35 replies to this topic

[Terry White]

---"Snip"----

Now, I'm biased about this as I gave up on the GSO scope that I owned - I just could not get it correct - and paid up for the CDK that I now own. 12.5" is a much scope as is useable in most locations. The 12.5 gets the same results (FWHM) as the 23" does 75 feet away from each other. When I read about these struggles with RC's I really wonder how much savings there is over just biting the bullet and getting a PlaneWave or AG Optical in the first place. 

 

Apologies for hijacking - I just read this and feel so sorry for the OP. Still, maybe he's having fun with all this! YMMV as they say. 

 

Rgrds-Ross

What's annoying is when a moderator hijacks a thread, offers no constructive help to the OP, only to tell us that he's biased because he couldn't hack it, implying that the product must be bad. Then the moderator says he's sorry for the OP, but then adds sarcastically, "maybe he's (OP) having fun with all this!"

Edited by Terry White, 30 June 2020 - 11:51 AM.

[Tom Gwilym]

I'm the OP on this thread.  Not offended by the hijack but I do understand his frustration with the RC that he expressed.  I have learned the difficulty with these scopes.  I have learned that it's most likely off my personal list, there was a time that I was very interested in a smaller RC for my own observatory but I re-think that now.

Strangely, in between the cussing, swearing, and pulling out my hair, I have had -some- fun with it.  I guess it's just the peek I get sometimes that shows how fast this thing sucks in photons!  

 

What's annoying is when a moderator hijacks a thread, offers no constructive help to the OP, to tell us that he's biased because he couldn't hack it, and therefore the product must be bad. Then the moderators says sarcastically, "maybe he's (the OP) having fun with all this!"

 

[Darth_Takahashi]

Honestly, your last image, M20 the Trifid is starting to look very repectable. The stars look a lot sharper now at least. Its difficult to say from a screenshot but its looks to me like you have some round stars in there on the righthand side of M20. The left still has some astigmatism but its acceptable. Nonthing that you couldn't clean up when image processing. I think you could produce a very respectible image with this RC now and refine it over time.

 

Regards

 

 

Neil

Edited by Darth_Takahashi, 30 June 2020 - 03:10 PM.

[Tom Gwilym]

Yeah, I'm making progress on the beast.  I'm determined not to let it beat me, and a little cropping isn't bad as long as I can get something that looks fairly decent.   I did revisit the DSI method and have been working on the primary mirror now since I think I got the focuser/secondary pretty close.   I do re-check those each time I start messing with things.  I may go out tonight and try some more primary tweaks.  Part of my problem was that I was making too large of screw twits.  TINY 1/16 movements or less is all this thing tolerates.  I'll be an expert on this thing soon!  

Honestly, your last image, M20 the Trifid is starting to look very repectible. The stars look a lot sharper now at least. Its difficult to say from a screenshot but its looks to me like you have some round starts in there on the righthand side of M20. The left still has some astigmatism but its acceptable. Nonthing that you couldn't clean up when image processing. I think you could produce a very respectible image with this RC now and refine it over time.

 

Regards

 

 

Neil

 

[Darth_Takahashi]

Part of my problem was that I was making too large of screw twits.  TINY 1/16 movements or less is all this thing tolerates.  I'll be an expert on this thing soon!  

That sounds about right to me. The issue is the metric thread pitch is 1.25mm. Its too course for these telescopes and is the one modification that I plan to make when the telescope is out of warranty and the primary needs some TLC(cleaning). These are what I'll be using.

 

 

https://www.newport....justment-screws

 

Its the primary that needs them most. Something to consider for the future! I look forward to seeing more progress and images soon!

 

It's been raining here the last couple of days. :-(

 

Regards

 

 

Neil

[Tom Gwilym]

Cool! Kind of a "Bob's knobs" for an RC scope.  Thanks for the link, I'll read up on that.

Super clear forecast tonight other than a bright moon.  I'll probably go mess with the mirror some more and see what I can do.  I do see that the Primary mirror is the one to really move now since I think I have the focuser and secondary fairly close.   Again, just looking for round stars (a bit oversampled since I have an ASI071MC Pro on it) that look fairly pretty.  This will be a public outreach scope, so just really want some pretty photos....but being an astrophotographer, I'm just kind of picky about nicely formed stars.    :-)

I'll share whatever results I get.

 

Tom

 

That sounds about right to me. The issue is the metric thread pitch is 1.25mm. Its too course for these telescopes and is the one modification that I plan to make when the telescope is out of warranty and the primary needs some TLC(cleaning). These are what I'll be using.

 

Precision Thread adjusters.jpg

 

https://www.newport....justment-screws

 

Its the primary that needs them most. Something to consider for the future! I look forward to seeing more progress and images soon!

 

It's been raining here the last couple of days. :-(

 

Regards

 

 

Neil

 

[Tom Gwilym]

I spent more time tonight on this thing.  This time I carefully lined up the camera so the up/down left/right were correct, checked the laser to the middle of the secondary and found a good star to defocus on. I adjusted the primary until it was as round as I could get it, then tightened it down.  I wish I took a picture to prove I actually had it, but was so excited that I put the bahtinov on focued and tried slewing around to see how it worked.   Diffraction spikes looked nice and sharp and stars looked pretty good.   I then ran into trouble again with T-point (the Paramount is a whole different thread) so spent some time re-plotting stars so it could steer accurately again.  SkyX isn't my friend yet, but with the mount I'm stuck using it.

Stars then looked double once again, defocused and just started cussing again. I shut it all down again and called it quits for the night. 

I guess I'm close, but not sure if something slipped or what.  I'm just again annoyed with this scope once again, and logged another 3 hours on top of the 40+ I've spent on this thing.  GAAAAHHHH!!!!!!

 

 

[Darth_Takahashi]

I seems like the primary might be moving slightly when you're slewing the scope to the target etc... Don't dismiss this suggestion too quickly. Since you already know that small movements can have a big impact on alignment. I would unscrew the centre baffle and check the concentricity of the mirror bore and holder. See if the primary moves when slewing to different positions. You can do this all in day light, a 0.5mm to 1mm movement could be your issue?

 

When this is me and I found some movement here I would use some shim material around the holder/inside the bore of the mirror to try and prevent it.

 

On the smaller telescopes you can see people removing all of the cork from the mirror cell and replacing it with 3M Velcro pads but that would be a bigger job. Therefore, I'd try and shim out the gap first to prove that the fix worked.

 

Regards

 

 

Neil

[Tom Gwilym]

I wonder also if I needed to tighten the locking screws just a little more?  I just turn it until snug.

It was looking really nice and I was very pleased for a while. Then I tried M-16 and noticed stars appeared bloated again (It is low in the sky and atmosphere does have effect), then slewed higher again and noticed despite sharper, the stars were egg shaped/slightly double again.   Any idea if adjusting it to looking good, do a meridian flip, adjust again would help? 

All this about shims, felt, shift and such is so much more work for something that should be set when the scope arrives from the factory (I would hope!).   I'm familiar with Meade mirror 'flop' and hoped that this would be different, but I guess not.  

 

This scope is almost too much work to be enjoyable.  I haven't lost all patience yet, but I get closer with every hour I waste tweaking this thing. 

 

I seems like the primary might be moving slightly when you're slewing the scope to the target etc... Don't dismiss this suggestion too quickly. Since you already know that small movements can have a big impact on alignment. I would unscrew the centre baffle and check the concentricity of the mirror bore and holder. See if the primary moves when slewing to different positions. You can do this all in day light, a 0.5mm to 1mm movement could be your issue?

 

When this is me and I found some movement here I would use some shim material around the holder/inside the bore of the mirror to try and prevent it.

 

On the smaller telescopes you can see people removing all of the cork from the mirror cell and replacing it with 3M Velcro pads but that would be a bigger job. Therefore, I'd try and shim out the gap first to prove that the fix worked.

 

Regards

 

 

Neil

 

[akulapanam]

Be very very careful here. GSO primary mirrors are notorious for being easily pinched. I seriously doubt the primary is moving. What he is describing sounds like focuser sag to me. He is using the original focuser with a substantial camera and this is the weakest link in the system in my view.

Edited by akulapanam, 01 July 2020 - 06:34 PM.

[Tom Gwilym]

Thanks for the warning.  Is there a way to know if that is happening or just make sure I loosen and tighten opposite when I'm adjusting the mirror? 

I have the standard focuser with an ASI294MC Pro, ZWO OAG, ASI120MC, and a Starlight instruments motor focuser on there too. 

That does sound reasonable if it's sag, I did slew around to the other side of the sky and noticed things looked ugly again.  

 

Be very very careful here. GSO primary mirrors are notorious for being easily pinched. I seriously doubt the primary is moving. What he is describing sounds like focuser sag to me. He is using the original focuser with a substantial camera and this is the weakest link in the system in my view.