Guidelines for SetRise Tool^®

The SetRise Tool^® is used in the following way:

1. Preparing your SLR camera

Turn your SLR camera up side down and remove the lens. You should now be able to see the downside of the prism, thought which one normally looks. This is most of the time a matte surface and one can sometimes see the scales for the exposure time or other things.
Downside of prism in an Olympus OM10
2. Creating a cutting template for the slides

Cut the EMPTY slide in such a way that it fits above the prism. Usually you can cut away the green part, but start with fewer cuttings so that you can create a template for cutting the other slides.
EMPTY slide on the prism
3. Calibrating the focal length of the lens

If you have a fixed focal length lens of 50 or 55 [mm], one can assume that it is calibrated accurately enough. So go to the next step.
In case one has a zoom lens the following procedures can help calibrating the zoom lens at 50 [mm]:
• Installing calibration slide

Cut the CALIBRATION slide (15° as function of focal length F) slide in the same way as the EMPTY slide (so that it fits on the prism).
CALIBRATION slide
If you don't have the slide:
print this picture at 208 pixels/cm on acetate foil.

Put the calibration slide on the prism. Keep the camera upside down while attaching the lens. Look through the eye piece (camera still upside down!). In principle one should see a normal camera view with the calibration slide overlaying it.


Calibration slide overlaying the normal camera view
• Finding a reference object and camera location

We now have to determine a reference object that will have a width comparable to an 15° angle-of-view from the  camera lens. Find an object with in width of around 3 m (like a window sill, two vertical poles, part of a house, etc.), and measure its width as accurate as possible. The camera lens must be located at: width-of-reference-object * 3.8 [m] from the reference object. So if the window sill width is 3,05 [m], the distance of the lens to the window sill must be 11,58 [m] (3,05 * 3.8).
Width: [m]
the distance: [m]

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• Checking the focal length of the lens

The reference object must now be viewed through the camera (camera still upside down). Now position the reference object in such a way in the camera view that it is just between the two angled lines, while keep the distance the same!. One can read now the actual focal length of the lens from the scale (the red numbers and the additional 5 [mm] blocked steps).
For using the SetRise Tool^® the focal length should be between 50 and 55 [mm], otherwise you need to get another SetRise Tool^®.
4. Explanation of the other slides

Cut all the other slides in the same way as the EMPTY slide was cut. These slides (SUMMER..., EQUINOX, and WINTER...) have all comparable layouts:
• two azimuth scales (depending on the slide),
• an apparent altitude scale (between 0° and 10°) and
• a latitude series (between 50° and 60°).
Azimuth
The azimuth scale can be seen for RISE (normal way to put the slide on the prism) and SET (by turning the slide upside down on the prism).
The green azimuth lines are at:

Season	RISE	SET
SUMMER...	50°	310°
EQUINOX	95°	265°
WINTER...	145°	215°

The green azimuth line can be determined with the compass.
Don't forget to compensate the compass reading with the difference between magnetic and true north:
magnetic azimuth = green azimuth - difference magnetic and true north
                                                    (east is positive and west is negative)
Green azimuth: [°]
Difference magnetic and true north: [°](east is + and west is -)
the magnetic azimuth: [°]

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Or when using information from a map:
magnetic azimuth = green azimuth - difference magnetic and map north + difference true and map north
                                                    (east is positive and west is negative)
Green azimuth: [°]
Difference magnetic and map north: [°](east is + and west is -)
Difference grid and true north: [°](east is + and west is -)
the magnetic azimuth: [°]

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Apparent altitude
The green apparent altitude line is the 0° apparent altitude reference line (the 0° has to be determined with a hand level).
Latitude
The latitude can be determined by map or GPS.
5. Aligning the slides

For the phenomena one wants to study, one takes the appropriate slide and puts it on the prism (like done with the EMPTY slide). After one has determined the green azimuth and green 0° apparent altitude line in the real world, one points the camera in such a way that the green lines of the slide are over the real green world directions. Now one can see in the camera where the first/last gleam of the sun/moon around 2250 BCE would have be seen: at the point where the actual latitude line crosses the real horizon.
6. Storing the slides

To keep your slides tidy (dust and so on are bad for the internals of the SLR camera!), put them in a plastic film containers (these are easy to carry and water proof).