eyepiece proyection

Manuel,

Eyepiece projection is usually termed variable eyepiece projection if you have the correct adaptor. Your first consideration is if the eyepiece will fit inside the projector adaptor. After that choice is made; you are down to focal length and eye relief. A medium focal length works best (easiest) and keeps effective focal length to a manageable level. If using film, your image size will be significant and shorter focal lengths are appropriate. If using a CCD or webcam, the image scale will be small but appear magnified when viewed on your computer.

Start with as long a focal length as practical and pay strict attention to vibration. With a film camera, one which has a mirror lock will be helpful, but any form of mechanical shutter dramatically increases chances of vibration. As a rule of thumb, you cannot hand hold a camera whose focal length in mm is greater than the shutter speed in hundredths of a second. Example: you should not hand hold a 35mm camera with a 250mm focal length lens for any shutter speed less than 1/250th of a second. Using a tripod allows shutter speeds 2-4 times slower. So, if you use eyepiece projection at f90 (typical with eyepiece projection) on a 200mm diameter scope, your effective focal length is 18,000mm. This will magnify any vibration immensely, so a steady mount and complete stillness of the astronomer is an absolute must along with as short an exposure which will capture the desired level of detail is essential. It’s not easy, but obviously some folks are able to achieve it.

Oh yea, great seeing is essential for success. Hope this helps