8 Replies Latest reply: Sep 24, 2010 5:48 PM by simonsaith RSS

    What to do when 1 x Minimum Distance is too close

    grampus45 Community Member

      The guidelines suggest 1, 2, and 5 x Minimum Distance for focal distances.  With the 14-42mm on the Olympus E-510, the minimum distance at 42mm is about 4 inches, and at that distance only a small fraction of the target completely fills the view finder.  How, pray tell, is one supposed to take 9 separate images, each of which fills no more than 1/2 the field?  What is the proper procedure for this situation?

       

      thanks, grampus45

        • 1. Re: What to do when 1 x Minimum Distance is too close
          MadManChan2000 Adobe Employee

          A couple of options. One is that you can print the target at a smaller size. Another is that if you never practically use the lens at such close focus, then don't bother building the profile for that setup, either.

          • 2. Re: What to do when 1 x Minimum Distance is too close
            grampus45 Community Member

            Thanks, Eric.  If, however, one prints the target at a smaller size, what sort of point information should one input in the software?  Should one use the same information as is on the target, or should one scale it to the same degree as the reduction in size?

             

            If one doesn't reduce the target, but pulls back (significantly) to make the target fill a reasonable portion of the view finder, what are the various distances that should then be used? Should that distance now be considered the 1 x? and then use 2 and 5 x that distance (which might start to get very long)?

             

            thanks, grampus45

            • 3. Re: What to do when 1 x Minimum Distance is too close
              phototrek Community Member

              I have never printed targets to scale. Rather, I pick a target that's about right, print / mount it, and then I measure the actual size of the squares in points. The size of the target "in squares" is still the same, and from the measured size of the squares the software will actually do the right thing.

              • 4. Re: What to do when 1 x Minimum Distance is too close
                James Patmore Community Member

                That doesen't make sense in terms of the original question.  The questioner asked about sizes outside the PDFs offered by Adobe.Essentially, he needs a new size target. A previous answer suggests scaling an existing target. I believe when entering data into the program one enters the numbers of squares and their pixel size without entering data which identifies the originating chart? Presumably when one comes to print the chart from the pdf file one chooses a set of dimensions that is appropriate. I am in the same boat as the original questioner and cannot get small enough charts. Couldnt Adobe add a few more charts with the charts themselves placed on a larger background say A4 (for europeans)so as not to give rise to problems on smaller paper?

                • 5. Re: What to do when 1 x Minimum Distance is too close
                  grampus45 Community Member

                  Phototrek and James.  Thanks to you both (and to Eric).  Yes, I think I've got this straight now.  I can get a target that is the proper size at close range (very near minimum focus distance) with full zoom to allow a full 9 shots at roughly 1/3 viewfinder coverage if I reduce the 9 x 15 at 36 points by 1/4 during printing.  The resulting target is 9 x 15 at 9 points, and that's what I assume is the proper software input.  Thanks again,

                  • 6. Re: What to do when 1 x Minimum Distance is too close
                    MadManChan2000 Adobe Employee

                    Hi, if you print the targets smaller, then scale down the size entered into ALPC's "Print Dimension" field accordingly. For example, if the original target print dimension in the PDF says 36 pt, but you print it at 50% (i.e., half the size in each dimension), then enter 18 pt into the Print Dimension field in ALPC.

                     

                    Ultimately, this info is used to estimate the focus distance.

                    • 7. Re: What to do when 1 x Minimum Distance is too close
                      James Patmore Community Member

                      I wish it were that simple! I chose the smallest target I thought was appropriate which had dimensions of 6" x 9". I loaded this into Photoshop. I then scaled the image (now reported in Metric) to 9 cm on the longest side, constraining proportions. I then increased to canvas size to A4 so the chart sits neatly in the middle. Do I calculate the new point size dividing the original chart size by 2.54, or by measurement? In either case, one is likely to have fractions of a point. Will the program accept a non integer as a valid entry? Couldn't Adobe give us a few smaller targets to work with? If there is distortion on a lens it is likely to be more severe the closer one gets.

                      • 8. Re: What to do when 1 x Minimum Distance is too close
                        simonsaith Adobe Employee

                        Hi James,

                         


                        The PDF charts that shipped with the ALPC are in Adobe Illustrator file format. It is a lot easier (for me at least) to transform things in vector format. That said, whatever scaling you did and maybe additional scaling during print, you can determine the "Print Dimension" of square on the printout by phyiscally measure the square using a ruler. As Eric said the value only affect the focus distance estimation for the profiles.

                         

                        Hope this helps,

                         

                        -Simon