f/4 8in PYREX astrograph mirror project

Discuss making your own telescope!
Post Reply
User avatar
BABOafrica
Milky Way Ambassador
Articles: 0
Posts: 1746
Joined: Tue May 07, 2019 2:41 pm
2
Location: Kenya

TSS Awards Badges

TSS Photo of the Day

f/4 8in PYREX astrograph mirror project

#1

Post by BABOafrica »

I was home visiting my Mom in DC before Christmas. One of my sisters asked what I do for a hobby. I mentioned making telescope mirrors. She pulled out her phone and bought an 8in PYREX blank for me.

I was not intending to make a mirror this year... but... I got the mirror blank for free ... so, here I am doing another mirror.

I want this one to be for an astrograph ... so BIG secondary and f/4 primary.

Pictures show (in the following order): 1) the blank // 2) the backside // 3) the thickness // 4) the mirror after finishing the rough grinding


BABO 8in Pyrex 01 - beginning r.grind.jpg

BABO 8in Pyrex 02 - back.jpg

BABO 8in Pyrex 03 - edge.jpg

BABO 8in Pyrex 04 - #220 r.grind.jpg

BABO
"In lumine tuo videbimus lumen."

Scopes: Celestron SCT C8 / Williams Optics 66mm APO

Mounts: Orion Atlas EQ-G / Celestron AVX

Cameras: QHY163m / Fujifilm X-A1 (modded) / Fuji X-A2 (not modded) / Orion StarShoot Auto Guider
User avatar
BABOafrica
Milky Way Ambassador
Articles: 0
Posts: 1746
Joined: Tue May 07, 2019 2:41 pm
2
Location: Kenya

TSS Awards Badges

TSS Photo of the Day

Re: f/4 8in PYREX astrograph mirror project

#2

Post by BABOafrica »

I've been slow but steady progress.

Not quite polished out yet. Here's some pictures of Ronchigrams (outside RoC) and K-E.

BABO

Early on in the polishing -- basic spherical shape

BABO 8in f-4 astrograph R-gram 01.jpg

Knife Edge shot:

BABO 8in f-4 astrograph K-E 01.jpg
AS IT STANDS NOW:

BABO 8in f-4 astrograph R-gram 02.jpg
"In lumine tuo videbimus lumen."

Scopes: Celestron SCT C8 / Williams Optics 66mm APO

Mounts: Orion Atlas EQ-G / Celestron AVX

Cameras: QHY163m / Fujifilm X-A1 (modded) / Fuji X-A2 (not modded) / Orion StarShoot Auto Guider
User avatar
Gordon
Site Admin
Articles: 704
Posts: 5691
Joined: Wed Apr 24, 2019 10:52 pm
2
Location: Cottonwood, AZ
Contact:

TSS Awards Badges

TSS Photo of the Day

I Broke The Forum.

Re: f/4 8in PYREX astrograph mirror project

#3

Post by Gordon »

Congratulations on the 'gifted' mirror!

I will be watching your progress and hope to see the finished scope soon!!
Gordon
Scopes: Explore Scientific ED80CF, Skywatcher 254N, Orion ST80, Orion Atlas EQ-g mount, Orion SSAG guider. Baader MPCC MkIII coma corrector, Vixen 70mm refractor. Lunt LS35THa solar scope. Skywatcher EQ5pro mount. Imagers: ZWO ASI1600 MM Cool, ZWO ASI533mc-Pro, ZWO ASI174mm-C (for use with my Quark chromosphere), ZWO ASI120MC Filters: LRGB, Ha 7nm, O-III 7nm, S-II 7nm Eyepieces: a few, Primary software: Cartes du Ciel, EQMOD, SGP, Nebulosity, Photoshop, StarTools V1.4
Blog: http://ghswen.blogspot.com/
Image
User avatar
BABOafrica
Milky Way Ambassador
Articles: 0
Posts: 1746
Joined: Tue May 07, 2019 2:41 pm
2
Location: Kenya

TSS Awards Badges

TSS Photo of the Day

Re: f/4 8in PYREX astrograph mirror project

#4

Post by BABOafrica »

Proceeding nicely,

Latest Ronchigram (outside RoC) side by side with the computer generated ideal:

BABO 8in AG 004 Ronchi-out.jpg
.............
BABO 8in AG 004 Ronchi IDEAL.jpg

BABO
"In lumine tuo videbimus lumen."

Scopes: Celestron SCT C8 / Williams Optics 66mm APO

Mounts: Orion Atlas EQ-G / Celestron AVX

Cameras: QHY163m / Fujifilm X-A1 (modded) / Fuji X-A2 (not modded) / Orion StarShoot Auto Guider
User avatar
John Donne
Orion Spur Ambassador
Articles: 0
Posts: 834
Joined: Mon Oct 05, 2020 5:34 am
1
Location: US

TSS Awards Badges

TSS Photo of the Day

Re: f/4 8in PYREX astrograph mirror project

#5

Post by John Donne »

Wow. This is an interesting thread.
Thank you for posting with iimages of your grinding progression.
SCOPES :ES127 f7.5, SW100 f9 Evostar, ES80 F6, LXD75 8" f10 SCT, 2120 10" f10 SCT, ES152 f6.5.
MOUNTS: SW AZ/EQ5, MEADE LXD75, CELESTRON CG4, Farpoint Parallelogram.
BINOCULARS: CL 10X30, Pentax 8X43, 25X100 Oberwerks.
EP: Many.


"I am not ashamed of the good news..." Rom 1:16
User avatar
Graeme1858
Universal Ambassador
Articles: 1
Posts: 5196
Joined: Mon Jun 24, 2019 7:16 pm
2
Location: North Kent, UK

TSS Awards Badges

TSS Photo of the Day

I Broke The Forum.

Re: f/4 8in PYREX astrograph mirror project

#6

Post by Graeme1858 »

What John said!

I missed this one when you first posted in February. Looking forward to seeing how the project progresses.

Regards

Graeme
______________________________________________
Click Here for the AP Processing Challenge!
______________________________________________
Celestron 9.25 f10 SCT, CGX mount.
ZWO ASI294MC Pro, Canon 600D, Altair GPCAM2 290C.
Celestron 80mm Guidescope, QHY5-II Mono.
APM 11x70 ED APO Binoculars.
Image
User avatar
Makuser
Moderator
Articles: 0
Posts: 4366
Joined: Mon May 06, 2019 12:53 am
2
Location: Rockledge, FL.

TSS Awards Badges

Re: f/4 8in PYREX astrograph mirror project

#7

Post by Makuser »

Hi Joe. I remember back in the 1960's when several of us went to the Adler Planetarium near downtown Chicago to grind and polish 6" and 8" f/8 Newtonian parabolic mirrors. At the time, we used red rouge (iron oxide), but the preferred optical polish is now cerium oxide. Your Ronchi patterns look quite good Joe, and thanks for keeping an otherwise "lost art" alive.
Marshall
Sky-Watcher 90mm f/13.8 Maksutov-Cassegrain on motorized Multimount
Orion Astroview 120ST f/5 Refractor on EQ3 mount
Celestron Omni XLT150R f/5 Refractor on CG4 mount with dual axis drives.
Orion 180mm f/15 Maksutov-Cassegrain on CG5-GT Goto mount.
Orion XT12i 12" f/4.9 Dobsonian Intelliscope.
Kamakura 7x35 Binoculars and Celestron SkyMaster 15x70 Binoculars. ZWO ASI 120MC camera.
>)))))*>
User avatar
yobbo89
Moderator
Articles: 0
Posts: 2265
Joined: Sat May 11, 2019 7:44 pm
2
Location: australia qld brisbane

TSS Photo of the Day

Re: f/4 8in PYREX astrograph mirror project

#8

Post by yobbo89 »

here is a silly question , do you grind a mirror as such to be spherical or parabolic to deal with coma for a fast mirror ?
scopes :gso/bintel f4 12"truss tube, bresser messier ar127s /skywatcher 10'' dob,meade 12'' f10 lx200 sct
cameras : asi 1600mm-c/asi1600mm-c,asi120mc,prostar lp guidecam, nikkon d60, sony a7,asi 290 mm
mounts : eq6 pro/eq8/mesu 200 v2
filters : 2'' astronomik lp/badder lrgb h-a,sII,oIII,h-b,Baader Solar Continuum, chroma 3nm ha,sii,oiii,nii,rgb,lowglow,uv/ir,Thousand Oaks Solar Filter,1.25'' #47 violet,pro planet 742 ir,pro planet 807 ir,pro planet 642 bp ir.
extras : skywatcher f4 aplanatic cc, Baader MPCC MKIII Coma Corrector,Orion Field Flattener,zwo 1.25''adc.starlight maxi 2" 9x filter wheel,tele vue 2x barlow .

Image
User avatar
notFritzArgelander
Infinity and Beyond Ambassador
Articles: 0
Posts: 12919
Joined: Fri May 10, 2019 4:13 pm
2
Location: Idaho US

TSS Awards Badges

Re: f/4 8in PYREX astrograph mirror project

#9

Post by notFritzArgelander »

yobbo89 wrote: Sat Mar 13, 2021 5:41 pm here is a silly question , do you grind a mirror as such to be spherical or parabolic to deal with coma for a fast mirror ?
You can't get rid of coma on a mirror. If you grind to a sphere you get spherical aberration and fuzz. If you grind to a parabola you get coma but sharp images on axis. You need to add a lens system to get rid of the coma.
Scopes: Refs: Orion ST80, SV 80EDA f7, TS 102ED f11 Newts: 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 III, Vixen Porta II, Celestron CG5, Orion Sirius EQG
User avatar
yobbo89
Moderator
Articles: 0
Posts: 2265
Joined: Sat May 11, 2019 7:44 pm
2
Location: australia qld brisbane

TSS Photo of the Day

Re: f/4 8in PYREX astrograph mirror project

#10

Post by yobbo89 »

notFritzArgelander wrote: Sat Mar 13, 2021 10:13 pm
yobbo89 wrote: Sat Mar 13, 2021 5:41 pm here is a silly question , do you grind a mirror as such to be spherical or parabolic to deal with coma for a fast mirror ?
You can't get rid of coma on a mirror. If you grind to a sphere you get spherical aberration and fuzz. If you grind to a parabola you get coma but sharp images on axis. You need to add a lens system to get rid of the coma.
I don't want to distract too much from babo,s post, i'll keep it short, so we need to make sure to have a parabola mirror? i kind of know what sphereical aberration is, been doing a little read up on hubbels wonky untested mirror :lol: ..

can we use spherical mirrors or lenses if that's the case for main optics at all ?
how does one determine the curve for the parabola grinding process,i assume it's little flatter on the edges of the mirror, does the focult test show the parabola curve on the test ?
scopes :gso/bintel f4 12"truss tube, bresser messier ar127s /skywatcher 10'' dob,meade 12'' f10 lx200 sct
cameras : asi 1600mm-c/asi1600mm-c,asi120mc,prostar lp guidecam, nikkon d60, sony a7,asi 290 mm
mounts : eq6 pro/eq8/mesu 200 v2
filters : 2'' astronomik lp/badder lrgb h-a,sII,oIII,h-b,Baader Solar Continuum, chroma 3nm ha,sii,oiii,nii,rgb,lowglow,uv/ir,Thousand Oaks Solar Filter,1.25'' #47 violet,pro planet 742 ir,pro planet 807 ir,pro planet 642 bp ir.
extras : skywatcher f4 aplanatic cc, Baader MPCC MKIII Coma Corrector,Orion Field Flattener,zwo 1.25''adc.starlight maxi 2" 9x filter wheel,tele vue 2x barlow .

Image
User avatar
notFritzArgelander
Infinity and Beyond Ambassador
Articles: 0
Posts: 12919
Joined: Fri May 10, 2019 4:13 pm
2
Location: Idaho US

TSS Awards Badges

Re: f/4 8in PYREX astrograph mirror project

#11

Post by notFritzArgelander »

yobbo89 wrote: Sun Mar 14, 2021 8:30 am
notFritzArgelander wrote: Sat Mar 13, 2021 10:13 pm
yobbo89 wrote: Sat Mar 13, 2021 5:41 pm here is a silly question , do you grind a mirror as such to be spherical or parabolic to deal with coma for a fast mirror ?
You can't get rid of coma on a mirror. If you grind to a sphere you get spherical aberration and fuzz. If you grind to a parabola you get coma but sharp images on axis. You need to add a lens system to get rid of the coma.
I don't want to distract too much from babo,s post, i'll keep it short, so we need to make sure to have a parabola mirror? i kind of know what sphereical aberration is, been doing a little read up on hubbels wonky untested mirror :lol: ..

can we use spherical mirrors or lenses if that's the case for main optics at all ?
how does one determine the curve for the parabola grinding process,i assume it's little flatter on the edges of the mirror, does the focult test show the parabola curve on the test ?
For a given aperture, if you make the focal length long enough the difference between a sphere and a parabola becomes negligible. IIRC for an 8" that's f9 or slower. Foucault testing can show the difference .
Scopes: Refs: Orion ST80, SV 80EDA f7, TS 102ED f11 Newts: 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 III, Vixen Porta II, Celestron CG5, Orion Sirius EQG
User avatar
BABOafrica
Milky Way Ambassador
Articles: 0
Posts: 1746
Joined: Tue May 07, 2019 2:41 pm
2
Location: Kenya

TSS Awards Badges

TSS Photo of the Day

Re: f/4 8in PYREX astrograph mirror project

#12

Post by BABOafrica »

Special thanks to nFA for the explanations. I would add to what he said, in case it's not obvious, that I working on a parabolic mirror for a Newtonian reflector. (There are different kinds of reflectors, e.g., SCTs, RCs, etc. Instead of using a parabolic primary and flat secondary, they have different primary and secondary mirrors.)

Anyway, that said, I am reporting on my current status.

I have only had time to do 6 figuring sessions total. But things are going smoothly. Here is where I stand now. (I started doing interferometry testing, now that I am getting close to parabolic).

RONCHIGRAM (outside RoC):
BABO 8in AG 006 Ronchi-out.jpg

Foucault test

FXP 0 AG 006_Surface NEW.gif



Wavefront from interferometer test:

BABO 8in AG 006 wavefront.JPG

BABO
"In lumine tuo videbimus lumen."

Scopes: Celestron SCT C8 / Williams Optics 66mm APO

Mounts: Orion Atlas EQ-G / Celestron AVX

Cameras: QHY163m / Fujifilm X-A1 (modded) / Fuji X-A2 (not modded) / Orion StarShoot Auto Guider
User avatar
notFritzArgelander
Infinity and Beyond Ambassador
Articles: 0
Posts: 12919
Joined: Fri May 10, 2019 4:13 pm
2
Location: Idaho US

TSS Awards Badges

Re: f/4 8in PYREX astrograph mirror project

#13

Post by notFritzArgelander »

This is looking very good so far!
Scopes: Refs: Orion ST80, SV 80EDA f7, TS 102ED f11 Newts: 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 III, Vixen Porta II, Celestron CG5, Orion Sirius EQG
User avatar
helicon
Co-Administrator
Articles: 219
Posts: 8824
Joined: Mon May 06, 2019 1:35 pm
2
Location: California

TSS Awards Badges

Re: f/4 8in PYREX astrograph mirror project

#14

Post by helicon »

I remember grinding my own mirror back in the 80's. It was a fun project. Congrats on your progress BABO!
-Michael
Dobsonian: 10" Zhumell f/4.9
Refractors: ES AR152 f/6.5 Achromat on Twilight II, KOWA 90mm spotting scope
Grab-n-go: AWB 5.1" Onesky Newtonian
Binoculars: Oberwerk 25x100, Celestron SkyMaster 15x70, Bushnell 10x50
Eyepieces: Explore Scientific line, GSO Superview, 9mm Plossl, Edmund 28mm RKE
Camera: ZWO ASI 120
Naked Eye: Two Eyeballs
User avatar
OzEclipse
Milky Way Ambassador
Articles: 2
Posts: 1378
Joined: Sat May 11, 2019 8:11 am
2
Location: Young, NSW, Australia, 34S, 148E
Contact:

TSS Awards Badges

TSS Photo of the Day

Re: f/4 8in PYREX astrograph mirror project

#15

Post by OzEclipse »

Nice work Babo. Looking good from what I remember of test patterns.
Joe
"34 South: The Hilltops Observatory"
Central West NSW
AUSTRALIA
Joe Cali

Bortle 1-2 skies, 148 E, 34 S

Amateur astronomer since 1978
Astronomical interests : astrophotography, visual observing, nightscape photography, solar eclipse chasing
asteroidal occultations, nightscape astrophotography workshops

web site : http://joe-cali.com/
Scopes: ATM 18" Dob, Vixen VC200L, ATM 6"f7, ED80, M70, Orion 102 Maksutov, ST80.
Mounts: Takahashi EM-200, iOptron iEQ45, Push dobsonian with Nexus DSC, three homemade EQ's.
Eyepieces: TV 31, 17, 12, 7 Naglers; D21, D14 Denkmeier’s; Pentax XW10, XW5, Unitron 40mm Kellner, Meade Or 25,12
Cameras : Pentax K1, K5, K01, K10D / VIDEO CAMS : TacosBD, Lihmsec.
User avatar
BABOafrica
Milky Way Ambassador
Articles: 0
Posts: 1746
Joined: Tue May 07, 2019 2:41 pm
2
Location: Kenya

TSS Awards Badges

TSS Photo of the Day

Re: f/4 8in PYREX astrograph mirror project

#16

Post by BABOafrica »

After some more work on this mirror, I finally finished it. Not as smooth as I would have liked it. But I think it will be ok. I sent it for the coatings (with Majestic in the US). It will probably take a couple of months before I get it back in Nairobi.

The mirror is an f/4 8" Pyrex (diameter = 195mm and FL = 777)

Here's the Ronchigram (outside of RoC) and the results from taking a series of igrams (with my DIY Bath interferometer & processed with DFTFringe).

I also include a shot of the Moon that I did with the mirror mounted in the OTA (using my Fuji X-A1)

BABO 195-1555 r-gram outside FINAL.JPG
...
wavefront capture 02 -- Screenshot 2021-11-19 160021.jpg
...
DSCF9202.JPG

BABO
"In lumine tuo videbimus lumen."

Scopes: Celestron SCT C8 / Williams Optics 66mm APO

Mounts: Orion Atlas EQ-G / Celestron AVX

Cameras: QHY163m / Fujifilm X-A1 (modded) / Fuji X-A2 (not modded) / Orion StarShoot Auto Guider
User avatar
notFritzArgelander
Infinity and Beyond Ambassador
Articles: 0
Posts: 12919
Joined: Fri May 10, 2019 4:13 pm
2
Location: Idaho US

TSS Awards Badges

Re: f/4 8in PYREX astrograph mirror project

#17

Post by notFritzArgelander »

Good to see that you are making excellent progress toward a happy conclusion!
Scopes: Refs: Orion ST80, SV 80EDA f7, TS 102ED f11 Newts: 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 III, Vixen Porta II, Celestron CG5, Orion Sirius EQG
User avatar
Lady Fraktor
Co-Administrator
Articles: 0
Posts: 7036
Joined: Mon Apr 29, 2019 9:14 pm
2
Location: Slovakia

Re: f/4 8in PYREX astrograph mirror project

#18

Post by Lady Fraktor »

Very nice Babo, it looks like you are progressing well with the mirror.
Refractors: Antares 105mm f/15 (modified), Bresser 102mm f/13.2, Celestron 150mm f/8 (modified), Homemade 70mm f/10 (LZOS K8/F8 doublet), Stellarvue NHNG Deluxe 80mm f/6.9, TAL 100RS f/10, Teleskop-Service 102mm f/11, Vixen ED115s f/7.7
EQ Mounts: Celestron CG-5, Celestron ASGT (modified), Skywatcher EQ-5, TAL MT-1, Vixen SXP/ Berlebach Planet
Az/ Alt Mounts: Celestron SLT (modified), Manfrotto 055B/ RC28, Manfrotto 028B/ Stellarvue M2C/ Argo Navis
Diagonal: 2” Astro-Physics MaxBright, 2” Stellarvue Deluxe, 2” TAL dielectric, 2” TeleVue Everbrite, 2” Baader DX-2 Amici prism, 2” Long Perng Amici prism, 2” Baader Herschel wedge
Eyepieces: Antares to Zeiss, definitely more than 1 person requires
Image
Post Reply

Return to “ATM”