131 replies to this topic

[Tom Gwilym]

Thanks.  I'll add this to my growing list of things to try....but put this further down as a later thing to try.  

 

Where B is you can see that locking ring... unscrew a it little by a few Millimetres

Hold the A casing and rotating a few MM and observe your image. I usually take one 5s image and compare after rotating .

Then once happy screw back B

Be careful not to push or pull the secondary casing as you could knock it out of collimation. I also found this changed the focal length by a few MMs


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[Jaspalchadha]

Also I found when I thought that I had done a good collimating using the tools and then trying on real stars my primary was out I got a few modifications made as the previously nuts were poor




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[Hawkdl2]

I don't know how the RC 16 is engineered, but my 10" GSO originally had the focuser attached to the mirror cell. I think newer versions have addressed this.  For a while, the folks at Moonlite (Ron) offered a tilt adapter that mounted the focuser to the rear plate of the OTA, uncoupling it from the mirror cell.   This had a noticeable impact on collimation.  Without the adapter, collimation was tricky and frsutrating, but with the adapter plate, collimation has not been that difficult, at least to achieve "good enough for me" precision. 

[Tom Gwilym]

Ours is the same mounting as the one in the photo in the previous message posted by "Explorer 1" where the focuser mount is on the left side of his photo.  It's bolted to the back plate and has 2 locking screws on each side of the 3 larger bolts.   I usually put the Glatter laser on and center those screws to get it pointing in the middle of the secondary. Then again, the DSI method (from what people say) may prove that the center mark on the secondary mirror may not be totally accurate.  When I do center the laser, It does seem to be brightest there too since it's bouncing back and forth on itself too.

I don't know how the RC 16 is engineered, but my 10" GSO originally had the focuser attached to the mirror cell. I think newer versions have addressed this.  For a while, the folks at Moonlite (Ron) offered a tilt adapter that mounted the focuser to the rear plate of the OTA, uncoupling it from the mirror cell.   This had a noticeable impact on collimation.  Without the adapter, collimation was tricky and frsutrating, but with the adapter plate, collimation has not been that difficult, at least to achieve "good enough for me" precision. 

 

[Jaspalchadha]

How you getting on Tom


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[Jaspalchadha]

I stacked around 15 x 10 min subs of Ha, I think I am happy ish with the collimation. I’ve cropped some of the image because of some left and right tilt, some vendors are saying I need a flattener to get rid of this issue. I am done spending money on this one scope!




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[Tom Gwilym]

I had a little setback last week when I screwed up the T-point module of SkyX and couldn't aim the scope and stars I wanted to used for my attempts.  I'm still trying to force myself to like SkyX for the Paramount, but it's a tough friendship!  I was out last night and ran about 40 stars with T-point and got it slewing properly again.

A step backwards on one thing, step forward, and now back to collimating again.  Last time I messed with it, I lined up the focuser with the laser, then use the Takahashi to make things look symmetical in the secondary, now I'm trying to use the DSI method to visually line up the primary mirror.  I had some fairly promising results last time I tried that, but still off center.  I'll try that again maybe tonight since we have a clear night here.  Again, not looking for research quality, just round stars and pretty.  I know my stars will be a bit oversampled due to the long FL and smaller pixels of the ASI071 camera. 

 

 

How you getting on Tom


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[Tom Gwilym]

Nice image!  I don't mind cropping some of the distorted crud off the sides as long as I get something that looks nice.  I just need to get the cruddy stuff  moved off to the cropping sides.  :-)

[Jaspalchadha]

If it helps nothing is perfect in life, you may have to account for your seeing conditions etc

Get it as good as you can and get imaging


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[Tom Gwilym]

Yeah, that is my plan.  I just want pretty photos with round-ish stars.  I think I'm closer.   During my T-point run last night, it's easy to see how the long 3200+ mm focal length magnifies atmosphere when it's low in the sky.   I could really see "soft" stars low and sharper as I went up higher.  Definitely a high-object scope for the best views. 

If it helps nothing is perfect in life, you may have to account for your seeing conditions etc

Get it as good as you can and get imaging


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[TxStars]

Once you have your collimation and tilt issues somewhat under control a Flattener will increase the usable field of view and a Reduce-Flattener will increase it even more.

But if the tilt and collimation is off the image can be much worse than without either one of them.

[Tom Gwilym]

I do have a 6.3 reducer for the scope that I bought when I got the camera.  I just need the adapter ring to attach it between the tube and the 2 inch eyepiece connector.   I know the good of reducers, they hide ugly blemishes in my images!  

I learned that was vital when I was using my own 12" LX200 Classic.  Don't ask me about my years of autoguiding frustration with that mount.  The EQ6R-Pro I have now is wonderful!  (A whole different topic since that is my home observatory).

I know I need to re-visit the tilt of the camera on the 16 inch RC since there is a tilt adjustment plate on that camera.  I did play with that a bit, but just need to get the collimation closer first on that thing.

 

Once you have your collimation and tilt issues somewhat under control a Flattener will increase the usable field of view and a Reduce-Flattener will increase it even more.

But if the tilt and collimation is off the image can be much worse than without either one of them.

 

[Darth_Takahashi]

Hows the collimation going Tom?

 

Regards

 

 

Neil

[Tom Gwilym]

Making progress on it!   I did get to the point that I stopped messing with the secondary and concentrating on the primary mirror using the "DSI method"  Got the star fairly round, I still have to tweak it a little more, but for for now we are kind of taking a break from that and since we got some fairly round stars, have been working on the OAG autoguiding - another challenge to find a good star sometimes that will work as a guide star. 

Guiding has worked and did a few longer exposures on NGC7331 recently and got results that were far better than horrible - which seemed to be the cast for a long time. 

 

I do make some tweaks to the focus mount to keep the laser in the center of the secondary, but I blame the weight of the cameras on that. 

Slowly getting happier with this monster now. 

 

Tom

 

You can see the stars aren't prefect here, part autoguiding error and and some need to adjust the primary a little more.

 

 

Hows the collimation going Tom?

 

Regards

 

 

Neil

 

[Tom Gwilym]

....and one more good test from M13.  Always a tricky one if you are looking for round stars!

[Darth_Takahashi]

Wow Tom, now this beast is really starting to shine. I love M13, those are some great looking stars. Your Sunflower Galaxy looks too purple for me and need a little re-processing. Still you have brought this RCT to life now, well done.

 

Just remember that you don't need perfection, just a working RCT which I believe you have now. You can always tweak it little by little in the hours between Sun down and astronomical sunset.

 

Regards

 

 

Neil

[Tom Gwilym]

Thanks!  I think I'm learning enough from my mistakes that I'm starting to get smarter on this thing.  Ha!

Seeing the galaxy image again on this page, I do see the purple/red in there now.  I processed it, shared it on the club Facebook page, then copied the URL here to post the image.  I think things happen to quality as soon as it's posted on Facebook sine we know images will change there. 

I also blame my red/green colorblindness which does cause me to miss the purple colors a lot.

 

I think I'll wait a week for the next bright moon nights when imaging isn't ideal, and try to gently fine-tune the primary a bit more.  It's VERY close, and making -- tiny -- turns of the bolts (and a camera that is in the correct orientation as the screen image) is really the key to success. 

 

Tom

 

Wow Tom, now this beast is really starting to shine. I love M13, those are some great looking stars. Your Sunflower Galaxy looks too purple for me and need a little re-processing. Still you have brought this RCT to life now, well done.

 

Just remember that you don't need perfection, just a working RCT which I believe you have now. You can always tweak it little by little in the hours between Sun down and astronomical sunset.

 

Regards

 

 

Neil

 

[Jaspalchadha]

I’d say little more tweak then leave it alone. I’ve finally got mine done to the best of my ability


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Edited by Jaspalchadha, 24 July 2020 - 01:58 PM.

[Darth_Takahashi]

I think I'll wait a week for the next bright moon nights when imaging isn't ideal, and try to gently fine-tune the primary a bit more.  It's VERY close, and making -- tiny -- turns of the bolts (and a camera that is in the correct orientation as the screen image) is really the key to success. 

 

Tom

Exactly, I was literally just cracking the stiction on the bolt to make the final adjustments. Anyway its good to see you making progress so that its all been worth while.

Edited by Darth_Takahashi, 24 July 2020 - 01:58 PM.

[xthestreams]

Reminds me of my own journey witch my 12”, reading this thread because I’m considering a 16 despite some of the challenges. 

 

I have learned the hard way not to trust a Tak for my scope. It seems I can’t get the vanes to line up without making things worse.

 

My new daytime technique involves a Glatter with concentric rings and a lot of fine tuning to get the rings as uniformly illuminated as possible. 
 

Stars now seem much better, still not perfect,  but might also be the diabolically bad seeing at the moment. Point being that if I look through the Tak, it tells me I’m way off, but experience tells me the oppposite. 

 

ill post images for comment if that’s not too off topic. 

[Tom Gwilym]

Seeing that it's nearly a year since I started this thread, I figured I'd update what I've done.

 

The GSO focuser that came with this scope is crap.  I recently talked the club into a Feathetouch focuser.  I attached the motor on it and it works SO much better.  No stall, sticking, slipping or any problems. It has a 15 lb capacity, so it holds the cameras with no sag.

 

The does seem to hold the collimation (or rather lack of it) better, but I STILL can't get this thing collimated to my satifaction.  Latest thing I did:

• cranked the 3 bolts on the focuser all the way in, then undid them each 2 full turns.  I had one that had reached it stop for the most part an wouldn't tighten in much more.
• I re-centered the secondary with the Tak scope, lasered the focuser to the center of the secondary, and made the vane and circles all concentricc with the Tak and the primary
  • The good:   it got my FL down to 3252mm (factory says it's 3250mm) originally was at 3286mm.
  • A test image did show I had tighter stars finally.  I took a few shots and was pretty happy with it.
  • The bad: went back the next night, and wasn't so happy again.  The stars were elongated still after I looked closer.
• Several hours later, I'm again ready to give up.

I figure over the last year, I've probably spend around 100 hours on trying to make this thing work.  I'm really at a loss now what to do short of convincing the board of directors we should box it up, sell it on Cloudy Nights, put the C14 on the mount again (I'm confident I could really do wonders with that old thing), and look for a decent replacement for this RC??

 

I've had great ideas for online public outreach (especially with the pandemic!), but haven't been able to move forward with any of that due to the constant attempts to make this thing work.

 

I really don't think I like Ritchey Chretien scopes now. 

 

Tom

 

 

 

M51 looking fairly decent. At first I associated the star elongation since I wasn't autoguiding.  Then realized it wasn't that.

 

• 

A fairly decent image. This was taken the night before M51 above when I thought I finally had this thing tamed.  Nope.

[xthestreams]

G'day Tom - I'm also the "victim" of a GSO RCT but the 12" variety and in teh past year have learned a thing or two about them that might be helpful.

 

Looks like you're dancing on the knife edge of collimation that is trying to align two hyperbolics - your'e super close, now comes the nerve wracking part.

 

A few thoughts;

#0 - if you haven't already, drop everything and buy a copy of Chris Woodhouse' amazing book (latest edition) @Chris_W has a whole section dedicated to these beasts and his writings and experience here are most helpful

#1 - invest in a set of cone tipped M5 grub screws to replace the push screws on the primary (

#2 - the Tak and or a Howie was only able to get me so far, after fettling (adjusting) the Howie to the point of what looked like perfection, it was quite clearly less than perfect with extra-focal stars (ovals as you are finding) - the trick is now to use the DSI method to get you to perfection

#3 - that I was at least able to get to a reasonable degree of collimation using these tools provides the perfect starting point for star testing and collimation

#4 - grab a stiff drink/coffee/sedative (you can also try mixing all three - the precise cocktail is still something I have yet to figure out)

#5 - wait for the clouds to clear. Avoid sucker holes at all costs :-)

#6 - preferably using your Red filter to cut the degree of atmospheric disturbance, grab your dog eared copy of the DSI manual and SLOWLY start tuning. One thing worth trying here is to make all adjustments with teh scope pointing as close to the zenith as possible to ensure that large lump of silicate isn't shimming itself around under gravity

#7 - long exposures are super helpful, I made the mistake of using shorter ones thinking I could adjust in real time - most of the time I wound up chasing the seeing

#8 - CCD inspector isn't the BEST tool in the world, but with the right star field it can help you eek out the last few % of aspect ratio that the eye fails to see

#9 - consider but do not rely on a tool like the Gold Astro collimation mask - I tried using it myself, but frankly it was quicker for me to do it by eye

#10 - Stare longingly at the Planewave website at least once a day, Google the value of a human kidney and ask yourself seriously whether Robert Redford *might* pay $1M to spend the night with you, perhaps a little makeup? ;-)

 

In all seriousness I have found that I can now take the thing completely OUT of collimation (including accidentally pinching the mirror by over tightening one of the Allen key heads near the rear cell fans that had come loose!) and get it back to a very acceptable state in under an hour or two at most - each time I find my muscle memory helps me converge on a better and better collimation.

 

It's not ideal, but then neither is trying to find a 16" scope with these sort of optics at a 1/4 the price of a Planewave. If you're ready to give up, I'll DM you my shipping address here in Aus ;-)

[Tom Gwilym]

Ha! Thanks for the humorous response, I needed the smile. 

Comments inline below yours:

 

#0 - if you haven't already, drop everything and buy a copy of Chris Woodhouse' amazing book (latest edition) @Chris_W has a whole section dedicated to these beasts and his writings and experience here are most helpful

Looks good.  I haven't seen that book, but the intro on Amazon looks like something I would enjoy.

 

#1 - invest in a set of cone tipped M5 grub screws to replace the push screws on the primary (

I have had those suggested.  They do look like they would turn a lot better than the rough stainless bolts in the back of this thing.

 

#2 - the Tak and or a Howie was only able to get me so far, after fettling (adjusting) the Howie to the point of what looked like perfection, it was quite clearly less than perfect with extra-focal stars (ovals as you are finding) - the trick is now to use the DSI method to get you to perfection

I do have the Tak, and at the time, the only Howie pattern I could find is the grid pattern.  I can't find anywhere that describes very well how to use that one.  It also would require I take this 90 lb beast off the mount, adjust it, then risk bumping things out of whack when we put it back on the mount.  Therefore, I've been trying to depend on the single laser point, Tak scope, a clear star and plenty of cussing.

 

#4 - grab a stiff drink/coffee/sedative (you can also try mixing all three - the precise cocktail is still something I have yet to figure out)

The adult beverages after I quit for the night (maybe I should try before?) have been the only thing that has gone right. Dulls the suffering!

 

#5 - wait for the clouds to clear. Avoid sucker holes at all costs :-)

Yes, I've worked on this 3 nights this week, I gave up last night, and we have probably 2 more good nights.  I may use my own observatory tonight to regain my love for the hobby,  my refractor, dome, EQ6R mount are all working 95% perfectly!

 

#6 - preferably using your Red filter to cut the degree of atmospheric disturbance, grab your dog eared copy of the DSI manual and SLOWLY start tuning. One thing worth trying here is to make all adjustments with teh scope pointing as close to the zenith as possible to ensure that large lump of silicate isn't shimming itself around under gravity

Red filter? That is the first time I heard that tip.  I use an ASI071MC Pro one-shot color on the scope (yeah, the pixel size does have oversampling, but it's also good $$), does the red clear up some of the glare or something? I feel that  most things have gone well and look good - then I get to the primary mirror and the DSI method.  I arrange the camera/display on screen/merdian side so I match the 'hand quadrant" test and start twisting bolts. For some reason, I never seem to make much difference when trying to tighten the bright part of the star or loosen the opposite side to get a nice ring.  I need more convincing that the DSi actually does anything at this point - since I usually fail to see it.   I then look through the Tak and see all I've done is ruin all the symmetry and mis-line all the reflections of the spider vanes.  I know the mechanics of the baffles and such could be off from the factory, but I just mess it up.

 

#7 - long exposures are super helpful, I made the mistake of using shorter ones thinking I could adjust in real time - most of the time I wound up chasing the seeing

How long?  I usually pick a medium star and use about 2-3 seconds exposure.  I try lower gain too, but seems if I go too long it just gets overexposed to see the details very well.  I've been pointing at clusters so I have plenty of similar distorted stars to pick from - and move one of them to the center, then recenter after twisting.

 

#8 - CCD inspector isn't the BEST tool in the world, but with the right star field it can help you eek out the last few % of aspect ratio that the eye fails to see

I see  there is a 30 day trial on that.  Usually when I try a trial I end up with 32 days of clouds once I install it!  Then the price of the software.  I already squeezed nearly $2,000 more out of club funds in my efforts and have nothing good to show.

 

#9 - consider but do not rely on a tool like the Gold Astro collimation mask - I tried using it myself, but frankly it was quicker for me to do it by eye

I have been reading about these masks a bit now too.   I'm tempted to cut my own or buy one.  Cutting my own would be a nice mind numbing activity during pandemic - anything to numb my mind over the daily current events is a good thing - and a drink - but need to cut straight! 

 

#10 - Stare longingly at the Planewave website at least once a day, Google the value of a human kidney and ask yourself seriously whether Robert Redford *might* pay $1M to spend the night with you, perhaps a little makeup? ;-)

For that price, does it come with a telescope expert to help get round stars?  GSO has really made me upset.  Nice looking gear, but.....ugh!   I do still have a kidney I could donate to the cause, that would add "hero" to my list of achievements for the club!

 

In all seriousness I have found that I can now take the thing completely OUT of collimation (including accidentally pinching the mirror by over tightening one of the Allen key heads near the rear cell fans that had come loose!) and get it back to a very acceptable state in under an hour or two at most - each time I find my muscle memory helps me converge on a better and better collimation.

I guess I'm a very slow leaner, or it takes me more time since I have to run up and down a ladder to get between the secondary and the focuser with my Allen key in hand.  I've probably got 100 hours of "learning" now, but only make very small progress.

 

It's not ideal, but then neither is trying to find a 16" scope with these sort of optics at a 1/4 the price of a Planewave. If you're ready to give up, I'll DM you my shipping address here in Aus ;-)

I'll keep you in mind as I pass this by the board of directors.  Ha!   I have a home Ebay business that sells heavy gear, so I'm very experienced shipping freight - something I have learned  better than collimating an RC. 

 

Tom

 

[xthestreams]

Ha! Thanks for the humorous response, I needed the smile. 

Comments inline below yours:

That's what friend are for!

 

#0 - do, don't hesitate. It's truly a great book

 

#1 - do, worth the small $ for teh helpful upgrade - get them 25mm long (that's a metric thing, hmmm, how to explain modern measurements to a Yank???) ;-)

 

#2 - I use my Glatter on teh mount - just point it toward a uniform flat surface on the ground - you're going to readjust anyways. If you are using a laser make sure and rotator your Crayford/focuser around to three uniformly spaced points (120 degrees apart) and ensure the dot isn't moving, you may not have your focuser attachment (or focuser) collimated - this is a BIG scope, minor imperfections are amplified - that dot should not move as you rotate the focuser

 

#6 - it will often look worse in your Tak after it's actually collimated. My advice here, tape over one of the adjustments (usually the top -12 o'clock ones for me) and then make a single very big but precise change (eg: 1/2 turn in or out) on one of them and note what happens. Then try the reverse. Then move it back. Do the same on teh other side. Don't be afraid to make dynamic changes at the start, this will help you dial in the relationship between the changes you're making and what it does to the on-axis coma. Once you've tried each side, then try both - eg: both 4 & 8 o'clock out 1/2 turn and then in 1/2turn (ie: 1 full turn back) to see what it does. You should notice some very clear patterns to the changes. If you don't - call me and we can setup a TeamViewer session.

 

In fact, can you post some of your extra-focal images for us to take a look at?

 

#7 - you should be able to get to 8 seconds or so - you might be using too bright a star - a nice, dim open cluster works best - NOT Alnitak ;-) The longer the exposure the more you can remove the atmosphere from the process - same for using a red filter.

 

#8 - good point, the weather here is already awful, if it clouds over again soon I'll know you're sent money and none of us will forgive you

 

#9 - the software is the thing you'll need - my advice, get good at doing it by eye first, this will (possibly) just help you get the last 5% out of it

 

#10 - yes. His name is Dave Rowe. You pay the money because he worked out a way to get "near" RC level performance without the buggerising around. A MUCH more forgiving design being based on a spherical secondary. 

 

Hang in there mate, you're close. I can see it in the image you shared. Another, related question, what mount are you using and what length subs are these?

 

I ask only because at this focal length, there are a LOT of other things that can hurt your image beyond collimation - not least of which can be things like people stomping around a poorly isolated pier during a 600 second exposure. Or poor PA, PEC, image train mechanicals - it pretty much amplifies any and every flaw in your system.

 

Although looking at it, it seems to me like you're secondary could be adjusted to "balance" the image (per DSI method) - a nice open cluster at an extra focal length will help us figure that out. Perhaps setup a DropBox rather than post them all here.

[xthestreams]

If yiu are struggling with getting anything to change as you adjust the primary, yiu may have slightly pinched optics. I’m not expert here, but I did it to myself and the bloody thing would not come to more than a crappy collimating until I remedied that.

 

‘’one other thing, it’s hard work with just one person on a 12”, I guess it’s a nightmare on a 16”. Hoping you’ve got a friend.