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I've never had any success with my C9.25 when trying to get DSO's. I've seen images other people have taken and they have good round stars. I can never get these.
I've tried collimating the best that I possibly can, and adding the Celestron f/6.3 focal reducer but I still can't get round stars. I could understand it if the stars at the edges had comma, but the stars near the centre are showing comma too.
I've changed my back focus both in and out to no real difference, I'm just wondering what I'm doing wrong?
I took the two attached images last night. One shows my out of focus star from the camera, and the other image shows an integration of 120 x30 sec subs of M63 Sunflower Galaxy. The camera is an ASI 1600mm Pro. These are both full frame, not cropped.
When I've plate solved the individual frames for M63 they give a focal length of 1483mm. 1480mm would be f6.3 on this scope, which the focal reducer is supposed to give indicating my back focus spacing is about correct.
One thing I have noticed is that on the focus star the rings are concentric and clean, but the small reflections inside the smaller ring are not central. Is this normal for an SCT? I'd have thought the central reflections would be centred too.
I've wondered if the star comma was down to guiding errors, but would a 30 sec sub-frame show this much error? Incidentally, my guiding last night was the best I've ever had and I don't think it was down the guiding. When I use my refractor (although shorter focal length) the stars are perfectly round with this mount - NEQ6.
A few years ago I removed the secondary mirror to remove a large dark mark from it which was obscuring my views (it was a fleck of black paint from the inside of the tube). When I removed the secondary, I accidentally rotated it when unscrewing. Would this make a difference? I know that the corrector plate shouldn't be rotated, and wondered is it was the same with the secondary? I've searched online but can't find an answer to that.
I love this scope, but hardly use it nowadays because of the image quality.
Hope someone can offer some helpful advise.
Found various threads on here and other forums about flocking dobsonians/newtonians but couldn't find specific images of disassembly of the very popular SkyWatcher Heritage 130p flextube and flocking of the OTA.
So having ordered some DC-Fix black velour sticky back material (can be got from various places including FLO) I thought i'd share some photos of the process from start to finish as it may help someone else in the future...
Images below with notes...
1. Focuser and shield flocking
This was the easy bit. A strip stuck inside the focuser, and just unscrew the shield, draw round it, cut the material and align and smooth down. In the last image above you can already see the significant improvement on reducing reflections comparing the flocked shield to the unflocked tube...
Notice my version of Bob's Knobs on the secondary mirror which are just black steel M4 25mm knurled thumbscrews bought off ebay for about £7 - along with the thumbscrews already on the 130P primary mirror this makes any fine collimation easy and completely tool free!
For full stealth mode I've also painted the edge and rear of the secondary mirror, and any exposed screw heads with blackboard paint to reduce reflections.
2. OTA disassembly and tube before
Note the cutout in the lower primary housing and the top ring. This aligns with the ridge of the tube seam, and means there is only one way to reassemble the telescope tube and mirror and one place for the handful of screws (4 at the bottom, 3 at the top). You'll also need an allen key to remove the 3 bolts for the dovetail mount. Simple!
Now you're ready to Flock 'N' Roll! 👍🏻
3. Flocking the tube
You'll need approx. 50cmx29cm of the material to do the tube in one go, starting along the seam. As others have described just take your time here, peel off about an inch of the backing and get the edge aligned with the tube seam stick down firmly and smooth out any air bubbles.
Then slowly keep peeling more backing (rip and remove if the excess gets in the way) and smooth down as you go, turning the tube and affixing the velour material.
4. Finished flocking and close up during application so you can see contrast/reflection comparison of before and after.
All in all only took around an hour so not a hard job as long as you prepare and concentrate! I ordered one sheet of 45cm x 1m material which was plenty, however if your not as confident you'll get it right first time then order 2m so you have more to spare if you need to start again.
Looks great, so as always I now just need clear skies to go play and see the difference it makes!
It's been a long time since I've posted in this forum, anyway I've picked up a Skywatcher 200p F/6 dobsonian as a DIY project whilst I continue to work on a new telescope from scratch, (I've started to grind the mirror).
I'll be making improvements to this dobsonian as a project and learning experience, I've already got a temperature controlled fan which has a probe that can measure both mirror and ambient temperature. I'll be measuring the primary mirror with my in progress Foucault/Ronchi/Bath Tester when that's finished in the next couple of weeks, may even refigure it depending on results.
But I'm most excited about this right now. The blackest Black Paint as an alternative (hopefully better alternative) to flocking!
This stuff is seriously black and flat, I backed it on kickstarter and received 3 bottles along with goodies.
I plan on painting the area opposite the focuser, area around the primary mirror, inside the focuser drawtube, potentially the secondary mirror holder and edge of the secondary also.
It's a shame I don't have any flocking to compare it with but it looks incredible.
This video shows just how impressive it is (moreso than my little tester I've done).
I'll try and get some decent before and after pics.
Celestron C9.25 OTA with ADM Losmandy dovetail
Everything in very good optical and mechanical condition
Cosmetically, there are the usual few small scratches on the paintwork, but no significant damage.
ADM Losmandy dovetail was £84 new 18 months ago
Reason for sale is recent upgrade of OTA.
Collection from Worcester, or Kelling Heath or SGL star parties, or could possibly meet halfway.