Pimp my RC8 and collimate with OCAL

[mldee]

After many moons of my RC8 and other scopes slumbering in my obs, which has a decidedly heavy 10" truss f4 Newt astrograph firmly attached to the CEM60, never to be removed, I decided to resurrect the RC8 on a second external pier with a recently completed small roll off shed for pier cover. That's now all done.

So, time to get the RC8 into working order, and after reading up on all the latest forum news, it's been full steam ahead. First item was to purchase the 90mm to 42mm adaptor plate to allow OCAL direct connection to the rear mirror threads. Done.

Second was the GSO tilt adaptor plate to rectify any tilt in the imaging train. Done.

Third was to procure a decoupling adaptor plate to detach the imaging train from the mirror assembly. In process. Basically just The Big Pimp. Guy on the FB RC8 forum design:https://tinyl.io/93aM

The collimation steps started with no imaging train, Laser then OCAL connected direct to the mirror then collimate. Pretty straight forward after watching all the YouTube videos on the subject.

Check and adjust imaging train for tilt using laser + flat mirror technique, then connect imaging train to OTA and adjust secondary mirror for good laser return spot.

Connect OCAL to imaging train camera position, preferably threaded. Check and fine-adjust mirror and tilt as necessary until optical alignment seems correct. See pic below. Repeat laser and OCAL steps until both are good.

Place the RC8 on a mount and confirm with defocused star test. Fine adjust secondary mirror screws to achieve a perfect donut shape. It should only require minor movement of the screws. I did it in the freezing cold in about 2 minutes.

Finally, replace the stock GSO focuser with the TS optics rack and pinion model, due to slippage and subsequent unreliable autofocus in NINA. Done and the TS version highly recommended and easy to install the ZWO EAF bracket.

Hopefully all this was not just a lipstick/pig effort:P

Now I get to do low-elevation northern imaging with Bortle 2 exposure durations:D

Pics show RC8 Pimp/collimation setup and OCAL results.

[Leo.G]

Sorry, I have an RC 8 and am completely ignorant in operations as I haven't had it out much (weather and health).
What does the adapter in the image do?


https://www.iceinspace.com.au/forum/attachment.php?attachmentid=308738&d=1690772476


I have seen mention of some person in America who manufactures stronger focus holders or whatever it is, instead of the focuser mounting directly on the mirror. He machines them himself and recommends anyone interested send their rear plate to him in The U.S.A., he do the modifications and ship it back for assembly. To me that would be a very expensive option but I'm thinking of having an engineer friend machine something similar of my own design (when I get to it).
I understand the focuser can distort the primary mirror, hence the design and implementation of such devices but do they make a great deal of difference?


I guess that's also dependent on intended use.
My intended use is photography (Astro) so I'm guessing it would be a worthwhile mod.


Your GSO focuser is that the earlier model with a flat centre (where the autofocus motor plate mounts and lock screw is) or the later version which is a steel track type design, 47 little steel balls running in each track?
I replaced the steel balls in one spare focuser I have with ceramic. The original mechanism was a little worn, the ceramic balls have made the focuser much smoother but it was an absolute pain to do. I have enough ceramic balls for the primary focuser but don't think I'll go to the bother at this time.


I love the slide off shed and the use of the stump to support it and an old battery keeping it in place as an anchor (strap down point). My kind of engineering, making use of what I already have laying around.

[mldee]

Thanks for the comments Leo, I just sort of wrote a "memory dump" of what I have been doing with my RC8 that may be of benefit to others considering such things or perhaps dissatisfied with their scope's performance. The RC family can be quite cantankerous.
I've commented in the quote below.

[Leo.G]

Thanks for the reply Mike.
I got mine out last night and though it's stated they are not the most suited for moon and planets I got a semi decent shot of the full moon. It was too bright to try and capture anything else and I'd replaced worm drives on my mount through the week and got some ND filters for the moon I wanted to try out. Plus I needed to get my 80mm Megrez aligned on the Losmandy plate as a guide/finder scope and last night was a beautiful night to play.


https://i.postimg.cc/3rk49gBd/Moon-HDR-LR-DEV-1-5867x3897.jpg

[mldee]

Nice moon pic, hope you get the Megrez set up OK. I also have one of those, it's due to do a spell in the Dunny-Doo soon for some widefield stuff when the Bortle 15 moon goes away. They're a lovely scope, and mine has been resting for a year or so, time to soon give it some exercise.
Cheers.

[Joshua Bunn]

Hey Guys,


Regarding the replacement tilt plate on the back of the OTA, I can make them to your requirements if you like. Light-weighted aluminum, CNC machined and anodised. I'm in Western Australia.


Cheers
Josh

[Leo.G]

Thanks Joshua!
I'll have to do some research and see exactly what I want to do.

[mldee]

Hi Josh, thanks for the heads up. I would be interested in getting one made. Could you send me further details on proposed design/appearance, cost etc, either by pm or post here. I presume you've had a look at the link I provided to the European guy's design. It included the two 3d printer files, but happy to work with you on a simple mechanical design if you want to finalise for CNC.

I suspect that there may be a modest market for this both here and overseas.
Cheers,

[Joshua Bunn]

Thanks Mike,
I have had a look at the file, and will be in touch with you soon to discuss your specific requirements.


Cheers, Joshua

[Joshua Bunn]

No worries Leo, sounds good.

[Leo.G]

I'd like to be kept in the loop if possible.


From what I understand the focuser attached to the mirror introduces strain/image shift. By removing the focuser and fitting a dedicated mounting point the mirror can't get the distortion.
I hang a heavy Nikon D810 full frame camera off a heavy home design 2 inch aluminium adapter which weighs (wait, I'll check)........


OK, my adapter sans eyepiece (12mm Vixen Lanthanum) weighs around....
CRAP, I forgot, here goes again....


https://i.postimg.cc/gcZmK64K/IMG-1797-4146x3110.jpg


https://i.postimg.cc/151P75j1/IMG-1798-4146x3110.jpg


https://i.postimg.cc/SRC4QwjP/IMG-1799-4146x3110.jpg


Sorry!
The adapter sans eyepiece weighs around 440 grams. It's my design I had an engineer friend machine, 2" extension heavy build which accepts a 1.25" eyepiece and works reasonably well for eyepiece projection and straight photography. I could have designed it to be thinner and lighter but that would have taken longer and cost more to machine. Sadly I'm an old school heavy welding type person (former forklift technician, everything has to carry a big load), if the bridge has to hold the weight of 2 cars it's going to also support the row of Sherman tanks following.
Not good for astronomy.


The camera body alone weighs 980 grams from what I found online, add in the extension rings (I think with my adapter I still had to use the 2" extension ring to achieve focus with an eyepiece), it all adds up to near enough to 1500 grams hanging a reasonable distance from the mirror where the focuser attachment ring attaches.


In mention of CNC stuff, the fellow on the astronomy forum who does the custom CNC units and suggests sending the rear plate to the US offered me full cnc specs to try and make one myself. That would be so easy if I had a cnc machine, half a brain and an idea as to how to use it.


Funny mention, he even offered to convert the offsets to metric believing no one in Australia would understand imperial. I did until I did my 4th form leaving certificate at high school in metric after being taught imperial for so many years......


Following is a stitch of 3 images (vertical sectioning) through the 12mm eyepiece through my extension set up. Focus was not great but my eye sight isn't the best. The issue with focus could be the very strain on the primary mirror I'm talking about:

https://i.postimg.cc/sg2YkyMw/Crater-Stitch-1-2-3-9825x3663.jpg


Here's the thread in Cloudy nights which I hope is allowed,soory if it's not:


https://www.cloudynights.com/topic/827768-finally-made-an-rc-collimation-adapter/

[mldee]

Thanks for the Cloudy Nights info, Warren, I hadn't seen the detailed photos before.

Josh, the above design does seem overly complex to me, but I have no experience with CNC programming.

If possible, I would still like to proceed with a simpler version from you, but if it reduces your programming load, does it make sense to take up the kind offer of the CN designer to provide a set of his CNC specs, as a starting point for you?

BTW, Josh, do you have an RC8? If not, I would be happy to send my rear plate for fit and function checks if needed.

Cheers,

[Leo.G]

I agree Mike, the design on cloudy nights is extremely complex and I honestly don't see the overall form being more significant than what you have done with the 3D printer.
In saying that, it's a hobby for the fellow, it does look cool and show off his skills but I'm positive it adds a lot of unnecessary weight to the rear of the tube assembly where there's already a lot of weight at the back when trying to get the units balanced on a mount without adding a weight bar attachment at the front of the tube, especially when hanging a heavy imaging load like I'm doing.
I forgot I have a small vixen clamp to hang off the vixen dovetail bar on the scope to drop a Kg or two under the nose of the scope. Next time.


My 80mm Megrez (original model but still nice) didn't help as I had it more to the rear on a large Losmandy plate so I could get to the diagonal to see for finding my targets.


I'm trying my best not to add too much weight, my mount is only an EQ5 PRO GOTO mount though I changed the standard RA bearing to a tapered roller unit and it runs both smoother and seems to handle the loads better. My above full moon shot is a stack of 50 images done without any form of star alignment (my locale makes that extremely difficult). I slewed to the moon, kicked the tripod legs around till it was centred (no accurate south or permanent positioning of mount) and came inside for around 1 hour and the moon had not moved from my eyepiece. Over the 50 images I took there would have been less than 0.5mm shift in all of the images in total so I'm guessing I got VERY lucky with alignment on that night.



Leo

[Joshua Bunn]

Hey Guys,


Thanks for the input, I'll get back to you both shortly :thumbsup:


Regards
Josh

[Joshua Bunn]

Hello Mike and Leo,


I looked through the CN thread, and I see what a good job he is doing!


Mike, I would rather start my design from scratch. I don't own a RC8, so if you would like to send me your backplate, that would be great, and would help in getting you a efficient design. thankyou for the offer. I can model it and use that for future changes if need be.


Ill send you both a PM a go from there.


Best

Joshua

[mldee]

Josh,

I'll take it off over the weekend and mail it to you next week. That will also give me a chance to clean the mirror and add the extra baffle piece as recommended for the earlier models.

Cheers,

[Leo.G]

Mike I haven't remotely looked at disassembling mine in any way. I purchased it a while ago and it had been used only 3 times when I bought it used. I've used it a further 3 times with our crappy weather.
A question you may know from the strip down:
Any sort of focuser holder, will that leave a gap between the mirror and new focus attachment point where a tube of some kind would have to be put in to stop the light leaking out before it gets to the more rear focus attachment point?


Thanks!

[jwoody]

Hello Josh.
I would be very interested in one to suit an RC10 if and when they become available.
I will keep an eye on this thread.
Thank you
Jeremy

[mldee]

I'm about to go down the rabbit hole of finding out. Google will be my first friend, then (hopefully) slow but sure exploration.

It would appear that as long as I pay attention to the internal baffle tube, the whole rear assembly should come out after carefully removing the four backplate fixing screws. Obviously I'll remove the imaging train first and have plenty of soft towelling to support the mirror etc on removal.

I'll then be in a position to take some more pics and check out potential light leaks etc.

Will probably do all this on Monday and will keep you informed.

I disassembled my previous C8 a few times, so not too scared, and I'm confident of the laser + OCAL for future recollimation.

With all that, I did once manage to drop a C8 Schmidt front corrector plate while cleaning it. The pieces were very sharp........

Cheers,

[Joshua Bunn]

Hi Jeremy.
No worries, I'll keep you in the loop.
Regards Joshua

[mldee]

Spent the morning removing the RC8 rear end plate to send to Josh, it was a straight forward, with a selection of Allen keys and a Philips head screwdriver being the only tools needed, plus a bunch of soft towels and such.

After removing the baffle tube and mirror retaining ring, using lots of care, the mirror slid out onto a soft cloth without any drama. It's still sitting up side down on the cloth in the pics, waiting for a clean. I put some red dots on the Backplate internal thread edge, mirror chamfer and back plate screw ear so they can all go back together in the same circular location.

Back plate and tilt adjuster have now gone off to Josh for the decoupler design phase.

[Leo.G]

Mike does that baffle run from the mirror to the focuser mount?
Maybe not a baffle but a sleeve from the mirror to where the threaded ring the extension tubes and focuser attach to.

That would mean nothing would be required between the mirror and any accessory focus holder I think?

[mldee]

Hi Leo,
No, the baffle, which btw is a simple one piece aluminium tube threaded at the mirror end, screws onto the top of the small mirror retaining ring which you can see at the bottom of the tube.

The small mirror retaining ring sits above the mirror and is threaded to the mirror adjustment collar shown in the front view of the 'Back plate less mirror' pic. The mirror slides over the white teflon washers, then the retaining ring is screwed down and two small hex screws lock to the adjustment collar. The baffle is then screwed on to the second top thread of the retaining ring. This also retains the mirror in position once hand tightened.

I'll attach some pics of the mirror retaining arrangement. No light leakage there, but since the new decoupler will sit just outside the periphery of the backplate mirror adjustment plate, there could be some potential for leakage there, but it will be a consideration factor in the design. Pic #4 shows the light path from the baffle to the imaging train. The new decoupler will separate the imaging train from the mirror adjustment plate thread.

Cheers,

[Stonius]

I'd be interested in that too, if at all possible!

[Joshua Bunn]

Hey mate, of course! I'll post the results here. Cheers!

[MarkInSpace]

Hi Josh
Can you pls keep me in the loop as well? I am getting my RC8 next week and would like to do this sort of upgrade.
Cheers
Mark

[Joshua Bunn]

Will Do Mark,
If Mike doesn't mind, we can all use this forum post to keep the conversation in one place, or we can start a new thread. Is this Okay with you Mike?


Cheers,
Joshua

[mldee]

Hi Josh,

Absolutely no objections whatsoever.

The more participants, the better the user experience for other RC8 owners, and the more potential business opportunities for you.

EDIT: forgot to answer the main gist of the question. The title of this thread is based on a rather painful attempt by me at humour and may be off-putting to some, so probably better to start a fresh thread with a more accurate descriptive title and perhaps (not sure how you do it) refer to this one if needed.

As Josh is the central contact point in this project, I'll leave it up to him to come up with a suitable thread title.

Cheers,

[Joshua Bunn]

Thanks Mike,


Ill start a new thread, with reference back to this thread. Anyone who is interested in getting this modification to their RC6, 8, 10 etc, can post in there, and we can go from there :)


Cheers!
Joshua

[Leo.G]

Thanks Mike and Joshua, I'm looking forward to seeing what comes of this.

[dugnsuz]

Good to see Josh providing this service in Australia - I got a plate made for my RC6 by Nateman_doo on Cloudy Nights. Great guy and well made but US Postal prices were the killer for the return trip of the backplate.


2 nights of frustration have melted away with a 3rd glorious night (well, 10 minutes - clouds rolled in) of round stars.


The frustration came from winging it - so went back and read all the relevant CN posts and very happy with my brief glimpse (damn clouds) of what's possible with the added decoupler plate

[Leo.G]

I chatted with ND through PM several times, he seems like a very nice fellow. He'd suggested me sending my back plate and I explained return postage would be worth more than the job so decided not to go ahead with anything.


It does look like an impressive machining job nonetheless.

[dugnsuz]

Yep, I didn't do due diligence and was surprised that US Post could charge $100USD for return postage:shrug:, but I was committed by that time - live and learn!!??

[Leo.G]

Sadly I've learnt that in the past with the US postage costs, even if Aus post do deliver signature required packages totally off the grid and 6 minutes from where you live (after seeing the delivery guy go past my house awaiting said delivery) and have to go around and find the package the next day, opened, touched and damaged (flexible circuit board material bent and covered in some mongrels grubby fingerprints despite the label not being addressed to him in a BIG box).
Aus post are IDIOTS, morons working for them can't read but they are cheap, sometimes.......

[mldee]

Things are moving along well in fabricating the adaptor, Joshua has completed the design, made the drawings, done the lathe work and is now into the milling stage.

While all this was going on, I started musing about fixing the design fault in the early GSO RC's baffle tube length, which can allow adjacent bright starlight to interfere with images. My CF OTA, bought used off IIS in 2011, no doubt suffers from this, although I haven't recognized it. :P

Anyway, I thought while I had the scope in pieces, it would be silly not to add the simple 3d printed extension which is available from overseas, so I rushed off and purchased one from the UK yesterday. (Cheapest postage). Then, chatting with Joshua today, he mentioned that he has a 3d printer and if anybody wants one for 6, 8 or 10" RC's, he could fab them.

Once I have installed it all, I will try and document the little adventure and post it here.

[Leo.G]

Thanks Mike and Joshua!
I've seen mention of those baffle problems in the past but my RC is one of the newer models and apparent;y GSO had rectified the issue by then.
And yes, postage from the UK is more than reasonable in comparison to from the US of A. I've often purchased from the UK in preference, especially with our weak dollar.
I'd love to see what the plate is looking like.

[MarkInSpace]

It’s great to see this work continuing!
When the plate is done, how do we attach it?
Also, I have a used carbon RC8, unknown year of manufacture . How do I check if I need the baffle extension ? FWIW, the central tube in my RC8 is a straight cylinder.
Cheers!
Mark

[mldee]

Hi Leo and Mark,

Once the completed adaptor and baffle tube extension both arrive, I'll be sure to document all the bits and steps involved in reassembling and testing/collimating the OTA. This is where the OCAL will come in handy. (See my original post in this thread)

Mark, I'll check my baffle tube dimensions and post here so you can compare. I also seem to recall there are some internet posts describing the new and old GSO tube designs.

Edit: The adaptor plate sits just proud of the existing rear 90mm thread and is attached to the black OTA backplate by 9 tapped screws, with a template to be used for hole location. Drawings and photos will be available (hopefully) soon:D

[mldee]

Mark, dimensions of the old-style baffle tube and pic.
(Dimensions +/- 1mm)

Overall length 150mm
Main tube length ~120.5mm, diameter 71mm
Step 1 length ~14.5mm, diam 69mm
Step 2 Length ~13.2mm, diam 67mm

The new plastic extension is just a push-fit into the mouth of the top step. I plan on using just a smidgin of Loktite or similar to ensure it doesn't want to fall out.

The tube is fully internally micro-ribbed and has threads at the bottom to attach to the mirror retaining ring.

Also, note in the pic the six attachment holes in the CF tube that align with the six threaded ears on the backplate. Two holes under each of the top and bottom mounting rail attachments plus one either side.

Carefully remove these six screws and the complete backplate + mirror + baffle tube assembly can be easily pulled out of the CF tube. Make sure you do it on some soft surface in case you slip/drop it!

[MarkInSpace]

Thanks for posting that picture! That is exactly what I have. I’ll need that baffle extension, sounds easy to install! I’m a little less certain about tapping the backplate, but I’m willing to give it a go!!

[Joshua Bunn]

Hey Guys,


Mickes adapter is still being made, but to answer a few of your questions, If you want to do the install your self, I will supply a threaded collar, threaded inside and out, it will screw onto the original m90 thread on the back of the scope, and my adapter will thread over this. This ensures it and the original thread are concentric with each other. Once its screwed down and in the correct orientation, you can center punch the drill holes in the back plate, through the 9 clearance holes in my adapter, they can then be drilled and taped. This is the basics of it, but I will supply a link to video instructions with everyone's units.


I have attached a couple of pictures for you to see the basic design. Note, Michael didn't want the tilt adapter version of this adapter as he is using a separate tilt adapter, but for people who want a tilt adapter built into this, I can supply that also.



Best,
Joshua

[Leo.G]

That looks great Joshua!
I also have the tilt thingie for collimation, it came with the near new CF RC I bought off a member here, used 3 times I believe (the scope).
I do have a question, I see how this system bolts to the rear housing/cover. but I've a little confused because currently the focuser mount ring attaches directly to the mirror. This is the thread this 90mm collar screws onto, I understand that part but I have to detach the original collar from the mirror first.
In saying this I better read again, I think I just somehow confused myself and maybe answered my own question at the same time.
Migraines do this to me, too frequently sadly.





OK, that is what I read. I haven't pulled my RC down but I'm guessing detaching the original collar from the mirror shouldn't be a major problem.
Drilling and tapping the end cover shouldn't be a big problem either but what is the material it will be attaching to?
I guess I have a magnet here and can check that myself, I haven't looked. If it's carbon fibre is that easy to drill (and more importantly, tap?)
Oh OK, my son just said he believes it's alloy, that's easy.

[mldee]

Joshua just sent me a photo of the first unit, after anodising. Progressing well.

[joshman]

daaaamn, that is sexy. makes me really want to get an RC8 just so i can get one of these.

[Leo.G]

That looks stunning!


My previous questions, I went through the thread again and answered them myself. My memory is getting worse by the ...What's that time thingie again?

[mldee]

The adaptor does look nice, really itching to try it out.

An interesting point that Joshua pointed out while doing the design is that in the basic GSO setup, the complete baffle tube + mirror + image train assembly, which would weigh a few kilos and be upwards of 600mm long, is attached to the OTA via only the 3 (three!) 4mm mirror collimation hex screws, leading to the possibility of collimation change due to flexure as OTA elevation varies. You can see the three (inner) screw holes in the attached photo.

That's why his adaptor uses NINE attachment points to the backplate, ensuring the image train is solidly mounted to it while totally offloading it from the mirror assembly, so the mirror collimation screw load is significantly reduced to just the mirror and baffle tube.

I believe Joshua's adaptor should provide significant improvement to the overall collimation stability and imaging load carrying performance of the unit.

[Joshua Bunn]

Thanks Leo, Josh and Mike,


Yes, I am quite perplexed how everything is supported on those 3 screws, with only about 3.8mm of thread depth. Anyone who knows about thread sheer stress, knows aluminium threads are required to be 2.5 x thread diameter for steel bolts to withstand the stress that might be placed on the bolt... This is why I have 9 bolts.

Some people might say, 9 x m6 cap head bolts is a little overkill, and I know it is, But there is flex in everything, and I mean everything (not refering to GSO here) but metal fixtures and plates will always flex minor amounts, its a matter of minimising it. So 9 bolts will go a long way to keeping flexure at the camera interface to a minimum.

[Leo.G]

I like over engineered, I've spent my entire life doing it from specialist forklift attachments to what I called "a spider", a collapsible steel (and plank) structure to aid in safe assembly of silos and never had a device fail.

[Joshua Bunn]

That sounds like some interesting Work, Leo :)

[mldee]

Just a quick update for those who may be following the RC8 major upgrade. I mentioned in an earlier post that I was going to install the baffle tube extension as recommended, and it arrived a few days ago from FLO UK, (cheapest postage).

Very lightweight 3d printed, with good non reflective surface inside and out.

It's a good medium friction fit into the baffle tube, and seems quite secure without need for glue or screw fastening etc. Some pics attached.

[Leo.G]

Mike I don;t believe the extension is necessary for the later model unit I have. I haven't been game to strip mine as of yet, deciding to wait till an adapter is available and do collimation only once. Plus I may get it out and use it in the interim till the adapter is available.
I'lll have to set up my mill to drill and tap the holes unless I get my engineer to do them, not sure yet.
It seems I have a lot happening in different areas of my life at the moment and I have no idea when I might even get to it once I have the upgraded rear plate.

[MarkInSpace]

How can you tell if the extension is required? I bought mine used, and don’t know the manufacturing date.

[mldee]

I would guess Google is the best way to find out. Cloudy Nights, Stargazers Lounge or FB RC user group being the immediate suggestions. My RC8 was also bought used back in 2011, and IIRC, the corrected baffle version came out much later than that, but I don't remember when.

I sent you dimensions of my baffle on P2 of this thread, but I guess you have to remove the rear assembly to get at the baffle and see if yours is the same. If it's longer, then I would suspect you have the newer version.

As I also mentioned earlier, I don't even know if I had any of the bright-star reflection problems, just decided to put in the extension as insurance while I had the scope in pieces.

I also think that with a little determination, the ~10g extension could be inserted from the front without any disassembly.

[DiscoDuck]

I can confirm it is possible. My hands/arms are not the thinnest, and yet I was able to manage it. JUST managed to squeeze past the secondary.

[Leo.G]

How is the development coming along Joshua (or Mike)?

[Joshua Bunn]

Hello Leo.
Mike's backplate will be finished today and sent back to him.
Regards Josh

[Leo.G]

Thanks Josh!
I'm looking forward to hearing from Mike.

[Joshua Bunn]

Hi Guys,
Mikes rear cell has been sent back to him, I have attached some photos from along the way.
I am currently working on 2 others, one having a tilt attachment built in (Mike opted to not have the tilt version as he has a separate tilt adapter). I will post this over in the dedicated thread for these parts (hopefully a duplicate is alowed)


Thanks, Josh

[Leo.G]

That looks AMAZING Josh!

[mldee]

The RC8 backplate with adaptor has arrived from Joshua, he did a super job and it looks even better than the photos. A photo with the RC spacers and my tilt adaptor attached follows.

Now to document the assembly and collimation. First task is to clean the primary mirror, which is still sitting upside down on a towel in the obs since the disassembly. Better late than never.

I'll make another post to list the steps in assembly and collimation.

[Leo.G]

Thanks Mike and that does look amazing!
I've been in contact with Josh and as soon as I have the finances I'm going to either order one or send my rear cell down to him. I can drill and tap the thing and have everything here to do it. Whether or not I do it accurately with my poor sight is however in question. I'm sure positioning centrally is crucial to the collimation of the scope as far as getting the focuser aligned with mirrors goes.



Quick question about your tilt adapter. I've read several threads on varying forums about this, I've often seen mention of it being on the rear of the extension rings but I've also frequently seen mention it is recommended the tilt adapter is fitted as close to the tube as possible and from memory that's stated by the tube manufacturer (I could be wrong on that point, little sleep and migraines make my brain mushy).
I notice you have yours sitting on an adapter or is that adapter necessary as an attachment between the rear cell/Josh's unit and the focuser?


The collimation process has me a little wary, I've seen so many horror stories I haven't been brave enough to even check mine.



Thanks!

[mldee]

Hi Leo,

I'm sure you'll be happy with Josh's product!
As to the tilt adaptor, I've just spent ten minutes staring at the photo wondering where I should now put it.

It's not so much due to possible tilt factors, as the whole imaging assembly should now be very rigid, subject to the quality of the actual focuser mechanism and camera connection. Obviously all-threaded is the best way if one can afford it and if the necessary threads are available.

I just finished discussing a few points on an email with Josh regarding the need to collimate the OTA mirror assemblies before attaching his adaptor to then do the same for the complete imaging train.

If the OTA is not perfectly collimated, especially with hyperbolic mirrors, then trying to collimate the total image train becomes an exercise in frustration.

To cut a long story short, if you get the OTA right, then you can put the tilt adaptor at the bottom, but it then covers the mirror adjustment screws on the RC8. (Which should not by then need further adjustment). This then gives the tilt adjuster total control over the full image train.

However as I need the spacer to get correct focus distance, I'll probably just leave the tilt adjuster at the top of the spacer so I can easily fiddle with the mirror screws if I choose to go down that hole. I guess we'll know more when I've finished.

The critical task in reassembly is to ensure the OTA is correctly collimated before attaching the adaptor and imaging train, this requires a COLLIMATED laser and preferably an OCAL setup. A good set of E-bay T-handle ball-end Hex keys is also a good investment.

News at 11 :D

[Leo.G]

Thanks Mike!



Hex keys I have by the...Too numerous to count. I spent too many years working in mechanical and have a lot of tools.
Collimated laser I do not have. I have a couple of laser modules I was going to play with and turn up sleeves to fit 1.25" and 2" holders but that's something I may get to one day on the lathe or may not get too. I haven't even welded up the stand for the milling machine as of yet and the compound table is still at the engineers to be drilled and tapped (I hate cast iron) to hold the milling machine.
I guess I could be out welding today but welding and migraines are never a great mix.


I've seen mention of OCAL numerous times but not looked into what it is, I'll do a search now.

[mldee]

Just a quick note on the Laser. I wouldn't go down the DIY route, been there, done that. Life's too short for that! Too many factors to consider in coming up with a successful design. I have a Farpoint unit, built like a battleship, pinpoint laser spot and perfectly collimated, with a 2" body. However, quite expensive from the US.

It is possible to find good quality lower cost ones that also include the return laser 45degree body target (highly desirable) from the reliable astro shops (looking at you Bintel) or even Ebay or used on IIS. Perhaps if you call them they can make some recommendations.

Maybe some IIS readers also have some recommendations. Without a good laser you're really making it hard for yourself, and no, the Takahashi Collimator doesn't sit well with poor eyesight and it's just or more expensive than a good laser.

I'll do a more detailed post on my recommended toolkit for doing the RC (Makes me sound like I'm an expert - NOT), just that my experiences with this very unit go back to 12 years ago of trying to collimate units with Pmrid (Peter) at his dark sky property. We both gave up in frustration. I now have 20/20 hindsight and the right tools!

Looking back, the reasons for me were lack of knowledge, lack of correct tools and lack of decent information out there.

As to OCAL, Google is your friend, Basically an electronic camera with specialised chip-and-software version of the Tak unit, that allows you to see everything on a big screen. Not difficult to use, but takes a few goes to get your head around it. It's the last daytime kitchen table tool before the StarTest!

GoodLuck;)

[Leo.G]

I looked up the OCAL 3, that's only one decent lotto win away. That's how I scored an used Nikon D810.
The disability pension isn't the best source of financing for astronomy tech.
One day!
But yes, I'll keep an eye out for laser collimators when finances permit or hopefully get lucky on a day when finances permit.


Not so sure on hindsight but I get close to 20/20 vision on occasions, that's the times when I have 3 pairs of reading glasses stacked to look at something and when my son says anything about having a look for me I usually scream "I'm not blind you know!" in a kind scream, never in anger. Sort of a laughing and cryng point at the same time.


I look forward to reading up on the procedure because if I send my end cap out I'm going to need to understand something to ever use the telescope again.

[Joshua Bunn]

In terms of where to place the tilt adapter, if the only source of tilt error is at the camera chip, it is best as close to the camera as possible. The further you move away from the camera, the more lateral adjustment you introduce, which just moves the chip off axis... not what you want.

[mldee]

If the camera chip is the only tilt contributor, agreed, the closer the better. Unfortunately I have no knowledge of how much, if any, is also introduced by the other image train components, such as spacers, focuser, OAG, filter wheel, backfocus adaptors and finally camera coupling adaptor. I will be attempting to evaluate these factors during my reassembly.

It's also the reason why I keep harping on about getting the basic OTA collimated before moving to the image train.

The trick I read about for the imaging train that has already worked well for me is the "laser mirror collimation" which involves taking the assembled image train, less OTA and camera, standing it vertically on a horizontal mirror and doing a laser return dot test. Simple and verifies alignment of everything except the camera chip, and most modern cameras have chip tilt adjustment anyway.

Might as well do these things anyway, because visibility outside here due to bushfire smoke is about 2km:sadeyes:

[raymo]

Hi Mike; I stopped short when I saw the title of your first post. I've never
heard of people pimping their scopes. How much does yours charge for a night?:D
raymo

[mldee]

I guess it depends on whether you want to mount it or just collimate it:D

[raymo]

:lol::lol::lol:
raymo

[mldee]

Took a bunch of photos today for preparing the assembly and collimation docs. Re-attached the assembled backplate/mirror/baffle tube to the OTA and did a quick dry run collimation check. It was close and tomorrow I'll try and improve it before installing Joshua's decoupling adaptor, which for clarity I am calling it the JB adaptor.
A couple of photos showing the drilled and tapped backplate (done by Josh), the JB adaptor front and rear, showing the light-sealant foam Josh installed between the adaptor and now unused mirror threads.

My plan for the docs is to incorporate the photos with text instructions in three pdf documents (assembly, install and collimation) that I can post here, rather than just a plethora of posts and pictures.

Anyway, here's some happy snaps of the reassembled RC8.

[Leo.G]

Thanks Mike, anything that aids both myself and others who don't understand the procedure will be great and much appreciated!

[mldee]

Thanks Leo, sometimes being retired in the bush has benefits for lots of spare time, hence all my RC8 posts!
More happy snaps below for your edification, showing the first check of OTA collimation using the OCAL. It was also very close and only took a few minutes of finetuning both mirrors to bring it to my satisfaction.

The thing to look for in the OCAL picture is concentricity of all the rings compared to the green, red and blue OCAL alignment marker rings, which are adjustable and perfectly concentric. The cross hairs show the alignment with the centre dot, which is the OCAL chip sensor and should be smack bang over the secondary mirror donut.

After the initial Basic OTA collimation yesterday with the lasers, it was pretty close, and with the OCAL this morning, slight main mirror collimation screw adjustment moved the bright inner white circle under the blue marker ring, then secondary mirror screws fine tuned the sensor position under the cross hairs and Viola! it was done.:thumbsup:

[Leo.G]

I'll have to save up for an OCAL unit. It won't be before Christmas.
It's a pity there isn't a rental service for some of this equipment.

I've been retired since I was 31, not by choice. I have all of the time in the world, just no money to enjoy it, the health doesn't permit a lot of enjoyment either.

[mldee]

I hope you manage to eventually obtain an OCAL, they're a very handy tool and can be used on Newts, SCT's and RC's.

It would be great to see an astro test equipment rental business, I'm way too old to be starting businesses again, perhaps some young folks might consider it. It sounds like a business one could run from home, just not sure if the volumes would be sufficient.

Anyway, my RC8 efforts must be coming to fruit, as it's now started to rain here:rolleyes:

I just remembered how to zoom the OCAL screen using the mouse, so I've attached a few more snaps showing the secondary mirror donut with OCAL sensor right behind it and cross hairs, which are now aligned on the four mirror spiders. I also changed the colour of the blue marker to yellow for better visibility.

[MarkInSpace]

Hi Mike,
My rc8 secondary mirror doesn’t have a doughnut sticker.
Can I still use the OCAL?
Cheers
Mark

[Leo.G]

Thanks Mike, I appreciate the information and I'm sure others will too!
Yes, rental would be good but probably very risky and insurance would be a killer, speciality equipment requiring certain skill levels to use it.
I'll keep an eye out here, I see OCAL units come up occasionally.


There is an OCAL in accessories right now.:
OCAL Pro 2 electronic collimator

I can't afford it at the moment, another will come upafter Christmas when I'm a little more financial, hopefully (hopefully financial and hopefully another unit for sale).

[mldee]

Hi Mark and Leo,

Mark, not sure what brand of RC you have, but without a donut, off the top of my head I can't think of an easy way to do even the first laser collimation step.
My suggestion would be to ask IIS/Google if others know how to add a donut to an RC secondary. Removing the spider and mirror would not be a big deal, also not sure just how critical the spot needs to be. Perhaps just measuring in equidistant from the spiders' tips and pop a donut there might do the trick.

Leo, OK on the OCAL, mine is the Mk 1 version, and seems to work just fine.

On looking at my above posted zoom pics of the OCAL screen, I've decided that most OCAL users, me included, are continuously asking themselves "What the heck are all those different blurry circles that make up the picture?"

I've become quite familiar in the last few weeks with the various views looking down the rear of the OTA, so I'm going to make a pdf with pics, lots of pointers and comments, explaining what the various black, gray, shiny etc rings are to help interpret the OCAL screen a little better.

[Leo.G]

I know there are stencils/paterns available online for primary mirrors which simplify the task. Simply print them out.

I'm sure a similar thing would exist for secondary mirrors too. I'll have a look later.


EDIT: That's my ignorance, there appears to be no such beast because it's not just the physical centre of a secondary mirror.
Apparently there's a book which may explain the mathematical process of spotting a secondary, I saw both positive and negative mention of it in various Cloudy Night threads relating to secondary mirror centres.
The Dobsonian Telescope by Kreige and Berry

[mldee]

After a few days of laziness, I finally got around to tweaking the OTA to my satisfaction and installed the JB adaptor and 1" RC spacer. I then screwed the 90-48mm adaptor to it and then the 48-42 to OCAL and checked the results. Only a smidgen of difference to the OTA-only result, and as promised, I didn't re-adjust the OTA further.

I then added the tilt adaptor and set all its adjustment screws to zero tilt. There was a very slight shift in OCAL result, and I then spent about ten minutes fine tuning the tilt adjuster screws to come up with a reasonable looking result. As I still need to install the focuser, I didn't bother aiming for total perfection.

Thunder and lightning around, so called it a day. Pics below.

[Leo.G]

That's looking good Mike!

[mldee]

Thanks Leo, progress is slow but sure, mainly due to daytime heat in the obs and laziness due to evening clouds discouraging future star testing.

Looks like storm clouds again tonight, but decided to post the status quo anyway.

Put the whole imaging train together a few days ago, only thing missing is the astro camera, but that's where the OCAL goes. The setup is still horizontal on the bench. Addition of the ZWO filter wheel seemed to introduce some mis-collimation, as shown in the second pic below, but a few minutes fiddling with the tilt adaptor got rid of most of that and I was satisfied that the system was close enough to warrant a star test, and that's where it sits. I suspect the larger white areas around the OCAL sensor in the pics is reflection from the filters and I didn't bother with it.

Mounting the setup on the AM5 pier also will give me the opportunity to evaluate any collimation shift with varying OTA elevation, which is the major objective of the JB adaptor.

News at 11.

[Leo.G]

Skies haven't been playing nice in my area either.

[mldee]

Between guests using the computer/bedroom during the only period of clear night skies and subsequent arrival of the wet/holiday season, the ready-to-be-star-tested RC8 with JB adaptor still sits forlornly on the obs bench.

Weather forecasts suggest it looks like it will be a "next year" project:mad2:

[Leo.G]

I'll be looking forward to hearing how it goes. I must contact Joshua soon, I want the adapter but I've just been short on cash this time of year, my son takes priority.