Updated: 6.23.03

Focal Reducer

The use of a focal reducer is essential for optimal framing, coping with varying imaging conditions and determining exposure times.

With my LX200 setup, I almost exclusively used the f/3.3 FR at f/4 and below in order to be able to track adequately. The mount was not up to the task of autoguiding at f/10. Only since my upgrade to a Losmandy Titan, have I been able to try longer FL imaging. The tradeoff with longer FLs is the longer times required. For every 2x increase in f/ratio, 4 times the exposure is required to generate an equivalent signal. Of course, the image scale doubles as well, so the object appears that much larger.

The f/3.3 FR comes with a 15 and 30mm spacer. I have also purchased additional 10mm spacers (2 of them) in order to provide 0, 10, 15, 20, 25 and 30mm spacings. Anything greater than 30mm has too much vignetting and coma to be useful. For several images taken with various spacings, I've generated a plot of spacer used and f/ratio.