Subject: Re: [sloan-25mlog 5211] 2.5m obslog 20201020 (SJD 59143)
From: John Downey
Date: Wed, 21 Oct 2020 09:12:22 -0600
>=20
> ---- Observing Summary ----
>=20
> (1) Optical collimation.
>=20
> We went through the full process and we were able to produce doughnuts =
that
> looked significantly better than what we saw last night. However, the =
total
> amount of X Tilt and Y Tilt required to get the best doughnuts was =
considerably
> more than usual and this creates problems -- when we try to command M1 =
to the
> optimum orientation for collimation, we get an error that the =
"Commanded
> orientation violates the mount limits." I.e., even though we were able =
to
> determine the required tilts and translations, we can't command M1 to =
that
> orientation because the move is too big.
>=20
> For some context, we determined that the max amount of (X Tilt, Y =
Tilt) we can
> supply to the collimation calculator and still get an accepted =
resulting 'move'
> orientation is ~75% of what we actually require (Img# 0066 is a =
reasonably close
> example of what that would look like on-axis). A decision will =
ultimately have
> to be made as to whether "somewhat collimated" is acceptable or not. =
See Log for
> details.
This sounds to me like the primary is off axis.  You can compensate for =
that with either tilt or translation to get back to the axis being =
normal to the sphere (I recall this be spherical but I don't really know =
- just something from an old conversation between Connie and Dan Long).
So I would suggest trying lateral and transverse shifts in whichever =
direction allows you to then reduce the tilts.
>=20
>=20