Quote:
Originally Posted by julianh72
The last two comparison images at the bottom of the page http://www.stanmooreastro.com/f_ratio_myth.htm are very misleading. If one was indeed taken at f/12.4 and the other at f/3.9, then they have been scaled differently, or were taken with different sized sensors. For example, if the f/12.4 image is the full capture over the sensor, then the f/3.9 image is roughly a 1/3 x 1/3 crop of the whole image. (Either that, or the sensor used for the f/3.9 image is only 1/3 the size of the f/12.4 image sensor.)
Using a focal reducer on a long focal length telescope lets you capture a bigger sky area on the same sensor, but doesn't alter the brightness of the image which is captured. |
You are wrong. It does alter the brightness of extended sources. Because now at a lower sampling rate more area of sky fits into each pixel