I have had an old DK lying around the shed for years now - waiting the return of some motivation to do something with it.
The recent post linking to the Lazzarotti Optics scopes was the tipping point for me and, as it happens, at least one other demented DIYer ( who I haven't named here in case he wants to distance himself from this insanity). So we now seem to have a serious project under way.
I have the primary and secondary mirrors and together they create a f22 system. Great for lunar/planetary stuff. So now, we begin the design phase.
I want to make best use of the bits I already have, so I am adapting the Lazzarotti concept around that. Since I have a good baffle tube assembly plus a well-machined flange to connect it to a focuser, I decided to start the design process there. As part of that I am on the scrounge - does anyone have an original GSO focuser they have taken off a GSO RC6 or RC8. (or any other focuser with a 90 mm flange). Over the years I must have replaced 3 or 4 of these but never had the sense to keep the old ones.
I decided that the axis of the baffle tube/focuser would need to be capable of adjustment in addition to and independently of the primary mirror. Hence this design.
Just wondering if you had considered the requirement to collimate the primary in that design. I will sketch up my thoughts on the design aspects of the rear end and the options for dovetail mounting. I have a couple of ideas regarding the secondary mirror too.
Do you by chance have the details from the original scope regarding the primary to secondary spacing? If not, are the mirrors marked with their specifics such that we can calculate this? If not I suppose having the secondary able to move up and down the tubular rails and using the tried and true solar projection would be enough for us to get the focal point to a reasonable position.
Mounting:
For the past few months now I have been toying with the idea of building a large pillowblock mount with these optics in mind. I've got a design on paper that I believe will be more than enough, my only sore spot is the worm wheel and gear. I know I could buy a byers 11" 359 tooth wheel with a worm gear and a motor for around $500 usd. And I know that would be superb. I wonder however for a scope that will be used for lunar and planetary only, is that overkill? I feel yes however I can't seen to find any other options.
Another aspect of the mount design that I was wondering was, G.E.M. or forks. Gem would possibly be easier however for lunar and planetary work the ability to go through the meridian undisturbed by a flip would be advantageous. I could modify the G.E.M. Design I have to allow for tracking a reasonable distance past the meridian.
For now. I need a coffee and to get back to my assignments but the pondering shall continue.
Ah, the other lunatic has outed himself!! Brave man.
On the collimation question. Yes.
Have a look at the attached images. I have pirated a focuser off another scope for illustration purposes. In the pics you'll see it attached to the flange and the flange sitting in place on the back of the primary cell.
What the pics don't show - because I have yet to drill the necessary holes and get hold of the necessary springs and bolts, is the push/pull antagonistic adjustment screws that will allow the focuser/baffle tube to be moved independently of the primary. And in these images, you'll also see that the oprimary cell also has good independent collimation screws in place. So we will have collimation both ways.
The design using these bits does away with the need for the vertical bar that the Lazzarotti has at the back. This only requires a short section of OTA tube (which I have) so the primary cell can be mounted in it. And then, that will have to be attached firmly to a couple of saddles (profile to suit the tube diameter).
The same goes for the secondary. I have a good spider and mirror holder. It, too, only needs a short section of OTA tube to hold it (and I have enough) and the same saddles to attach it to the main structural member.
I haven't thought too much about mounts yet. My idea was to take one of my exising scopes off and use that mount to get this design nailed and run some test images. I have both a Titan and an EQ8 - either of which can hold 45-50 kgs so in the short term, it isn't an issue.
I think that at this FL, we'll need at least an RA drive so an equatorial would probably work better. IMHO.
Moving forward with this scope - I expect to be able to assemble the thing tomorrow. Well enough to bench-test the optics at least.
The basic scope will be based on a 12.5 inch primary and should come in at about f21. So with a basic planetary CCD (like a Flea3 or QHY5l_ii) we ought to see an image scale in the general area of 2 x 3 arcminutes. I have an Orion StarShoot color Video I'm keen to try with it too.
Let's not talk about coma or guiding yet. They're both relegated to the too-hard basket for the time being.
I thought I might add some pics of the rear end which I more or less completed this afternoon. The idea was to be able to put the focuser/baffle tube assembly in an orthoganal relationship with the secondary independently of the position of the primary. The primary has its own collimation screws.
The baffle tube is internally baffled and goes through the centre hole on the primary.
Great project Peter. I hope you will give us a detailed report on performance when it's finished. I have always wanted to build a cassegrain. Started one a few times.
Hmmmm....very nice Peter. Wish I had an old DK sitting around in my shed...all I have is a mess. Wouldn't mind a 12"Cassegrain on the mount I'm building, might be more managable than an 8" frac. Will watch with interest.
Byers drives are beautiful things, well worth the money. I couldn't find any other maker of such things when looking recently. Old Celestron forks have Byers drives too...could rip one out of there. I bought an old Meade fork that has a nice worm and gear in it...if only I could work out how to open it up without destroying the fork to see if it can be re-used.
I bought an old Meade fork that has a nice worm and gear in it...if only I could work out how to open it up without destroying the fork to see if it can be re-used.
Matt
Hmmm! Sounds familiar. There is a time-honored tradition in my shed of fixing things until they break! I'm getting pretty good at it too.
Peter
Well, we had a whopper storm through here yesterday so no yard work for me today. Which means TINKER TIME.
Here are the progress shots. The basic scope is now assembled and ready for alignments and collimation.
The images below include a side-on of the primary from which you will see it is a full-depth beast and, not surprisingly, weigh a ton. But the primary cell is quite strong and I believe it will hold it well enough.
I have yet to make a shroud for the secondary. This needs to be quite long and, according to some opinions, also needs to be narrower as it goes out from the secondary - excluding peripheral reflections being the objective.
Well, we're getting close. Got the focuser/baffle tube orthogonal with secondary, then got the primary 90% of the way to collimated. Not worried too much about the secondary since it's spherical.
Built a 100mm shroud for the secondary and voila, we have liftoff. We have a viable scope.
Finished collimating this morning using a 2"Howie Glatter with the circular holo attachment. And the eye-test done at 6657mm FL with a 40mm EP (x166) and a 25mm (x266) and the lined it up with some trees on a ridgeline about 10km away. Bleedin' terrific. This baby will be great with planets and planetaries. Matching a sensor to that FL is always going to be difficult. The planetaries will probably need an OIII filter too. Hmmm! Thoughts anyone?
I should re-title this thread to something like DK Phoenix instead of hanging off the back of those beautiful Lazzarotti scopes.
Be that as it may, I have run off a couple more images to finish this off for now. The completed OTA is shown in a couple of attached images. It is a poor man's truss thanks to the wonderful invention "the disc grinder".
I also did a quick and dirty image through it with a DSLR. The attached images are of the image through the DK taken at mid-day on a 30 degree day (i.e. impossible seeing conditions) and only an approximation of focus. The other one is with a 300 mm lens on the same camera and with the DK image shown in the little insert panel.
I think that when I can get it mounted and imaging on some point-source objects, I ought to be able to get focus (better at least) and give it the proper testing.
It came together so quickly too! Will you be using it visually or just for photography? I would be very interested in a report on the visual performance when you have it mounted.
It came together so quickly too! Will you be using it visually or just for photography? I would be very interested in a report on the visual performance when you have it mounted.
Rod
Hi Rod. I have a loosely-defined plan (with AlexN) to develop some techniques for imaging small planetaries using this scope. They've always fascinated me.
In my obs I have 3 piers/mounts and I presently plan for this scope to be mounted on my EQ8 so it should be pretty stable and track well enough. Seeing will be the major limiting factor. My site is in bushland about 100 km out of Brisbane so we have pretty fair seeing when the weather allows. This will be an extended project and may even lead to something else. Who knows?
Well, it's up!!! On the EQ8 as intended. Not easy to manhandle onto the mount - mainly because of size rather than sheer weight. I haven't weighed it but having hoisted C14s and the like around in the past, I would put only a small margin of error on my best guess at 25-28 Kgs.
