Heydes Actino photometer User manual

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Heydes Facile Actino_photometer.
     He.yde's Actino-photoneter  consists of a small
 rnagnalium box in   tr.l,o
 rvithin the other, u,ith   iilil:.""1;::1*:: In the interior of the box", is a pdsrn of a special
 kind of blue glass. The color of the glass is
 graftrated in intensity, anci b-y the rotalion of
the box front first frorn the lightest to the dar-
kest shade can be brought before the eyepiece.
For clouds, seascapes.and the pfrotogrupiing of
glaciers, etc., a further darkening oi trr" pi"-
may be necessary and for this purpose a colo"ed
glass can, by moving a knob on the front of
the instrument, be brought in front of the prism.


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              lnstructions for the use of HeYdes
                    Actino-Photometer.
             Turn the box so that the index stands at O,
          and see that the supplementary colored glass is
            not in position (in front of prism). Observations
            through the Actino but slightly reduce the inten'
              sity of the light prevailing at the time.
               Determine in which part of the subject lies
            the principal interest of the picture, and therefore
            requires the correct exposurel should it  for
            example be a portrait in rvhich detail is required
             in both the high lights and the shadows, obser-
            vation should be made not upon the brightest
             portions but oPon the shadorvs.
               Speaking generally it  will be found to be
           always advantageous to direct the Actino upon
             the deeper shadows in order that these may be
             adequately exposed, as the instrument can only
             give the correct exposure for the portion of the
              subject selected for observation.



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The instrument is now held with one hand
              before the right eye, the other being closed to cut oft
            the extraneous light. The selected shado.w por-
             tion of the subject, which at zero should appear
             clear and distinct, is now observed, and the box
             rotated untii   it becomes indistinct.  Now
           read off the number given in the upper row in
           the index aperture. If the number 10 has been
            reached and the picture still remains clear, the
             scale is returned to zero and the supplementary
            glass brought into position by means of the knob
         on the front of the instrument. Observation is
          once more made, but the under scale is now
            read (10-20). In the summer (also in the tropics)
           box is turned until the object is but just visible.
                   If still greater accuracy be desired,. the in-
          strument is directed upon the subject and the
           index set to -t0 or 20. The box is then slowly
           revolved until the object becomes distincily
           visible: the index is now read off, and the
       mean between this number and that obtained
        by the previous method of procedure taken as
           the exposure number,





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          On reference to the tables engraved on the
            insttument the exposures required for the different
          numbers of the following apertures f/8,  fi 11.3,
                fi16,  f i22.6, fl32 and fl45.2 can be immediately
          seen. The exposures for the other apertures in
            general use are given in the tables ptinted on
           pages 12-15.
           By first taking the number u'hen the object
            becorres indistinct and then reversing the opera-
           tion and noting the nunber when the object
           becomes distinct, and accepting the mean as the
             real exposure number, so great an accuracy  is
            obtained that repeated tests will scarcelv produce
         an alteration. With practice  it  lvill be found
            that a single test is suflicient. A glance at the
            tables shows that a ciifference of even trvo of
            the figures is scarcely of irnportance unless very
           dark objects are under consideration, but with
            these the possibility' of over-exposure may be
              excluded.
            The methocl of using the instrument is very'
             simple. and the result so reliable, that whoever




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has once used the Actino will dispense rvith it
 with difficulty. Those using spectacles
 will  find  it advantageous to have the
.cover glass replaced by a similar lens to
 that fitted in their spectacies, rvhich can
 be done b.v any optician at a small cost.
   The exposures indicated by the Actino-
 m e ter are for plates or {ilms o f 2b                                            0 Wa rn e rke
 (H. & D 160). For plates of 220 Warnerke
 (H. & D 80) the indicated exposures should be
 doubled, and for those of 2i 1/s0 W. (H. & D 2,10)
halved. For snowscenes, clouds or sea-
 scapes it will be found better to err on the side
 of under-exposure, and the indicated exDosufe
should be halved. The same rules apply
also when objects at a greater distance than
i000 yards from the camera are bbing photo_
graphed and the number exceeds 11.
   Should the lower readings of the index be
between two numltbrs the exposure (the mean
between the two) can without difficultv be calcu-
lated. Tt should, however, be remarked that with

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            dark objects ra'hich give a reading under 4, the
           lower number can be adopted without fear of
            ovef exposufe. The amateur must of course be
            acquainted with the apertures of his lens, and
            also with the speeds of his shutter, information
            concerning which can be had from the makers
             of the camera.
            The exposures indicated by the Actinometer
            are always for light, rich in violet or ultra violet
             rays, such as daylight, the electric arc light and
          magnesium light. For other sourges of illumi-
            nation, gazlight for instance, the spectrum of
           which are deficient in there rays and are there-
             fore not most suited for photographic purposes,
            the indicated exposures should be multiplied six
              times.
                               Examples.
                      1 st. Photograph of a woodland landscape
           with bright foreground, right side shade, left
              side sunny. The shady part, irl which lids the prin-
              cipal interest of the picture must be clear and
             well defined on the negative.. The Actino being




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             set at zero, the darker portion is obscured so
I           thatmenttheis thentrees directedappear justupondistinct.a dark objectThe instru-on the
           sunny side. The mean of the two numbers is'I          then taken and the exposure for the desired stop
             read off. As the subject of the picture is the trees
             lying in heavy shadow choose a somewhat iower
           number than the mean and expose accordingly.
               Suppose the trees give the reading 7 and the
              sunlit meadow in the foreground 15, the mean
             is  1 1.  It will, however, be better to expose
               for 9 and so obtain greater detail in the shadows.
             2d. Photography of distant objects. The
             Actino-Photometer should be revolved until the
           horizon (mountain tops etc.) is no longer
            visible. For those subjects in which no object
            in the distance can be seen clearly with the eye,I            especially in hazy weather, a well iiluminated
              object as distant as possible, but still clear and
              distinct to the eye should be selected as the
            point of observation and the instrument rotated
              until this becomes indistinct.

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                    3 d.  Portraitu re  in the open air.  For
          such subjects proceed exactly as described in
           our first example. Select the darkest portion of
            the face or head in which it is desired to have
               detail and direct the Antinometer upon this.
              4th.  Portraiture in a room. With this
           branch of photography amateurs experience the
            greatesi difficulty. The sitter should be so
           placed that the light from the window can be
               distinctl-v seen upon the shadou,y portion of the
         head. The Actinometer is used in the same
           manner as previously described, the photographer
            standing by the side of the camera .when usins
            the instrument.





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                  Note.
 1. Always direct the instrument upon the
   darkest portion of the subiect which is to
   have detail in the negative.
 2. Set the Actinometer at zero before using  it.
3. Should the object be still distinct when the
   No. 10 is reached, return the index to zero
  and by the knob on the front of the instru-
  ment bring the supplementary colored glass
   beforetheprismandreadthe  scale from 10to20.
4. For Telephotography  (objects more than
   1000 yards distant) all exposures obtained
  by readings over 11 should be halved.
5. For instantaneous exposur€s of  street
   scenes, the Actinometer will give the correct
   exposure, but a bright object should be
   chosen for observation.
             Gustav Heyde,
                            Dresden.



            Printed by R. Lincke, Dresden.

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