BirdForum is the net's largest birding community dedicated to wild birds and birding, and is absolutely FREE!

Register for an account to take part in lively discussions in the forum, post your pictures in the gallery and more.

Reply to thread

Message: <blockquote data-quote="WJC" data-source="post: 3160190" data-attributes="member: 25191">This . . . . . . is London. Oops, wrong intro. I see a lot of talk about f/1 mirrors, f/1.5 mirrors, and the like, and I would like to interject a few small chunks of reality.I don’t care who you are, unless you have the budget of the federal government backing you up, your chances of getting it into an instrument that works well is about .001%. I have encountered a number of people, in my last 40 years in telescope making, who have gone weak in the knees over some f/1 mirror acquisition they made from Edmund Scientific, Surplus Shed, eBay, and the like and had big plans as to what they were going to make with it. However, I have yet to see any one of these projects come to fruition! I’ve grown Jaded; don’t give me hopes, dreams, and plans; show me products . . . with photos of a star field.“Regardless how elegant the plan, from time to time you need to look at the RESULTS.”—Winston Churchill Furthermore, I have never heard the starry-eyed discuss the secondary. An f/1 mirror is going to take a secondary of about 70% obstruction! Oops! There went the contrast you wanted. According to Rayleigh, you can’t achieve a diffraction limited system with it having more than an 18% obstruction. When planning a system, you have to plan the WHOLE THING! Elements and aberrations don’t live in a vacuum.And, if you’re making the mirror:* Small f/10 mirrors may be left spherical.* f/9 mirrors produce very subtle shadows. Making them is not for the faint of heart or patience.* f/7-f/8 mirrors can be made by anyone with patience and common sense.* f/6 mirrors are beginning to get tough.* f/4-f/5 mirrors separate the men from the boys.* Below f/4, problems increase exponentially with EACH new f/ratio.* F/1? God is still trying to finish his first!Cheers,Bill</blockquote>

Verification