neo
professor emeritus
Reged: 02/12/08
Posts: 618
Loc: Iasi, Romania
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Oh ...I see. You place the LED right behind the razor and it will move with the KE in the same time. It's a slitless tester with a moving source.
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Russian 15x50 binos
Home made 8" f/5 Newton on eq mount
Home made 70mm f/6 (Rodenstock Rotelar lens) Apo refractor
www.astronomy.ro
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Gary Fuchs
scholastic sledgehammer
Reged: 05/22/06
Posts: 867
Loc: Easton, PA, USA
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Hi Bart,
It's probably clear by now but just in case...here's my version:
I marked this up a while ago so please ignore anything not relevant. Or the whole thing...
The knife edge is slid right to block about half the LED and from then on stays put with just the stage tipping and moving forward and back. The LED is fixed and your eye goes right above it as close above as possible. I put some tape over the top of the LED so it wouldn't shine in my eye. The knife almost touches the front of the LED.
Some more details here if needed. Please scroll down to my longish post.
Gary
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Bart Wide
super member
Reged: 05/16/08
Posts: 160
Loc: YRP
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Neo, Gary, many thanks for the insighful info and help 
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Bart Wide
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22" f/3.61 David Lukehurst Ultra-Portable Dobsonian, mirror set by John Nichol
Nagler 26 mm, Ethos 13 mm, Ethos 8 mm, Nagler 3.5 mm
TV Paracorr
Lumicon 2" UHC, Lumicon 1.25" H-Beta, Orion 2" ND 13% transm.
Unihedron - SQM-L
Canon EOS 350d
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Bart Wide
super member
Reged: 05/16/08
Posts: 160
Loc: YRP
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Hi, all went well, I just have one question remaining. When they say, the eye should be placed as close to the knife edge as possible. Is approx. 1 inch distance between the retina and the knife edge too far, or will that work?
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Bart Wide
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22" f/3.61 David Lukehurst Ultra-Portable Dobsonian, mirror set by John Nichol
Nagler 26 mm, Ethos 13 mm, Ethos 8 mm, Nagler 3.5 mm
TV Paracorr
Lumicon 2" UHC, Lumicon 1.25" H-Beta, Orion 2" ND 13% transm.
Unihedron - SQM-L
Canon EOS 350d
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neo
professor emeritus
Reged: 02/12/08
Posts: 618
Loc: Iasi, Romania
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I guess there isn't a precise measurement. You place the eye as close as possible to get a comfy view of the mirror and shadows. In the same time you can use a small scope placed behind the KE to see the mirror (about 2-3X magnification) or a camera to take pictures.
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Russian 15x50 binos
Home made 8" f/5 Newton on eq mount
Home made 70mm f/6 (Rodenstock Rotelar lens) Apo refractor
www.astronomy.ro
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Gary Fuchs
scholastic sledgehammer
Reged: 05/22/06
Posts: 867
Loc: Easton, PA, USA
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Bart,
I don't think it matters too much how far away your eye is. I think what's important is that you be viewing close to the level of the LED. If you can see the entire mirror lit up without the knife edge in front of the LED, and can see the shadow move across the entire mirror when you have the knife edge in front, I think you will be fine. Be comfortable, no need to scrape your eyeball...
If you use a camera it should be enough to hold the lens up close to the opening without actually touching it - there's some wiggle room. (Try setting to infinity and a longish zoom.)
I doubt you'll need a scope unless your mirror is very small (<6") and extra long radius - like say, 11ft.
Gary
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neo
professor emeritus
Reged: 02/12/08
Posts: 618
Loc: Iasi, Romania
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Sure the scope isn't necessary but in a way it's more comfy to watch the mirror. Without the scope u have to keep your head pretty steady to get a stable image of the shadows.
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Russian 15x50 binos
Home made 8" f/5 Newton on eq mount
Home made 70mm f/6 (Rodenstock Rotelar lens) Apo refractor
www.astronomy.ro
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Biff
Carpal Tunnel
Reged: 09/04/05
Posts: 2372
Loc: Courtice, Ontario
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Quote:
Sure the scope isn't necessary but in a way it's more comfy to watch the mirror. Without the scope u have to keep your head pretty steady to get a stable image of the shadows.
I use a small scope too, and for me I find it much more comfortable. A little magnification is nice too for long FL mirrors. I made a little scope that I can change the EP in to adjust magnification, generally I use 2.5x magnification (25mm EP).
I'm not sure if it helps or hinders the accuracy of the test though.
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Ryan
Antares 200mm f/6 Dob & 130mm f/5 Travel Dob.
Projects on the go...
- a couple 80mm SS refractors on the back burner.
- a few small mirrors awaiting polishing
- 260mm f/7.15 mirror... still polishing
Member of DRAA
 My house.
 DRAACO
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Bart Wide
super member
Reged: 05/16/08
Posts: 160
Loc: YRP
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Thx for your opinions guys, I appretiate it.
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Bart Wide
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22" f/3.61 David Lukehurst Ultra-Portable Dobsonian, mirror set by John Nichol
Nagler 26 mm, Ethos 13 mm, Ethos 8 mm, Nagler 3.5 mm
TV Paracorr
Lumicon 2" UHC, Lumicon 1.25" H-Beta, Orion 2" ND 13% transm.
Unihedron - SQM-L
Canon EOS 350d
--------------------------------------------------
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rwiederrich
Goldfinger
Reged: 11/17/05
Posts: 8330
Loc: Bremerton Washington
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I use a scope I built for testing all my mirrors. I tend to make f/6 and longer mirrors and an 18"f/6 is a pretty long test. 216"..so a scope is nice. I tested an 8"f/4 yesterday and its 64" test is pretty close so no scope was needed.
Hey..I have a question...some folks are setting their KE so it splits the light exiting the LED before it strikes the mirror. Does it make much difference if you split the light after it hits the mirror and is returning to the tester?
Rob(I don't seam to be having any trouble with my setup)
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www.goldmtobservingcenter.com
A great place for amateur astronomers, and ATM's to come and enjoy their hobby.
http://tech.groups.yahoo.com/group/HomemadeRefractorTelescopes/ My homemade refractor group.
www.vimeo.com/6014031
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neo
professor emeritus
Reged: 02/12/08
Posts: 618
Loc: Iasi, Romania
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Hi Rob!
I'm not sure I understand the question. 
By spliting the light you mean the light that come from one half of the LED, the other half being covered by the KE?
If it's so, I don't see another option. Arrr....maybe I'm a knuckle head at this hour (it's 1:00 am at my place). 
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Russian 15x50 binos
Home made 8" f/5 Newton on eq mount
Home made 70mm f/6 (Rodenstock Rotelar lens) Apo refractor
www.astronomy.ro
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mark cowan
Vendor (Obsidian Optics)
Reged: 06/03/05
Posts: 2159
Loc: salem, OR
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Quote:
Hey..I have a question...some folks are setting their KE so it splits the light exiting the LED before it strikes the mirror. Does it make much difference if you split the light after it hits the mirror and is returning to the tester?
Say what? In a slitless tester the KE used for reading the mirror also cuts across the LED. That's how you produce the "virtual slit". Maybe this diagram will help explain it? (edit - I had the virtual slit upside down - now it's correct.)
Best,
Mark
Edited by mark cowan (06/25/09 01:14 PM)
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Bart Wide
super member
Reged: 05/16/08
Posts: 160
Loc: YRP
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Hi, so this is my creation, I am attaching some fotos, especially the back and front of the knife edge with the LED turned on. The 8" blank is almost on its way from Germany, I guess I will start grinding in August. Won't be using the tester untill polishing. I hope I designed the tester correctly and that the LED is properly cut and diffused.
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Bart Wide
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22" f/3.61 David Lukehurst Ultra-Portable Dobsonian, mirror set by John Nichol
Nagler 26 mm, Ethos 13 mm, Ethos 8 mm, Nagler 3.5 mm
TV Paracorr
Lumicon 2" UHC, Lumicon 1.25" H-Beta, Orion 2" ND 13% transm.
Unihedron - SQM-L
Canon EOS 350d
--------------------------------------------------
Edited by Bart Wide (06/25/09 06:24 AM)
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Bart Wide
super member
Reged: 05/16/08
Posts: 160
Loc: YRP
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Here KE closeup 1
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Bart Wide
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22" f/3.61 David Lukehurst Ultra-Portable Dobsonian, mirror set by John Nichol
Nagler 26 mm, Ethos 13 mm, Ethos 8 mm, Nagler 3.5 mm
TV Paracorr
Lumicon 2" UHC, Lumicon 1.25" H-Beta, Orion 2" ND 13% transm.
Unihedron - SQM-L
Canon EOS 350d
--------------------------------------------------
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Bart Wide
super member
Reged: 05/16/08
Posts: 160
Loc: YRP
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KE closeup 2
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Bart Wide
--------------------------------------------------
22" f/3.61 David Lukehurst Ultra-Portable Dobsonian, mirror set by John Nichol
Nagler 26 mm, Ethos 13 mm, Ethos 8 mm, Nagler 3.5 mm
TV Paracorr
Lumicon 2" UHC, Lumicon 1.25" H-Beta, Orion 2" ND 13% transm.
Unihedron - SQM-L
Canon EOS 350d
--------------------------------------------------
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Gary Fuchs
scholastic sledgehammer
Reged: 05/22/06
Posts: 867
Loc: Easton, PA, USA
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Looks fine. When you test a mirror things (if there are still any questions) will likely fall into place.
If you can lay your hands on, or make, a screen for Ronchi, that can make testing easier.
Gary
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Bart Wide
super member
Reged: 05/16/08
Posts: 160
Loc: YRP
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Thx Gary. I have the Ronchi screen, although I had some problems using the file accessible on the Stellafane site. When reduced to a small size, the lines get all messed up. I thought it might have something to do with the graphic card, but the same problem occurs on several computers,it also occured on the computer where I went to have the screen printed to the transparency film. So my temporary Ronchi screen is in bad shape, I'll hve to find a better solution. Apropos, I reckon the Ronchi screen is placen exactly where the knife edge is at the moment and the green light then passes through the middle of the screen at the bottom through the Ronchi screen, reflects fro the mirror and returns to meet the eye behint the screen. Anyway, I hardly wait to start playing with the device.
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Bart Wide
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22" f/3.61 David Lukehurst Ultra-Portable Dobsonian, mirror set by John Nichol
Nagler 26 mm, Ethos 13 mm, Ethos 8 mm, Nagler 3.5 mm
TV Paracorr
Lumicon 2" UHC, Lumicon 1.25" H-Beta, Orion 2" ND 13% transm.
Unihedron - SQM-L
Canon EOS 350d
--------------------------------------------------
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johndavid24
member
Reged: 12/19/05
Posts: 41
Loc: ohio
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(having a tester will not make you a kenndedy or zambuto, but testing optics is 78.98% of making a mirror. )
Are you out of your mind!!! do something yourself!!! You must be a mad man..... if you talk to a "Meade service" person.
Thats what they made me feel like after asking for a wire harness to the GPS unit, they want me to send the 16" LX200R to them to plug in a 18" long wire ! The little arm inside the GPS fork arm caught on the wire and pulled it from the plug , loosing the pinout location,Is it me or is there something wrong with this picture? does anybody out there know the pinout of this 7 wire harness? Is it straight up or are the wires mixed in position to the other end of the plug, Thanks in advance. I'll post this question on it's own also, I know it really shouldn't be here.... really fired up at the moment!!!
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Biff
Carpal Tunnel
Reged: 09/04/05
Posts: 2372
Loc: Courtice, Ontario
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Manufacturers usually say stuff like that because if you pooch it you may come back to them and say they owe you a new mount or get bad advertising because of your borked mount. It's usually more liability based than the fact they want to make a few $$$ charging you for them to do it.
BUT, I had a 26" monitor that wasn't working right and the manufacturer (after some back 'n' forth and trying some things) determined the issue was a bad circuit board. They asked me if I was comfortable changing the board myself and I told them yes. I got the board in a couple days did the switch and voila! A working monitor. Saved us both a lot of time and shipping. I was impressed. It was a cheapie monitor that I would never have bought my self (it was a gift) but I will probably support that company again because of that kind of service. The company was Sceptre.
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What does everyone here use to clean their mirrors to test for polish? I spent I think a lot more hours polishing since everytime I tested it for polish (laser pointer method) there was always just a hint of the laser dot on the surface... so I kept polishing. On a whim I did some experimenting and found out it was what I was using to clean the mirror, I was using 99% isopropyl. I tried a bunch of different brands and purities of isopropyl plus a couple others like accetone and found the local drugstore house brand 70% to be the best, oddly. After a cleaning with that there was no more laser dot.
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Ryan
Antares 200mm f/6 Dob & 130mm f/5 Travel Dob.
Projects on the go...
- a couple 80mm SS refractors on the back burner.
- a few small mirrors awaiting polishing
- 260mm f/7.15 mirror... still polishing
Member of DRAA
My house.
DRAACO
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scopemankit
super member
Reged: 01/27/09
Posts: 137
Loc: south africa
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I use a simple Foucault tester amounted on the cross-slide of my lathe. Here is a series of pics showing progress in in the shape of a not so good mirror sent to me for re-figuring. Still a bit to go and still a lot to learn about takinf focograms.
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Chris
Cape Town
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