Primary Mirror Cell

Hello Everyone.

I have a Coulter 13.1” scope and want to change the primary and secondary mirror cells.

The first to be changed is the primary cell, so I’m looking for any suggestions for mirror cells. I’ve looked at the University Optics light weight aluminum cell that is made for the mirror specifically, but I’m concerned with having only 3 support arms and possible mirror sag, opposed to a 9 or 12 point cell.

Also, I would like to keep the mirror captive so I don’t have to remove the mirror during transport with the OTA laid on its side.

As for the secondary, a classic 4 vane spider is what I’m looking for.

Any suggestions are greatly appreciated.

Just so you know why I’m doing so, the current primary wood cell is pinching the mirror and diffraction rings are triangular shaped. The mirror is about ¾” thick and even after 4 hours of stabilization the diffraction patters got better, but still triangular in nature. Not sure if this can be resolved, but though I’d mention it.


Thanks for your help!


Joe

Joe:

I think you are on the right track... I have one of the UO cells in the 12.5 inch version, I don't recommend it for a thin mirror... I replaced mine with a Novak but those are pretty rare and expensive these days. There seems to be a definite lack of quality mirror cells these days, most folks design them and then build them it seems.

Jon

Joe Ramacciotti said:

Hello Everyone.

I have a Coulter 13.1” scope and want to change the primary and secondary mirror cells.

The first to be changed is the primary cell, so I’m looking for any suggestions for mirror cells. I’ve looked at the University Optics light weight aluminum cell that is made for the mirror specifically, but I’m concerned with having only 3 support arms and possible mirror sag, opposed to a 9 or 12 point cell.

Also, I would like to keep the mirror captive so I don’t have to remove the mirror during transport with the OTA laid on its side.

As for the secondary, a classic 4 vane spider is what I’m looking for.

Any suggestions are greatly appreciated.

Just so you know why I’m doing so, the current primary wood cell is pinching the mirror and diffraction rings are triangular shaped. The mirror is about ¾” thick and even after 4 hours of stabilization the diffraction patters got better, but still triangular in nature. Not sure if this can be resolved, but though I’d mention it.


Thanks for your help!


Joe

The 13.1" UO cell is plenty strong enough for transporting the mirror. But not a good match for thin mirrors, because the support points are in the wrong configuration. Diffraction patterns show it. It sags.

Joe,

University makes a 9 point floatation version of their standard mirror cell from 14" on down. They listed them for a short while last year but took them off their web page. I called a month ago and found out that they will still make them, you just need to call or e-mail and it will take a few weeks. They aren't that much more expensive either.

Jerry

Hello Everyone.

Just an update to the Coulter 13.1" scope I've been working on. I've installed a JMI RCF focuser and it works very nicely. Also, I have received everything needed for my upgrade plans (Sky Commander, encoders/installation kit, 2.5" secondary mirror and 4 vane spider, and the primary mirror cell).

I went bonkers and picked up two primary cells; a new U.O. cell and a used Novak 9 pt floating cell. I've decided to go with the Novak as it appears that it will support the mirror better, although the UO cell is very nice and if I didn't come across the Novak I'd be happy with it.

I've attached the secondary mirror to the holder with some G.E. silicone and it will be ready for installation Sunday. In the mean time I'm heading out to the garage to start on the primary cell. I'm hoping to complete the primary cell installation today as I want to use the scope tonight before I install the secondary tomorrow.

Next w/e I’ll be focusing on installing the Sky Commander. I’ll send an update accordingly.


Thanks again for all the help!


Joe