Handleiding Meade ETX-105AT (pagina 41 van 60) (Engels)

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Photography through a long lens, such as the ETX, requires special technique for

good results. The photographer should expect to use several rolls film in acquiring this

technique. Long-lens photography has its own rewards, however, which short-focus

lenses cannot duplicate.

A Few Tips on Photography

1.Use the standard tripod or the optional table tripod ( see OPTIONAL ACCESSORIES,

page 43) as a platform for the telescope. At effective focal lengths of 1250mm to

1450mm (ETX-90AT), 1640mm to 1830mm (ETX-105AT) or 1900mm to 2310mm

(ETX–125AT), 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

photo port, the telescope can be rotated vertically only 45°. Moving past this

point may damage the telescope and camera.

2. Use a cable-operated shutter release with your camera. Touching the camera body

to operate the shutter will almost certainly introduce undesirable vibrations.

3. Focus the image with extreme care. While observing the subject through the

camera’s reflex viewfinder, turn the ETX's focus knob (

8, 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 an ETX model may have an 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 an ETX model 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 an ETX model 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

EQUATORIAL (POLAR) ALIGNMENT, page 51).

Note: Long-exposure photography of deep-sky objects is not practical with

an ETX model, since this type of photography requires special electronic and

optical guiding devices not available for this telescope.

Photography with a Digital Camera

Although digital cameras still cannot match the quality of images provided by

traditional 35mm cameras, they provide some significant advantages to the casual

astrophotographer: You do not have to develop the images (instant images), lower

costs, computer and internet readiness. And because unwanted photos are easily

discarded, they provide the freedom to experiment.

Digital cameras present some problems for the astrophotographer: Many models

have lenses that cannot be removed, difficulties in attaching to a telescope, possible

vignetting, lack manual focusing and shorter exposure times.

Shorter exposure times is one of the biggest drawback. Long exposures with digital

cameras introduce undesirable noise and artifacts into a digital image. This limits the

range of astro images to the Moon, planets and bright stars.

Some tips for better photos:

• If you cannot remove the lens to your camera, look for a commercially available

digital t-adapter. New solutions for attaching a digital camera to a telescope are

becoming available as time goes by.

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