The objective arrived from iStar this afternoon. I was initially very happy to see it, but it was clear the box had been through the wars (see photo). I noticed that there was dirt (or a small scratch) inbetween the objective glass elements - pretty much right in the middle. I have to wonder how it could have been checked prior to shipment.
I have emailed Ales in the Euro office about this and sent him the photos.
Pretty disappointed, and this is going to throw my entire build project up in the air and I have stopped work for now. If I send it back, it's going to cost me, and add probably three weeks minimum to the build. I don't think I should have to disassemble it and try to clean it .
Glen that is certainly disappointing to see. I know the anxiety of waiting a long time for a fragile product to arrive. If it is dust then it can be cleaned out easily enough. Best discuss it with Istar before proceeding to dis-assemble the lens.
When I purchased mine it came very well packed in paper and a moulded foam shell inside the carton. Mine came with a test paper that looked like a test report but it is kind of a generic thing, the lens doesn't have a serial number. The lens star tests very well.
This objective does have a serial number. I would not want to try and disassemble it as special tools seem to be required. I am just going to send it back for a replacement under warranty.
Here is the scope built along similar lines. From CN ATM post a pic of your homemade scope page 20.
A real shame about the objective, had some real rough treatment by the look of it.
Just a quick update, I have been waiting on iStar to get back to me on the replacement objective. I received the tracking number so it is on its way now. Maybe by the end of next week if I am lucky.
In the meantime, I received the flocking material from the supplier (DC Fix black velour felt). I also have the 2mm neoprene sheet that I am planning to use for any needed baffling. Once the tube frame is finished (clear coated with spray polyurethane, I will apply the flocking material to the inside of the stuts to stop side stray light reflection into to the focuser or objective. After seeing the original objective in person, I realised I will have to fabricate a collar to mount it to the front plate; I had thought it would slip inside the front plate but it won't and I don't want to machine it (the front plate) any thinner and a collar will add strength and allow the use of the collimation screws (which for some reason iStar do not supply with the objective (guess you have to buy their front plate). I have two options for the objective collar, a solid aluminium collar cut from plate or laminate four 2.5mm sheets of MDF into a plate (this would be epoxy bonded and sealed and could be painted prior to coating to mimic the ply frame rings).
I have a 10mm plate of aluminium but its going to be much easier to cutout the mdf laminate. If I could machine the aluminium I'd probably go that way. Anyone have a recommendation on cutting 10mm aluminium plate in circles? I have seen the many drill holes technique, which is alot of work.
Anyone have a recommendation on cutting 10mm aluminium plate in circles? I have seen the many drill holes technique, which is alot of work.
I have used a router for cutting al plate, on a circle cutting jig you just take it slow and if you have got a good router bit quite nice results can be achieved.
I cut three sections out of 12mm plate and screwed it to the plywood cell on my scope. Worked well but have never had to use the collimation bolts as the whole thing is straight anyway! Maybe try the objective first? Could save a bit of time if you can just screw it in and leave it. You have collimation at the focuser end, is that correct?? That's as good as at the objective end but a whole lot easier to use.
Update: The replacement objective arrived today from iStar. This one was packed better, and it is pristine - no debris in between the lenses. I will get it onto the tube frame tomorrow for the focal length test so that I can fix the backplate into position. I have made an adaptor collar for the objective to sit in. I tried the aluminium plate for the adaptor but my router was hopeless at getting through it, or maybe it was the dull bit. In the end I used good old ply again, at least it will match everthing else. Re collimation of the objective, I see it as a nice thing to have; sure I can collimate the focuser.
Update: The objective is installed on the tube and tonight I did the preliminary test to set the backplate/focuser distance. I ran through both 1.25" and 2" diagonals with all the EPs I have (2"30mm right down to 6.7mm and the 2x barlow combinations) to make sure I could achieve focus on everthing. It was clear that I had it initally set up too far back but that's the reason for leaving the backplate loose until now. I even tried out the binoviewer, which requires fairly agressive in travel.
I can report that the R30 lense, and the long fl, really control CA. Looking at the moon tonight I could not see any fringing at all.
I need to get some imaging guys to give me some info on how long imaging trains can be, and what the impact is on the focuser setup. I imagine no diagonal is required, and that can affect fl. I won't fix the backplate until I get some info on that.
I have attached a photo of the scope under test on my Vixen Porta II mount. I strapped the scope mount plate to the dovetail bar and it worked pretty well, and allowed movement but wasn't very stable.
BTW I weighed the scope once the objective and focuser) were installed, it came in at 8.1kg total, pretty good for a 127mm long fl refractor; my estimate was 8.4kg. That's the weight without the 2" diagonal or an EP.
Cool scope
I bought a SkyView alt-az and like the Porta it was too low for refractors , so I ditched the standard legs for a surveyors tripod ($100 from tool specialist) and now the vixen clamp can be up to 2m tall !
Just a few word on stray light scatter on my tube scope, I intentionally setup near the house where I would pickup some scatter, and yes there is some as expected as the internals are not flocked yet, nor did I have the front or rear light shields in place. The long struts and the mount board do seem to be the major source as they have flat shiny sides that face inward and can bounce light into the other bits. I was waiting for the first light test to determine how I would address light management, and now believe that I will probably have to spray the internal structure surfaces with a black non-reflective coating (whether Plastidip, bed armour, or just paint, is still a question). Baffling is also a possibility, and I have some thin neoprene which can be cut into baffles and attached to the frames. I need to do another light ray string exercise to work out placement. If I spray the frames (internally) then I can just glue a small baffle ring of the right aperture to the frame itself. More on this later.
Update on light scatter remediation. The problem: Is this a telescope or a piece of furniture (my daughter thought it was a wine rack).
So to flocking and finishing, I gave the scope a preliminary coat of satin finish Capot's polyurethane, just to see how the furniture approach would go, and while it looks good,... I think I will probably go ahead with a full paint job and cover up all that timber. It seems the only reasonable way to address the stray light issue, especially if it is painted black, and I do not have to spend hours getting every little imperfection out of the epoxy fillets and joints. If painted black I can also forget about baffles (or reduce them).
My Kendricks Dew shield arrived today, the front one will be a standard dew shield and have a heater in it. The second one goes behind the objective to shield it from stray light and provides an effective baffle going down towards the focuser.
I will put up a new photo when I have finished the paint job and have the bits permanently installed.
Have managed to get abit more done over the past couple of days. The painting is all completed, after doing an initial coat of satin polyurethane to see how it would look, I decided to ditch the whole furniture approach and put three coats of satin black on it. By painting it black I do away with any flocking requirements on the struts. I redid the ray model today and finished the baffles for the frames. The baffles are just 2mm neoprene sheet which are superglued to the frame members, very light and they already have the flocking finish on them. I put the dovetail bar on and checked the balance point.
I put it all together this evening and did a quick collimation. The focuser was easy to setup with the laser as I had tried it before and I have a mask with a centre spot from when I made the frames. The cheshire was a nightmare, as the crossed wires were in the way and flaring the light making it hard to see the reflected circles (green and yellow). I moved the objective around and got the circles close but I am not happy with it and will do it again at some point.
Took it outside tonight for a star test, and while it provided great lunar, mars and saturn views it was obvious on stars that the collimation needed some more tuning. Despite the concerns raised by the structural engineer, there is no evidence of frame flex during this evenings test. I will need to get it on the NEQ6 and start tracking from side to side at extreme angles to see if I need to brace it. I have the Dyneema cord and turnbuckles ready if I need to do it.
I have attached some photos of the baffle install.
As indicated in the last post, the collimation was giving me troubles, mainly because I was trying to shim the heavy objective. Shiming is time consuming and in my case the shim material kept falling out when I moved the lock bolts.
If you can't afford to buy a suppliers counter cell (iStar makes one for their objectives but they are over $250), make it out of plywood like I did (and some others).
I should point out that this approach will only work if your objective is setup for Push-Pull counter cell mounting (ie has push holes in the rim that may, or may not, be tapped for set (grub) screws). If your push screw holes are not tapped it is easy to run a tap through them (they are all aluminium) and cut your own).
To turn your ply mount ring into a Push-Pull Cell try this:
1. Check your ring squareness with the rear backplate to insure that the alignment will be close. As you can see from the attached photo, I had to trim my front cell slightly to square it up with the rear plate.
2. Mount your objective using the normal bolt holes (or the pull holes). Then screw three push bolts into the objective so that they push into the ply (this is normally why ply is a bad choice for push pull cells - it gives and gets sloppy).
3. Remove the objective. you will see three distinct depressions in the ply ring where the bolts pushed against the ring. Centre drill these three depressions with a very small drill bit (no more than 4mm is all that's needed).
4. Get three stainless steel nails ( I had a pack of fibre sheet nails from Bunnings that worked fine). You want a nail head that is just the same size of larger than the push screw that you will use). Cut the head off the nail leaving a small shaft tail to go into the hole you drilled. Put some five minute epoxy into each of the little holes and tap the nails into the holes flush with the ring surface.
5. Finish off your paint and remount the objective and adjust to reach collimation as normal in push-pull setup. This is also now field adjustable if required, something that would be a nightmare with shims.
That's it you now have a push pull counter cell for next to no cost compared to a shim cell.
As indicated previously Julian, I have the string bracing equipment ready to go onto the frame. I will be giving it a good workout at Bretti this coming new moon period. It will be riding on my new NEQ6. BTW final weight of the OTA is 8.4kg, less than 2/3rds of the weight of the production tube based scope made by iStar.
In your calculations I hope you have allowed for the bracing effect of the epoxy fillets at each joint, which effectively extend a 90 degree brace over twice the distance of each joint. These are non-flex joints, only the oak batten can possibly flex in between the frame stations, and they work in a combination of three spaced 120 degrees around the circle frame (which cannot compress). The oak batten flex over the short distances between frames could not be induced when I stood on them. I am not saying there would not be some flex if say it was used as a see-saw over a small fulcrum however there is a 300mm dovetail bar mounted on an oak mounting board (with a lamination strip) which spans three of the frames separately to the oak struts. The objective weighs 3kg and sits only 350mm from the mounting board/frame combo. The string brace will run from the bottom of the objective ring to the top of the middle frame, paired with a similiar string brace from the rear focuser plate to the same middle frame
Hmm, I don't seen to recall engaging your services so certainly won't be paying. The model is nice but the devil is always in the detail, for example the dimensions of those struts, the span, and not the least of which is the epoxy composite techniques used to create a monocoque structure. The struts are, as is the entire structure, completely epoxy resin encapsulated (two coats applied wet on wet to bond - of International HT9000 boat building resin (not some cheap stuff you buy at Bunnings)). The joints are HT9000 resin using International Glue Powder mixed in the ratio required to achieve maximum strength.
This epoxy system is the same used to construct Sydney-Hobart race boats, and many long distance and private commission global roaming vessels). The epoxy encapsualtion stabilises the strut much more than a naked strut that relies only on it's material properties. Epoxy resins saturate the wood, creating not just a coat but a increase in stiffness that radiates into the fibres of the strut. I'd suggest some reading on the 'Wood Epoxy Saturation Technique' if your really interested in how composite structures work.
