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  #81  
Old 26-11-2017, 11:15 AM
Kunama (Matt)
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I keep pressing the "LIKE" button but nothing is happening !!!

Just awesome work Stefan, my kingdom for your lathe, mill and machining skill .....
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  #82  
Old 26-11-2017, 01:48 PM
Stefan Buda
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Quote:
Originally Posted by Kunama View Post
I keep pressing the "LIKE" button but nothing is happening !!!

Just awesome work Stefan, my kingdom for your lathe, mill and machining skill .....
Thanks, but wait until you see the focuser. Originally I designed something along the lines of the Officina Stellare RH200 but I could only get about 27 millimetres max between the focuser and the focal plane. That was perfectly ok for my QHY8 OSC camera but not enough to eventually move on to a mono camera with filter wheel. So back to the drawing board I went and came up with a design similar to the Clement focuser, but without flexural hinges... Stay tuned.

Last edited by Stefan Buda; 27-11-2017 at 07:55 AM.
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  #83  
Old 09-12-2017, 12:08 PM
Stefan Buda
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Here comes the focuser. About 40 hours work.
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  #84  
Old 09-12-2017, 09:17 PM
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FlashDrive (Col)
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Just gobsmacked at the work and care that has gone into making this beauty ..... what craftsmanship when you have the right gear ... lathe / milling machine / etc

A labour of Love ...

Col..
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  #85  
Old 10-12-2017, 08:56 AM
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multiweb (Marc)
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+1 Been following this and it's just sub zero cool. The mechanical engineering is incredible but the optics making is mind boggling. The focuse looks like a clement design. Not too sure how the little yellow wheel makes the whole thing go up and down. Is it just a simple threaded bush? Couldn't quite make it from the spare parts shot
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  #86  
Old 10-12-2017, 10:23 AM
Stefan Buda
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Quote:
Originally Posted by FlashDrive View Post
Just gobsmacked at the work and care that has gone into making this beauty ..... what craftsmanship when you have the right gear ... lathe / milling machine / etc

A labour of Love ...

Col..
Thanks Col, but it also takes a bit of insanity, I think.

Quote:
Originally Posted by multiweb View Post
+1 Been following this and it's just sub zero cool. The mechanical engineering is incredible but the optics making is mind boggling. The focuse looks like a clement design. Not too sure how the little yellow wheel makes the whole thing go up and down. Is it just a simple threaded bush? Couldn't quite make it from the spare parts shot
Thanks Mark,
The phosphor bronze part, second part from bottom right corner, screws into the back plate and the thumb wheel has a threaded shaft that engages it. The threaded shaft has been split to act as a spring and has an M3 grub screw down the middle in order to spread it apart in a controlled way. The spring action is needed to get rid of backlash. The split shaft is made of hard alloy - Al7075 - and is hard anodised.
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  #87  
Old 10-12-2017, 10:35 AM
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multiweb (Marc)
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Quote:
Originally Posted by Stefan Buda View Post
The phosphor bronze part, second part from bottom right corner, screws into the back plate and the thumb wheel has a threaded shaft that engages it. The threaded shaft has been split to act as a spring and has an M3 grub screw down the middle in order to spread it apart in a controlled way. The spring action is needed to get rid of backlash. The split shaft is made of hard alloy - Al7075 - and is hard anodised.
That's a very peculiar system. Is it your own brew?
I would imagine with all the moving parts, angles and hinges the machining tolerances and fit would be extremely tight and challenging.
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  #88  
Old 10-12-2017, 11:01 AM
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Atmos (Colin)
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My building ability starts and ends with a hammer and a pinch bar (tools for destruction!), it’s great seeing this slowly come into action.
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  #89  
Old 10-12-2017, 11:38 AM
Stefan Buda
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Quote:
Originally Posted by multiweb View Post
That's a very peculiar system. Is it your own brew?
I would imagine with all the moving parts, angles and hinges the machining tolerances and fit would be extremely tight and challenging.
I like coming up with unorthodox solutions..
You are absolutely right about the tolerances. I even had to shim the Z-axis of my milling machine to get the necessary orthogonality.
The axle rods for the hinges are precision guide rods, recycled from CD and DVD drives, and the holes in the hinges had to be diamond lapped after anodizing. Not agricultural machinery standard.
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  #90  
Old 10-12-2017, 11:50 AM
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multiweb (Marc)
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Quote:
Originally Posted by Stefan Buda View Post
I like coming up with unorthodox solutions..
You are absolutely right about the tolerances. I even had to shim the Z-axis of my milling machine to get the necessary orthogonality.
The axle rods for the hinges are precision guide rods, recycled from CD and DVD drives, and the holes in the hinges had to be diamond lapped after anodizing. Not agricultural machinery standard.
I'm just amazed that given the geometry of the whole assembly that third hinge axle rod went in without a fight.
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  #91  
Old 10-12-2017, 12:08 PM
Stefan Buda
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I'm just amazed that given the geometry of the whole assembly that third hinge axle rod went in without a fight.
Yep, it did require a well thought out procedure and many tricks to insure success. The first picture shows one trick that guaranteed that all the positions of the holes in the hinges were the same. Keep in mind that the machine has digital readout to 0.005mm.
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  #92  
Old 11-12-2017, 05:53 PM
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ZeroID (Brent)
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OK, I give up, I can't see how it works. But geez, it's beautifully made.
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  #93  
Old 29-12-2017, 08:12 PM
Stefan Buda
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I intended to finish this project before the end of the year but things got in the way as usual..
At least I managed to get the Mangin out of the way. I just have to do some coatings now and will be ready for preliminary assembly over the coming weeks.
The front surface of the Mangin is the fastest surface I ever tested with a Ronchi setup. Amazingly my light source was able to illuminate it evenly, despite the f/1.29 ratio. The lines looked very straight on both sides of focus, however I don't think that is due to my wonderful skills and perfect polishing lap, but rather has to do with the lack of sensitivity of the Ronchi test as this sort of extreme f-ratio.
For the back surface I also used the Ronchi tester, through the front surface. Due to the near concentricity of the two surfaces the Ronchi lines were nearly straight. The longitudinal focal spread, according to ray tracing, was only 0.25mm and it was very difficult to measure even though I 3D printed a zonal mask for it.
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  #94  
Old 29-12-2017, 09:17 PM
Wavytone (Nick)
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Sheesh... wow. Just wow. Stefan you could make that focuser a commercial product, if you wanted to.

Last edited by Wavytone; 29-12-2017 at 10:43 PM.
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  #95  
Old 30-12-2017, 02:01 PM
Stefan Buda
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Sheesh... wow. Just wow. Stefan you could make that focuser a commercial product, if you wanted to.
I may be forced to go in that direction as the laser industry is declining in Australia. When I became self employed, in 2000, there were three businesses building laser cutters in Melbourne - now there are none.

Seeing other people's battles in trying to source adequate focusers for their astrographs, I think there is a niche for a good motorised 3" focuser.
The main difficulty is in coming up with a design that can be produced cost effectively.
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  #96  
Old 30-12-2017, 02:12 PM
Wavytone (Nick)
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Make a 2" as well. The Bellerophon (www.clementfocuser.com) is no longer available as a 2".

Looks like I'll have to settle for a Starlight FTF2015BCR-RP and have a backplate made locally to suit.
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  #97  
Old 02-01-2018, 05:34 PM
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I always look for this thread to see how things have developed with this project. I bow down to you Stefan, your skills are exemplary and I marvel at this project. I look forward to more updates and the final product. Incredible workmanship.
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  #98  
Old 02-01-2018, 07:53 PM
Stefan Buda
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Originally Posted by Wavytone View Post
Make a 2" as well. The Bellerophon (www.clementfocuser.com) is no longer available as a 2".

Looks like I'll have to settle for a Starlight FTF2015BCR-RP and have a backplate made locally to suit.
I think the Clement focuser is still protected by patent, although it does not apply to my version with plain hinges.
However I'm thinking about something more along the line of the Atlas focuser, but cheaper if possible.

Quote:
Originally Posted by Paul Haese View Post
I always look for this thread to see how things have developed with this project. I bow down to you Stefan, your skills are exemplary and I marvel at this project. I look forward to more updates and the final product. Incredible workmanship.
Thanks Paul - shame that I have to work for a living, as I wish I had more time for this sort of projects.

Meanwhile, I managed to evaporate some aluminium on the optics and assembled the OTA on the 31st of December.
I found that the focal plane is about 1.5mm further out from where it should be, indicating a potential problem. Maybe it is the unfigured back surface of the Mangin responsible. It will be a long iterative process to get this sorted.

And nearly forgot: Happy New Year everyone!
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Last edited by Stefan Buda; 02-01-2018 at 10:00 PM.
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  #99  
Old 04-01-2018, 02:16 PM
Stefan Buda
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Last night I captured some extra focal images of Canopus and sent them over to Bratislav for Roddier analysis.
This morning he sent me the results and I'm happy to report that the instrument is free from astigmatism. However the spherical aberration needs to be cured.
So, I pulled out the Mangin and measured R4 as I suspected that it was the culprit. Sure enough the spherometer showed a sagitta increase of 5 micron, corresponding to an increase of radius of 1.5mm. The damn polishing lap was working a lot harder on the inner edge than on the outer, despite of me using rather long strokes on the polishing machine - never trust a polishing lap even if you have performed exorcism on it. Optical polishing remains a black art, but I could have noticed the problem by periodically testing the surface with the spherometer.
Anyway, I decided to go back to fine grinding rather than try to polish it back to specs.
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  #100  
Old 04-01-2018, 11:06 PM
Wavytone (Nick)
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Yup you have SA with a touch of astigmatism, the astigmatic axis runs from 10 o'clock to 4 o'clock. Could have told you that from the image, never mind the roddier analysis.

The $64 question is whether the astigmatism is induced by strain in the optic by whatever is holding it (pinching) when the image was taken, or whether you've actually figured it that way. Only you can work this out.

You know what you have to do... though to remove a high zone of 5 microns I'd be practicing the gentle art of hand figuring with pitch and rouge, pressing with petal-shaped card templates to control where the contact zones are... forget fine grinding - far too drastic, and even cerium oxide is too drastic. Rouge is far more gentle when it comes to figuring.

Only downside is rouge is very, very, messy stuff to use, though it does come off in a washing machine. Just hope your wife just doesn't look closely at what goes in.

Last edited by Wavytone; 04-01-2018 at 11:30 PM.
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