Orion 52084 Choosing a Site for Astro-imaging, Using Focal Reducers and Barlow Lenses

5.If the star drifts north, the telescope mount is pointing too far west. If the star drifts south, the telescope mount is pointing too far east. Determine which way the star drifted and make the appropriate correction to the azi- muth position of the mount. Rotate the entire mount (and tripod) slightly east or west as needed or use the azimuth adjustment knobs (if your mount has them) to make fine adjustments to the mount’s position.

6.Next, point the telescope at a bright star near the eastern horizon and near the celestial equator (Dec. = 0).

7.Let the telescope track for at least five minutes, and the star should begin to drift north or south.

8.If the star drifts south, the telescope mount is pointed too low. If the star drifts north the telescope mount is pointed too high. Observe the drift and make the appropriate correction to the mount’s altitude (or latitude); most mounts have some sort of fine adjustment for this.

Repeat the entire procedure until the star does not drift significantly north or south in the eyepiece. When this is accomplished, you are very accurately polar aligned, and should be able to produce good (unguided) images of up to several minutes long, assuming the mount’s drives track well with little periodic error.

Choosing a Site for Astro-imaging

Once you have a focused image, you may find your image shifting and washed out. This can be caused by many environmental factors. Poor seeing (move- ment of molecules in the air, such as heat rising) and poor transparency (mois- ture, smoke, or other sky contaminants) will all serve to reduce image quality. That is why most major astronomical telescopes are on high mountains in thin air, to get above much of the transparency and seeing problems. Also, wind will move your telescope and affect images. Your eyes viewing through an eyepiece can change slightly to compensate for disturbances like these, but the camera can not. Keep these factors in mind when choosing an observing site for astronomical imaging.

For the best astro-images, we recommend finding a location with dry air, some altitude, and away from city or streetlights. Even a nearby hilltop in the coun- tryside can provide better viewing conditions than many convenient backyard locations.

Using Focal Reducers and Barlow Lenses

Focal reducers and barlow lenses change the effective focal length of a tele- scope. These lenses are inserted between the camera and telescope when imaging to change image scale.

Focal reducers serve to decrease the focal length of your telescope. This increases the field of view seen by the camera (decreases camera magnifi- cation). This can be very useful for obtaining images of wide-field deep sky

40