The saga of the North America Nebula

[Domain105]

Sorry for the long post but it has been a painful and costly journey moving from a DSLR to a dedicated astro cam. so many things when wrong but it all has come good in the end.  Apologies if this in in the wrong sub forum.

 

Having spent the last few months upgrading from:

• Canon EOS 350D
• Skywatcher 0.9x Coma Corrector

to:

• Risingcam IMX571 OSC camera
• Anlia ALP-T filter

using my:

• Skywaycher 150PDS
• HEQ5 mount with Rowan belt mod

What I thought was a straightforward move from one camera to another became a long tale of woe and heartache. One issue would spawn another and so on to the point I wanted to just give up.  I finally overcame my long list if issues which came apparent after the camera upgrade:

• Not being able get the correct back focus without spending £££ on all sorts of extension rings
• Getting horrible white circles in the middle of my lights and flats due to the ALP-T and coma corrector reflecting off each other
  • Decided to flock the scope in case it was that causing the reflections
    • Realised that once I took everything apart I couldn't get the secondary mirror to align correctly and need to collimate
    • As everything was stripped away from the OTA to flock it, the tube was bent out of shape which meant the secondary mirror vanes were all over the place.
      • I attached one of the tube rings to the very end and tightened very hard to keep a circular shape as I put the vanes back.
      • Overall the tube rings are needed to keep the OTA's circular shape so once I added then back on, things were better.
    • Realised that I had tilt in the focus tube so any adjustments to the focus tube meant collimation was out again
    • Using a cheshire eyepiece I would get what I thought was collimation bang on but using a laser collimator (collimated to 20 meters) the alignment off both secondary and primary was way off
    • Got in to a vicious circle of fixting tilt and then collimation would be off, fixing the collimation and the laser collimator was way off.  - spend a month in this cycle
    • finally purchased a concentric collimation eyepiece and managed to get the secondary and primary aligned ok
  • Figured out that flocking made no difference to the reflections so bought a Baader MPC MKIII to see if it would help
    • Baader made matters worse as no matter what I did - even with adjustments of 0.1mm, stars in the corners were still showing massive coma. top left was worse due to some slight tilt still in the focus tube
    • Thought I'd fix the tilt issue by purchasing a Baader click lock as the eyepiece screws on the focus tube were shifting the angle of the coma corrector
    • Realised the Baader click lock might not let me achive focus as it was too fat on the end of the focus tube
      • Tried it with the Skywatcher 0.9x coma corrector and focus would be at around -1500 thats 1500 steps after the tube is fully in!!
      • Tried the click lock with the Baader MPC MKIII and that got me focusing ok as it was not a reducer so focus was around 3000 steps (focuser range was 0-18000 steps).
      • Still had the problem with the dodgy stars on the edges even with the click lock holding things tight
    • Through experimentation figured out that the Antlia ALP-T needed to be infront of the coma corrector for no reflections (did try facing the filter in different directions facing the camera but that made no difference!). 
      • So ditched my Starlight Xpress filter wheel which has the filter between the camera and coma corrector and screwed it in front of the coma corrector instead
      • This fixed the horrible white circle reflections !!!!!
• Started reading up on the Skywatcher F4 aplanatic coma corrector so though if it can fix coma on a F4 then it should be better on a F5. so finally purchased on from FLO
  • Test it at 54mm backspace and the coma was virtually gone, even the slight tilt that I had in the upper right corner was gone!!!
  • Thought I'd test the white reflections issue again with the filter wheel so I added the ALP-T into the filterwheel again (instead of in front of the coma corrector) and oh my goodness, there were no horrible white circle reflections in my lights or flats.

All this transpired over 7 or so months. At times, I was close to thowing everything out and giving up but I'm glad I didn't.

With everythging working and some clear skies at last, I took the follwing image of the North America Nebula. Forgot to take RBG stars but I'll do that another day

68 x 180s subs using the Anlia ALP-T filter  @ -10c

32 flats + 32 dark flats

20 x 180s flats

I live in inner city Birmingham so a very Bortle 8 all around and the moon was also very bright having just past full moon. 

Processing was using PI (SPCC, BXT, GHS, NXT, SXT with some saturation and curves modifications, HOO normalisation plugin) and not much else.  I am very pleased with the image - especially after the saga I had to go through. Not sure the colours will suit everyone's taste as I am colour blind LOL

Having read through this site in search of answers, I have found the following which might be useful to others:

• Narrow band filters such as the ALP-T and other HA filters will likely cause reflections on Baader MPC and skywatcher F5 coma correctors if you have them between the camera and coma corrector (using a filter wheel) - screwing the filter to the end of the coma corrector will likey fix the reflections issue. There are a number of posts about this issue on SGL and elsewhere
• There are some posts about a Baader click lock not allowing for focus to be reached on 150PDS OTAs. I found this to be true when using the Skytwatcher 0.9x coma corrector but with the Baader MPC MKIII and the Skywatcher F4 aplanatic coma corrector, the scope reaches focus about 15mm from the focuser barrel tube.
• The Skywatcher 150PDS focuser can carry a lot of weight. I have a heavy Skywatcher F4 Coma corrector, Starlight Xpress 2" filter wheel, Risingcam IMX571 camera hanging of the focuser and it is handled with no issues with slippping etc . I have tried it straight up and down for push / push scenarios. The focuser is connected to a ZWO EAF which holds the weight well with no issues
• Even the tiniest push from the eyepiece holder screws can push out a laser collimator - hence the use of a click lock. Make sure your laser colimator is also collmated
• Cheap chesire collimation eyepieces from Amazon / ebay did not seem to be centered in my focuser tube, using a concentric collimation eyepiece was the only thing I could get decent collimation with.
• The skywatcher F4 aplanatic coma corrector works extremely well with a 150PDS. With the Skywatcher 0.9x I found it was brilliant with my DSLR up to the corners but moving to a dedicated camera of the same chip size (APS-C) it just struggled with coma.  The Baader MPC MKIII was even worse but could let me focus using the click lock
  • One thing I didn't appreciated until now was that both the Skywatcher 0.9x and Baader MPC soften the stars so they are not sharp like in the good astro photos we see here. the F4 gave me really sharp pinpoint stars. My FWHM improved with the F4 CC too when comapred to the other coma correctors

The image below is the first one I have taken since things started to work. so looking forward to lots of new images with my setup.

I've covered a lot of things here but please let me know if you need any more detail on the issues I've has incase it can help you with something similar.

 

 

 

Edited September 4, 2023 by Domain105
image moved to the end

[simmo39]

Nice image after the fun and games you had.

[Domain105]

2 minutes ago, simmo39 said:

Nice image after the fun and games you had.

Thank you. 🙂 Was so close to throwing the scope out the window at times !

[simmo39]

9 minutes ago, Domain105 said:

Thank you. 🙂 Was so close to throwing the scope out the window at times !

I have been there a few times, when it all comes together its just brilliant but getting there is like juggling jelly.

[geeklee]

Really glad you got a happy outcome @Domain105 As an owner of a 150P-DS, I really enjoyed the write up of the various options and issues.  I purchased mine second hand so it had some really useful tweaks done already.  I use the 0.9x SW Reducer but on a small sensor.  I recently added the solid secondary spider from Backyard Universe - a noticeable upgrade to collimation stability and minor aesthetic improvements.

Am I right in saying you now have the Baader ClickLock + SW F4 CC?  Does the combination of these mean the draw tube is further out overall, so doesn't protrude into the tube so much?

 

[Domain105]

55 minutes ago, geeklee said:

Really glad you got a happy outcome @Domain105 As an owner of a 150P-DS, I really enjoyed the write up of the various options and issues.  I purchased mine second hand so it had some really useful tweaks done already.  I use the 0.9x SW Reducer but on a small sensor.  I recently added the solid secondary spider from Backyard Universe - a noticeable upgrade to collimation stability and minor aesthetic improvements.

Am I right in saying you now have the Baader ClickLock + SW F4 CC?  Does the combination of these mean the draw tube is further out overall, so doesn't protrude into the tube so much?

 

Hello Lee, thanks for the comments. 🙂 

Yes I now have the Baader click lock and the SW F4 CC.   the click lock is fatter than the native SW focus tube connector so you lose some mm to that from the overall focus tube but I found that focus is achieved with the focuser set to around 2000 steps.  0 being the tube fully in the OTA (as much as the click lock allows due to it's thickness) and 18,000 being the focus tube fully extended.  The SW F4 CC seems to be the same size as the focus tube itself so fully inserted, it does not protude outside the focus tube. 

With the focus tube only a cm or so out side of the OTA at step 2000 to achieve focus, I was expecting pacman stars with the focus tube obstructing the light path but this isn't happening at all. My stars seem to be round and okay. So no need to cut the focus tube or the SW F4 CC getting in the way of the optical path.  

One thing I didn't mention, that is helping with star and spikes is that I 3D printed a primary mirror clip cover to cover the mirror clips so the diffraction spikes are more clean now.

[geeklee]

Nice one @Domain105 thanks for the follow up  

14 hours ago, Domain105 said:

One thing I didn't mention, that is helping with star and spikes is that I 3D printed a primary mirror clip cover to cover the mirror clips so the diffraction spikes are more clean now.

Yeah, this is a useful mod - mine came with the same.  

My drawtube protrudes into the tube too but I don't think the star impact is too intrusive.

If you wanted to see the single piece secondary spider, I have an image here.

[Domain105]

Those look awesome. I'm not sure I'm brave enough to touch the scope again for a while 😄 I'll add the vanes to my next round of upgrades. Thanks for the info on these.