Hi,

Last week I posted some details about a homemade collimation eyepiece. When I finally tried collimating with a proper combination tube, I realized that my primitive homebuilt secondary holder was just too primitive and was preventing proper collimation. It suddenly struck me that if I was going to spend the time to build a goto telescope, I should invest some effort to allow good collimation. This sounds like a no brainer, but its easy to get caught up in more interesting details and overlook something so basic but just as important.

I am currently building a better secondary holder with collimation screws. This has turned out to be an incredibly simple and inexpensive little project (also fun); so far only about 2-3 hours fabrication time, some spare hardware, and a $1.25 washer. I have posted a few fabrication photos on my web site (OTA webpage). Below is a direct link to the secondary holder section.

 http://www.astronomyasylum.com/ota.html#Secondary_Mirror_Mount

Bill 

Hey, that's really cool. 

I might have to borrow that idea for my sheet metal scope v2.0.  I'm thinking of trying some different sized secondary mirrors for my next version scope.  I could keep the spider and adjustment screws and put a wood-block diagonal on there.

How do you intend to hold the mirror onto the diagonal block?  I used a dab of silicone sealant on mine.

-StarNerd

Hi,

I was planning on doing exactly the same thing-using silicone. Right now my secondary is epoxyed to my current secondary holder. Its actually not too bad to remove the epoxy from the back of the quartz diagonal-its bonded well enough to keep the secondary in place but it can be pried off pretty cleanly (at least it wasn't too bad last time I did this).

I'm also open to other suggestions if anyone can recommend a better adhesive.

Bill

 Hi,

Heres an update on the new secondary holder test fit into the OTA. I had planned on using bicycle spokes to suspend the secondary holder, but then found some scraps of bicycle brake cable. This was both thinner and stronger than bicycle spokes. My secondary box is very narrow, so I had to retrofit something to anchor the secondary holder. In this test, its clamped onto three threaded M6 rods with washers and lock nuts. I will fabricate a better locking mechanism in the next few days. I have uploaded a few new pictures to my webpage.

Below is a direct link to the secondary holder section.

 http://www.astronomyasylum.com/ota.html#Secondary_Mirror_Mount

Bill 

Trying to access your page, but get nothing but a blank.

Hi,

 If you are having problems accessing my webpages, just try again later. I use a free web host provider and sometimes it gives problems due to high traffic. I currently can't log in or upload a new page update, so I will also just wait a while and try later.

Bill

I siliconed the secondary mirror onto the mirror mount and installed the assembly in the secondary mirror box. Unfortunatley there were problems. The brake cable couldn't be tensioned enough to dampen vibrations and the secondary mirror vibrated too much as the OTA was elevated. I removed the brake cable and fabricated a more traditional spider from small scraps of aluminum. This holds the secondary mirror in place (vibration free) and works. I will upload a few new pictures to my website in the next few days.

Bill

Below is a direct link to the secondary holder section.

http://www.astronomyasylum.com/ota.html#Secondary_Mirror_Mount

Hi,

The secondary holder is completed and installed in the OTA. I designed for a lot of adjustment options and am very happy with the system. The secondary can easily be raised, lowered, adjusted to center and even rotated.....and of course also collimated. Total cost = $1.25 for a large washer plus several left over scraps of aluminum and bolts.

I have updated my web page with all construction details at the below link. The below picture shows the installed secondary holder and a close up of the adjustable coupling (left and right, respectively).

Bill

http://www.astronomyasylum.com/ota.html#Secondary_Mirror_Mount