3. Focus the image with extreme care. While observing the subject through the camera's reflex viewfinder, turn
the ETX-90EC's focus knob (9, Fig. 1) to achieve the sharpest possible focus. Note that some 35mm
cameras may have an optional focusing screen (available from the manufacturer) for use with a long
telephoto lens. This screen provides a brighter and clearer image to focus and is highly recommended.
4. Correct shutter speeds vary widely, depending on lighting conditions and film used. Trial-and-error is the
best way to determine proper shutter speed in any given application.
NOTE: The camera used with the ETX-90EC may have a built-in exposure meter that is still active
when the standard lens is removed and the body is connected to the telescope with the T-Mount. If
used for terrestrial photography, the camera meter should be acceptable. If used for
astrophotography, the meter probably will not provide good results since camera meters are not
made to compensate for a dark sky.
5. Terrestrial photography through the ETX-90EC is sensitive to heat waves rising from the earth's surface.
Long distance photography is best accomplished in the early morning hours before the earth has had time
to build up heat.
6. Photography of the Moon and planets through the ETX-90EC can be especially gratifying, but points 1
through 4 should be particularly noted in this case. Lunar or planetary photography requires that the
telescope be polar aligned (see
Polar Alignment Procedure
), and that the telescope's motor drive be in
operation (see
Electronic Controller Modes
).
NOTE: Long exposure photography of deep-sky objects is not practical with the ETX-90EC, since this type
of photography requires special electronic and optical guiding devices not available for this telescope.
Fig. 20: Example of Format 1 Photo
(1250mm).
Fig. 21: Example of Format 2 Photo
(1450mm).
