Date: Wed, 13 Jun 2018 16:59:21 -0600 Subject: Re: [sloan-25mlog 4129] Re: 2.5m obslog 20180612 (SJD 58282) From: "Daniel Oravetz" Hi John, We were really close to the M2 limit the other night when I was on shift, too, so there are a few numbers still relatively fresh in my mind when I was looking things up then. I'll include those here. The first thing is "a 10C temperature mismatch (between ambient and drill/design) can be corrected by translations of 2.4 mm and 2.0 mm for the primary and secondary, respectively." (see http://iopscience.iop.org/article/10.1086/500975/pdf) Here are some useful numbers from looking at last night's example where M2 was at it's limit for cart. 5, 8314: Time Inst Scale M1 M2 Focus Az Alt Temp Wind Dir -------------------------------------------------------------------------------- 05:41 5-8314A 1.000431 -4255 -5657 150 169.2 83.3 18.0 25 130 nan boss 05:58 5-8314A 1.000431 -4255 -5657 150 196.5 83.2 17.8 20 132 nan boss 06:14 5-8314A 1.000431 -4255 -5655 150 217.4 81.5 17.6 21 130 nan boss 06:31 5-8314A 1.000431 -4255 -5653 150 229.8 79.1 17.4 20 128 nan boss 06:47 5-8314A 1.000431 -4255 -5651 150 237.1 76.4 17.2 22 148 nan boss 07:03 5-8314A 1.000431 -4255 -5647 150 241.4 73.4 17.4 27 137 nan boss 07:20 5-8314A 1.000431 -4255 -5642 150 244.0 70.3 17.3 25 134 nan boss 07:36 5-8314A 1.000431 -4255 -5636 150 245.5 67.2 17.2 24 136 nan boss 07:53 5-8314A 1.000431 -4255 -5630 150 246.4 64.0 17.4 22 136 nan boss FYI, with M2 having been at its limit, then the M2 piston value of about -5650 um reported in the above table corresponds to a Galil value of about -7.2 million steps. The second thing is, how much more travel do we have available for the M1 piston to begin with? I.e., if M2 were to move 4 mm, is there enough piston range left for M1 to "utilize" that whole amount during scale changes? It looks like (also according to http://iopscience.iop.org/article/10.1086/500975/pdf) M1 has 12 mm of total piston range available. Last night, when we were at the M2 piston limit, the M1 piston was at -4255 um. If the primary moves between -6000 um and +6000 um (i.e., equally centered around moves of scale factor = 1.000000), then the primary only had -1745 um of piston range left before it hit a limit itself. That would mean that M2 should move at least as far as is necessary to take advantage of that full remaining M1 piston range, I think, right? Using the 2.4/2.0 ratio of M1-to-M2 translation from above, that would mean moving M2 by (2.0/2.4)*1745 = ~1.5 mm. Hopefully I understand these numbers correctly, but I do tend to get confused on units between what's in the night logs, what's in the TPM, and what STUI reports in certain places, so I'll have to double check for my own peace of mind. Dan >> >> Notes: >> ====== >> * Cart 5 - We were at the M2 limit for the entire duration of the plate, >> so we >> could not account for additional scale and focus adjustments. At the >> same time, >> we were also battling clouds, high seeing, and high altitude bad guiding >> for the >> first few exposures. >> >> * Cart 17 - Again, at the mirror limit, and severely out of focus. Still >> some >> clouds around. There are no other plates to observe. > > We're working on a plan to fix the M2 position problem first thing during > the summer, the tricky part is building something stiff enough to take a > physical measurement so we can avoid recollimating and taking sky > measurements to see if we've improved things - I'm hoping this will speed > the process such that we will finish in a day or two rather than a week or > more. > > One thing that would be a big help would be an actual target number for > how far we need to move the M2 support frame out from the primary. The > figure I remember from discussions last fall is 4mm, but since we don't > want to move too far it would be good to confirm this. > ____________________________________________________________ > Logs of Nightly APO Activities > https://trac.sdss.org/tracmailman/browser/private/sloan-25mlog/index.html >