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
Now I get to do low-elevation northern imaging with Bortle 2 exposure durations
Pics show RC8 Pimp/collimation setup and OCAL results.
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?
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.
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.
Quote:
Originally Posted by 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? That's a 3d printed version of the rear adaptor to decouple the imaging train from the mirror assembly, there's a second pic that shows one sitting on the rear of the OTA, minus the imaging train that would screw on to it. I think it could still be simplified further with a little thought, perhaps just a round disc instead of the arms, or even a small threaded upper disc and a lower attachment disc, welded together, There's not really much of any precision apart from the three bolt holes and the thread. It should be doable on a lathe.
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). Yes, I have a picture of that one from Cloudy Nights, but it's very involved and as you said, probably quite expensive to replicate.
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? Probably not, but hey, it's just a hobby, so I'll try it anyway. Great bragging rights, too
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. Only thing it may hurt is the wallet....
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. Earlier model, my scope's about 10 years old. My problem was mainly the focuser bracket attachment and related screw pressure, because the bottom plate is slightly curved and I'm a lousy craftsman.
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. One of the benefits of rural life:)
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.
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.
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.
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
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,
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
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....
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:
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.
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.
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.
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.
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?
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
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
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!
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........
