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Swift 831

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#1 camman

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Posted 07 January 2022 - 09:48 PM

Got a Swift 831 today. from a member on a UK Astro forum

great condition. Lunar shot taken under poor conditions

 

DSC00165.jpg

 

DSC00178.jpg

 

swift-sgl-60-png-no-d-png-b.png

Attached Thumbnails

  • SWIFT Startest 2 cn.png
  • SWIFT Startest 1 cn.png

Edited by camman, 08 January 2022 - 04:32 AM.

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#2 camman

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Posted 08 January 2022 - 08:48 AM

Its possible there was dewing on the lens when this star test was taken


Edited by camman, 08 January 2022 - 08:50 AM.


#3 Retiredbob

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Posted 08 January 2022 - 09:18 AM

I can't assist with your questions, but your Moon picture is beautiful!  Thanks for sharing.



#4 Bomber Bob

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Posted 08 January 2022 - 09:32 AM

Near-Perfect Lens in a Beautiful Package -- CLASSIC.

 

I could've been a Swift Fan from way back, but they were the most expensive Dept. Store refractors of my younger years.  When I did see them in stock, my eyeballs would poke out at the price tags!


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#5 camman

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Posted 08 January 2022 - 10:21 AM

I can't assist with your questions, but your Moon picture is beautiful!  Thanks for sharing.

Thanks for the kind comments.



#6 camman

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Posted 08 January 2022 - 10:23 AM

Near-Perfect Lens in a Beautiful Package -- CLASSIC.

 

I could've been a Swift Fan from way back, but they were the most expensive Dept. Store refractors of my younger years.  When I did see them in stock, my eyeballs would poke out at the price tags!

Yes Around 290 dollars i belive. Which now could buy a Tak. 

Or did it. (ive seen the debates)


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#7 camman

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Posted 09 January 2022 - 09:30 AM

More testing 

Scope may have needed more cooling

Attached Thumbnails

  • 2.jpg
  • 3rd.jpg

Edited by camman, 09 January 2022 - 03:57 PM.

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#8 deSitter

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Posted 09 January 2022 - 10:12 AM

More testing 

Scope may have need more cooling

Nice star test but too many rings. You should use high, high power and do 3-4 rings. What stands out here is the smooth edge of the pattern - that means a very high polish on the glass. A rough optic will have a "hairy" edge.

 

-drl


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#9 camman

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Posted 09 January 2022 - 10:29 AM

Nice star test but too many rings. You should use high, high power and do 3-4 rings. What stands out here is the smooth edge of the pattern - that means a very high polish on the glass. A rough optic will have a "hairy" edge.

 

-drl

Hi thanks for the feedback i wondered what others would make of them. Reason i did this magnification. Is with a barlow its going to be oversampled with the zwo 178mm camera. I have noticed one side of focus the shape of the changes appearing slightly more egg shaped. So one side round the other egg shaped. wondered if this was astigmatism. I will show a better example in a bit. you can see it when you blink between the two sides of focus



#10 camman

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Posted 09 January 2022 - 10:43 AM

Nice star test but too many rings. You should use high, high power and do 3-4 rings. What stands out here is the smooth edge of the pattern - that means a very high polish on the glass. A rough optic will have a "hairy" edge.

 

-drl

Here is another two pics showing the effect. if you copy both images and blink between the two using photo viewer 

You can see a elongation on on the 2nd image

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  • 1st.jpg
  • 2nd.jpg

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#11 deSitter

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Posted 09 January 2022 - 10:48 AM

Possibly it is simply out of collimation. You need to go down to 3-4 rings to get a good gauge on it. And one in focus showing the Airy disk.

 

-drl



#12 deSitter

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Posted 09 January 2022 - 10:51 AM

Also, I don't know what Barlow you are using, but that is far more likely to be a source of astigmatism than the objective. I've never seen a classic with even a trace of astigmatism. I doubt Japan would allow the gold sticker in that case :) You can check by rotating the Barlow and see if the pattern follows it.

 

-drl



#13 firemachine69

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Posted 09 January 2022 - 10:53 AM

Hi thanks for the feedback i wondered what others would make of them. Reason i did this magnification. Is with a barlow its going to be oversampled with the zwo 178mm camera. I have noticed one side of focus the shape of the changes appearing slightly more egg shaped. So one side round the other egg shaped. wondered if this was astigmatism. I will show a better example in a bit. you can see it when you blink between the two sides of focus

 

 

Might just be the weight of the camera pulling on the focuser drawtube.



#14 camman

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Posted 09 January 2022 - 11:05 AM

Also, I don't know what Barlow you are using, but that is far more likely to be a source of astigmatism than the objective. I've never seen a classic with even a trace of astigmatism. I doubt Japan would allow the gold sticker in that case smile.gif You can check by rotating the Barlow and see if the pattern follows it.

 

-drl

With the 178 camera i used no barlow this is straight in 



#15 camman

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Posted 09 January 2022 - 11:08 AM

Might just be the weight of the camera pulling on the focuser drawtube.

If you copy and blink the images there is a big difference in the shape of the stars. between the two sets. if it was the drawtube it would affect both sides equally surely. I will use a barlow to test more. But by doing so. the images will be oversampled with the 178mm cameras pixel size ? 



#16 camman

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Posted 09 January 2022 - 11:09 AM

Possibly it is simply out of collimation. You need to go down to 3-4 rings to get a good gauge on it. And one in focus showing the Airy disk.

 

-drl

When you say out of collimation wouldnt that affect both sides ? 



#17 deSitter

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Posted 09 January 2022 - 11:20 AM

When you say out of collimation wouldnt that affect both sides ? 

Yes, the Airy disk will not be centered in the diffraction ring at focus, and the "target" pattern will not be symmetrical. True astigmatism will show up as an egg-shaped Airy disk at best focus. Really bad astigmatism will show up as a cross pattern at best focus. A small collimation error will show up as a first diffraction ring around the Airy disk that is brighter on one side. You can't tell much from your picture because it is too far out of focus.

 

Another test you can do is to use a low-power eyepiece and rack WAY in and out of focus until the rings seem to blend together into a smooth disk. The disk should appear uniform on both sides of focus with no brighter or darker zones. That means the rings are evenly spaced and there is excellent spherical correction.

 

-drl


Edited by deSitter, 09 January 2022 - 11:20 AM.


#18 Bomber Bob

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Posted 09 January 2022 - 11:25 AM

Yes Around 290 dollars i belive. Which now could buy a Tak. 

Or did it. (ive seen the debates)

Well... your star test pix could've been from any of my 4 Taks.  Doesn't prove anything; and yet...

 

For sky testing, I follow Dave G's advice:  I start with an eyepiece FL that's equal to the frac's f/R -->  F8 frac gets an 8mm eyepiece.  Then, I bump up the power to check for consistency at higher & higher magnifications.


Edited by Bomber Bob, 09 January 2022 - 11:27 AM.

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#19 camman

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Posted 09 January 2022 - 11:33 AM

Taken with a 462c camera. no barlow. i am guessing a barlow is recommended to try this in focus test. 

First is 200% resize. second 400%

Attached Thumbnails

  • 200.jpg
  • 400.jpg

Edited by camman, 09 January 2022 - 11:34 AM.


#20 camman

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Posted 09 January 2022 - 11:36 AM

Well... your star test pix could've been from any of my 4 Taks.  Doesn't prove anything; and yet...

 

For sky testing, I follow Dave G's advice:  I start with an eyepiece FL that's equal to the frac's f/R -->  F8 frac gets an 8mm eyepiece.  Then, I bump up the power to check for consistency at higher & higher magnifications.

Fair enough but what i am seeing is mimicking exactly what i am capturing. Or as near as i can determine 



#21 camman

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Posted 09 January 2022 - 11:39 AM

Yes, the Airy disk will not be centered in the diffraction ring at focus, and the "target" pattern will not be symmetrical. True astigmatism will show up as an egg-shaped Airy disk at best focus. Really bad astigmatism will show up as a cross pattern at best focus. A small collimation error will show up as a first diffraction ring around the Airy disk that is brighter on one side. You can't tell much from your picture because it is too far out of focus.

 

Another test you can do is to use a low-power eyepiece and rack WAY in and out of focus until the rings seem to blend together into a smooth disk. The disk should appear uniform on both sides of focus with no brighter or darker zones. That means the rings are evenly spaced and there is excellent spherical correction.

 

-drl

Thats interesting i think i am seeing a slightly brighter first diffraction ring on the stacks unbarlowed. Hard to see this through the scope. 



#22 deSitter

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Posted 09 January 2022 - 11:56 AM

Taken with a 462c camera. no barlow. i am guessing a barlow is recommended to try this in focus test. 

First is 200% resize. second 400%

No astigmatism there! it is slightly miscollimated as seen by the diffraction ring being brighter on one side. Rotate the OTA and do it again and compare.

 

-drl



#23 camman

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Posted 09 January 2022 - 12:05 PM

No astigmatism there! it is slightly miscollimated as seen by the diffraction ring being brighter on one side. Rotate the OTA and do it again and compare.

 

-drl

Thanks for the help. Certianly worth trying to get the best out of it. When you say rotate the OTA do you mean rotate the tube assembly ?



#24 deSitter

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Posted 09 January 2022 - 12:25 PM

Thanks for the help. Certianly worth trying to get the best out of it. When you say rotate the OTA do you mean rotate the tube assembly ?

Yes, and the ring brightness should follow. This will be the starting point of getting it accurately collimated.

 

-drl



#25 camman

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Posted 09 January 2022 - 12:41 PM

Yes, and the ring brightness should follow. This will be the starting point of getting it accurately collimated.

 

-drl

Bit confused by that how will rotating the tube assembly in the rings of the mount affect collimation ?




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