PHOTOGRAPHY WITH THE ETX-90EC
Photography through the ETX-90EC requires the addition of the optional #64 T-Adapter (see
OPTIONAL
ACCESSORIES
). With the #64 T-Adapter attached to the telescope (Fig. 19), through-the-telescope photography is
possible with any 35mm camera body with a removable lens. In this way the telescope effectively becomes the lens
of the camera.
For through-the-telescope photography, turn the flip-mirror control, (5, Fig. 19) to the "down" position, allowing light
to pass straight through the telescope and out the photo port (17, Fig. 1). With the flip-mirror control in the "down"
position and the photo port's dust cover removed, the front lens of the telescope can be seen when looking through
the photo port. The #64 T-Adapter threads on to the photo port, followed by a T-Mount for the particular brand of
35mm camera being used, followed in turn by the camera body itself (with camera lens removed).
Note that the #64 T-Adapter consists of two sections (1 and 2, Fig. 19) which
are threaded together in shipment. Either of the following photographic
mounting formats may be used to couple the camera body to the telescope's
photo port thread.
•
Format 1
(1250mm focal length):
Camera Body + T-Mount + Section
(1) of the #64 T-Adapter (7, Fig. 19).
Format 1 utilizes the short
section only of the #64 T-Adapter to permit close-coupling of a
camera body to the telescope at an effective photographic speed of
f/14 and a transmission value (the so-called "T"-value) of 18. In this
format vignetting will occur: the photographic image will appear on
film with a slight darkening at the corners of the 35mm frame (see
Fig. 20).
•
Format 2
(1450mm focal length):
Camera Body + T-Mount +
Sections (1) and (2) of the #64 T-Adapter (see Fig. 19).
Format 2 utilizes both sections of the #64 T-Adapter
threaded together to form a rigid unit as shown in Fig. 19, the telescope is operating at a photographic
speed of f/16 and T-value of 23, but without any field vignetting: images are illuminated to the edges of a
standard 35mm frame (see Fig. 21).
To frame an object in the viewfinder of the 35mm camera body, loosen slightly the knurled ring (3, Fig. 19) which
threads the #64 T-Adapter to the telescope's photo port; rotate the camera body to achieve proper framing of the
object; then re-tighten the knurled ring.
Photography through a long lens such as the ETX-90EC requires special technique for good results, and the
photographer should probably expect to waste a roll or two of film in acquiring this technique. Long-lens
photography has its own rewards, however; rewards that short-focus lenses can not duplicate.
A few tips on photography through the ETX-90EC:
1. Use a rigid tabletop or the optional
#883 Deluxe Field Tripod
as a platform for the telescope. At effective
focal lengths of 1250mm (Format 1) and 1450mm (Format 2), even small external vibrations can easily ruin
an otherwise good photo.
CAUTION: With the #64 T-Adapter and a camera body mounted to the ETX-90EC photo port, the
telescope can only be rotated vertically 45°. Moving past this point may damage the telescope and
camera.
2. Use a cable-operated shutter release. Touching the camera body to initiate shutter operation will almost
certainly introduce undesirable vibrations.
Fig. 19: Using the #64 T-Adapter. (1) Short
Section of #64 T-Adapter; (2) Extension Section
of #64 T-Adapter; (3) Knurled Attachment Ring;
(4) T-Mount; (5) Flip-Mirror Control in "down"
position; (6) 35mm Camera Body; (7) Inset
shows Format 1.
