NavList:

This mornings exercise was to observe Sun and Venus lunars using the perimeter field of the scope. I was surprised at how much deflection there was in my reductions when compared to center scope field observations. Nearly a full minute of arc. To verify this effect the sextant was set to zero and the Sun images were adjusted to touch limb to limb. The Sun images were then observed spreading apart as the field of view was shifted to the perimeter. So take extra care to keep bodies centered for extra precision.

Another little important detail is to be aware of lens fog from condensation and breath. Keeping lenses and filters clean should go without saying. Sometimes optics get a film on the inside of the ocular and objective lens which requires disassembly of the scope to clean. Very old optics can grow mold and fungus on lenses and prisms which also requires optic disassembly for cleaning.

Greg Rudzinski
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