Modified SW130pds

[Kiwi_Brad]

Just after some help with my 130PDS. I have taken it apart cleaned, flocked and added a few 3D printed parts.  Including a secondary mirror holder. 
 

I have attached an image before and after the rebuild. I was trying to help the primary mirror clip issues around bright stars mostly.   I have clearly introduced several issues into my images in doing all these. 
 

I believe I have aligned the focuser tube and secondary and collimated suitably well but I can’t tell the different between pinched optics bad collimation and the thousand other things I could have introduced. 
 

The two images are both of the southern pin wheel and a single frame.  Different exposures but you can see the differences in the images.  The second image is using the L-enhance filter.  I have a pds130. Eq6-r mount and use a Nikon DSLR which I am not convinced is all nice and square within itself let along the focuser tube.  I guide with an OAG and ZWO220mm mini (seemed to make my guiding worse from my 120mm). 

I am just outside the recommended back spacing due to my OAG etc. About 59mm to a Badder MPCC coma corrector.

Corners seem to be doing different things and now I have an extra diffraction spike?!

If someone could have a look at the images and give me some guidance that would be appreciated. 
 

Thanks Brad
 

 

[malc-c]

Can you post a picture of your new printed secondary holder.  I spent ages trying to eliminate a 5th spike on bright stars.  The cause was unsilvered edges on the stock secondary.  I'm just wondering if the edges of the minor axis of the secondary has been compromised by your new design.

[Kiwi_Brad]

23 hours ago, malc-c said:

Can you post a picture of your new printed secondary holder.  I spent ages trying to eliminate a 5th spike on bright stars.  The cause was unsilvered edges on the stock secondary.  I'm just wondering if the edges of the minor axis of the secondary has been compromised by your new design.

Below is some images of the scope and my most recent collimation then star test. I think I have resolved most of my issues given my back spacing problem until I get a dedicated camera.  Focus looks better but still an extra diffraction spike just not split now.   I read and fixed this as the secondary mirror holder not be square to the OTA tube itself. So measure from the edge to the edge of the tube it was out about 2mm.   Also my laser collimated badly needs collimating so didn’t use that at all.   Don’t have an image across the whole field but any comments on collimation welcome. 
 

Thanks 

 

 

 

 

 

[malc-c]

Thanks for uploading the images.  The star image is not the same as when I was having similar issues.  Yours is even, and both sides.  I'm no expert, and hopefully someone with more knowledge of these thins will chime in, but my thought was that the focus tube is protruding a fair bit into the light path.  If I can use a clock to explain my logic, your 3d spider has vanes at 2, 4, 8 and 10 which looking at the image results in spikes at the same 2, 4, 8 and 10 O'clock positions.  The focus tube axis is a line through 9, and 3 which again the rouge spike appears in the same position.

As I said, I'm no expert in optics, so my logic could be way off. 

[AstroMuni]

On 30/05/2023 at 09:55, Kiwi_Brad said:

The two images are both of the southern pin wheel and a single frame.  Different exposures but you can see the differences in the images.  The second image is using the L-enhance filter.  I have a pds130. Eq6-r mount and use a Nikon DSLR

I would suggest taking images where the stars are slightly out of focus so you can see if its collimated properly. Its tricky to get the back focus distance correctly and it took me a multiple tries to achieve a situation where I was happy with it. Also worth checking the tilt as I struggle with getting the camera+CC perfectly in line with the focal plane. Have you upgraded the eyepiece clamp to a compression ring one so that this can be better addressed?

Edited May 31, 2023 by AstroMuni

[alacant]

Hi

Assuming the optics are good, there's something interfering with the light path, but as we don't know the full story as to what has been changed,  perhaps the best (only?) way to diagnose is by elimation.

But before that struggle begins, I can see some bright areas around the new secondary spider rim. Perhaps screw heads? These coincide well with the new spike.

Next, go one at a time removing filter, cc... Then replace the original secondary holder, reverse whatever you did to the primary, remove the tube flock, try a friend's camera, remove 12mm from the protruding focuser barrel, blacken mirror edges, collimate and collimate again...

Here's hoping you find something obvious early on in the diagnosis.

Cheers and HTH

Edited May 31, 2023 by alacant

[Kiwi_Brad]

13 hours ago, malc-c said:

Thanks for uploading the images.  The star image is not the same as when I was having similar issues.  Yours is even, and both sides.  I'm no expert, and hopefully someone with more knowledge of these thins will chime in, but my thought was that the focus tube is protruding a fair bit into the light path.  If I can use a clock to explain my logic, your 3d spider has vanes at 2, 4, 8 and 10 which looking at the image results in spikes at the same 2, 4, 8 and 10 O'clock positions.  The focus tube axis is a line through 9, and 3 which again the rouge spike appears in the same position.

As I said, I'm no expert in optics, so my logic could be way off. 

Thanks for that I do think you might be right. It protrudes quite far.  I have heard of people shortening the tube but the focuser itself really isn’t overly great but not sure I want to spend the money on that as an upgrade.  I certainly could trim a good 20mm off it  … 🤔

[Kiwi_Brad]

13 hours ago, AstroMuni said:

I would suggest taking images where the stars are slightly out of focus so you can see if its collimated properly. Its tricky to get the back focus distance correctly and it took me a multiple tries to achieve a situation where I was happy with it. Also worth checking the tilt as I struggle with getting the camera+CC perfectly in line with the focal plane. Have you upgraded the eyepiece clamp to a compression ring one so that this can be better addressed?

I have just replaced the eyepiece clamp to a compression ring so it wasn’t in those images but was in the latest close up stat image of Acrux.  Hopefully it will help as it is much better. 
 

I know I am outside the backfocus limits because of using a Nikon DSLR and OAG. I can’t find one smaller than 11mm which I use now.  So probably have to accept some issues through the corners.   One day I will find money for a new camera! 
 

Thanks 

[Kiwi_Brad]

5 hours ago, alacant said:

Hi

Assuming the optics are good, there's something interfering with the light path, but as we don't know the full story as to what has been changed,  perhaps the best (only?) way to diagnose is by elimation.

But before that struggle begins, I can see some bright areas around the new secondary spider rim. Perhaps screw heads? These coincide well with the new spike.

Next, go one at a time removing filter, cc... Then replace the original secondary holder, reverse whatever you did to the primary, remove the tube flock, try a friend's camera, remove 12mm from the protruding focuser barrel, blacken mirror edges, collimate and collimate again...

Here's hoping you find something obvious early on in the diagnosis.

Cheers and HTH

Yes I will blacken the cut screw heads tonight. I think the only things I have done that could be causing it are those screws or the focuser tube but of course that was there before but now with a darker flocked  tube and a lot of stray light being dealt with it is more directed into the focuser tube and creating the spike? Maybe… stretching. 
 

I will cut the tube slightly and blacken those screws and report back. 
 

Thanks

[Kiwi_Brad]

I blacked those screws, loosened the mirror clips and shortened the focuser tube. 
 

it seems to be pretty good now in terms of spikes. I do still see on the sides or corners where n a defo used star the edge of the star missing.  Is this a misalignment of the secondary and focuser tube? 

diffraction pattern is looking quite tidy and the additional spikes have gone.  Longer spikes on one axis than the other though  

 

why do I have the top quarter or more of the outer ring missing? 

 

this image is the centre of the fov 

[alacant]

9 hours ago, Kiwi_Brad said:

top quarter or more of the outer ring missing

That's the cc doing its job. On a focused image you'll not see donuts.

9 hours ago, Kiwi_Brad said:

this image is the centre of the fov 

On a well collimated Newtonian telescope, the circles would be concentric. 
But look at the processed images. If they're to your liking, ignore.

Edited June 7, 2023 by alacant

[AstroMuni]

9 hours ago, Kiwi_Brad said:

this image is the centre of the fov

The overall image is looking much better. I think the reason for the oval shapes in the left hand side is a combination of tilt and collimation. If you are getting similar ovals on the right hand side which are like mirror images of the ones on the left then you will also need to look at adding or remover a spacer between CC and camera. 

And as alacant says, take a look at your processed images and decide if you still wish to improve it.

Edited June 7, 2023 by AstroMuni

[Kiwi_Brad]

23 hours ago, AstroMuni said:

The overall image is looking much better. I think the reason for the oval shapes in the left hand side is a combination of tilt and collimation. If you are getting similar ovals on the right hand side which are like mirror images of the ones on the left then you will also need to look at adding or remover a spacer between CC and camera. 

And as alacant says, take a look at your processed images and decide if you still wish to improve it.

Great thank you to all it will be spacing of my baader cc. I am outside it’s backspacing and with a DSLR I can’t get any mess with my OAG. Sadly. 
 

Thank you for your help everyone. 

[AstroMuni]

7 hours ago, Kiwi_Brad said:

I am outside it’s backspacing and with a DSLR I can’t get any mess with my OAG

Where in the train is your OAG? If you put OAG first thing after the scope and then CC, DSLR you should be able to get backfocus is my guess?? Guiding doesnt need coma free stars

Edited June 8, 2023 by AstroMuni

[Kiwi_Brad]

10 hours ago, AstroMuni said:

Where in the train is your OAG? If you put OAG first thing after the scope and then CC, DSLR you should be able to get backfocus is my guess?? Guiding doesnt need coma free stars

No it does I had never thought about trying this to be honest.  I will def see what I can do.  Just always thought I wouldn’t be able to reach focus with it that early but will have a play around! Again great idea thanks.