Posts Made By: Keith Lawson

Test setup. 5" F/9 versus 10" F/10

Whew! Got the scope up and mounted. I'm gettin' too old for these kinds of antics Anyway, Jupiter was well seen at 240x. Lots of details. The moons were showing disks of differing sizes despite the 5/10 seeing. The color correction is very good. I was again surprised. Jupiter had a faint tight halo that was less than my 5" F/9 refractor. This is not a standard achromat. I'm guessing that the slightly yellow tinted crown element is in fact a lanthanum lens (55 year old lens). A 10" achromat at F/10 should have much more color. I pushed the lens to 420x on Jupiter trying to get the color to be more obvious but to my surprise it was less. My guess was a more precise focus? Saturn revealed all the usual details. The image was seeing limited. Altair revealed above average color correction as well.

250lpi glass ronchi at 3 bands revealed good spherical correction and a clean edge. Seeing was not good enough for critical star testing. The stiff mount didnt help.

The DOB mount in the pic is a massive beast. Heavy, and a lot to move around. Buttery smooth DOB motions? NOT!

Keith (Scopejunkie)

Lots of rework. Tube is split into three components. Much easier to load up and assemble. DOB mount needs some work. Will use it till I get the Cave mount that came with all the parts back in working condition. Reweighed the lens assembly. It actually only weighs 20lbs. My estimate was quite a bit off. Still tinkering

Keith (Scopejunkie)

Aligned the focuser and the lens. Reworked the DOB mount. This will do till I can get the GEM up and running. Still hacking...

Keith (Scopejunkie)

Well... let us see what we can see...

Keith (Scopejunkie)

The scope hurt me bad enough that the I sold the lens. Took me couple of weeks to recover from the weeks of handling the instrument and scope rework. I thought I could deal with it like many of the other monsters I have had in the past but, at 65, the body says no. The optical tube assembly alone was about 60lbs. After weeks of use I realized that it's not something I would enjoy to putting up every night I want to observe. If the deal wasn't so tempting I probably wouldn't have bought it in the first place.

It was a good performer. The planets were well seen. Building a 8" cass currently.

Keith (Scopejunkie)

I suggest a good star charting program. Pluto is easy to confuse with the faint background stars. When I observed it with my C14 I had to identify it by its position among the other faint stars in the eyepiece field. I was going to re-identify it a few weeks later by its motion among the stars but I was so unimpressed by viewing it that I never did. Viewing it did allow me to check it off of my unobserved object list though.

Keith (Scopejunkie)

Bob,

Good hunting! Let us know how it goes. BTW, what scope will you be using for your Pluto quest?

Keith (Scopejunkie)

Excellent sky hunting with your yard cannon! 

Keith (Scopejunkie)

All,

Though this is not telescope making, it is a telescope mod. I'm hoping that this post might help someone that has a large SCT the won't maintain "star level" collimation. I noticed on my "OLD" C-14 that the collimation would shift when viewing different parts of the sky. I'm not talking about gross mirror tilt. I'm speaking of the type of primary tilt that shifts the diffraction ring on an in focus star at high power (300x or greater).

My scope has really great optics so this minor tilt became quite annoying to this multiple star observer. When I pulled the primary the retaining ring was still in contact with the primary but was not "tight." I installed 3 nylon tipped set screws (10-24) into the retaining ring. I reinstalled the ring tight then screwed down the set screws firm but not overly tight. The problem appears to be fixed. After star level collimation (in focus) the first diffraction ring has remained centered on the airy disk over the past week of observations. We shall see how well this works long term.

I made this mod because I don't want to have to take this scope apart again for as long as I own it.

Keith (Scopejunkie)