Mirror mounting

Hi All,

Another topic that I'm pretty sure there's no consensus on - but I'm interested in hearing everybody's thoughts.

I know that large / thin mirrors have to be properly mounted or there will be very significant performance degradation. However, if you're dealing with a small and full thickness mirror, say a 6", can you get away with the "silicone blob method" without problems? I've seen some experts make disparaging comments about "bathtub caulk" but it's not clear whether they apply to small mirrors.

It's not so much that I don't want to spring for a proper mirror cell, it's that I'm building an OTA that will ride on an EQ mount so I want to have the mirror firmly mounted without diffraction effects from retainer clips. As far as I can tell there is no way to avoid the clips if you use a free-floating mirror design. (Am I mistaken?)

Also: What thickness spacers are to be used during gluing to ensure the "blobs" set at the right thickness? 1/8"?

I will most likely be using Discovery optics and according to their website the back of the mirror is properly ground flat. (I don't know if that matters or not...).

Thanks,

Mike

Silicon Blob is fine for relatively small mirrors.

As for thickness of spacers, I use nails. It think 16 penny, but cannot remember.

Alex

Silicone glue is quite strong. If the surfaces are clean it will bond a 6" mirror without a doubt. I think the round toothpick spacer is about right. 3 blobs about 1" when squeezed to the toothpick should be enough for a 6", plus a 3 point mount is the preferred for this size. You can use Plop to find the best spacing and position for the spots. This would certainly make it simpler for an EQ mount and you would not even need clips, except for mental relief!