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.
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.
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.
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!
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.
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.
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
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?
raymo
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.
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.
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.
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
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.
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).
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.
My suggestion would be to ask IIS/Google if others know how to add a donut to an RC secondary
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
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.
