Posts Made By: P. Lee Stock

Hi David,

If you plan to position the focal plane relative to your focuser so the drawtube travel will encompass all of TeleVue's eyepieces, then almost every non-TeleVue will come to focus within your focuser's range also. The advantage of using TeleVue as the standard is that all of TeleVue's eyepieces have published "flange level" specifications. Flange level is a relative measurement of the distance from focal plane to the eyepiece's flange, or where it seats against the drawtube.

Of all TV's eyepieces, the 31mm Nagler requires the most in-travel (more than almost every other eyepiece out there, including the notoriously in-travel needy Speers-Walers, IIRC). The 31mm Nagler has a flange level spec of -0.38". Others have much higher flange numbers, up somewhere around +0.75" or so. This means that an eyepiece with a flange level of +0.75" will come to focus 1.13" farther out than one with a -0.38" flange level. So, your drawtube need only travel something like 1.25" to adequately cover the range.

Not owning a 31mm at present, I now use my 32mm TV plossl which has a published flange level of +0.25". +0.25" is 0.63" farther out than the 31mm Nagler, and 0.53" farther in than the 12mm Nagler with a flange level spec of +0.78". So, I rack the focuser out around 3/4" with the 32mm plossl in place (the 31mm will require 0.63" additional in-travel than the 32mm plossl, so 3/4" ensures I have the in-travel I need + a little extra) and adjust the mirror until stars focus. Works every time. Also, I use actual stars to prevent errors.

You can find the flange level specs at this site. They are in column "F". Just find your TV eyepiece on the chart and compare it's flange to the 31mm Nagler to find how far out you should rack your focuser before moving your mirror to focus on a star.

http://www.televue.com/engine/page.asp?ID=144

Hi Bill,

I assume you are already aware of the Chromacor, but perhaps you are looking for a more permanent and specialized solution than that.

Take care,

Lee

Sounds like fun. For more finishing touches, you could wrap the upper cage baffle in cherry veneer.

Funny that you break from the mainstream wood dob crowd to make an original all-metal truss dob and now someone wants you to add some wood accents ;^). I've seen people refer others to you because they wanted to get away from all these "amateur" wooden telescopes . I swear, you just can't make everyone happy all the time!

Hey Walter--very clean job you did there. Can you list the McMaster-Carr part number for the stuff you used so I can compare it to the Fidelio 1000-Black dress velvet I get from JoAnn Fabrics?

Thanks!

I did notice the impromptu curved vane spider solution. How does it work? Protostar units have a threaded nut attached with a roll pin that might pivot and not permit this unless the nut were soldered/epoxied rigidly to the vane, but there's no reason anyone couldn't do this so long as it stays put.

Clever idea.

Lee

I like the idea of having things handy and in the same relative location without having to move an observing table around the scope to keep things close at hand. Good job.

Right--larger diameter, not thicker wall.

I wouldn't say the bandsaw is "all we need", but it sure is helpful for the myriad of small cutting jobs where a perfectly straight line isn't paramount. I consider the router the one tool I could use for almost everything ATM, plus a few handtools.

A back end view of the same 8" f/6 Zambuto:

An 8" f/7 Mike Spooner mirrored maple finish scope I made a couple years ago. Probably the most perfect mirror I ever looked "through". Here it is sitting in Rob Teeter's shop--he bought and owned it for a few weeks.