View Single Post
Old Saturday 16th August 2014, 03:28   #17
Registered User

Join Date: Oct 2013
Location: Wilmington Mass
Posts: 1,898
I finally got a night clear and stable enough for pinpoint stars.
At 117x, things were pretty sharp and clear, and the brightest point did generate a little donut.
It was quite symmetric, but I've learned this is not unusual with long barrels...I'm at
at 70mm-f/10. The longer the barrel the less critical the alignment. People worry about this
mainly for short refractors and very-short reflectors.
Things have a little color at 175x, but that's a useless power due to dimming.
That and the tripod falling short of ideal.

I got a nice porcelain mug with various font sizes for eyechart-style resolution testing.
I can read the .06 inch high font crisp and distinctly at 92 feet. That's 11.2 arc-seconds high.
Optometrists say you need 5 units of pair-seperation to recognize letters, so that puts
the resolution somewhere well below 2.2 arc-seconds. It was early dusk...I can extend the test distance
with some strong light.

I souped-up a 50mm - f/12 for fun..
that just barely resolves makes the font in question, with issues. The next font up is solid.
So...that's probably about 2.5 arc-seconds. Makes a crisp image at 40x. On a heavy Bogen
tripod (has 1/4" threads) it's actually a lot of fun.

You need decent eyepieces, of course. Kellner to 40x, Plossl to 60-100x, super-Plossl
to get a wide apparent field.

Last edited by OPTIC_NUT : Saturday 16th August 2014 at 03:32.
OPTIC_NUT is offline  
Reply With Quote