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Equipment Discussions >> ATM, Optics and DIY Forum

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Carpal Tunnel

Reged: 12/05/07

Loc: SW Michigan
Re: How tall is your secondary cage? new [Re: Dick Jacobson]
      #5533754 - 11/22/12 11:09 AM

My secondary assembly is currently a 3/4" thick flat ring. There's a full circumference thin aluminum baffle with a hole cut into it for the light path exit, it's 2.25 inches from this inner baffle to the end of the focuser draw tube, where theres an annular baffle, then a long focus draw tube. The full circumference baffle is just not tall enough when there's local lights-- I wanted the secondary assembly to store on top of the mirror box, so I was 'limited' by this design requirement. The assembly is a square shape with the circular aperture cut into it. While this made for a very convenient shape for the strut attachment (parallel), it dosn't make a convenient shape for attaching baffles opposite the focuser. On top of that, the spider is 4-vane, which complicates things further.

Overall, the scope is a VERY effective design-- perfectly balances, butter smooth, and handles everything from my 35mm Pan with a coma corrector to a 7mm Plossl alone.

My reason for a potential re-build is two-fold: Increase stray light control, and make the mirror box smaller and hopefully lighter. The lighter part creates some serious difficulties in designing the secondary assembly while addressing the stray light control.

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Carpal Tunnel

Reged: 12/05/07

Loc: SW Michigan
Re: How tall is your secondary cage? new [Re: KerryR]
      #5535513 - 11/23/12 01:27 PM

From the OP:

I may not need a re-build if:
1) I abandon the 'need' for a 1/2" fully illuminated field. Based on Gary Seronik's article, it looks like this isn't necessary for most observing requirements.
2) I abandon the 'need' to not vignette the %75 percent field. Again, based on Seronik's article, as long as edge of field doesn't drop below %50, things should be fine.

Based on hand ray tracing, Doing those things means I only need 2" more extension above or below my current uta if I make the first exit-ray baffle smaller. I can do this without cutting any of the %100 ray, and still keep over %60 at the very edge of the FOV.

Seems like a worthwhile pursuit considering I'm otherwise very pleased with my current scope's design... though weight and bulk reduction would be nice...

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David L

Reged: 11/12/07

Loc: Lee County Iowa
Re: How tall is your secondary cage? [Re: KerryR]
      #5536375 - 11/23/12 10:21 PM

I made a focuser baffle out a 3-inch PVC floor drain, grinding out the grating part and some of the flange to hold it in place. The flange fits under the mismatched curve of the GSO focuser on my 16-inch Lightbridge. I blackened the baffle with black sticky back felt. Dave

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