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Re: [PanoToolsNG] Sigma 8-16 and PTGUI

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  • Cuffsmaster
    what lens is it? ... [Non-text portions of this message have been removed]
    Message 1 of 13 , Aug 5, 2011
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      what lens is it?
      On Aug 5, 2011, at 6:12 PM, alfred.molon wrote:

      > I bought this (rectilinear) lens for my APS-C DLSR and just out of curiosity tried to stitch two images taken at 8mm (12mm equivalent focal length in 35mm). These were two horizontal images, overlapping perhaps by 20%.
      >
      > When I open PTGUI (version 9.0.4) the automatic image alignment does not work. I have to define the control points manually. Then I create the pano and despite having the camera held manually the max. control point distance is only 5 pixels.
      >
      > However (took a pano of the interior of my flat) one of the door comes out ovalised, i.e. fat in the middle and some walls are bent. Even setting the centre of the image to the shooting height and rotating the pano so that it is horizontal does not help solve the problem. It turns out that PTGUI has detected the lens as circular fisheye with 12mm focal length.
      >
      > After setting the lens to rectilinear (normal) PTGUI generates a clean pano with no ovalised door. Strangely PTGUI shows 8.6mm focal length even if the lens was set to the wide end, which should be 8.0mm.
      >
      > Some questions:
      >
      > 1. Why isn't PTGUI able to automatically set the control points with this lens?
      > 2. Why does it select circular fisheye when the lens is rectilinear?
      > 3. Why does it compute erroneously the focal length (8.6 vs 8mm)?
      >
      >



      [Non-text portions of this message have been removed]
    • Cuffsmaster
      woops I was it was a sigma in the subject LOL ... [Non-text portions of this message have been removed]
      Message 2 of 13 , Aug 5, 2011
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        woops I was it was a sigma in the subject LOL


        On Aug 5, 2011, at 6:12 PM, alfred.molon wrote:

        > I bought this (rectilinear) lens for my APS-C DLSR and just out of curiosity tried to stitch two images taken at 8mm (12mm equivalent focal length in 35mm). These were two horizontal images, overlapping perhaps by 20%.
        >
        > When I open PTGUI (version 9.0.4) the automatic image alignment does not work. I have to define the control points manually. Then I create the pano and despite having the camera held manually the max. control point distance is only 5 pixels.
        >
        > However (took a pano of the interior of my flat) one of the door comes out ovalised, i.e. fat in the middle and some walls are bent. Even setting the centre of the image to the shooting height and rotating the pano so that it is horizontal does not help solve the problem. It turns out that PTGUI has detected the lens as circular fisheye with 12mm focal length.
        >
        > After setting the lens to rectilinear (normal) PTGUI generates a clean pano with no ovalised door. Strangely PTGUI shows 8.6mm focal length even if the lens was set to the wide end, which should be 8.0mm.
        >
        > Some questions:
        >
        > 1. Why isn't PTGUI able to automatically set the control points with this lens?
        > 2. Why does it select circular fisheye when the lens is rectilinear?
        > 3. Why does it compute erroneously the focal length (8.6 vs 8mm)?
        >
        >



        [Non-text portions of this message have been removed]
      • AYRTON
        Alfred, Sorry but why don t you try the PTGUI List ? Joost, the brain behind ptgui is there to answer all infos, with questions like: Why ptgui does this or
        Message 3 of 13 , Aug 5, 2011
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          Alfred,
          Sorry
          but why don't you try the PTGUI List ?

          Joost, the "brain" behind ptgui is there to answer all infos, with
          questions like: Why ptgui does this or that ?

          But for sure some guys here will be able to reply to you too with some infos

          best
          AYRTON


          On Fri, Aug 5, 2011 at 7:12 PM, alfred.molon <alfred.molon@...> wrote:

          > I bought this (rectilinear) lens for my APS-C DLSR and just out of
          > curiosity tried to stitch two images taken at 8mm (12mm equivalent focal
          > length in 35mm). These were two horizontal images, overlapping perhaps by
          > 20%.
          >
          > When I open PTGUI (version 9.0.4) the automatic image alignment does not
          > work. I have to define the control points manually. Then I create the pano
          > and despite having the camera held manually the max. control point distance
          > is only 5 pixels.
          >
          > However (took a pano of the interior of my flat) one of the door comes out
          > ovalised, i.e. fat in the middle and some walls are bent. Even setting the
          > centre of the image to the shooting height and rotating the pano so that it
          > is horizontal does not help solve the problem. It turns out that PTGUI has
          > detected the lens as circular fisheye with 12mm focal length.
          >
          > After setting the lens to rectilinear (normal) PTGUI generates a clean pano
          > with no ovalised door. Strangely PTGUI shows 8.6mm focal length even if the
          > lens was set to the wide end, which should be 8.0mm.
          >
          > Some questions:
          >
          > 1. Why isn't PTGUI able to automatically set the control points with this
          > lens?
          > 2. Why does it select circular fisheye when the lens is rectilinear?
          > 3. Why does it compute erroneously the focal length (8.6 vs 8mm)?
          >
          >
          >
          > ------------------------------------
          >
          > --
          >
          >
          >
          >


          --

          + 55 21 9982 6313 - RIO
          + 55 11 3717 5131 - SP
          http://ayrton360.com
          twitter.com/ayrton360


          [Non-text portions of this message have been removed]
        • alfred.molon
          I m sorry, but isn t this the PTGUI list? If not, where is this list? Is it a Yahoo group? Alfred
          Message 4 of 13 , Aug 6, 2011
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            I'm sorry, but isn't this the PTGUI list?

            If not, where is this list? Is it a Yahoo group?

            Alfred

            --- In PanoToolsNG@yahoogroups.com, AYRTON <avi@...> wrote:
            >
            > Alfred,
            > Sorry
            > but why don't you try the PTGUI List ?
            >
            > Joost, the "brain" behind ptgui is there to answer all infos, with
            > questions like: Why ptgui does this or that ?
            >
            > But for sure some guys here will be able to reply to you too with some infos
            >
            > best
            > AYRTON
            >
            >
            > On Fri, Aug 5, 2011 at 7:12 PM, alfred.molon <alfred.molon@...> wrote:
            >
            > > I bought this (rectilinear) lens for my APS-C DLSR and just out of
            > > curiosity tried to stitch two images taken at 8mm (12mm equivalent focal
            > > length in 35mm). These were two horizontal images, overlapping perhaps by
            > > 20%.
            > >
            > > When I open PTGUI (version 9.0.4) the automatic image alignment does not
            > > work. I have to define the control points manually. Then I create the pano
            > > and despite having the camera held manually the max. control point distance
            > > is only 5 pixels.
            > >
            > > However (took a pano of the interior of my flat) one of the door comes out
            > > ovalised, i.e. fat in the middle and some walls are bent. Even setting the
            > > centre of the image to the shooting height and rotating the pano so that it
            > > is horizontal does not help solve the problem. It turns out that PTGUI has
            > > detected the lens as circular fisheye with 12mm focal length.
            > >
            > > After setting the lens to rectilinear (normal) PTGUI generates a clean pano
            > > with no ovalised door. Strangely PTGUI shows 8.6mm focal length even if the
            > > lens was set to the wide end, which should be 8.0mm.
            > >
            > > Some questions:
            > >
            > > 1. Why isn't PTGUI able to automatically set the control points with this
            > > lens?
            > > 2. Why does it select circular fisheye when the lens is rectilinear?
            > > 3. Why does it compute erroneously the focal length (8.6 vs 8mm)?
            > >
            > >
            > >
            > > ------------------------------------
            > >
            > > --
            > >
            > >
            > >
            > >
            >
            >
            > --
            >
            > + 55 21 9982 6313 - RIO
            > + 55 11 3717 5131 - SP
            > http://ayrton360.com
            > twitter.com/ayrton360
            >
            >
            > [Non-text portions of this message have been removed]
            >
          • Erik Krause
            ... No, this is a more general list about panoramas. However, your question is well on topic here. Your problem: PTGui should be very well able to stitch those
            Message 5 of 13 , Aug 6, 2011
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              Am 06.08.2011 09:32, schrieb alfred.molon:
              > I'm sorry, but isn't this the PTGUI list?

              No, this is a more general list about panoramas. However, your question
              is well on topic here.

              Your problem: PTGui should be very well able to stitch those fisheye
              images, but it's no good idea to start with handheld shots of a room
              with an uncalibrated lens. The fact it didn't find control points
              indicates that there might be too large parallax errors. If you set few
              control points manually PTGui might distort the images such that the
              control points fit which causes heavy deformations in some areas.

              > If not, where is this list? Is it a Yahoo group?

              No, it's a google group: http://groups.google.com/group/ptgui

              --
              Erik Krause
            • Erik Krause
              ... Sorry, I was too fast. Just read this is a rectilinear. In this case PTGui most likely assumed it is a fisheye lens, due to the short focal length. Set it
              Message 6 of 13 , Aug 6, 2011
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                Am 06.08.2011 09:44, schrieb Erik Krause:
                > PTGui should be very well able to stitch those fisheye
                > images,

                Sorry, I was too fast. Just read this is a rectilinear. In this case
                PTGui most likely assumed it is a fisheye lens, due to the short focal
                length. Set it to rectilinear manually (uncheck automatic) on Project
                Assistent tab and you should get much better results.

                --
                Erik Krause
              • alfred.molon
                Indeed if I set the lens to rectilinear, PTGUI finds automatically the control points and the pano looks quite decent. However in the first run it sets all
                Message 7 of 13 , Aug 6, 2011
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                  Indeed if I set the lens to rectilinear, PTGUI finds automatically the control points and the pano looks quite decent.

                  However in the first run it sets all control points in the central part of the image and calculates 9.6mm focal length.

                  After adding control points at the borders of the overlaps it recomputes the focal length as 8.6mm.

                  That is still not completely correct (the focal length should be 8mm). I wonder if this mistake comes from the manual shooting, although the max. control point deviations are small (max 8 pixels).

                  Alfred

                  --- In PanoToolsNG@yahoogroups.com, Erik Krause <erik.krause@...> wrote:
                  >
                  > Sorry, I was too fast. Just read this is a rectilinear. In this case
                  > PTGui most likely assumed it is a fisheye lens, due to the short focal
                  > length. Set it to rectilinear manually (uncheck automatic) on Project
                  > Assistent tab and you should get much better results.
                • Fernando Chaves
                  ... Hi, 1)Calculation method in Ptgui and Sigma are probably not the same. I would t worry about this. You can make some test images shooting brick walls, or
                  Message 8 of 13 , Aug 6, 2011
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                    alfred.molon wrote:
                    > Indeed if I set the lens to rectilinear, PTGUI finds automatically the
                    > control points and the pano looks quite decent.
                    >
                    > However in the first run it sets all control points in the central part of
                    > the image and calculates 9.6mm focal length.
                    >
                    > After adding control points at the borders of the overlaps it recomputes
                    > the focal length as 8.6mm.
                    >
                    > That is still not completely correct (the focal length should be 8mm).

                    Hi,
                    1)Calculation method in Ptgui and Sigma are probably not the same. I
                    would't worry about this.
                    You can make some test images shooting brick walls, or any other regular
                    pattern, load them in Ptgui, fix all problem, remove bad control points,
                    etc, optimize and stitch. Then you save your 8~15 lens in the lens
                    database ("Lens settings" tab) and load it the next time you need.
                    You can find lots of information on Ptgui website and list.
                    2)What's your opinion about this lens? Is this good, bad, very good? Are
                    happy with your purchase?

                    Best regards,
                    Fernando
                  • Hans
                    ... Alfred This is normal for all lenses, especially zoom lenses. When Sigma gives you the numbers 8-16 it is just an approximate. There is no correct way of
                    Message 9 of 13 , Aug 6, 2011
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                      --- In PanoToolsNG@yahoogroups.com, "alfred.molon" <alfred.molon@...> wrote:
                      >
                      > Indeed if I set the lens to rectilinear, PTGUI finds automatically the control points and the pano looks quite decent.
                      >
                      > However in the first run it sets all control points in the central part of the image and calculates 9.6mm focal length.
                      >
                      > After adding control points at the borders of the overlaps it recomputes the focal length as 8.6mm.
                      >
                      > That is still not completely correct (the focal length should be 8mm). I wonder if this mistake comes from the manual shooting, although the max. control point deviations are small (max 8 pixels).

                      Alfred

                      This is normal for all lenses, especially zoom lenses.
                      When Sigma gives you the numbers 8-16 it is just an approximate.

                      There is no correct way of calculating a lens focal length as it depends much on how the lens is built and how it is used.
                      The Canon 15mm for example gives me
                      an optimized focal length of 15.47mm as fullframe crop and 15.6 with circular.

                      Hans

                      >
                      > Alfred
                      >
                      > --- In PanoToolsNG@yahoogroups.com, Erik Krause <erik.krause@> wrote:
                      > >
                      > > Sorry, I was too fast. Just read this is a rectilinear. In this case
                      > > PTGui most likely assumed it is a fisheye lens, due to the short focal
                      > > length. Set it to rectilinear manually (uncheck automatic) on Project
                      > > Assistent tab and you should get much better results.
                      >
                    • John Houghton
                      Alfred, Go to Tools- Options- EXIF which details the rules for deciding whether to use rectilinear or fisheye. Adjust the parameters so that you get the
                      Message 10 of 13 , Aug 6, 2011
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                        Alfred, Go to Tools->Options->EXIF which details the rules for deciding whether to use rectilinear or fisheye. Adjust the parameters so that you get the appropriate choice for your lens.

                        You will get more accurate values for the lens parameters if you shoot a full 360 degree panorama and rotate the camera about the entrance pupil of the lens (no-parallax point). This will avoid parallax distorting the parameter values. Be sure to include the lens shift parameters in the optimization (by selecting "heavy+lens shift" on the "Minimize lens distortion" field.

                        John

                        --- In PanoToolsNG@yahoogroups.com, "alfred.molon" <alfred.molon@...> wrote:
                        >
                        > Indeed if I set the lens to rectilinear, PTGUI finds automatically the control points and the pano looks quite decent.
                        >
                        > However in the first run it sets all control points in the central part of the image and calculates 9.6mm focal length.
                        >
                        > After adding control points at the borders of the overlaps it recomputes the focal length as 8.6mm.
                        >
                        > That is still not completely correct (the focal length should be 8mm). I wonder if this mistake comes from the manual shooting, although the max. control point deviations are small (max 8 pixels).
                        >
                        > Alfred
                        >
                        > --- In PanoToolsNG@yahoogroups.com, Erik Krause <erik.krause@> wrote:
                        > >
                        > > Sorry, I was too fast. Just read this is a rectilinear. In this case
                        > > PTGui most likely assumed it is a fisheye lens, due to the short focal
                        > > length. Set it to rectilinear manually (uncheck automatic) on Project
                        > > Assistent tab and you should get much better results.
                        >
                      • Erik Krause
                        ... You should know that PTGui will change all parameters you allowed to optimize in order to match the control points as good as possible. If you have only
                        Message 11 of 13 , Aug 6, 2011
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                          Am 06.08.2011 16:53, schrieb alfred.molon:

                          > That is still not completely correct (the focal length should be
                          > 8mm). I wonder if this mistake comes from the manual shooting,
                          > although the max. control point deviations are small (max 8 pixels).

                          You should know that PTGui will change all parameters you allowed to
                          optimize in order to match the control points as good as possible. If
                          you have only few control points chances are high that PTGui will find a
                          good fit (small maximum error), but this doesn't necessarily mean that
                          you don't get visual stitching errors. From handheld shots you can't
                          tell anything about a lens.

                          Even in a panorama shot precisely from the no-parallax-point the
                          calculated focal length can differ significantly from the nominal focal
                          length.

                          What PTGui needs to know for it's calculations is not the focal length
                          but the field of view. It might be surprising, but the focal length and
                          the field of view are only loosely related, even if the sensor size is
                          precisely known (which isn't the case most of the time). Influencing
                          factors are focusing distance and lens distortion - not to speak from
                          manufactoring tolerance.

                          It's even worse for fisheye lenses, where an identical lens is sold
                          under different labels and with a "focal length" from 6.5mm to 8mm.
                          There is no agreed on formula to calculate the focal length for fisheyes...

                          --
                          Erik Krause
                        • alfred.molon
                          The amazing thing is this extremely wide angle of view. No other lens for APS-C cameras is as wide. The quality is high, both for what concerns the optics and
                          Message 12 of 13 , Aug 7, 2011
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                            The amazing thing is this extremely wide angle of view. No other lens for APS-C cameras is as wide.

                            The quality is high, both for what concerns the optics and the build.

                            However I'm still learning how to use such a beast. For years I didn't care about extreme wide angle lenses, because I could achieve whatever angle of view with pano stitching, but this lens is a new avenue to photography. Instead of guessing what kind of shot you will get (as is the case with pano stiching), you can precisely frame and immediately see what the end result is.

                            And once again, those 8mm are really amazing.

                            Alfred

                            --- In PanoToolsNG@yahoogroups.com, "Fernando Chaves" <fc@...> wrote:
                            >
                            > 2)What's your opinion about this lens? Is this good, bad, very good?
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