I'd like to know how successful people have been with salvaged optics from things like projectors, binoculars and such to build anything from finders on up.
Welcome to CN, I see you are new here !
Your question indicates you don't know the fundamental equations that define the relationships between the curves of lenses and their focal length, plus the basic aberrations. To work well lenses are designed for the specific application, not picked at random.
I tried, as a kid... ultimately I threw all that stuff out as being useless - I had cannibalised old slide projectors, an overhead projector, plus a box of prisms and doublets left over from binocular production.
I'd have to say don't waste your money on junk optics - there really is a reason they are junk. Save your cash and buy something more useful that actually works well.
1. These days you can buy cheap Chinese objectives on AliExpress and by all accounts they work quite well, and are coated (which you cannot DIY). You can even buy a cell.
2. if you have aperture fever you can grind and polish your own mirrors as I and many other older members have done; all it requires is two glass blanks (from the CN classifieds), a place to work (its a bit messy), the abrasives and polishing materials (sold as a kit) and a Foucault or Ronchi tester (you make that yourself). Borrow a copy of the SciAm ATM books or Texereau, the whole process is amply described.
3. As for eyepieces... dont bother.
While you can cobble a 40mm Plossl using a pair of PCX achromats from binoculars, even the cheap eyepieces on AliExpress will work better than what you can make at home without access to a workshop.
Once you've made a decent 6" or 8" mirror, learnt how optics work, and seen the views from it you won't look at the junk again. NB I started at the age of 12 and by 17 had made a 6" f/8, 6" f/5, 8" f/7, 4" f/4, and a 6" f/19. a few years later a 12" f/4 and cassegrain secondary followed.
Edited by luxo II, 18 January 2025 - 02:09 AM.