coldlegs
29-05-2013, 08:32 PM
On May the first last year I finally bit the bullet and ordered a 10"/F5
conical primary mirror from R.F.Royce. My 25 year old Meade 10"/F10 couldn't quite cut the mustard and my old 6"/F5 newt has been so abused/drilled and hacksawed it was time to semi retire it. Maestro Royce indicated a July/Augustdelivery date but little did he know he was about to suffer a serious medical problem that would shift the delivery date out nine months to February this year.
Meanwhile I had some decisions to make. Tube or truss? Truss won hands down as not only could I make it in my shed but the lack of tube air currents was a major plus as well as being able to easily get to everything. As it was to be mounted on an NEQ6Pro a Serrurier type truss seemed logical given it's mechanical superiority to the other truss types.
The next design considerations were all about "back focus". My old 6" newt had to have it's rear end chopped off to get enough back focus to make some set-ups work so it was going to need plenty. Also had this serious itch to use an "On Axis Guider" but they needed 66mm extra back focus and there was the coma corrector consideration.The Baader MPCC needs a 55mm spacing but only loses about 45mm back focus so to run both at least 111mm was required. Started running designs on "Newt for the web"
and came to the realisation that the focuser really needed to be a flat plate
to work well. Fortunately in my junk box were two precision caged bearing guides that gave me the solution.
Not sure if starting a scope build with the focuser and focuser cage is the right way to do it but I did. I ordered some 245×315×4.5mm Carbon Fibre plate from eBay, trimmed it down and attached it two guides supported by struts. Then bought a second hand 30" long 1/4" ball drive rod with anti backlash nuts. Chopped that in half and used it to drive either corner of the focuser plate which added more structural support. Added some steppers driven in parallel by a "USBnStep" interface and geared them down
give some oomph when raising and lowering an expected 1-2kg of camera/onag etc. The gearing worked out to about 10,000 steps per cm so it aint fast! Bought a starlight Instruments 3" to 2" compression ring adapter and cut off all the excess aluminium then
drilled a large hole in the plate to fit. Tapped a dozen or so holes in the adapter and screwed it onto the plate. With the camera/mpcc/onag plugged in I ended up having 15mm spare back focus and no vignetting. Just made it. Added a cut off steel ruler to measure focus points.
Then came the truss. Hate to admit it but this scope could be called the “Bunnings thin wall riveted special” as all the material is either 19mm thin wall square tube or 25mm thin wall round tube with an utterly amazing amount of rivets holding it together. Plus a some bits of wood on the end. Over the nine months wait for the mirror the truss went through several iterations of various sections due to design errors or weight considerations or just plain “nah..don't like that”.
The secondary end is an Antares optics 2.14" 1/30 wave diagonal mounted on a "Destiny" 4 vane curved spider with dew heater. Finder started out as a Meade 8x50 with a modified toucam stuck on the end but changed to a Celestron 9x50 modified to accept an Orion starshoot autoguider camera so it could easily be used for wide-field guiding. (mod can be found here http://astroturtle.com/wp/tag/9x50/). The starshoot used to be on the ONAG but that changed to a Lodestar for increased sensitivity. Started to get interested in wide-field stuff so hacked apart a celestron camera mount and riveted in onto the front of the scope to grip my QHY10C OSC with a lens attached. Crudely first tried the idea with releasable tie wraps but decided a proper camera mount was the way to go.
The rear end is a five ply plywood structure, partly to save weight to get the Serrurier balance correct and partly to get the correct distance for the mirror. Two Sunon Maglev fans (30 and 60mm) blow air on the main mirror to speed up mirror cooling (large fan) as well as breaking up air layers on the front of the mirror (small fan). Had a matt black cloth shroud around the rear but an hour of dew turned it into a wet rag so a water proof one is on the cards sometime. For the moment I have turned the observatory into a black bucket which is working reasonably well.
Got it all up and running early May and spent the last month figuring focuser settings for different set-ups with one last one to go. Going to try to capture at F10 and guide through the onag at F5. Got an adapter that adapts the front of a 2X Big Barlow to the onag but not sure if the Lodestar will come to focus. That's pretty much it but give me a day or two and I'll think of a modification! Final weight was about 12Kg which is about 5Kg less than my Meade sct with guide scope so the mount is happier.
Tried to get some reasonably serious test shots but the clouds and the moon have been against me so did an hour or so HA which don't look too bad so far. Early days.
Cheers
Stephen
conical primary mirror from R.F.Royce. My 25 year old Meade 10"/F10 couldn't quite cut the mustard and my old 6"/F5 newt has been so abused/drilled and hacksawed it was time to semi retire it. Maestro Royce indicated a July/Augustdelivery date but little did he know he was about to suffer a serious medical problem that would shift the delivery date out nine months to February this year.
Meanwhile I had some decisions to make. Tube or truss? Truss won hands down as not only could I make it in my shed but the lack of tube air currents was a major plus as well as being able to easily get to everything. As it was to be mounted on an NEQ6Pro a Serrurier type truss seemed logical given it's mechanical superiority to the other truss types.
The next design considerations were all about "back focus". My old 6" newt had to have it's rear end chopped off to get enough back focus to make some set-ups work so it was going to need plenty. Also had this serious itch to use an "On Axis Guider" but they needed 66mm extra back focus and there was the coma corrector consideration.The Baader MPCC needs a 55mm spacing but only loses about 45mm back focus so to run both at least 111mm was required. Started running designs on "Newt for the web"
and came to the realisation that the focuser really needed to be a flat plate
to work well. Fortunately in my junk box were two precision caged bearing guides that gave me the solution.
Not sure if starting a scope build with the focuser and focuser cage is the right way to do it but I did. I ordered some 245×315×4.5mm Carbon Fibre plate from eBay, trimmed it down and attached it two guides supported by struts. Then bought a second hand 30" long 1/4" ball drive rod with anti backlash nuts. Chopped that in half and used it to drive either corner of the focuser plate which added more structural support. Added some steppers driven in parallel by a "USBnStep" interface and geared them down
give some oomph when raising and lowering an expected 1-2kg of camera/onag etc. The gearing worked out to about 10,000 steps per cm so it aint fast! Bought a starlight Instruments 3" to 2" compression ring adapter and cut off all the excess aluminium then
drilled a large hole in the plate to fit. Tapped a dozen or so holes in the adapter and screwed it onto the plate. With the camera/mpcc/onag plugged in I ended up having 15mm spare back focus and no vignetting. Just made it. Added a cut off steel ruler to measure focus points.
Then came the truss. Hate to admit it but this scope could be called the “Bunnings thin wall riveted special” as all the material is either 19mm thin wall square tube or 25mm thin wall round tube with an utterly amazing amount of rivets holding it together. Plus a some bits of wood on the end. Over the nine months wait for the mirror the truss went through several iterations of various sections due to design errors or weight considerations or just plain “nah..don't like that”.
The secondary end is an Antares optics 2.14" 1/30 wave diagonal mounted on a "Destiny" 4 vane curved spider with dew heater. Finder started out as a Meade 8x50 with a modified toucam stuck on the end but changed to a Celestron 9x50 modified to accept an Orion starshoot autoguider camera so it could easily be used for wide-field guiding. (mod can be found here http://astroturtle.com/wp/tag/9x50/). The starshoot used to be on the ONAG but that changed to a Lodestar for increased sensitivity. Started to get interested in wide-field stuff so hacked apart a celestron camera mount and riveted in onto the front of the scope to grip my QHY10C OSC with a lens attached. Crudely first tried the idea with releasable tie wraps but decided a proper camera mount was the way to go.
The rear end is a five ply plywood structure, partly to save weight to get the Serrurier balance correct and partly to get the correct distance for the mirror. Two Sunon Maglev fans (30 and 60mm) blow air on the main mirror to speed up mirror cooling (large fan) as well as breaking up air layers on the front of the mirror (small fan). Had a matt black cloth shroud around the rear but an hour of dew turned it into a wet rag so a water proof one is on the cards sometime. For the moment I have turned the observatory into a black bucket which is working reasonably well.
Got it all up and running early May and spent the last month figuring focuser settings for different set-ups with one last one to go. Going to try to capture at F10 and guide through the onag at F5. Got an adapter that adapts the front of a 2X Big Barlow to the onag but not sure if the Lodestar will come to focus. That's pretty much it but give me a day or two and I'll think of a modification! Final weight was about 12Kg which is about 5Kg less than my Meade sct with guide scope so the mount is happier.
Tried to get some reasonably serious test shots but the clouds and the moon have been against me so did an hour or so HA which don't look too bad so far. Early days.
Cheers
Stephen