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Old 24-10-2012, 07:40 AM
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Satchmo (Mark)
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Join Date: Dec 2005
Location: Sydney
Posts: 1,858
Congrats on mirror improvement. Just use a whiteboard marker to make a temporary collimation dot in the center- it will wipe off when you need to. I use them to mark areas to polish in normal figuring operation.


Quote:
Originally Posted by sopticals View Post
Just returned my reworked #1 22.2" mirror to the dob structure, after further figuring work was required, to remove a rolled down edge 88% radius out, and further improve correction over the inner the inner regions.

Star testing, using a 133 lpi Ronchi ocular last night, revealed a vast improvement since test previously carried out, after the original figuring. As a test subject I used Rigel Kent. The test was carried out using the eyepiece focused at various numbers of lines from 1-8. The most useful numbers being in the 6-8 region. The image seen revealed straight,clean,parallel lines edge to edge except at the extreme top and bottom of lines which indicates the existence of some TDE. However as I let the star image transverse the FOV I was unable to notice any bowing of the lines as they came onto/exited FOV. I conclude from this that TDE must be quite narrow. When image was reduced to 1-3 lines seeing caused to much image movement to see the TDE condition.

Replacing the ronchi eyepiece with my regular 2" eyepieces (ES30,24,TV Nagler 20) I viewed Rigel as the spectacular double it is, nice separation. Did note at this point that collimation is off by quite a bit,(not easy to collimate an uncoated optic with no center spot), as star images flared somewhat to one side. Also looked at the 63% waxing moon, which gave nice sharp high relief images in both ES eyepieces, but a smidgen off being absolutely sharp in the Nagler. Placing on a 20.7" aperture mask cleaned that up somewhat. This removed the TDE, slowed the focal speed,and probably compensated to a degree for the miscollimation.

Overall the test revealed a great improvement in the mirror figure. Previously I rated this optic as a 3.5/10. Now at this point I would rate at a 7/10. Excluding the TDE section I would think mirror would be close to 1/4 wave accuracy.
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