Thread: secondary size
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Old 24-08-2011, 01:06 PM
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alistairsam
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Join Date: Nov 2009
Location: Box Hill North, Vic
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some pics with the difference in height between the two focusers.
its allowed me to move the primary back by about 30mm.

from what I've read, the primary reason for larger secondaries is because a few mm inward from most secondaries are not ideally usable.
did some eyeballing by keeping my eye at about where the dslr chip plane would be and there was roughly 7mm outside the reflection of the primary on the current 66mm secondary.

tried some calculations using mynewton software, results attached.
the 50mm secondary shows lower central obstruction but i don't know what the significance of the 100% FOV in degrees is (last line).
its 0.57deg for a 50mm secy and 2.04 deg for a 66mm secondary. what does this mean?
i've used 12mm as the desired 100% illumination FOV guessing that would cover the dslr sensor.

I also added wingnuts and two check nuts to the collimation bolts so it can be adjusted by hand. the wingnut is tightened all the way up and the two check nuts prevent it from loosening. works a treat.
i'll be using shorter bolts.
Attached Thumbnails
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Click for full-size image (secy1.PNG)
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Click for full-size image (secy2.PNG)
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Click for full-size image (IMG_4411.jpg)
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Click for full-size image (IMG_4405.jpg)
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