, and DOF
    > is not enough... I can allow for a small change in optics parameters,
    > like focal length if I move focus ring a little (never touching zoom)
    > but not too much.


    OK - now I understand what you want to do. And - yes - you want the kind
    of lens that I was searching for earlier, a lens that keeps the
    reproduction ratio constant. Maybe the micro-nikkor lens does that
    even when not using it for macro. Don't know.

    I also now understand why you cannot use Panorama Tools. You are
    not taking several pictures from the same spot (as I planned to do).

    But ... this is how I should do it today when I have my pictures in the
    computer.

    I would use a prime lens, i.e. a non zoom. For this lens I would
    make a table showing how the scaling varies with focussing, e.g.
    telling that at 5 meters the multiplication factor is 1.0234.
    Or maybe I should make a program that calculates thsi when needed.
    Then I should (for every picture I take) note the actual focussing
    distance. Then I should scale all picture in photoshop to be the
    same size.

    Does this sound reasonable?


    /Roland

    BTW - you don't buy a pinhole lens - you make it from e.g. brass foil.
    You will only get reasonable sharp pictures with pinhole cameras if
    you have a large film/sensor.
    Roland Karlsson, Sep 27, 2004
    #7
  8. Roland Karlsson <> wrote in
    news:Xns9571C08F072BAklotjohan@130.133.1.4:

    > I would use a prime lens, i.e. a non zoom. For this lens I would
    > make a table showing how the scaling varies with focussing, e.g.
    > telling that at 5 meters the multiplication factor is 1.0234.
    > Or maybe I should make a program that calculates thsi when needed.
    > Then I should (for every picture I take) note the actual focussing
    > distance. Then I should scale all picture in photoshop to be the
    > same size.


    Hmmm ... after some thougts I have to admit that this is not
    as easy as it sounds. You can only use a known formula for
    a single lens, not a compound one.

    OK - so you have to modify it somewhat.

    First - avoid lenses with any inner focussing - e.g. with lens
    groups that move relative to each other. The scaling factor might
    be a very complex function of the focussing distance for such
    a lens.

    Second - meassure the scaling factor for some focussing distances.
    If you are lucky your 50 mm lens scales as if it was a 100 mm lens.
    Then you can use a formula for a 100 mm lens instead. Otherwise you
    have to make a table and do interpolations.

    BTW - a true tele centric lens do have the property you want. Olympus
    says that their 4/3 lenses are tele centric. If they are not exaggerating,
    then you want an Olympus E1 with a nice fixed focal lens.


    /Roland
    Roland Karlsson, Sep 27, 2004
    #8
  9. Antonio Martos

    brian Guest

    Roland Karlsson <> wrote in message news:<Xns9571C48BDB6A9klotjohan@130.133.1.4>...
    > Roland Karlsson <> wrote in
    > news:Xns9571C08F072BAklotjohan@130.133.1.4:
    >
    > > I would use a prime lens, i.e. a non zoom. For this lens I would
    > > make a table showing how the scaling varies with focussing, e.g.
    > > telling that at 5 meters the multiplication factor is 1.0234.
    > > Or maybe I should make a program that calculates thsi when needed.
    > > Then I should (for every picture I take) note the actual focussing
    > > distance. Then I should scale all picture in photoshop to be the
    > > same size.

    >
    > Hmmm ... after some thougts I have to admit that this is not
    > as easy as it sounds. You can only use a known formula for
    > a single lens, not a compound one.
    >
    > OK - so you have to modify it somewhat.
    >
    > First - avoid lenses with any inner focussing - e.g. with lens
    > groups that move relative to each other. The scaling factor might
    > be a very complex function of the focussing distance for such
    > a lens.
    >
    > Second - meassure the scaling factor for some focussing distances.
    > If you are lucky your 50 mm lens scales as if it was a 100 mm lens.
    > Then you can use a formula for a 100 mm lens instead. Otherwise you
    > have to make a table and do interpolations.
    >
    > BTW - a true tele centric lens do have the property you want. Olympus
    > says that their 4/3 lenses are tele centric. If they are not exaggerating,
    > then you want an Olympus E1 with a nice fixed focal lens.
    >
    >
    > /Roland


    I tried posting here earlier, but it didn't seem to stick. I think
    you're partially right, and I think that the O.P. is looking for a
    lens having focus breathing correction. This means that the chief ray
    angle in object space is constant through focus. Its a common
    requirement in cinematography and broadcast television, but is
    practically unheard of in normal still photography.

    A normal fixed focal lengh lens with simple extension focusing won't
    cut it. You need a lens that has a pronounced reduction in focal
    length as you focus. The 70-180 Nikkor mentioned earlier does this to
    a degree, but not enough to fully correct breathing. Many recent zoom
    lenses (24-120mm Nikkor is an example) use variator focusing, which
    also reduces focal length as you focus closer. These will have less
    breathing than a simple fixed lens, but probably won't be fully
    corrected for it.

    Brian
    www.caldwellphotographic.com
    brian, Sep 28, 2004
    #9
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