Question on Focus

[bbrock]

I have a few questions. What is "Prime Focus"? and What is a "Focal Reducer"? I keep reading these terms but I honistly don't know anything abut them. <br /><br />Bill

 

[Saiph]

Mirrors and lenses have a focal length where objects situated at infinity (basically stars and planets) will be projected and brought to sharp focus.<br /><br />Prime Focus is focal point of the main mirror or lense.<br /><br />A Focal Reducer is used to catch the light before it gets to it's final destination (your eye or an instrument) and bring the object to focus sooner. Advantages of this are changes in image size so that it can fit on your instruments viewport, and it can decrease (IIRC) the time required to expose an image. <div class="Discussion_UserSignature"> <p align="center"><font color="#c0c0c0"><br /></font></p><p align="center"><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">--------</font></em></font><font color="#999999"><em><font size="1">----</font></em></font><font color="#666699">SaiphMOD@gmail.com </font><font color="#999999"><em><font size="1">-------------------</font></em></font></p><p><font color="#999999"><em><font size="1">"This is my Timey Wimey Detector.  Goes "bing" when there's stuff.  It also fries eggs at 30 paces, wether you want it to or not actually.  I've learned to stay away from hens: It's not pretty when they blow" -- </font></em></font><font size="1" color="#999999">The Tenth Doctor, "Blink"</font></p> </div>