49
Does the PEC function make unguided astrophotography possible? Yes and no. For solar (filtered), lunar, and piggyback (up
to 200mm), the answer is yes. However, even with PEC, off-axis guiding is still mandatory for long exposure, deep sky
astrophotography. The optional Reducer/Corrector lens reduces exposure times making the task of guiding a little easier.
Terrestrial Photography
Your
telescope makes an excellent
telephoto lens for terrestrial (land) photography. Terrestrial photography is best done
will the telescope in Alt-Az configuration and the tracking drive turned off. To turn the tracking drive off, press the MENU
(9) button on the hand control and scroll down to the Tracking Mode sub menu. Use the Up and Down scroll keys (10) to
select the Off option and press ENTER. This will turn the tracking motors off, so that objects will remain in your camera's
field of view.
Metering
The CGE Pro Series telescope has a fixed aperture and, as a result, fixed f/ratios. To properly expose your subjects
photographically, you need to set your shutter speed accordingly. Most 35mm SLR cameras offer through-the-lens metering
which lets you know if your picture is under or overexposed. Adjustments for proper exposures are made by changing the
shutter speed. Consult your camera manual for specific information on metering and changing shutter speeds.
Reducing Vibration
Releasing the shutter manually can cause vibrations, producing blurred photos. To reduce vibration when tripping the shutter,
use a cable release. A cable release keeps your hands clear of the camera and lens, thus eliminating the possibility of
introducing vibration. Mechanical shutter releases can be used, though air-type releases are best.
Blurry pictures can also result from shutter speeds that are too slow. To prevent this, use films that produce shutter speeds
greater than 1/250 of a second when hand-holding the lens. If the lens is mounted on a tripod, the exposure length is virtually
unlimited.
Another way to reduce vibration is with the Vibration Suppression Pads (#93503). These pads rest between the ground and
tripod feet. They reduce the vibration amplitude and vibration time.
CCD Imaging
SCT telescope's versatility allows it to be used in many different f-number configurations for CCD imaging. It can be used
at f/6.3 (with the optional Reducer/Corrector), f/10, and f/20 (with the optional 2x Barlow) making it the most versatile
imaging system available today. This makes the system ideal for imaging deep-sky objects as well as planetary detail.
The key factors for good CCD imaging are; exposure time, field-of-view, image size, and pixel resolution. As the F/# goes
down (or gets faster), the exposure times needed decreases, the field-of-view-increases, but the image scale of the object gets
smaller. What is the difference between f/6.3 and f/10? F/6.3 has about 2/3 the focal length of f/10. That makes the exposure
time needed about 2.5 times shorter than at f/10, the field of view 50% larger compared to that of f/10. (see Table below)
