13.4" f/4.75 Homebuilt w/Lockwood refigured primary
Keeper of the Swamp Gas Observatory "This R2 unit has a bad motivator" AR127, CG4 CGE1100 1984 tasco 60mm 49TR F/13.3 refractor 1976 Vixen Polaris 80mm F/15 refractor Denkmeier Big Easy BV'er Astro-Tech Titan 38mm 70* Astro-Tech Titan 20mm 70* Astro-Tech SR6 12mm 60* Meade MA25mm Jap. Meade MA9mm Jap. TMBpII 5mm ES 1.25" FX
Quote:I collimated my Newtonian then added the imaging hardware and slewed to a target. As usual, the image quality was compromised by oblate stars even at the center of field. This time I attempted to improve star symmetry by making adjustments at the secondary mirror and not the primary. By imparting very small motions, I was able to "stumble" on a position that provided round stars and an essentially flat field even with the ASA coma corrector installed. I am happy with the last nights imaging performance though I wonder about my ability maintain or recreate it. I need a way to walk into this alignment using the collimation tools as opposed to random tweaks imparted to the full up telescope prior to imaging. Though it worked out great last night, I can envision (more often than not) making matters worse. Even a well made secondary/spider has poor angular dynamics compared to the behavior of a typical PM cell. I still have to try out Glenn's suggestion of collimating with a suspended weight to mimic the effect of the imaging hardware. Since my mount can carry it, I will soon be going for a much more rigid (and heavy) telescope tube to combat this nonsense. I wish you could order a telescope "build to design" so that the customer can select the specific hardware elements that go into the delivered unit. I surely would never "intentionally specify" a 0.030" thick steel tube to support an imaging Newtonian (or visual for that matter). Properly designed systems do exist if you are willing to pay around $5,000.00 (or more) for an 8" Newt. Why are there no vendors that attempt improve on the standard, affordable imaging Newtonians in meaningful way? How big of a deal is it to provide a stable tube?Do the vendors feel that weight savings is more important than stability? Peter
Quote:Hi Don:I plan to follow one of the paths you mentioned and purchase a sufficiently rigid tube for my optics. I was unaware that the cost curve was that tight in consumer telescopes. Though I have no experience in running a business, it is not apparent to me that a manufacturer could make a profit selling essentially the same telescope with an upgraded (optional?) tube. Based on my experience, the spiders, focusers, optics and primary mirror cells are not the weak link in most of the lower cost Newtonian telescopes. I would bet that many here would pay an additional $150.00 to $175.00 for such an upgrade. I am able to make these mods myself, but why bother if you can buy it for a few extra dollars? This is the only gripe I have with the current offerings by the major manufacturers. Peter
Quote:You can make these systems work. It is just ends up not being a reasonable solution. My steel tube Newtonian (with custom optics and spider) worked very well the last time out. The problem is that the scope has really poor stability. When you re-point the scope, all bets are off.