The Mary Rose has returned from Santa’s Dobsonian Makeover (SDM) workshop with some fantastic upgrades. In fact, it looks and feels like a new scope!
Santa (Peter Read) has fitted the Mary Rose with new Delrin split blocks, an 80mm Stellarvue finderscope (scope is fully balanced), a new Moonlite filter slide with built in dew strap, a Feathertouch focuser, higher quality finer collimation screws for the primary mirror cell, and a new quieter lower amp fan at the base of the primary mirror with spider web/alien themed grill. He has also replaced the Kydex in the secondary cage to stained Plywood. He has also tidied up some wear and tear, and improved the wiring. What’s more, the Mary Rose now has gold lettering to mark her out on the observing field!
A problem that truss dobsonians the world over that use a wooden split block system to house the truss poles is that the blocks can be very sensitive to environmental changes. In particular, in warmer weather, wooden blocks can expand, meaning that the insertion hole for the poles becomes tighter. In extended warmer weather, it can become a very tight fit to squeeze the poles in. Another problem some have is that the blocks actually split (this has not happened with SDM’s blocks because of their hardy construction).
On a recent week long stay in Coonabarabran, I experienced a major problem with block expansion, and spent a number of hours battling to ease one of the truss poles in so that I could observe.
Peter’s fix, which is now to become standard on all SDM scopes, is to use split blocks made of Delrin. Delrin is an industrial plastic which is entirely unchanged by heat and cold (Peter even tried using a blow torch on it, and it was completely unaffected).
The Delrin blocks are a dream to use in practice, the poles sliding in with an almost lubricated feel. Although the black of the delrin material markedly differs from the appearance and finish of the marine ply of the Mary Rose, the new split blocks have an industrial beauty that does not detract at all from the overall appearance of the scope. More importantly, I now have spilt blocks that will last a lifetime without warm weather bloat!
Peter kindly re-machined the poles so they look shiney and new, and more importantly, so that they fit into the delrin blocks perfectly.
As I become a more experienced observer, I want to go more and more off the beaten track. While the Argo Navis computer has a wonderful list of user-objects and can be uploaded with user lists of yet further objects, I rather enjoy opening a page of Uranometria, and searching out objects like unidentified double stars, or little known galaxies. For this sort of work, I am heavily reliant upon a finderscope for star hopping and field orientation. I decided it was time to get a bigger and better finder than the 50mm GSO finder I have previously been using.
I have also been wanting to have greater opportunity to view some of the large scale objects which simply cannot be seen through the narrow gaze of a large dobsonian telescope. Enter the 80mm finder, which with the SV supplied 23mm crosshair EP offers a 4 degree FOV at 13x. The crosshair EP has a detachable red light illuminator.
The finder comes with a helical focuser and can fit any 1.25 inch eyepieces. At f/3.5 the SV will perform best at the edges with a better corrected wide field ocular, such as a Nagler. I am planning to purchase a 13T6 at some stage, which will give me a 3.5 degree FOV at 23x.
The SV80 finder also has a straight through function, which takes 2 inch eyepieces. I am yet to work out how this operates, the but the thought of being able to look at rich Carina starfields through a 31 Nagler in the SV80 has me salivating!
Peter has balanced the scope beautifully to allow for the weight of the SV finder. It required about 4kg of extra weight in the mirror box!
The finder has a lovely black matte finish which I think complements the black of the delrin blocks rather nicely.
When I first took delivery of the Mary Rose in March 2007, it had a Moonlite filter slide. I have found this device to be immensely useful (the alternative of changing filters manually on individual eyepieces through the evening can be a real chore). The slide has space for three 2 inch filters to be fitted at once, as well as having an open position (filterless).
The only problem I have encountered with the filter slide in the past is the tendency for it to dew up on particularly wet nights. Placed near the top of the secondary cage, the filters are unfortunately rather more exposed to the elements.
The filter slide now has heating for those wet nights. No more dewy filters. Ah, that is better!
I originally had a Moonlite focuser (tri focuser style) to marry the Moonlite filter slide. The Moonlite focuser has slowly become less buttery smooth than it was at the beginning.
The Moonlite focuser has bearings running directly on the anodized draw tube and over time the draw tube inevitably ends up with tram tracks dug into the tube. As a consequence, the focuser had developed a tendency to clunk slightly out of focus for some observers if the focus point coincided with a point where the scoring on the draw tube was at its worst. I could probably have replaced the draw tube, but I thought I might take the opportunity to try the Feathertouch focuser instead!
The Feathertouch draw tube rides on stainless steel rails and so I have my fingers crossed that it will be more long-lasting solution. Its feel is truly beautiful and smooth. It doesn’t get any better than this!
Peter has developed a way to couple the Moonlite filter slide with the Feathertouch focuser (there is apparently no solution otherwise commercially available to create this combination). So I can have my Christmas cake, and eat it!
Since Kriege first built his prototype truss dobsonian at the start of the 1980s, a black plastic material called Kydex has generally been used around the world to line the secondary cage. Obviously this is a light weight and very flexible material, and being black, it is the right colour for the internal lining of a telescope. However, most truss dob users find over time that the Kydex is prone to warping, particularly as it can be exposed to high temperatures at star parties in warmer climes.
The Kydex on the Mary Rose was in reasonable condition after two and a half years, but Peter took it upon himself to overhaul it to a new plywood construction. The end result is superb – it looks almost identical to the Kydex, and will not warp. I am hoping that it will be far more durable.
Bearing in mind all of the heaters etc drawing power on the Mary Rose, Peter has installed a lower amp cooling fan behind the primary mirror. It is whisper quiet to boot!
It also has a groovy golden web design grate with an alien face. Pretty neat, huh?
The collimation screws the Mary Rose had a large thread and did not allow well for precision collimation Peter has fitted collimation screws that allow for very fine collimation movements.
I understand that Peter Read has also developed a remote collimation system…..maybe I can afford this next time!
SDM has attended to some other fixes for me while in the workshop. It is hard to contain the irrepressible Peter Read from his perfectionist ways…No doubt I will never notice some of the improvements, but here are the ones I have noticed so far:
* changed the primary mirror sling from a black polyester strap to a more convenient stainless steal wire.
*I had broken the heater for the Telrad, so this has been replaced.
* changed the set up of the connection points to take power up to the secondary cage. We now have banana points at both top and bottom.
*colour-coded all of the heaters so that even a technically challenged person like me can work out what goes with what.
* tidied up the scope lid, which had a misadventure coming home from the Pony Club one night, as well as putting a seal around the lid to keep unwanted dust out of the primary mirror box.
* straightened the end of one of my truss poles, and placed identification stickers on each pole so each pole is positioned correctly in the correct delrin block.
*adjusted the azimuth encoder arm so it is easier to remove if necessary
*repaired the wheelbarrow handles (which had become a bit loose), including using stainless steel cord to attach the pin to the handle
*fixed a problem with the secondary mirror heater.
* resolved a problem with some unplanned movements in the triangular base plates under the primary mirror.
* replaced the SDM logo on the secondary cage
*fixed a couple of broken cable attachment points for the Argo Navis
*regreased and improved the operation of the mirror locks (which enable the scope to be wheeled in and out of the garage fully set up).
SDM is currently converting SDM#8 to a folded mirror design. If Peter Read perfects this system, I am considering using a folded mirror system on the Mary Rose. It would mean being able to observe from a seated position like the old days when I had my hydraulic chair to observe with my 10” LX200.
Then of course there is Servo Cat….but one thing at a time.
I fear I have condemned the Central Coast of NSW to an entire month of snow and blizzards. Please accept my humble apologies. I WILL make it up to you on the observing field, if you want to come and have a look some time!
Congrats on the update its looks like a work of art !
I have an SV 80M finder you should have a threaded backing plate
with the 2" helical attached. When mine came all I had was the helical
focuser , the new backplate was missing and I had to email SV for
a replacement. So assuming you have the bits then you unscrew the
whole backplate (can be a bit tight) and screw on the new backplate
with the 2" focuser attached. No need to undo any screws just undo
the the whole back as it is.
Enjoy
Mark
Quote:
Originally Posted by Rodstar
As I become a more experienced observer, I want to go more and more off the beaten track. While the Argo Navis computer has a wonderful list of user-objects and can be uploaded with user lists of yet further objects, I rather enjoy opening a page of Uranometria, and searching out objects like unidentified double stars, or little known galaxies. For this sort of work, I am heavily reliant upon a finderscope for star hopping and field orientation. I decided it was time to get a bigger and better finder than the 50mm GSO finder I have previously been using.
I have also been wanting to have greater opportunity to view some of the large scale objects which simply cannot be seen through the narrow gaze of a large dobsonian telescope. Enter the 80mm finder, which with the SV supplied 23mm crosshair EP offers a 4 degree FOV at 13x. The crosshair EP has a detachable red light illuminator.
The finder comes with a helical focuser and can fit any 1.25 inch eyepieces. At f/3.5 the SV will perform best at the edges with a better corrected wide field ocular, such as a Nagler. I am planning to purchase a 13T6 at some stage, which will give me a 3.5 degree FOV at 23x.
The SV80 finder also has a straight through function, which takes 2 inch eyepieces. I am yet to work out how this operates, the but the thought of being able to look at rich Carina starfields through a 31 Nagler in the SV80 has me salivating!
Peter has balanced the scope beautifully to allow for the weight of the SV finder. It required about 4kg of extra weight in the mirror box!
The finder has a lovely black matte finish which I think complements the black of the delrin blocks rather nicely.
Thanks for the excellent pictures and running commentary. She looks gorgeous!
I can relate to what you describe.
Andrew's 25" came back from a makeover by Peter and I looked at it briefly last
month when Andrew pulled the covers off to show me. It also included the refinements
such as the new split blocks and Peter had given the woodwork a nice new stain.
All in all the scope looked like new and was fabulous to look at.
Looking forward to seeing Mary Rose up close and personal and hopefully
we can get together for some observing very soon.
I went and saw the hull of the original Mary Rose there in Portsmouth
many Moons ago when and she was continually being misted with water to
keep her preserved. Nevertheless I think if we left Peter alone with her for
a few weeks, she would come out looking like brand new and would once again be
the pride of Henry's fleet.
The "Mary Rose" is looking stunning as she always does!
I can imagine the upgrades that Peter has done will be that little bit closer to having perfection in a truss tube dob. As we both know and have spoken about numerous times his work is second to none as I'm sure all other SDM owners would also attest to.
Anna and I are both looking forward to when we pickup "Edwin" with his upgrades on our return from Tassie. I'm sure Peter will also have excelled himself once again.
Looking forward to when "The Mary Rose" and "Edwin" once again scour the skies together in March.
SDM is currently converting SDM#8 to a folded mirror design. If Peter Read perfects this system, I am considering using a folded mirror system on the Mary Rose.
Is that design an on-axis fold with a 33% circular flat at the top and elliptical tertiary or just a larger secondary angling the light at 135 degree rather than 90 degree to the optical axis?
Scope Turbo-Charge: The Mary Rose Reborn!
!!!
.
