Telescopes

Re: What are wavy lines?

zachsdad — Tue, 15 Apr 2008 20:33:16 GMT

That's a good article, Ripps1. Thanks for the link.

Re: What are wavy lines?

Ripps1 — Tue, 15 Apr 2008 20:09:35 GMT

Here's a good write up on the topic ( go down about 1/3 of the page to "How to collimate the reflector" )

http://legault.club.fr/collim.html

Re: What are wavy lines?

E_Look — Tue, 15 Apr 2008 15:15:13 GMT

How high is high enough magnification?

Re: What are wavy lines?

Ripps1 — Tue, 15 Apr 2008 15:00:03 GMT

The fact that you were seeing a doughnut instead of concentric rings usually means you have either racked the focuser too far or you are not using high enough power.

The concentric doughnut is the least sensitive test for collimation. The concentric rings are more sensitive. Upping the magnification further results in an airy disc at focus which is very sensitive ( and very difficult to achieve unless you have a night of excellent seeing ).

Since your images are sharp and you are seeing good detail, I would presume your collimation is very close if not dead on.

Re: What are wavy lines?

Arawn75 — Tue, 15 Apr 2008 11:49:11 GMT

The lines definitely calmed down a little bit. I was out until about 11 so plenty of time for the temperature to equalize. I could still see some lines but not as much. I thought maybe those were a result of turbulent seeing. The scope seemed to perform well. I got nice crisp points when I would have a star in focus. On a bad note the neighbor was working in the garage. Every couple of minutes he was back and forth to the house. Well with the motion detectors on his lights the driveway next to me looked like a landing strip at O'Hare. A bit disappointing. I did get some great views of Saturn. The moon was also a target. I got some great detail along the terminator. Not too bad of a night but I was hoping for some clusters. Maybe this week.

Re: What are wavy lines?

mr Q — Tue, 15 Apr 2008 03:59:35 GMT

Arawn75 - I agree. The wavy lines or "boiling" effect are caused by tube air currents and sometimes atmospheric seeing instability. As long as all the circles were concentric with each other, the scope is in great shape. Sometimes you have to rack the focus in or out to observe the rings. To help minimize the "cooling down" time, I leave my tube parallel to the ground so cool air can "drip" out the bottom of the tube end and warm air can rise out the top of the tube end. I find doing this cuts down the time by about 30-40% of the time leaving the tube opening straight up. Mr Q

Re: What are wavy lines?

chipdatajeffB — Tue, 15 Apr 2008 01:40:15 GMT

I think you're right: those are most likely the result of tube currents at the face of the mirror.

What are wavy lines?

Arawn75 — Tue, 15 Apr 2008 01:16:16 GMT

Okay I collimated the scope the other day in hopes of a clear night. I have the scope outside now and I decided to do a star test. I looked at a few sights for procedures. I locked onto eith Procyon or Pollux. I put in the appropriate eyepiece and de-focused until I had the donut. Instead of seeing concentric circles I saw a perfect circle with the dark circle in the middle. The area of the donut that was supposed to be concentric circles was full of wavy lines. The only thing I thought of was that the scope had only been out for about 30 minutes and maybe it was not cooled down enough. Is it that or am I seeing something else?