I've recently bought an 80mm x 400FL objective and an 1 1/4 focuser. Looking to make a short tube (F 3.75 ?) OTA for solar observing. Can anyone advise a source for 100mm ID Steel or Aluminium tubing in NSW. Would be good if it could be purchased to quoted length and ends machined square as I don't have easy access to a lathe nowadays.
I just bought the same objective assembly as you Bill - the 80x400. I'd be interested to see what you come up with - as long as I don't find it first (in which case I'll let you know)!
Aluminium and a good textured powdercaot in off-white. yummm
Well I to have been following the SS lenses for sometime on the CN Forums and they seem to be pretty good. Here is a thread on a particular tube design that seems fairly easy to DIY. http://www.cloudynights.com/ubbthrea...l/fpart/2/vc/1
There a number of "not a nother SS shed telescope" threads on this subject.
My thoughts at the moment are to dummy it up using 100mm pvc so I can work out the required tube lengths etc and then replace it with metal. Did have one thought later that car exhaust tubing is pretty thin even at 100mm ID, and would even be lighter than the heavier grades of pvc, so will look into that with the exhaust shop up the road.
Thanks for the advice re the alloy tube Bird, will look up the supplier when I've worked out the required length.
Interesting threads on the SS 80x400 Netwolf, given me a few other ideas, thanks mate
Just finished the prototype using PVC stormwater fittings.
The focuser fits just nicely inside 90mm stormwater pipe and is held in place with a couple of self tappers as it isn't a push fit.
The objective holder is a perfect fit inside a 100mm Pad Repair fitting. A 100x90 reducing bush is stacked on the other end. The ridge the pipe normally butts onto was removed with a file and a bit of work with a scraper took enough pvc off the inside to let a 90mm pipe slide through. At present the two outer fittings are held together with gaffer tape, might glue them later.
The tube just slides through the ridge on the inside of the pad repair fitting so the tubes remain parallel as they are slid in and out. The inner tube initially goes right down so its end contacts the objective housing.
The outer tube is 245mm from the end of the objective housing to the end of the reducer fitting. After a bit of trimming and testing the inner tube was cut down to 260mm. Thats a trifle short but by sliding the inner out a bit the best length can be arrived at.
Materials cost so far $20, 2hrs of assembly.
Once I've finish the assembly intend to write a blow by blow account, Another thought occured, since I've seen people talk about focal extender/reducers for imaging this design might be a good way of varying the focal length without resorting to the purchase of "extra bits".
netwolf, very little is required in the way of tools or skills. If you can cut a straight line with a hacksaw, you'll do it easily.
Tools used so far are :
Philips screwdriver, Hacksaw, piece of A4 paper to wrap around tube to give straight line for cutting, half round file to remove ridge inside fitting, some rough and smooth sandpaper or a triangular scraper to open out the inside diameter of the 100x90 reducer, a drill for the self tapper holes in the tube, and of course a tape measure for the tube lengths. As the saying goes, it ain't rocket science LOL
Well, just had a look at Jupiter, and while I can bring it to focus, there's a bright, slightly off centre halo around it. Same with any bright object. Back to the drawing board, this requires more thought and tweaking
Could be the coating on the objective or an internal reflection in the tube/focuser. Hhhhmmmmmmmmmm!!
I had a look this morning at the internals and we're both thinking along the same lines netwolf and Omaroo. The (plastic) focuser tube has a chrome coating and the inside of the tube is still plain white PVC. I'll have a look in the hardware shop later for some sort of flat black paint. The internal baffles also occured to me, but will try the paint first.
Quality was a bit ordinary, but it was hard to tell with the halo around it. The edges looked pretty sharp. Tried it with a 25, 15 and 6mm plossl. Noticed that the halo was absent with dimmer stars.
Bill - did you get around to flocking or baffling this machine? My objective hasn't arrived yet (ordered it on 28th Sept, 8 working days so far) but I'm keen to do an aluminium tube for it if it's at all worthwhile. From what you've experienced so far it isn't looking at all promising though.....
The objective is around the WRONG WAY AROUND Bill!
Hi Bill - just got mine in the mail today.
There is a sheet of paper in with mine explaining that you use it the other way around from what you think. The part you actually have inserted into the tube (judging by the photo) is actually where the dew shield is meant to slide on. The actual scope tube is meant to slide INSIDE the other end. It explains that if you have it the wrong way around you'll get flaring. It goes on to say that as long as you keep the two elements relative to each other - turn them around inside the objective cell and you should be OK!!
Thanks Chris Had me scratching my head after blacking the tube inside etc.
Here's my latest incarnation. The dew shield and cover are made from a Pad Repair Fitting and 100mm pipe cap. The Repair fitting is a lovely tight fit over the front spigot, no fixing required. I cut the minor diameter section back 50mm from the angle, this allows the end of the lens housing to just protrude through into the major diameter.
Was wondering why your lens fitted neatly over the 90mm tube as mine was a bit sloppy. Found that heavy duty 90mm did the trick as it has slightly thicker walls.
I've used a plastic focuser so assembly comes in at 1Kg with the 25mm eyepiece fitted.
You've done a beaut job of yours. JJJnettie is right, it sure is nice when you look at it and think "I made that"
