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First Scope - 6in F8

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#51 Pinbout

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Posted 12 July 2019 - 04:28 PM

warm press, let cool, cold press... as long as the channels are same-same all over, you won't mess it up...unless the glass is still warm. lol.gif



#52 Matthew Paul

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Posted 12 July 2019 - 04:31 PM

Doing a warm press now. Figured I'd give it a half hour under the weights. And trust me, I can mess up any piece of glass smile.gif

 

I was looking at nova optical. http://www.nova-optical.com/Ronchi.Htm

 

Looks like its maybe 1/4 or so, like you said. I'd like to get it closer to at least 1/8, ideally perfect. But I'm going to take it slow to try to sneak up on ideal. 


Edited by Matthew Paul, 12 July 2019 - 04:33 PM.


#53 Matthew Paul

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Posted 12 July 2019 - 06:30 PM

Well. I think that's it. I did 20 strokes, counting each set of forward and back as one, not the entire w pass as one stoke. 

There is a little bit of tilt to something in the system, not sure if it's the way that the primary has to sit with the secondary location, but that's probably it I'd guess. But it looks really good to me!

Now I just need to wait for it to get dark. 

What do we think?? This is double pass AC, testing the entire scope against an 8in flat. 

final 6if8.jpg


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#54 Pinbout

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Posted 12 July 2019 - 06:33 PM

That looks real sweet. Great job.

 

take some star test images using shims under a 8mm eyepiece.



#55 Matthew Paul

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Posted 12 July 2019 - 06:44 PM

Thank you! The shims are to facilitate swapping inside to outside without racking the focuser?


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#56 Pinbout

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Posted 12 July 2019 - 07:49 PM

https://youtu.be/QxUQJjjsdW4


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#57 Matthew Paul

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Posted 12 July 2019 - 08:34 PM

It is bar far the sharpest that this scope has ever been, with ether my home made mirror or the gso mirror that I put in it while I was working on mine. Star test shows a little bit more light on the 2nd/inner diffraction ring outside of focus when compared to inside of focus, but it is slight.
I am very happy and will be silvering the primary tomorrow.


Edited by Matthew Paul, 12 July 2019 - 09:24 PM.


#58 Pinbout

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Posted 13 July 2019 - 08:16 AM

 

Star test shows a little bit more light on the 2nd/inner diffraction ring outside of focus when compared to inside of focus, but it is slight.

the first thing to look at is the 2ndry shadow size differences ...

 

sounds like its still under...good.

 

getting dpac results like above will prove better than 1/8~front. great job.


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#59 Cameron_C

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Posted 13 July 2019 - 08:59 AM

It is bar far the sharpest that this scope has ever been, with ether my home made mirror or the gso mirror that I put in it while I was working on mine. Star test shows a little bit more light on the 2nd/inner diffraction ring outside of focus when compared to inside of focus, but it is slight.
I am very happy and will be silvering the primary tomorrow.

Great job. I am very jealous!


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#60 DAVIDG

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Posted 13 July 2019 - 09:18 AM

 Matt,

   DPAC looks excellent, it tells the truth so your mirror is very good. A star test will show the same.  As Danny  said  for a star test  look at  the size of the shadow of the secondary on each side of focus using an eyepiece that focal length close to the F-ratio of the scope. So for you 8mm.  You want to defocus just a very small amount, so you just start to see the shadow of the secondary become visible and defocus the same amount on each side of focus.  Many make the mistake of defocusing too much and the sensitivity goes down which makes the optics look better then they really are.. If the shadow is larger on the inside vs the outside of focus it is under corrected, you'll see the opposite if it is   over corrected. You can watch the mirror change correction during the night as it cools.  My own 6" f/8 figured by DPAC will start off star testing like a sphere when I take it out on a cool/cold night and within 30 minutes show perfect correction. 

   Jupiter with that mirror will show you a "spacecraft fly by " type image, just full of detail that is lost with poorer optics.

 

                     - Dave 


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#61 Matthew Paul

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Posted 13 July 2019 - 10:14 AM

Great job. I am very jealous!

Thank you!

 

the first thing to look at is the 2ndry shadow size differences ...

 

sounds like its still under...good.

 

getting dpac results like above will prove better than 1/8~front. great job.

Thank you. I'll check that tonight and see what it looks like. 

 

 Matt,

   DPAC looks excellent, it tells the truth so your mirror is very good. A star test will show the same.  As Danny  said  for a star test  look at  the size of the shadow of the secondary on each side of focus using an eyepiece that focal length close to the F-ratio of the scope. So for you 8mm.  You want to defocus just a very small amount, so you just start to see the shadow of the secondary become visible and defocus the same amount on each side of focus.  Many make the mistake of defocusing too much and the sensitivity goes down which makes the optics look better then they really are.. If the shadow is larger on the inside vs the outside of focus it is under corrected, you'll see the opposite if it is   over corrected. You can watch the mirror change correction during the night as it cools.  My own 6" f/8 figured by DPAC will start off star testing like a sphere when I take it out on a cool/cold night and within 30 minutes show perfect correction. 

   Jupiter with that mirror will show you a "spacecraft fly by " type image, just full of detail that is lost with poorer optics.

 

                     - Dave 

I'll try again tonight and see what it looks like. I broke out the ol start testing book to skim over again this morning. Jupiter showed good promise last night uncoated, though it was very muted color wise. The moon was exceptionally sharp even with a 6.5mm cheep no name eye piece. 

I just finished silvering the mirror. Unfortunately the glass is very scratched, but its too late to do anything about that now. Ill be trying it out tonight and hopefully it gives me great results on Jupiter! I was rather displeased with the view prior to this. A 4.5in scope that a nice lady had made up in Vermont had shown more detail that this one did. Hopefully it is better now. 

it is difficult for me to keep debris off of the glass when polishing as I did this one in my blacksmith shop, and the one that I'm working on now, I'm doing at the end of a vegetable farm. Both very dusty and dirty environments without running water. 

IMG_0122.jpg

 



#62 Matthew Paul

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Posted 13 July 2019 - 10:09 PM

Super happy with the results of this mirror. I can see cloud detail in jupiter that I never could have in this scope before. Bulges in the bands and darker spots near the polar regions. When I first pointed the scope at jupiter I thought something was wrong as there were four dots in a mirrored geometric shape.  The moons were just in an uncommon location, haha, whoops! Very happy though.  Thank you to everyone that helped me through the process. Your assistance is very much appreciated.  I'll see how this scope does with some planitary photography later this week. I have a feeling that it will do well.



#63 Matthew Paul

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Posted 22 July 2019 - 09:32 AM

Though I did not  build the scope for imaging, I wanted to share what it is capable of under not so ideal conditions. Very happy with the results of the optics. I need to build a better OTA for it. It's rather flimsy, the spider is not rigid, the tube flexes, and the focuser is just a plastic rack and pinion, but it works very well for now, and the hard part (the optics) are done. Thank you again to everyone that offered information and assistance as I worked on the mirror. 

MVI_0140-3.jpg


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#64 ed_turco

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Posted 22 July 2019 - 10:32 AM

Though I did not  build the scope for imaging, I wanted to share what it is capable of under not so ideal conditions. Very happy with the results of the optics. I need to build a better OTA for it. It's rather flimsy, the spider is not rigid, the tube flexes, and the focuser is just a plastic rack and pinion, but it works very well for now, and the hard part (the optics) are done. Thank you again to everyone that offered information and assistance as I worked on the mirror. 

attachicon.gif MVI_0140-3.jpg

That image ought to give apo owners pause.


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#65 JamesMStephens

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Posted 22 July 2019 - 11:42 AM

There is real poetic justice in how well a good Newtonian telescope performs.

 

Jim


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#66 Matthew Paul

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Posted 26 July 2019 - 08:45 AM

There is real poetic justice in how well a good Newtonian telescope performs.

 

Jim

 

That image ought to give apo owners pause.

Thank you very much. I posted this in the imaging forum already, but this is my first image of Saturn... I was very surprised with the results.  I'll have the scope up at Stellafane next week, if I make it there. 

Saturn07-24-19.jpg


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#67 DAVIDG

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Posted 26 July 2019 - 09:05 AM

 That is power of stacking images and optics made by double pass autocollimation. None of the errors that Foucault testing have so when you have straight Ronchi bands the optics will be excellent. Hope to see you at Stellafane and that you enter your scope in the optical judging.

 

                          - Dave 


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#68 Matthew Paul

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Posted 26 July 2019 - 12:35 PM

If I made it up, Ill see you there. Hopefully everything works out so that I can come. 



#69 Matthew Paul

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Posted 06 August 2019 - 04:19 PM

I'm not posting this to brag, but share my joy and surprise. I was hoping to receive an honorable mention at best. Completely blown away. Thank you to everyone who gave me input throughout the process.

...Made my heart go "pitter-patter" when they called my name. 

Three of use actually were awarded 1st prize, and no 2nd or third as there were 3 who scored "within .5pt of each other." Always a good time up there in VT, so many kind and knowledgeable people.

1stoptics.jpg

 


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#70 tim53

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Posted 07 August 2019 - 10:26 AM

Yeah I'm not using a flat... so if my test looked like that, I would have a spherical mirror. But, if I had a flat....

 

Am I missing something? 

Edit:  Oops, I was responding to an old post.

 

Look up using an oil flat for DPAC testing.  It's cheap, but you do have to set your mirror on a stand facing down, in such a way that it can't fall.

 

I've done it with whole OTAs.  Here's a Cave 8" f/7 being tested.  I take the focuser off and set a camera with the ronchi screen up on a stand that I can adjust position on.  Taking the focuser off gives me more room to find the reflection:

 

post-6788-0-94936300-1450056947.jpg

 

 

-Tim.


Edited by tim53, 07 August 2019 - 10:54 AM.

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#71 geovermont

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Posted 07 August 2019 - 11:28 AM

Matthew,

Congratulations! I'm in complete agreement with you about the experience of standing up there in the shadow of so many great telescope artisans. I felt the same way.

George Springston


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#72 Matthew Paul

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Posted 07 August 2019 - 11:52 AM

Matthew,

Congratulations! I'm in complete agreement with you about the experience of standing up there in the shadow of so many great telescope artisans. I felt the same way.

George Springston

It was great to meet and spending some time with you and the telescopes, up there.

George also received a 1st place ribbon. His scope was phenomenal. George pushed his wooden tubed 6inF8 around the sky as we waited for the judges, looking at all types of different things. It was a wonderful time, and a super clear night for the first few hours. 


Edited by Matthew Paul, 07 August 2019 - 11:52 AM.


#73 bremms

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Posted 09 August 2019 - 08:16 AM

That image ought to give apo owners pause.

Yes.. A truly GOOD mirror will do this as most of us know.


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#74 geovermont

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Posted 10 August 2019 - 01:27 PM

I've found that a 6-inch f/8 newtonian is truly a versatile scope. No, it won't reveal the Veil Nebula in all its glory, but I did just complete the Messier Objects with mine. All except M74 were found using an Escopes (Coulter) commercial mirror. Last week I installed my hand-ground and figured mirror and it's now even better. I was finally able to pick out M74 last Monday evening--not sure whether it was better seeing conditions, more familiarity with the star field, or the improved optics. And of course I've had some excellent views of Jupiter, Saturn, the moon, etc. with the scope. In the coming months I'll be looking to see how close a double can be split with the new and improved scope (Epsilon Lyrae is quite easy) and I'll renew my attempts to view the companion to Sirius ("The Pup"). There's still plenty more to pick out with the 6 inch!

 

And that's just visual observing. Matthew's beautiful photo hints at what can be done with the new technology that is becoming available.

 

George Springston


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