Mirror cell upgrade for an 18 inch dob.

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NGC 1365 Australia
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Mirror cell upgrade for an 18 inch dob.

#1

Post by NGC 1365 »


I do a few ATM projects every year and this year I decided to upgrade the mirror cell of my 18 inch F4.5 scope and to build an 8 inch binoscope. Both projects are almost complete. The mirror cell is installed and working in the 18 inch (just needs painting), and the binoscope has been tested and I'm now making a few modifications to it.
The mirror cell originally was the standard kriege seat belt/ kevlar sling type and then a year ago I replaced it with a home made glatter sling complete with linear bearings riding on stainless steel pins/ bolts. After reading Mike Lockwoods article about mirror cells I decided to build a wiffle tree edge support cell on a moving plate. The original cell collimation bolts held the support triangles but in the new cell the collimation bolts move a plate which caries the support triangles, mirror and edge supports independent of the rear tailgate frame. This upgrade firmly holds the mirror in alignment, there is no side to side movement as in a sling setup, collimation holds a lot better, and views at low elevations are improved dramatically.
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Ivan
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Re: Mirror cell upgrade for an 18 inch dob.

#2

Post by Rainmaker »


Hello Ivan,

Just found this thread.... nice work on the cell upgrade, I'm curious if you found the wiffletrees to be any better than the sling?
I've read Mike's articles and spoke with him at Allan's SDM gathering, but everything I have seen has shown a "Glatter" sling at COG to be as good as the wiffles...

Cheers,
Matt
Matt in Oz
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Re: Mirror cell upgrade for an 18 inch dob.

#3

Post by NGC 1365 »


HI Matt, the wiffle tree edge support in my case works noticeably better than the belt sling and the glatter sling. Stars are tighter even down low in the muck ( I was able to see spiral structure in M51 from my observing spot at Blackheath in exceptional seeing and it was only 9 degrees above the horizon) The other benefit is that removing the mirror for cleaning and transport is a lot easier,I found it a chore with the slings. Thanks for the linear bearings you sent me a few years back, they worked great, but my home built sling and attachment hardware were the problem. At low elevation stars were a mess, there was too much movement in the stainless pins that the bearings ride on.
Ivan
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