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First Scope - 6in F8

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#26 Matthew Paul

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Posted 20 June 2017 - 03:46 PM

Narrow width and stoke? Or just narrow width W - full length strokes to smooth it out? 
Correction looks ok though? This seems like it is the closest that I've had it so far. 

You are judging that there is a hill by the very slight bowing of the very center of the middle white band? 



#27 Pinbout

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Posted 20 June 2017 - 03:46 PM

compare

 

6inf82lines.gif


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#28 Pinbout

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Posted 20 June 2017 - 03:48 PM

normal length narrow. it will be so easy to overcorrect it if you do much more.



#29 Matthew Paul

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Posted 20 June 2017 - 03:54 PM

Ah yes. Well thank you very much Danny. Ill give it a go tomorrow and see how it comes out. I'll post a photo once I'm done. 

Thank you again. You are very helpful. 


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#30 Pinbout

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Posted 20 June 2017 - 09:36 PM

Oh one thing

 

Warm press 1st (both mirror and tool) let cool for 15 mins then have at it



#31 Matthew Paul

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Posted 21 June 2017 - 06:29 AM

Sure thing.

I star tested it last night. I let the scope cool for hours to see if it was due to the rapid temperature drop or not, but the mirror is fairly over corrected. A little earlier breakout of the secondary diffraction ring and very bright secondary ring outside of focus. I guess I'll do a little tool on top and see if I can tone it down.


Edited by Matthew Paul, 21 June 2017 - 07:31 AM.


#32 Pinbout

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Posted 21 June 2017 - 06:39 AM

waytogo.gif



#33 Pinbout

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Posted 21 June 2017 - 08:06 AM

wait

 

what eyepiece were you using



#34 Matthew Paul

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Posted 21 June 2017 - 08:43 AM

Meade 9mm Plosle from the ext70 era. Not a 4000 or 5000 series. 



#35 Matthew Paul

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Posted 21 June 2017 - 08:47 AM

also, the radius of curvature is 93.625" not a true F8. I guess I should have mentioned that earlier but I just forgot about it. Ether way if it was figured to a true F8, it would be under corrected not overcorrected, no?

I wonder if that central hill is causing the brightening of the inner ring some... That would move the very center further out in focus, I think? Which would cause some brightening of the inner diffraction ring?


Edited by Matthew Paul, 21 June 2017 - 08:51 AM.


#36 Pinbout

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Posted 21 June 2017 - 09:09 AM

 

I wonder if that central hill is causing the brightening of the inner ring some...

no, its in the shadow

 

I only use TV's to star test, then test specific eyepieces against those to know if the eyepiece is adding correction or not.

 

barlows will add a lot of correction so nvr use one.



#37 Pinbout

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Posted 21 June 2017 - 09:22 AM

here's what 6inf7.8 looks like not much difference

 

I'd say your a little under corrected in the last .25" of the radius, but that's why its so hard to correct a mirror with ronchi simulations.

 

so was the glass at ambient temp, and again the eyepiece, is it adding the correction.

 

your so close you shouldn't be getting a very bright ring around the break out like

 

https://www.youtube....tdYBmSapio&t=2s

 

 

 

6inf7.8.jpg


Edited by Pinbout, 21 June 2017 - 09:26 AM.


#38 Matthew Paul

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Posted 21 June 2017 - 09:39 AM

Similar, to the video, yes. The temperature dropped a significant amount last night, maybe 25-30 deg in just a couple hours, but I did wait until 11pm to do the final check. Let me see if I have time this morning Ill try and get a foucault image and measurements. 



#39 Matthew Paul

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Posted 22 June 2017 - 10:34 AM

I finally figured out the issues Id been having with the Foucault Testing, my light source was too large. I made the light source much smaller with a pinhole mask and got some readings. I checked 3 or 4 times and came up with very close results every time. According to this recent check, it is over corrected by quite a bit. It pretty much has the correction of a 6in f6 morror, instead of a 6in F8. 

I've very happy that I got this working for myself, now I can fine tune it, instead of relying on the ronchi screen. 

It has .081 overall correction instead of .068
I don't know how figure XP works, and I'm no pro, but there is no way that a 6in F7.8 figured as a 6inF6 is a 1/18th wave mirror......

readings1.jpg
readings2.jpg


And this is what a 6in f6 would be
6inf6.jpg


Edited by Matthew Paul, 22 June 2017 - 10:44 AM.


#40 Pinbout

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Posted 22 June 2017 - 11:39 AM

 

but there is no way that a 6in F7.8 figured as a 6inF6 is a 1/18th wave mirror......

xp is optimistic

 

if you want to temper the optimism always x2.5 to the numerator to come up with a safer number.

 

2.5/18.02 = .1387

 

so your in 1/7-1/8 ~ range.

 

so now just smooth it out with some rouge tot and be done with it and enjoy the stars...planets.

 

so the over correction you saw in the star test must either be the temp change in the glass or the eyepiece or both.


Edited by Pinbout, 22 June 2017 - 11:42 AM.

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#41 Matthew Paul

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Posted 22 June 2017 - 06:46 PM

I did one rotation of narrow W, 1/3 stoke, tool on top - with thin red rouge. 

After six new sets of measurements, averaging each zone, the mirror looks much better. I may take another set of measurements and look at the ronchi bands after.

Zone two is 5 thousandths under, and zone three is 9 thousandths under. 

readings3.jpg
readings4.jpg



#42 Matthew Paul

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Posted 22 June 2017 - 07:35 PM

I think that I may have finally finished... I'll star test it and see how it goes.. It looks like that little hill is still in the center... but we'll see how that effects the image. 

JS9F4331.jpg
JS9F4336.jpg



 


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#43 Pinbout

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Posted 22 June 2017 - 08:02 PM

Now your on the under corrected side of the fence.

 

Very good.



#44 Matthew Paul

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Posted 22 June 2017 - 10:22 PM

Thanks. I just star tested it after letting it sit for two hours with the little cooling fan on, as the clous passed. I'm very happy with what I saw. Jerry similar inside and outside. I'd say that there is a slightly better filling of light between the two main diffraction rings inside of focus, and some slightly more defined diffraction rings between the main two outside of focus.

I'm pleased with this. Thank you for the assistance Sir. I'll let you know what they say up at Stellafane.

#45 Pinbout

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Posted 23 June 2017 - 07:22 AM

tell dick parker pinbout [its my adopted Burmese name] said what's up. lol.gif


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#46 Pinbout

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Posted 23 June 2017 - 07:48 AM

if your ke readings are close to the real thing you should see very straight line in the autocollimator test with 2, even 1 line.

 

the autocollimator is unforgiving for any stig or zones, since it doubles the errors, makes them look x2 as bad as they really are.


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#47 Matthew Paul

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Posted 23 June 2017 - 09:44 AM

We will find out soon. I'm curious to see how close my less than idea test equipment, and knowledge - is. Learning is fun, and so is making stuff. This mirror making is right up my ally. 



#48 Matthew Paul

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Posted 12 July 2019 - 03:40 PM

So a lot of time has passed and I had it tested up at in vermont, but with two years past, I forgot what they had said, and I had just been using the telescope. 

 

Fast forward to today. 

 

I have an 8in autocollimation flat, and tested the system this afternoon. It shows it to be under corrected if my mind is functioning properly. 

 

This is inside focus:

20190712_163334.jpg

 

This is outside focus:

20190712_163411.jpg



#49 Pinbout

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Posted 12 July 2019 - 03:47 PM

remember dpac makes it look twice as bad... you can figure it out with the diffract program but off the top of my head I'd say 1/5~



#50 Matthew Paul

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Posted 12 July 2019 - 04:15 PM

I'm going to give it a once around the barrel and see how it comes out. I've got it stripped to re silver at the moment anyway, I might as well mess it up  lol.gif




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