Techniques for Refiguring an 18" f/4.4 Telescope Mirror
ฝัง
- เผยแพร่เมื่อ 4 ต.ค. 2024
- Gordon Waite talks about an 18" f/4.4 telescope mirror that he is about to refigure. Gordon shows you pitch polishers, and demonstrates the various strokes and zones that will be changed on the mirror.
thank god for nerds like you to make life wonderful. cheers
Tulip lap is what I call the lap design you use where you trim the edges down to decrease the effect at the edge of the lap. The edges look like the tapered ends of the flower. Figuring is an art, and you are an artist for sure!
Garth Elliott Thanks, Garth, for your generous comments. Yes, the description you give for a tulip lap is, indeed, the way I cut these. At first I thought you were describing a "petal" lap which is normally a full-sized polisher with a pattern for parabolizing. That's something else entirely. You are exactly right, though, in your description here. Best of luck with all your projects!
Thank you for showing your precious video
Wow the whole comments section is rotating counter clockwise now
What amazes me is how you can make something accurate to a fraction of a wavelength of light just by shoving a tool around with your hands in various vaguely defined patterns. I mean, if it was done by some sort of computer-controlled machine, or even a purely mechanical gizmo that made repeatable motions, it would be easier to believe. But your hands! And to think, if you don't even have the rotating turntable, you can still do it with a stationary blank by walking around to work from different directions. It's totally incredible! I wonder how anyone ever figured out that this was possible?
One day after I made an 18" mirror, I calculated that my turntable had done about 75,000 revolutions during the fabrication. Each one does just a little bit of work!
@@GordonWaite And to think old Bernhard Schmidt did it with one arm! :-)
I love the Bad Story term, same initials as what anyone else would have called it
Hi Gordon.
Do you have any plans to make a video on making a 25" mirror from blank to finish showing every step and what's used? I need to learn the whole process to do my blank and don't want to mess it up as only have what I have. Do you maybe have a website showing the steps involved or any info on where I should do some study and research? I'm based far overseas and it's really hard to get big glass over here. TIA!
Thanks, Gordon for your great video.
I was wondering whether you can make a video on how to take scratches off a mirror. I have a 10-inch mirror with lots of scratches on it, took the aluminium coating off using your other video that showed how to do it, but now I want to grind down the glass surface to take the scratches off and then give it again to be coated.
Hi Afshin,
You can not "take away the scratches". You can only grind and polish (or only polish if the scratches aren't too deep) down to the bottom of the deepest scratches. You need to make a grinding/polishing tool and a pitch lap and you need to buy all the reqired materials. If the scratches are too deep to polish them out the mirror is practically ruined and it has to be considered a pre shaped mirror blank. Unfortunately in any case the parabolic shape will be lost in the process so you need to re figure the mirror after the scratches are gone. You need at least a focault tester and a zone mask to check for the actual shape multiple times during re figuring.
Even with good instruction you are probably looking at a 100 hour job as a beginner. I'd rather suggest you buy a new mirror instead or just use the telescope with the scratches if they are not too extreme.
Oh man, this video is fantastic! I figuring a 8" mirror, and thats is my second, but the foacal ratio is 3.8. My mirror is slightly undercorrected to, and i try to figure out how can i fix it. Then I found zour video.. THX!
hey gordon... i want to know what kind of motor you use on your equipament... do you use a/c motor with pullies or d/c motor ... and how much power? 1 hp... 1/2 or even 1/4 hp... Thanks. Greetings from brazil
sacrip tex I use mostly 3/4 hp motors. All are three-phase with inverters to run off 120V single-phase standard current. the inverters give you full control over motor speed, and good ones offer balanced torque over the whole speed range. I usually put a 30:1 gearbox on the motor, and drive the turntable from the gearbox, giving speeds from 0 to 60 rpms.
Where do you get a glass blank for homemade mirror anyways
Pretty awesome! Looking to get back to mirror making now that we're becoming empty nesters and I'm approaching retirement age.
How do you make the measurements you talk about?
mr. Waite I wonder where did you buy such a huge block of optical glass to work on
There are businesses that specialize in architectural glass, and they can provide large pieces of borosilicate glass.
Hey Gordon, do you have any experience with making scopes using spherical mirrors and flexing? If so, what are your thoughts? Spherical primaries are super cheap on eBay and obviously easier to grind for amateur makers, so it seems like spherical flexing scopes would've taken off, but I haven't heard too much about them...
If you have a well-polished spherical mirror, you are just a little more work away from having a finished parabolic mirror. Making a flexed mirror isn't all that easy. Lots of mechanical parts to make, and you have to learn to test a mirror anyway. Might as well parabolize it and feel really satisfied!
When you say "corrected" does that mean making it parabolic?
Pretty much.
Gordon, that long stroke with a one inch overhang could give you a turned down edge except you use a "tulip"lap, right? I have made two 24" and one 20" scope. One winning an award at Riverside. Would like to do a 30 or 32 inch ( on bucket list).
Garth Elliott Hi, Garth. The long stroke with the sub-diameter lap and the 1" or 1.5" overhang will add correction both in the center, and at the edge. It will put in correction faster at the center than the edge. As long as the outer zones can take the correction, you won't get a turned-down edge. But, as with any stroke that puts in correction toward the outside, if you use the stroke too long, you WILL get a TDE. And a very deep center! I don't use a "tulip" lap on any of my sub-diameter polishers, but I do "scallop" the edge a little. You should follow your heart and go for a 30 or 32-inch mirror. Especially if you can shoot for a fast optic, like an f/3.0 or around there somewhere. If you have the time to do the job right, the short-focal-length mirrors can be wonderful for wide fields and comfortable viewing. Good luck with your projects!
Garth Elliott Hi, Garth. The long stroke with the sub-diameter lap and the 1" or 1.5" overhang will add correction both in the center, and at the edge. It will put in correction faster at the center than the edge. As long as the outer zones can take the correction, you won't get a turned-down edge. But, as with any stroke that puts in correction toward the outside, if you use the stroke too long, you WILL get a TDE. And a very deep center! I don't use a "tulip" lap on any of my sub-diameter polishers, but I do "scallop" the edge a little. You should follow your heart and go for a 30 or 32-inch mirror. Especially if you can shoot for a fast optic, like an f/3.0 or around there somewhere. If you have the time to do the job right, the short-focal-length mirrors can be wonderful for wide fields and comfortable viewing. Good luck with your projects!
can you make a video on this subject? Would be great!
Check out Gordon's earlier videos. He speaks a bit about the machine and much on technique.
Pena não ser traduzido.
Boa aula.
Hello sir can you please tell me what should be the thickness at centre of the mirror
Mirrors vary quite a bit. A thin center would be 6 to 8 mm. More typical is 25 to 35 mm.
Sir what isgrid black? Is silicon?
It is Gugolz pitch.
The table seems to be running a bit jerky.
It is, but it gets the job done!
Can a good figured 400mm F3 mirror with a Parracor be a good performer on planets?
Any mirror with a good figure will perform well on planets, given it is at a stable temperature, well mounted, good secondary, etc. Your chances of having a good figure on an F3 are probably lower, though, than having a good figure on a longer focal length mirror. The difficulty of figuring short, fast mirrors goes up very quickly.
@@GordonWaite
❤️
Stroke game ONPOINT lol
Looks like clear glass not a mirror.
Mirrors are first made from clear glass. After the shape is perfected, they are given a coating a few molecules deep of aluminum to make them into reflective mirrors. Until then, they are transparent.