Help plz :) Geting an eye shaped airy disc not circular.

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Help plz :) Geting an eye shaped airy disc not circular.

#1

Post by TheButcher »


Hey all,

I just installed Bobs knobs on my secondary and when I went out tonight, I kept getting this shape when I go out of focus to see if it is collimated. I tried for a couple hours. Anyone know what went wrong? Also I was trying to add a rigel nstep focuser and took the knob off and the three screws to orange circular celestron mount plate. But The rigel nestep I got was not made for the C-11, so I put everything back (I only took them out for a bit after realizing I nee a different adapter Rigel plate, but then put back in and returned it to normal. Could that have anything do do with it or would it be the knobs that I just installed at the same time.

Thanks :)

Here is the photo

Image
Telescopes:Apertura AD12 Dob + Rings for EQ mode Mounts: iOptron CEM70 w/ Tri-Pier Barlows:GSO 2x Shorty Focuser: Rigel nStep Cameras: ZWO174mm

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Re: Help plz :) Geting an eye shaped airy disc not circular.

#2

Post by sdbodin »


Maybe one of the Bob knobs did not engage the captured nut and the secondary is pointing side ways quite a bit. That's my only guess, no clue on the focuser mod.

Steve
Scopes; Meade 16 LX200, AT80LE, plus bunch just sitting around gathering dust
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Re: Help plz :) Geting an eye shaped airy disc not circular.

#3

Post by John Baars »


Is this shot taken on the optical axis? If so, something is in the light path.
If not It seems to me that the left edge is the edge of the field and the right edge is the edge of a unfocussed star in a badly collimated telescope.
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Re: Help plz :) Geting an eye shaped airy disc not circular.

#4

Post by TheButcher »


Thanks guys

The shot was taken on the Optical axis I believe?. I just used my 1600mm and defocused the Star if that is what you mean John.

And I think Steve, when I adjusted the secondary I checked to see if all the knobs were engaged and they were and did some more test.
Here are some more photos below. The first one was taken before and just showing the same image with the focus in more. The second image is when I loosend the secondary knobs all the way until it came out (1 at a time while having two knobs of the secondary still in) It seems it made a little change. I kept trying but this was the best I could do last night with the clouds rolling in and the corrector dewing up. By the way the star was Vega.

I also just made sure the focuer screws holding the plate were not to tight and not to loose, but that did not seem to have any effect. The only noticeable changes were when I messed with the secondary. IT seems like part of the image is nto lining up and getting cut off in an arc part.

Photo of unfocused Star (Vega) focused in more and with lower gain. In the first picture I raised the gain a bit to show the effect I was having.
Image

Photo of when I loosend the secondary knobs all the way (1 at a time while having two knobs of the secondary still in to have it secured) Notice how the shape changed.

Image

Thanks again for the help guys. So from here, I may try to re install the original secondary screws? also is there a way to test it using a chesire indoors? I don't think I could set up an artificial star to test since my yard is not to big and have 6ft fences all around and can only view over 20 degrees and tonight and tomorrow night they are predicting mostly cloudy skies. Hopefully I can test another?

Also to mention I just looked at the original secondary screws and they seem to be alot shorter then the knobs. I will take a photo of the 2 types of secondary screws (Bobs knobs and the original).

Thanks again :)
Telescopes:Apertura AD12 Dob + Rings for EQ mode Mounts: iOptron CEM70 w/ Tri-Pier Barlows:GSO 2x Shorty Focuser: Rigel nStep Cameras: ZWO174mm

See All of my Images at: https://astronebula.com/slide-show/
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Re: Help plz :) Geting an eye shaped airy disc not circular.

#5

Post by sdbodin »


Well, seems to be a Bobs problem, put back the original screws and give Bob the boot.

Just guessing,
Steve
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Re: Help plz :) Geting an eye shaped airy disc not circular.

#6

Post by TheButcher »


yeah, one issue I noticed with them is that when I loosened them it took a while for them to screw out due to the length. And in order to make them a little tight I would have to screw them in more if not the knobs would be very loose. Maybe that explains it. I will get a chance to reinstall them in a few hours and take photos of the length comparison.

Thanks Steve :)
Telescopes:Apertura AD12 Dob + Rings for EQ mode Mounts: iOptron CEM70 w/ Tri-Pier Barlows:GSO 2x Shorty Focuser: Rigel nStep Cameras: ZWO174mm

See All of my Images at: https://astronebula.com/slide-show/
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Re: Help plz :) Geting an eye shaped airy disc not circular.

#7

Post by JayTee »


TheButcher wrote: Sun May 17, 2020 5:06 pm yeah, one issue I noticed with them is that when I loosened them it took a while for them to screw out due to the length. And in order to make them a little tight I would have to screw them in more if not the knobs would be very loose. Maybe that explains it. I will get a chance to reinstall them in a few hours and take photos of the length comparison.

Thanks Steve :)
I have a set of Bob's knobs in my toolbox that I bought for my C11. I too noticed that the thread lengths were longer than the factory installed screws that adjust the secondary mirror in my C11. This is why the Bob's knobs are still sitting in the toolbox.

Cheers,
JT
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Re: Help plz :) Geting an eye shaped airy disc not circular.

#8

Post by TheButcher »


JayTee wrote: Sun May 17, 2020 11:09 pm
TheButcher wrote: Sun May 17, 2020 5:06 pm yeah, one issue I noticed with them is that when I loosened them it took a while for them to screw out due to the length. And in order to make them a little tight I would have to screw them in more if not the knobs would be very loose. Maybe that explains it. I will get a chance to reinstall them in a few hours and take photos of the length comparison.

Thanks Steve :)
I have a set of Bob's knobs in my toolbox that I bought for my C11. I too noticed that the thread lengths were longer than the factory installed screws that adjust the secondary mirror in my C11. This is why the Bob's knobs are still sitting in the toolbox.

Cheers,
JT
Thanks for the clarification JT I don't want to go bald yet thinking what the possible issue was :)

I put the original screws in, but could not collimate. I am gona try to do the DIY in the house artificial star. I got about 75 ft that I can place the contraption that I make. I just read some tutorials but open for other ideas? It is gona be cloudy and rainy the next few days so I brought the whole setup to my basement to do some work on it an also do some software work with the mount, like control through Stelarium ect...


Anyway here are some photos that I took earlier today. I used my good old Celestron chesire eyepiece. Not sure if it would help with it, but looking into it I did notice the odd image and not matching the cross hairs. I then did another image of it which is the last when I red did the original screws in, but not collimated yet. But I saw a difference at least I think and all I did was just blindly re install them.

Picture comparison of both screw and knobs. I tried to accurately place them even with the camera angle as best I could.
Image

Look though the Cheshire Hole with Bobs Knobs installed. That kind of resembles of what I was seeing huh?
Image

Image of the original screws back in place with no collimation, I just put them in the best I could
Image

Thanks again all :)
Telescopes:Apertura AD12 Dob + Rings for EQ mode Mounts: iOptron CEM70 w/ Tri-Pier Barlows:GSO 2x Shorty Focuser: Rigel nStep Cameras: ZWO174mm

See All of my Images at: https://astronebula.com/slide-show/
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Re: Help plz :) Geting an eye shaped airy disc not circular.

#9

Post by sdbodin »


Yup, the posted alignment pic does show the tilt. I always follow this rule "If ain't broke, don't fix it"

Works for me,
Steve
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Re: Help plz :) Geting an eye shaped airy disc not circular.

#10

Post by JayTee »


Steve,

Make a Duncan mask and make your life easier. Use the CLEAN top of a large pizza box. Go here to see how to create the mask. It should take about 15-20 minutes. Once you use it, you'll never go back to using anything else.
http://alpha-lyrae.co.uk/2013/12/31/sch ... ncan-mask/

Cheers,
JT
∞ Primary Scopes: #1: Celestron CPC1100 #2: 8" f/7.5 Dob #3: CR150HD f/8 6" frac
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∞ G&G Scopes: #1: Meade 102mm f/7.8 #2: Bresser 102mm f/4.5
∞ Guide Scopes: 70 & 80mm fracs -- The El Cheapo Bros.
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Re: Help plz :) Geting an eye shaped airy disc not circular.

#11

Post by TheButcher »


That's a great thing JT, Thx for the tip. I am gona make one ASAP.
Telescopes:Apertura AD12 Dob + Rings for EQ mode Mounts: iOptron CEM70 w/ Tri-Pier Barlows:GSO 2x Shorty Focuser: Rigel nStep Cameras: ZWO174mm

See All of my Images at: https://astronebula.com/slide-show/
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Re: Help plz :) Geting an eye shaped airy disc not circular.

#12

Post by notFritzArgelander »


JayTee wrote: Mon May 18, 2020 12:51 am Steve,

Make a Duncan mask and make your life easier. Use the CLEAN top of a large pizza box. Go here to see how to create the mask. It should take about 15-20 minutes. Once you use it, you'll never go back to using anything else.
http://alpha-lyrae.co.uk/2013/12/31/sch ... ncan-mask/

Cheers,
JT
That's a great tip.
I installed Bob's Knobs on the MK66 with no problems. Clearly there is something amiss, though.
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Re: Help plz :) Geting an eye shaped airy disc not circular.

#13

Post by TheButcher »


I made the artificial pinhole with flash light star thing and tried it out in my basement about 40-50ft away and I was able to see a normal looking airy disc. It still needs to be collimated the disc was to big to fit on the screen to know which way to collimate plus I am gona do one of those Duncan masks that JT mentioned.

Thanks again all :)
Telescopes:Apertura AD12 Dob + Rings for EQ mode Mounts: iOptron CEM70 w/ Tri-Pier Barlows:GSO 2x Shorty Focuser: Rigel nStep Cameras: ZWO174mm

See All of my Images at: https://astronebula.com/slide-show/
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Re: Help plz :) Geting an eye shaped airy disc not circular.

#14

Post by TheButcher »


Just a little follow up here. I took out Bobs knobs and returned them and put the originals in.

This was the first image blindly putting in the original screws. It is only a bit off with no collimation attempts. The length of those screws must of had some kind of effect.

Image


Also I made a Duncan mask Thx JT. I bought a circular cutter for about $10 and some Foam board for a few bucks and a circular Compass for a couple of bucks.

And here is my 2nd attempt. The first one was too small. This seems to fit right, the inner circle is slightly larger then the secondary, but I think I will just put some good old painters tape or Duct Tape so it fits snug. Or just make another one, I enough board left for 3 more. I have not tried it out yet due to weather. But will post photos when I do.

Image
Telescopes:Apertura AD12 Dob + Rings for EQ mode Mounts: iOptron CEM70 w/ Tri-Pier Barlows:GSO 2x Shorty Focuser: Rigel nStep Cameras: ZWO174mm

See All of my Images at: https://astronebula.com/slide-show/
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Re: Help plz :) Geting an eye shaped airy disc not circular.

#15

Post by jbelden »


Nice, I think I might build one of these Dunkin masks. I agree that the Bob's knobs screw was tilting your secondary drastically, I honestly haven't seen any of my SCTs get that far out of whack, probably a good thing you didn't force the matter.
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