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Finally made an R/C Collimation adapter

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#376 Che

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Posted 15 December 2022 - 02:00 PM

On my 10 inch, I think is was about an inch .  As evidenced by the fact that I went from the 2 inch  extension to the 1 inch without changing the image train from the camera side.  I not exactly an inch because focus was in a different spot but probably not far off.   How much this differs from 6 to 8 to 10 inch scope I dont know.

Che



#377 astroboyabdi

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Posted 15 December 2022 - 07:50 PM

Awesome, thanks all, 

 

This rotator /oag combo has been the bain of my life, it just doesn’t seem to play nicely with anything i have, 



#378 ad701xx

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Posted 15 December 2022 - 07:52 PM

I received my 6" adapter (Thanks James, it looks good) and according to my calipers it adds 19.48mm when snugged all the way down.


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#379 astroboyabdi

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Posted 16 December 2022 - 08:34 PM

Legend thx



#380 nateman_doo

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Posted 20 December 2022 - 10:13 AM

On my 10 inch, I think is was about an inch .  As evidenced by the fact that I went from the 2 inch  extension to the 1 inch without changing the image train from the camera side.  I not exactly an inch because focus was in a different spot but probably not far off.   How much this differs from 6 to 8 to 10 inch scope I dont know.

Che

Yea, all of them are around an inch.  the 6" has shorter feet, but a cutout underneath to bring it closer to the stock threads, vs the 8" has taller feet but the main body itself has an extrude underneath.  



#381 nateman_doo

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Posted 02 January 2023 - 09:45 PM

Happy new year all!

 

ut6vuOdl.jpg


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#382 Che

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Posted 02 January 2023 - 10:14 PM

Happy new year all!

 

ut6vuOdl.jpg

Happy New Year James and all


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#383 Mert

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Posted 03 January 2023 - 04:25 AM

Happy and healthy new year to all!
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#384 Ancient Photons

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Posted 11 January 2023 - 02:32 PM

Alright, my collimation adapter from nateman_doo showed up a couple of days ago, and I was able to assemble everything and do some late night testing last night. First, though, let me explain my reason for getting the collimation adapter mod done.

 

With my iOptron (GSO) RC8, I noticed that collimation was changing with altitude. Anything below 70° altitude had odd-shaped stars. Anything near zenith looked round and perfectly collimated. Obviously, this implies there is flex/sag in the system somewhere.

 

Here is what the issue looked like (identical tight crop of central stars):

9h7qgag.jpg

 
 
8td00EI.jpg
 
You can clearly see the issue. These were 300-sec exposures with decent guiding (Sii filter), both from the same autorun sequence. To me, this defect makes the scope un-usable.

 

My imaging train is a bit heavy, consisting of an ASI2600MM, 7-position 36mm filter wheel, and ZWO OAG-L w/174mm mini. I first suspected the stock focuser was sagging, so I replaced it with a Baader diamond steeltrack. It's a beautiful focuser, but it unfortunately didn't fix my problem.

 

So, as we all know by now, the focuser is attached directly to the primary mirror cell on these RC8's. It's a major design flaw. A heavy imaging train is bound to put stress on the mirror cell and mirror itself, causing serious collimation issues. Nateman_doo's collimation adapter decouples the focuser from the mirror cell - hopefully fixing my dynamic collimation issues.

 

My first test shot after installing the collimation adapter was Elnath at 61° altitude, L filter, no flattener, 60s exp, only a bench collimation:

 

MPIhLFr.jpg
Given this is an APS-C size sensor, I was reasonably happy with the collimation, and happy to see nice central star shapes at 61° altitude.
 
Seeing that collimation was acceptable, I installed a Hotech SCA field flattener. To my surprise, it really cleaned up the corners nicely (same exposure/target as above):
YP5rxq7.jpg?1
 
Here's the ASTAP analysis (w/FF):
0cPLdTC.jpg
 
Definitely not perfect, but pretty good - and to my eye, the field looks great.
 
I tested other areas of the sky at various altitudes to see how well collimation held. All are 60s exposures, with FF (1609mm focal length). Guiding varied, but stayed between 0.5-1".
 
Betelgeuse at 50°:
y0PYdJX.jpg
 
 
Sirius at 32°:
n4xbH7p.jpg
 
And 10 Ursae Majoris at 80°:
TV6KoYJ.jpg
 
 
Overall I'm happy to see a much-improved field. Collimation is holding very well with slewing around. Looking forward to getting some clear skies so that I can complete a project soon.
 
Well done nateman_doo - you've given this scope a second chance. It was on its way out the door, honestly.
 

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#385 nateman_doo

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Posted 11 January 2023 - 09:05 PM

NICE!  I always wondered if a decent way to "star collimate" would be to center a super bright star, and center the halo around the star via primary.  Like in your picture of Betelgeuse.  Since the focuser and secondary are coplaner, just adjust the primary until the halo is centered around the star itself.  Anyone ever try that?  

 

I am about to move up to an APS_sensor on mine and I am dreading getting all the yuck back in the corners.  The debate is do I want to use my QHY 268C, or get another ToupTek mono.  I instantly fell in love with the camera, and the price-tag.  

 

Happy it worked out so well for you.  That scope has such a bad design with everything hanging on just 3 M3 screws. mirror cell, mirror, baffle tube and your entire image train all on what are supposed to be precise screws that you can bend like a coat hanger.  having the plate spaced out the OD of the scope, MUCH thicker screws you get a much more stable base to bear the weight of the image train.  


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#386 astroboyabdi

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Posted 12 January 2023 - 01:24 AM

Got my part today, looks solid. Only thing is I was wondering is there an issue with light leak between the new focuser thread and the old one. There appears to be a gap when looking in between. I haven’t yet fit the focuser but the drawtube might just go in there. 



#387 astroboyabdi

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Posted 12 January 2023 - 01:38 AM

And also my moonlite focuser doesn’t screw into the back directly without one of the extension pieces. Due to the primary mirror collimation screws not being accessible and clashing. That would eat into my back focus requirements. I may need to rethink my imaging train as I dont have the back focus allowance for it.



#388 nateman_doo

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Posted 12 January 2023 - 12:47 PM

Got my part today, looks solid. Only thing is I was wondering is there an issue with light leak between the new focuser thread and the old one. There appears to be a gap when looking in between. I haven’t yet fit the focuser but the drawtube might just go in there. 

The focuser should close that gap, but I think I forgot to put a line of foam tape. 

If you take the plate off you can get any type of foam tape and that works, or get some black gaff tape and lay a bit down from the adapter into the scopes opening with a few pieces nice and loose.  



#389 astroboyabdi

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Posted 12 January 2023 - 02:45 PM

I shall use some black foam tape, thank you:)



#390 Ancient Photons

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Posted 12 January 2023 - 03:48 PM

NICE!  I always wondered if a decent way to "star collimate" would be to center a super bright star, and center the halo around the star via primary.  Like in your picture of Betelgeuse.  Since the focuser and secondary are coplaner, just adjust the primary until the halo is centered around the star itself.  Anyone ever try that?  

 

I am about to move up to an APS_sensor on mine and I am dreading getting all the yuck back in the corners.  The debate is do I want to use my QHY 268C, or get another ToupTek mono.  I instantly fell in love with the camera, and the price-tag.  

 

Happy it worked out so well for you.  That scope has such a bad design with everything hanging on just 3 M3 screws. mirror cell, mirror, baffle tube and your entire image train all on what are supposed to be precise screws that you can bend like a coat hanger.  having the plate spaced out the OD of the scope, MUCH thicker screws you get a much more stable base to bear the weight of the image train.  

Good question about collimating on a bright star halo. The downfall would be that exposures take at least 30s to really see it well, I suppose.

 

If you're willing to use a flattener, an APS-C sensor is the way to go. It's a bit against the grain to use glass with these scopes, though - but I think for narrowband and mono, it's a decent tradeoff to get nicer stars in the corner. Here's a mosaic of a test shot with the Hotech flattener:

 

gAA7S6B.jpg

 

 

Yeah, I agree - the original design of three m3 screws collimating a primary while holding a heavy camera and EFW at the end of a 10-inch tube is a bad, bad idea. Thankful to finally have this solution.


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#391 nateman_doo

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Posted 12 January 2023 - 04:09 PM

I just wish it would clear up one night so i could start imaging.   


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#392 Ancient Photons

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Posted 12 January 2023 - 08:05 PM

I just wish it would clear up one night so i could start imaging.   

Yeah, it's been rough on the east coast lately. Weekend looks promising here in DC.



#393 nateman_doo

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Posted 12 January 2023 - 08:27 PM

Yea we are tracking that as well.  Have been jonseing for some clear skies.


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#394 astroboyabdi

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Posted 12 January 2023 - 10:13 PM

Well it’s frustratingly hot and clear during the day but precisely at astronomical dusk the clouds come in force. 

 

Can those with rc8 and a moonlight focuser help me with photos of their imaging trains, so i can get an understanding of the different options available to me. My present setup plan with the

qhy 268m cfw3 l fw 

scops oag

falcon rotator

and flattener

 

has hit a snag as one inch of back focus ive lost from the adapter and another one inch for the adapter under the moonlight to raise the height to allow access to primary collimation screws. And even then i only just sneak in my allen keys .

 

But ive lost 2 inches in BF length. But have managed to thread the flattner into the drawtube of the moonlight that helps.



#395 Ancient Photons

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Posted 17 January 2023 - 12:59 PM

Following up with some (hopefully) useful info for others who have the collimation adapter plate - or are thinking of getting one.

 

I'm not a fan of lasers. Half the time, they're not perfectly collimated, and the other half they don't register into the focuser properly. I have a 1.25" Hotech SCA laser - and what I've found is that it won't consistently register for me to get a solid adjustment of the focuser alignment. Same with a cheap Svbony laser. Further, the laser dot itself is difficult to pinpoint on the secondary donut. So, I really wanted to find a way to align the focuser without using one.

 

Having used a Cheshire extensively to collimate my RC8, I've become quite aware of what I'm looking at when I peek through the hole. The iOptron RC8 manual has a major flaw in this regard. It states that the optical axis is denoted by a thin outline of light around the perimeter of view (in the Cheshire). The problem with this, is that it assumes the focuser is perfectly aligned with the primary - which is rarely ever the case. Also, to see this "outline of light" on the RC8, you first need to remove the baffle extension, then attach the focuser directly to the OTA without spacers and rack the focuser in all the way. Here's their graphic:

jPVu5OD.jpg

 

You can see the sliver of light at the top left. They're saying you need to adjust the primary mirror to get the outline of light to be concentric around the entire circle. When I first received my RC8 from the factory, this was way off. I followed these directions, only to be disappointed by how awful collimation was under the stars. So from there on out, I decided to ignore the "outline of light" when collimating as I knew something was mechanically off with the scope.

 

Fast forward back to the present - I now have nateman_doo's collimation adapter on the back of my scope. Before my first test session, I used my Hotech SCA laser to align the focuser with the secondary. The issue I had was that the laser dot moved when I rotated it in the focuser. I had to assume that it can't be fully trusted. I checked collimation of the laser itself, and adjusted it - but the result was the same. I concluded that it was impossible to get it to consistently register in the focuser. I went ahead and finished collimation, and the star test results were decent, but not perfect - see post #384 in this thread for detailed results.

 

Right now it's all but impossible to get a Howie Glatter laser, and I really didn't want to dump another $300 into a tool for this scope.

 

Realizing that the focuser is now de-coupled from the primary mirror, I thought about that "outline of light" from the instruction manual. Surely this could be used to visually align the focuser to the tube itself, which theoretically has the secondary mirror centered precisely (or at least very closely). Since the collimation adapter backplate adds 35-40mm to the back of the scope, it's impossible to see the outline of light in the Cheshire. So I pointed the scope parallel to the ground and removed the entire baffle, resting it on the bottom of the OTA (not touching any mirrors). With the baffle removed, I could see a huge ring around the secondary. I racked the focuser all the way out so that the outline of light was much smaller, then made my adjustments to nateman_doo's adapter until the outer circle was perfectly concentric. I assumed this indicated the focuser was aligned to the tube, and therefore the secondary. After this, I re-installed the baffle and fine-tuned my mirror collimation as I normally do, using only a Cheshire.

 

A quick flat using my 294MM showed this:

 

lpblJg7.jpg

 

 

I had another clear night for testing, but seeing was quite bad. Regardless, my results are very promising. Here's a slightly out-of-focus shot to check collimation (ASI294MM, R filter, no flattener):

 

RGPYZza.jpg

 

 

And an in-focus shot (60s exp, R filter, auto-stretch):

 

G1StWhY.jpg

 

 

Popped the 2600MM in with Hotech SCA Flattener, and here's what the field looked like (60s, L filter):

 

Bgjpfgi.jpg

 

 

I'll reiterate, seeing was really poor - so I'll need to re-test on a better night to avoid star bloat and get better guiding. But, overall, I think this is the best collimation I've ever had on this scope - and it was 100% done on the bench during the daytime using only a Cheshire and a flashlight.

 

Here's a quickly-processed 21 minutes of RGB on M37 (Bortle 7 skies - 7 x 60s each filter, 2600MM, Hotech flattener). I'm leaving it uncropped so that you can see the edge stars:

 

rg66m6U.jpg

 

 

And then about 4 hours of Lum (120s subs) on the Leo Triplet - quickly processed. Again, uncropped to see the entire FOV. My AMF was inaccurate, unfortunately, leaving a nasty stacking artifact at the top.

 

UB8z4m5.jpg

 

 

So to sum up - with the de-coupled primary mirror and focuser, I believe it's possible to use the outer ring of light in the Cheshire (with entire baffle removed) to align your focuser first. If you don't have nateman_doo's adapter, you can use the same method using the commercially available collimation ring to align the focuser. Just be mindful that every time you adjust the primary, you will likely have to go back and adjust the focuser collimation ring again - and then do several iterations back and forth. That's one reason why decoupling is simply better.

 

Chad


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#396 Che

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Posted 17 January 2023 - 01:26 PM

Nice report Chad.  I will give that method a try.  We have had bad imaging weather since Xmas here in the Carson Valley NV just down the hill from Tahoe so I have not really been able to dial in the collimation on my RC10/nateman_doo adapter.  I also do my collimation on the bench with normal tools so will recheck my current collimation against your tips and see how it goes. To me your collimation looks about as good as I have seen.

Che


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#397 nateman_doo

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Posted 17 January 2023 - 01:36 PM

I have the same laser, but I grabbed a chunk of spare aluminum and machined a much higher tolerant 2"OD on it as well as bored out 1.25 and did the hotech thing tightening it in my adapter.  Then so threw the entire thing in my lathe and adjusted it until it ran true.  That solved my laser problem.  Now I never take it apart.  Before I attempt collimation i spin the part in the lathe beforehand.  I think the trick is to do it like you are going to put the camera in.  If you are going to wrech down on the screws then do the same with the laser.  Consistency is the closest thing we will get to repeatability. 


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#398 Ancient Photons

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Posted 17 January 2023 - 02:24 PM

I have the same laser, but I grabbed a chunk of spare aluminum and machined a much higher tolerant 2"OD on it as well as bored out 1.25 and did the hotech thing tightening it in my adapter.  Then so threw the entire thing in my lathe and adjusted it until it ran true.  That solved my laser problem.  Now I never take it apart.  Before I attempt collimation i spin the part in the lathe beforehand.  I think the trick is to do it like you are going to put the camera in.  If you are going to wrech down on the screws then do the same with the laser.  Consistency is the closest thing we will get to repeatability. 

Wish I had the machining skills you do! So you never take out the Hotech, now that you have fitted it in your 2" adapter? I love the SCA concept, but even when tightening down quite a bit, it still managed to not register perfectly/consistently. The tolerance might be fine for some applications, but I think it's far enough off to cause misalignment of the focuser, which will be noticeable in a star field.

 

I thought about getting the 2" SCA, but I'll hold on to my money for now.



#399 Ancient Photons

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Posted 17 January 2023 - 02:28 PM

Nice report Chad.  I will give that method a try.  We have had bad imaging weather since Xmas here in the Carson Valley NV just down the hill from Tahoe so I have not really been able to dial in the collimation on my RC10/nateman_doo adapter.  I also do my collimation on the bench with normal tools so will recheck my current collimation against your tips and see how it goes. To me your collimation looks about as good as I have seen.

Che

Hi Che - imaging weather is hard to come by these days around here. I'll be interested to hear how it goes on the 10". I'm assuming it's closed-tube. You'll definitely want to rack the focuser out as far as you can, or even add extensions if you really need to. I found it easier to get concentric when the ring on the outside wasn't too wide.



#400 nateman_doo

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Posted 17 January 2023 - 03:37 PM

Wish I had the machining skills you do! So you never take out the Hotech, now that you have fitted it in your 2" adapter? I love the SCA concept, but even when tightening down quite a bit, it still managed to not register perfectly/consistently. The tolerance might be fine for some applications, but I think it's far enough off to cause misalignment of the focuser, which will be noticeable in a star field.

 

I thought about getting the 2" SCA, but I'll hold on to my money for now.

step into my office...

 

This is what I made:

https://i.imgur.com/J9lpGUZ.mp4

 

Just a round chunk of aluminum. 

a283ceEl.jpg

 

having the version with the lines illuminates the donut I think


Edited by nateman_doo, 17 January 2023 - 03:39 PM.

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