9.5 mirror -- 2nd try at posting

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BABOafrica Kenya
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9.5 mirror -- 2nd try at posting

#1

Post by BABOafrica »


I just finished an f/7.5 9.5in mirror and loaded it into the OTA. The mirror is NOT coated yet. Just glass. Well, the secondary is coated but not the primary.

The OTA is designed as an astrograph. I want to use it for astrophotography.

I'm just experimenting. I doubt that it will work well. Probably got some serious flexure problems (as you will surmise from the pictures of the OTA included below.) I had to keep the weight down to 20 pounds total, so... the whole thing is a bit flimsy.

Yeah, so probably not going to be a good astrograph. But you know how it is when it gets cloudy and you have a shop full of junk just waiting to be assembled into something useful. Who knows, it might surprise me and work quite well.

I did the mirror myself and tested with a Bath Interferometer (which I also made myself). Attached is an image of the wavefront resulting from the interferometer test plus a Ronchigram for the same mirror. You can see the mirror is a bit rough. But that doesn't matter as much with such a slow mirror.

I took a picture of a distant telephone tower (very cloudy day yesterday and supposed to keep raining). The image looks quite sharp to my eye. When the clouds go away and the moon comes back, I'll try to get some lunar shots.

In the meantime, here are the pictures:

THE OTA with the new mirror loaded:

Image

Image



Image of distant telephone tower (I used a Fujifilm X-A1)

Image

Image



Ronchigram of the mirror (outside RofC):

Image



Interferometry test (using Bath interferometer and DFTF analysis) with Guassian blur set to 10%.
[[This is technically referred to as a "wavefront" showing the highs and lows on the mirror surface]]

Image


Rochingram generated by DFTF analysis of wavefront:
[[If the DFTF Ronchigram matches the REAL Ronchigram (see above), it means that your interferometer test is good]]

Image


Clears to YA!
BABO
"In lumine tuo videbimus lumen."

Scopes: Stellarvue SV80 Raptor Carbon Fiber ED Doublet / Celestron SCT C8
Williams Optics 66mm APO / DIY 8" f/4 Newtonian astrograph / Nikon 180mm f/2.8
Mounts: Orion Atlas EQ-G / Celestron AVX / DIY mini-equatorial
Cameras: QHY163m / Fujifilm X-A1 (modded) / Fuji X-A2 (not modded) / Orion StarShoot Auto Guider
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Re: 9.5 mirror -- 2nd try at posting

#2

Post by notFritzArgelander »


That's an interesting optic. DIY? Pretty good!

The tube might present flexure issues as you anticipate. Might I ask where the 20lb limit comes from? The available mount?
Scopes: Refs: Orion ST80, SV 80EDA f7, TS 102ED f11 Newts: AWB 130mm, f5, Z12 f5; Cats: VMC110L, Intes MK66,VMC200L f9.75 EPs: KK Fujiyama Orthoscopics, 2x Vixen NPLs (40-6mm) and BCOs, Baader Mark IV zooms, TV Panoptics, Delos, Plossl 32-8mm. Mixed brand Masuyama/Astroplans Binoculars: Nikon Aculon 10x50, Celestron 15x70, Baader Maxbright. Mounts: Star Seeker IV, Vixen Porta II, Celestron CG5
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Re: 9.5 mirror -- 2nd try at posting

#3

Post by The Happy Parrot »


Most impressive and resourceful BABO! I don't know anything imaging but I'm surprised you were able to get such a good image of the telephone tower without the primary being coated. That's just from light reflected on the untreated primary glass?
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Re: 9.5 mirror -- 2nd try at posting

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Post by BABOafrica »


notFritzArgelander wrote: Thu Jun 20, 2019 2:19 am That's an interesting optic. DIY? Pretty good!

The tube might present flexure issues as you anticipate. Might I ask where the 20lb limit comes from? The available mount?
Thanks for the comment, nFA.

Sorry it takes me a while to respond. I spend most of my available website time over at AF...

Yes, it is DIY. It's my 7th mirror. It's the first one for which I have taken the trouble to use an interferometer to test the figure.

One thing I like about figuring a telescope mirror and testing: you get to see how optics really work. You can't cheat yourself with pretty ideas of what should work and what you would like to work. You have to get it right by making it as close to a paraboloid as you can. You can see the image improve as you get closer to parabolic.

The 20lb limit … my mount is an Orion Atlas EQ-G. It's rated for 40 pounds. Since I'm experimenting with using the scope for AP, 20 pounds.

If it doesn't work, I'll just sell the mirror and try something else.

BABO
"In lumine tuo videbimus lumen."

Scopes: Stellarvue SV80 Raptor Carbon Fiber ED Doublet / Celestron SCT C8
Williams Optics 66mm APO / DIY 8" f/4 Newtonian astrograph / Nikon 180mm f/2.8
Mounts: Orion Atlas EQ-G / Celestron AVX / DIY mini-equatorial
Cameras: QHY163m / Fujifilm X-A1 (modded) / Fuji X-A2 (not modded) / Orion StarShoot Auto Guider
Filters: ZWO 7nm NB set / ZWO LRGB set / ZWO Dual Band / Astronomics UHC
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Re: 9.5 mirror -- 2nd try at posting

#5

Post by BABOafrica »


The Happy Parrot wrote: Thu Jun 20, 2019 1:04 pm Most impressive and resourceful BABO! I don't know anything imaging but I'm surprised you were able to get such a good image of the telephone tower without the primary being coated. That's just from light reflected on the untreated primary glass?
The glass reflects about 4% of ambient light. Once coated, it will reflect about 90%.

At night, with very little light coming from the stars, the mirror doesn't work well (except for the moon and the brighter planets).

During the day, you can get some pretty good reflection simply because it's so bright -- especially on the equator, which is where I live.

BABO
"In lumine tuo videbimus lumen."

Scopes: Stellarvue SV80 Raptor Carbon Fiber ED Doublet / Celestron SCT C8
Williams Optics 66mm APO / DIY 8" f/4 Newtonian astrograph / Nikon 180mm f/2.8
Mounts: Orion Atlas EQ-G / Celestron AVX / DIY mini-equatorial
Cameras: QHY163m / Fujifilm X-A1 (modded) / Fuji X-A2 (not modded) / Orion StarShoot Auto Guider
Filters: ZWO 7nm NB set / ZWO LRGB set / ZWO Dual Band / Astronomics UHC
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Re: 9.5 mirror -- 2nd try at posting

#6

Post by Lady Fraktor »


Very nice figure Babo, it looks like it is going to be capable of giving you some excellent images once coated.
See Far Sticks: Antares Elita 103/1575, AOM FLT 105/1000, Bresser BV 127/1200, Nočný stopár 152/1200, Vyrobené doma 70/700, Stellarvue NHNG DX 80/552, TAL RS100/1000, Vixen SD115s/885
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Re: 9.5 mirror -- 2nd try at posting

#7

Post by notFritzArgelander »


BABOafrica wrote: Tue Jun 25, 2019 5:03 am
notFritzArgelander wrote: Thu Jun 20, 2019 2:19 am That's an interesting optic. DIY? Pretty good!

The tube might present flexure issues as you anticipate. Might I ask where the 20lb limit comes from? The available mount?
Thanks for the comment, nFA.

Sorry it takes me a while to respond. I spend most of my available website time over at AF...

Yes, it is DIY. It's my 7th mirror. It's the first one for which I have taken the trouble to use an interferometer to test the figure.

One thing I like about figuring a telescope mirror and testing: you get to see how optics really work. You can't cheat yourself with pretty ideas of what should work and what you would like to work. You have to get it right by making it as close to a paraboloid as you can. You can see the image improve as you get closer to parabolic.

The 20lb limit … my mount is an Orion Atlas EQ-G. It's rated for 40 pounds. Since I'm experimenting with using the scope for AP, 20 pounds.

If it doesn't work, I'll just sell the mirror and try something else.
I think I may be a little more optimistic than you about the capabilities of the Atlas mount. I know that the standard rule of thumb is 1/2 the weight rating. But I collected data on the Atlas back when I owned one and I felt it could take into the mid 20s. So please consider if it doesn't work out that you spend ~4-7 lbs on reinforcing the OTA before abandoning it. The Atlas (if you've got a good one) might surprise you! :twocents: You've got a good optic there!
Scopes: Refs: Orion ST80, SV 80EDA f7, TS 102ED f11 Newts: AWB 130mm, f5, Z12 f5; Cats: VMC110L, Intes MK66,VMC200L f9.75 EPs: KK Fujiyama Orthoscopics, 2x Vixen NPLs (40-6mm) and BCOs, Baader Mark IV zooms, TV Panoptics, Delos, Plossl 32-8mm. Mixed brand Masuyama/Astroplans Binoculars: Nikon Aculon 10x50, Celestron 15x70, Baader Maxbright. Mounts: Star Seeker IV, Vixen Porta II, Celestron CG5
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Re: 9.5 mirror -- 2nd try at posting

#8

Post by Kanadalainen »


Nice work!! Did you build your own Ronchi testing equipment?
Ian

Fracs: Stellarvue 70T f6; SW 120mm Esprit f7; "Mark Mk. II" - 60 mm Tasco f6; C80 frac f 11.4
SCT: C8 Edge f10 or f7 with reducer
Dob: 14.5" homebuilt strut dob (f4.5 ZOC mirror), Nexus II, Moonlite focuser
Mounts - Ioptron Skyguider pro, Astro Physics GTO900
Cameras and lenses - ZWO 2600 mc, 290 mm mini, Canon 60D modded with Rokinon 10mm 2.8; Rokinon 135mm f2

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Re: 9.5 mirror -- 2nd try at posting

#9

Post by BABOafrica »


Kanadalainen wrote: Thu Aug 15, 2019 3:57 pm Nice work!! Did you build your own Ronchi testing equipment?
Ronchi testing equipment is a piece of cake. You just need a screen and an LED light source -- and a camera if you want to take pictures.

Making a Foucault tester is a little harder but manageable.

Building the interferometer was more complicated and learning how to use it -- it took me lots of advice and lots of attempts but I finally managed.

Well worth the effort.

BABO
"In lumine tuo videbimus lumen."

Scopes: Stellarvue SV80 Raptor Carbon Fiber ED Doublet / Celestron SCT C8
Williams Optics 66mm APO / DIY 8" f/4 Newtonian astrograph / Nikon 180mm f/2.8
Mounts: Orion Atlas EQ-G / Celestron AVX / DIY mini-equatorial
Cameras: QHY163m / Fujifilm X-A1 (modded) / Fuji X-A2 (not modded) / Orion StarShoot Auto Guider
Filters: ZWO 7nm NB set / ZWO LRGB set / ZWO Dual Band / Astronomics UHC
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Re: 9.5 mirror -- 2nd try at posting

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Post by Kanadalainen »


BABOafrica wrote: Fri Aug 16, 2019 9:52 am
Kanadalainen wrote: Thu Aug 15, 2019 3:57 pm Nice work!! Did you build your own Ronchi testing equipment?
Ronchi testing equipment is a piece of cake. You just need a screen and an LED light source -- and a camera if you want to take pictures.

Making a Foucault tester is a little harder but manageable.

Building the interferometer was more complicated and learning how to use it -- it took me lots of advice and lots of attempts but I finally managed.

Well worth the effort.

BABO
Thanks BABO,

Good to know about the Ronchi test equipment. I have most of that stuff. Will any wavelength LED work fine?

I'm starting on a Foucault tester based on the Stellafane model, and am collecting lenses and parts for a bath interferometer.

Ian
Ian

Fracs: Stellarvue 70T f6; SW 120mm Esprit f7; "Mark Mk. II" - 60 mm Tasco f6; C80 frac f 11.4
SCT: C8 Edge f10 or f7 with reducer
Dob: 14.5" homebuilt strut dob (f4.5 ZOC mirror), Nexus II, Moonlite focuser
Mounts - Ioptron Skyguider pro, Astro Physics GTO900
Cameras and lenses - ZWO 2600 mc, 290 mm mini, Canon 60D modded with Rokinon 10mm 2.8; Rokinon 135mm f2

Skysafari 6 Pro, Astro Pixel Processor, Pixinsight - using Mac tablet and ASIair pro to run the AP rig.

"Mothers! It is there!" - Rafael Gonzales-Acuna, 2018.
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Re: 9.5 mirror -- 2nd try at posting

#11

Post by BABOafrica »


Kanadalainen wrote: Fri Aug 16, 2019 12:45 pm
Thanks BABO,

Good to know about the Ronchi test equipment. I have most of that stuff. Will any wavelength LED work fine?

I'm starting on a Foucault tester based on the Stellafane model, and am collecting lenses and parts for a bath interferometer.

Ian
AFAIK, yeah, any LED -- as long as it's bright enough. I used a 5w red LED. But some people say it's better to use green.

I wish you the best with your ATM mirror testing!

BABO
"In lumine tuo videbimus lumen."

Scopes: Stellarvue SV80 Raptor Carbon Fiber ED Doublet / Celestron SCT C8
Williams Optics 66mm APO / DIY 8" f/4 Newtonian astrograph / Nikon 180mm f/2.8
Mounts: Orion Atlas EQ-G / Celestron AVX / DIY mini-equatorial
Cameras: QHY163m / Fujifilm X-A1 (modded) / Fuji X-A2 (not modded) / Orion StarShoot Auto Guider
Filters: ZWO 7nm NB set / ZWO LRGB set / ZWO Dual Band / Astronomics UHC
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Re: 9.5 mirror -- 2nd try at posting

#12

Post by notFritzArgelander »


BABOafrica wrote: Wed Aug 21, 2019 2:07 pm
Kanadalainen wrote: Fri Aug 16, 2019 12:45 pm
Thanks BABO,

Good to know about the Ronchi test equipment. I have most of that stuff. Will any wavelength LED work fine?

I'm starting on a Foucault tester based on the Stellafane model, and am collecting lenses and parts for a bath interferometer.

Ian
AFAIK, yeah, any LED -- as long as it's bright enough. I used a 5w red LED. But some people say it's better to use green.

I wish you the best with your ATM mirror testing!

BABO
Yes, green is better. It's a shorter wavelength. The Foucault test measures deviations from perfect figure in fractions of the wavelength used. So shorter wavelength means more stringent test.

Also the eye is more sensitive to green than red so a Foucault measurement in red will overestimate visual performance.
Scopes: Refs: Orion ST80, SV 80EDA f7, TS 102ED f11 Newts: AWB 130mm, f5, Z12 f5; Cats: VMC110L, Intes MK66,VMC200L f9.75 EPs: KK Fujiyama Orthoscopics, 2x Vixen NPLs (40-6mm) and BCOs, Baader Mark IV zooms, TV Panoptics, Delos, Plossl 32-8mm. Mixed brand Masuyama/Astroplans Binoculars: Nikon Aculon 10x50, Celestron 15x70, Baader Maxbright. Mounts: Star Seeker IV, Vixen Porta II, Celestron CG5
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