Last night was last light of the old 16" today came out a better / more stable /no movement / perfect balance totally different scope with the addition of 3 extra struts
Collimation now holds spot on when pushing and pulling it.
Many thanks to Trevor for the time and work he thoughtfully put into it.
All that left is to make a whole new rocker box ,get some turned knobs made up to replace the wingnuts on the struts, and paint the nuts on the inside of the lower and upper OTA,S
The primary and secondry mirrors were not inside the scope during the modifications.
And waiting on the encoders to get the argo-navis system setup
I have been doubtful about OTAs with 2 or 3 vertical struts , they simply can not be as rigid as OTAs with 6 struts forming 3 rigid triangles , unless they are huge and the connections at the top and bottom are super rigid (no movement permitted).
3 or 2 struts is cheaper than 6 , but to sacrifice OTA (surrier) rigidity by scimping on a few dollars per OTA by having a substandard strut and connector design is just stupid.
I knew this system wasn't going to cut it for astronomical purposes as
is. Especially when you have minute movements required at this aperture.
There is no stretch and compression in this arrangement, and is why it
is reffered to strut instead of truss. Truss where you have an equal
amount of members being compressed and stretched in any direction
you want to twist the Sec'cage, say 6-8 (3-4 pairs) members in a truss
dob arrangement the poles are angled/locked hence being stretched or
compressed and NOT bent laterially, you would of been better to attach
guy lines to each strut, as you will have only minimised movement/flex by
adding three more struts. However I was confident that the box nature
of the struts would of sufficed, but I do see they dont seat very deep.
But also the struts you have added, seat deep and are box you probably
could get away with leaving out the GSO struts.
Then there is the steal tube mirror box, which I guess unless it has baffles
down it's length will probably flex too. It's only strength really coming from
the mirror cell at it's base. Does it have baffles?
I'm not trying to knock your scope, but it's overall design needs to answer
a few Q's. But personally I really think take the optics out and hardware
and rebuild it. 16" is ok aperture and should be a pleasure to use.
regards,CS
Last edited by CoombellKid; 05-08-2008 at 08:21 PM.
Reason: adding extra
F 4.5 is unforgiving in collimation as just about everyone should know, dont get me wrong this is a fantastic scope but i love to tinker with things and during the course of the night i need to recollimate in the dark , and i feel i need to do this as it has to perform to my satisfaction.
The optics are superb and i cannot fault that.
Now i feel i got a great long lasting scope.............How many people buy a new car then put extra,s on it? ..........cheers Kev.
Have you considered ditching the original and additional struts and installing a proper triangle based 6 strut system to make the who optic assembly more robust and rigid ? wouldn't be hard to do or very expensive.
Have you considered ditching the original and additional struts and installing a proper triangle based 6 strut system to make the who optic assembly more robust and rigid ? wouldn't be hard to do or very expensive.
Not really Ian, the extra`s are just fine
There is no movement now between the bottom and top OTA`S
It would of been a better design if the original struts protruded past the cast rings .............I know i,m on the right track because it can clearly split Antares ,then swing the scope around back and forth hard then go back to Antares and slpit it again.
Before i would try that and the collimation would be out ....and yes the original primary springs have been replaced with stronger compression springs......cheers Kev.
There is no movement now between the bottom and top OTA`S
It would of been a better design if the original struts protruded past the cast rings .............I know i,m on the right track because it can clearly split Antares ,then swing the scope around back and forth hard then go back to Antares and slpit it again.
Before i would try that and the collimation would be out ....and yes the original primary springs have been replaced with stronger compression springs......cheers Kev.
Hi kev,
I can vouch for the quality of Kevs optics. Last Friday night had the pleasure of seeing the companion to Antares through a very nice 7mm Ortho in Kevs scope, a well resolves nice little green dot.
With kevs mods this scope now holds colimation quite well, using a double pass laser. Previously the laser return beam was dissplaced very easily by simply moving the scope around.
It needs further field testing to see how well things go over time but this is a definite improvement over the production version.
Have you considered ditching the original and additional struts and installing a proper triangle based 6 strut system to make the who optic assembly more robust and rigid ? wouldn't be hard to do or very expensive.
How do you invisage doing this? I am seriously considering this scope. I want to combine all the 'best features' of these chinese dobs (such as they are, can't afford a premium dob) I figured, purchase the scope with a feature I like that is the most easily modded with the best features of the others. In this case I am leaning towards this Bintel (GSO in my part of the world(Ireland)) for its Lazy Susan/Teflon AZ movements, Innovative ALT bearings, All Black (oh are those dirty words around here? ) paint and shape of base(will come to that later)
I'd take the 6 pole truss system idea from the lightbridge.
And from Orion I'd take the Intelliscope COL. I have this COL on my current XT12i and think its the business. I want to leave this system on my current scope to help re-sale. As many probably know, Orion do not sell the COL separately........except for a kit for their Skyview Pro GEM mounts. This has been modded to work wth a DOB. I pulled together all the info I could and proposed the idea on the Orion Skyquest Yahoo group and one of my 'proteges' beat me to the punch and purchased this kit and fitted it before me. Works like a charm!! Best thing. Orion had them on sale for USD$80 !! They are all gone now I am afraid. Probably still available at third party retailers though at full price $250-300. Even though I won't be purchasing this scope or doing the mods for a few months I ordered the kit at the sale price just in case. Lucky I did as they are dis-continued now a week later!! (Got a Cloudy Nights buddy to order it on my behalf and forward it to me here in ireland.)
Also pretty chuffed that I independently thought of the same ALT attachment scheme as the Argo Navis guys. Damn, should have patented it a few weeks ago!
Anyway, I'll have one of the best DSC systems on my new scope for the princely sum of USD$80. Not bad going
As for the size of the base. I heard that the OTA diametre is approximately 18 inches. Opened up various images of this scope and worked out the pixel per inch ratio. I was then able to have a rough idea of the dimensions of all the major parts. To fit in my small coupe, I'll need to remove the top of the base from the base boards and lie them on their side. I figure, instead of the wood hex screws holding the top section to the baseboards, I'll use captive t-nuts in the base board and then knobbed bolts that screw 'down' into these captive nuts. ie. Small cutouts in the side and front pieces for the knobbed bolts to screw down into the base/ground board. Thats were the solid base of this scope became an advantage. If I tried the same with a LB base with is cutouts/arches in its pieces, the cutouts for my knobs might fatally weaken the structure.
So really the only mod that I haven't worked out yet is the conversion of this scope to a 6 pole truss like the lightbridge. Firstly, I know that I would need to rotate the UTA lower tube ring to realign the strut brackets between the brackets on the LOTA for the triangular configuration. (Otherwise focusser would be out of position)
My problem is that without using the existing strut brackets would it not be a case of securing each pole individually to each hole on the LOTA and UTA tube rings. Impossible in other words. Yet if one removes the struts from the brackets, how would one attach the poles to the brackets??
Anyone got any ideas??
BTW, Hello from Ireland!! Long time Lurker/First Time Poster
Like I said I used paint.net to work out based on the mirror tub diametre of 18inches that the pixel/inch ratio was 12.22 pixels per inch in the photo I used. Thus was able to roughly work out some of the base dimensions.
The base of my XT12i does not fit standing up in my sloped roof coupe. It fits laying down on its back. This will not work for the bintel 402 base because of its larger groundboard diameter.
I figured that the bintel base height is bound to be even taller than the XT12i. It a longer FL and I just assumed the alt bearings would be proportionally further up the 'tube' necessitating an even taller base than my XT12i.
Well I just actually measured my XT12i base height from the rubber feet up to the top of the alt forks. Its 30 inches. I know my XT12i was just a bit too tall to fit under my car roofline standing up. However my paint.net measurements indicate the Bintel 402 base height is actually lower! @ 26-27inches.
It might actually fit in the car standing up without having to mod it at all. Typical that I can't verify this for sure right now as my brother borrowed the car today.
So that leaves me with only the one question. How would one convert this scope to a 6 pole Lightbridge style truss??
My advice is.... scrap buying one and go direct to GSO and buy a 16" mirror
set, I got mine for AUS$872.00. With the money you save on the total cost
buy the materials and build your own.
Some stainless steel cable or Bow string, Some eye hooks attached to the tube rings and a ratchet clamp/tightening thingy. ie You assemble the scope as normal. Run the cable/bow string up and down through the eyehooks till you get back to the starting hook. Feed the two ends of the cable into one of those climbers ratchet thingies that pulls the cable/string taut and puts it under tension. I don't know the name of the ratchet thingy but I have a picture of it in my head.
While I think I can manage some simple mods to scopes I don't think I have the carpentry skills nor technical knowhow to build my own I am afraid. BTW, your scope is absolutely stunning Rob.
Thanks mate, for your comments on my scope... just waiting for clear
weather and a moonless night to give it a whirl. I thought the same as you
regarding carpentry skills. Hadn't done any since leaving woodwork classes
in high school nearly 30 years ago. I built my first one at the end of last
year a lil 8" for my son. There is an excellent book you can buy called
"The Dodsonian Telescope: A Practial Manual for Building Large Aperture
Telescopes" by David Kriege and Richard Berry. It's an excellent book
for the layman and easy to understand and it goes right through everything
including the the mathmatics.
I think your idea is a good alternative. But the way your attaching the
tension lines will create stress on the SC as soon as you tighten them up.
I would attach directly to the strut as this is what you want to make rigid.
The problem here is if you go the full length of the strut you are more than
like going to have the mid section of the tension line traveling through the
light path. To get around this you could shorten them and attach them
midway up the strut and still retain a fair amount of rigidity.
I would use swaged FSWR with a hook on one end and a turnbuckle on the
other. A turnbuckle is two eyebolts/hooks joined by a turnbuckle. You
can use the turnbuckle to tension up the guys. Similar to the picture below.
The only other thing to consider with your alternative as well as what I
proposed above, is weight. Are the GSO's like the LB's being a little top
heavy especially when you have a reasonably heavy EP in the focuser?
The only other thing to consider with your alternative as well as what I
proposed above, is weight. Are the GSO's like the LB's being a little top
heavy especially when you have a reasonably heavy EP in the focuser?
regards,CS
Probably, yes but the GSO has the advantage over the LB of the needle roller friction brake in the altitude hub and also the adjustable COG. Why, do you think the wire trussses would have as much affect on weight as Kev's 3 extra box struts?
As for the wire crossing the Lightpath. I think it might be borderline regardless. ie. It may cross the arc of the tube rings alright but there is probably about 1 inch to spare anyway between the outside edge of the mirror and the inside edge of the OTA's.
Certainly if one used an eyebolt screwed into the top of each strut (ie. say between the 2 screwheads one can see on the outside surface of the struts) and then eyebolts into the side of the LOTA tube ring between each strut. Well then the wire would be well out of the lightpath I would imagine. Picture it using Kevs overhead picture above.
The question then, is would the tension applied be trying to splay the struts outwards. Does this matter when they are bound to the UTA with the brackets.
My advice is.... scrap buying one and go direct to GSO and buy a 16" mirror
set, I got mine for AUS$872.00. With the money you save on the total cost
buy the materials and build your own.
regards,CS
That would be my advice too .
You are better off spending a bit extra money on quality optics , a quality mirror cell and a quality crayford.
Plenty of places who do top quality 16" mirror and secondaries too.
The rest is not as important - but places like AstroSystems in the USA will be more than happy provide bits and pieces you can't make yourself (not all of us are handy with welders, and metal working tools, or with carpentry and power tools).
Probably, yes but the GSO has the advantage over the LB of the needle roller friction brake in the altitude hub and also the adjustable COG. Why, do you think the wire trussses would have as much affect on weight as Kev's 3 extra box struts?
Weight might become an issue as you are adding weight above above
the scope ALT pivot point. Where Kev's extend down pass the pivot point.
When you add up the weight of the gear to be used ie FSWR, swages,
eyebolts and turnbuckles etc...etc...
Quote:
Originally Posted by Calibos
As for the wire crossing the Lightpath. I think it might be borderline regardless. ie. It may cross the arc of the tube rings alright but there is probably about 1 inch to spare anyway between the outside edge of the mirror and the inside edge of the OTA's.
Certainly if one used an eyebolt screwed into the top of each strut (ie. say between the 2 screwheads one can see on the outside surface of the struts) and then eyebolts into the side of the LOTA tube ring between each strut. Well then the wire would be well out of the lightpath I would imagine. Picture it using Kevs overhead picture above.
The question then, is would the tension applied be trying to splay the struts outwards. Does this matter when they are bound to the UTA with the brackets.
Not knowing and seeing one in the flesh, I think you just have to play
around with all that. Remember the guy lines dont need to be too tense,
well... to the point where they are doing the job and not too tight that
they start warping things.
You are better off spending a bit extra money on quality optics , a quality mirror cell and a quality crayford.
Plenty of places who do top quality 16" mirror and secondaries too.
The rest is not as important - but places like AstroSystems in the USA will be more than happy provide bits and pieces you can't make yourself (not all of us are handy with welders, and metal working tools, or with carpentry and power tools).
Yup you could, but the GSO 16" are a pretty good deal, and I haven't yet
heard any complaints with them from any body. You only going to notice
anything possibly when compared side by side under excellent seeing. So
for me spending AUS$872.00 as appose to spending AUS$3500.00 on
something of optical brilliants doesn't fit my buget. However it will be
heading for a refigure in the future... right after I have my next mirror
made
) paint and shape of base(will come to that later)
beat me to the punch and purchased this kit and fitted it before me. Works like a charm!! Best thing. Orion had them on sale for USD$80 !! They are all gone now I am afraid. Probably still available at third party retailers though at full price $250-300. Even though I won't be purchasing this scope or doing the mods for a few months I ordered the kit at the sale price just in case. Lucky I did as they are dis-continued now a week later!! (Got a Cloudy Nights buddy to order it on my behalf and forward it to me here in ireland.)
. ie You assemble the scope as normal. Run the cable/bow string up and down through the eyehooks till you get back to the starting hook. Feed the two ends of the cable into one of those climbers ratchet thingies that pulls the cable/string taut and puts it under tension. I don't know the name of the ratchet thingy but I have a picture of it in my head.
