He he...You know, I wouldn't put it past you actually ...I predict at least a 16" in the future
Mike
That would be nice, but then I'd need something like a Paramount to put it on first.
Now let's see, I can build 5 of these 12.5" Serrurier truss OTA's incl. Royce mirror, for the price of one Paramount...
Looking like a telescope should. A Newtonian. Balance is always the issue as the aperture increases so does the mounts weight requirements. Good idea with the lighter mirror. Great work by the way.
Attached are some smaller versions:
1st image shows the old and new OTA side by side.
2nd image is the OTA with mirror in the obs.
3-4th image is Antares Optics 1/30 PV 4" secondary (it's huge!) sitting pretty and rock solid on 0.012" gauge guitar strings. The Moonlite focuser with stepper motor can also be seen.
5-6th image is the entire setup just barely fitting under the roof, and a closeup of the conical mirror.
I still need to fine tune collimation and spacing to the coma corrector, but it is shaping up nicely. I'm very impressed with the performance of the Royce mirror (see the other thread for details)
Thank you Marc I took a lot more care with the finishing of all the parts this time around, since I had plenty of time before the mirror arrived!
It all seems to be working like a charm, so now I just need some clear skies...
A few people out there spend endless hours tinkering building scopes, some end up lovely specimens of craftsmanship (and some not) but never really produce any decent images, for them it is the tinkering that is the attraction and fair enough, great....but with you, you do both, beautiful handcrafted scopes and beautiful deep sky images from them...take a bow
Amazing consistency in manufacture there too for hand made scopes
Thanks Mike, that is very kind of you to say
It's funny (and a bit crazy) to think that the only power tools used were a drill, and a jigsaw (for cutting the plywood rings). All alu parts were cut and finished with an old fashioned hacksaw and sandpaper.
It was pretty easy to copy the existing design from the 10" and add some improvements here and there.
Maybe I should consider building to order now.
No shroud yet but I have thought about getting one. It has never really been necessary though I cannot see any stray light on the chip unless the Moon happens to be shining directly onto the focuser hole. On those occasions I have just turned the scope to another target and all has been good.
I can't wait for some proper clear skies now. Everything is tuned to perfection and there is no coma in sight either. And the Ovision worm upgrade seems to have fixed the guiding issues I had in some of my later images. So, bring on the clear nights!
Very nice work Rolf. Looks great and like Mike said, you have a winning combination going.
Can you explain how you centered the secondary wrt to the OTA.
That seems to be my biggest problem, and have you tested collimation at different orientations using a laser and slewing to different angles to see if collimation holds?
I would've thought the weight of the secondary would stretch the strings slightly at different angles.
Are you using threaded adaptors for the focuser?
Very nice work Rolf. Looks great and like Mike said, you have a winning combination going.
Can you explain how you centered the secondary wrt to the OTA.
That seems to be my biggest problem, and have you tested collimation at different orientations using a laser and slewing to different angles to see if collimation holds?
I would've thought the weight of the secondary would stretch the strings slightly at different angles.
Are you using threaded adaptors for the focuser?
Cheers
Alistair
Hi Alistair, I just centered it approximately with a ruler. Once the strings are attached it's very easy to make adjustments in all three dimensions so that was no problem.
There are varied opinions on this topic but my philosophy is that it doesn't have to be perfectly centered, as long as collimation is perfect all is good. Collimation only requires the optical axis of the primary to coincide with that of the camera/eyepiece. Once that is achieved (I use star testing) then it really doesn't matter which direction the mirror points in and wether the secondary is centered and if the focuser is squared and all that kind of stuff. As long as there are no obstructions in the light path of course, otherwise you'll get vignetting to a degree.
I've tested different orientations and collimation holds fine, there was no observable shift. This is also because the secondary is hold solidly in place due to the geometry of the strings, not their tension.
I'm just using the compression-ring of the Moonlite focuser, it holds very firmly on to the Baader MPCC which sits completely square. I was happy that there was no issue with that
Thanks, and can you explain how you star test? I'm still to figure that out.
I did notice that the centering of the secondary makes a difference even if collimated with a cats eye, and is noticeable when you use a larger sized chip as the illuminated field of the F4 would be larger than the 8300 diagonal.
So 75% would be round but you'd notice comet shaped stars at the very edges. prominent in a dslr.
Hi Alistair, the secondary must be correctly positioned under the focuser yes, but centering within the OTA is less important. As long as you still have a clear field of view across the entire chip.
For an astrograph you'd also preferably have a secondary large enough to 100% illuminate the entire FOV.
I like the star testing method as it is the only one to directly measure star shape/sharpness which is all we really care about. This also means I don't have any tools for collimation as one doesn't need any with this method.
Thierry Legault has an excellent tutorial here: http://legault.perso.sfr.fr/collim.html
Another one is here: http://popastro.com/documents/PA_jan...tartesting.pdf
Thanks for the links Rolf. Have to try it out when it clears up.
what FL EP do you use and how do you know if you have to adjust the primary or secondary. sorry, don't mean to detract.
wow, an F4 and no tools for collimation? that's impressive.
Thanks for the links Rolf. Have to try it out when it clears up.
what FL EP do you use and how do you know if you have to adjust the primary or secondary. sorry, don't mean to detract.
wow, an F4 and no tools for collimation? that's impressive.
You'll have fun, it's actually easier than it sounds. Once you've aligned the secondary under the focuser so that it illuminates the entire field then you only need to adjust the primary to achieve collimation.
Most of the time I just use the camera instead of an eyepiece, which makes it even easier. This has the advantage that you can usually easily see where the point of best collimation is in the image. This is the point where the out-of-focus star doughnuts are perfectly round and concentric (it may initially lie completely outside the image though, if your scope is severely out of collimation).
It helps greatly to experiment and note down which way to turn the collimation screws in order to move the doughnuts around on the image. And you'll only need to adjust two of the three screws.
...I predict at least a 16" in the future 
I cannot see any stray light on the chip unless the Moon happens to be shining directly onto the focuser hole. On those occasions I have just turned the scope to another target and all has been good.
