The Ohio State University College of Mathematical & Physical Sciences Department of Astronomy

Attendees: Pat Osmer, Bruce Atwood, Paul Byard, Dan Papallardo Darren DePoy, Tom O'Brien, Mark Derwent, Jen Marshall & Rick Pogge,

Optics

Darren DePoy visited Hextek at the end of January while on a run at MDM. Inspected and accepted the 4 slumped collimator mirror blanks Found a couple of issues having to do with with the depths of the mounting bosses on the camera primary blanks, Tom is working with Hextek to on this. There were no problems with the collimator blanks.

One of the camera primary blanks was cracked during slumping. Hextek is in the process of remaking that one. The other three were OK. Other gross dimensions and detailing of all blanks are fine. Some details:

• Collimator blanks have 5mm of sag as predicted. Look great, and are ready for shipping (some already packed). All we need is for the order to be cut to tell them where to ship them.

• Camera Primary blanks are from an f/1 parent, and have 34mm of sag. This is visible in the pictures (coming soon to this website).

Since Hextek isn't going to throw away the cracked camera primary, it may be useful as a mechanical sample for building the cells and testing our mounting fixtures. We need to ask how much, and have it shipped here.

Paul Byard has received test sample of NZK7 and BK7 glasses from Schott to test for the reputed high background rate of BK7. If we verify this, we will order from NZK7 from Schott for the red camera field flatteners. Problem is electrons from beta-decay of 40K (1.3MeV) when used as a vacuum window in front of the CCD, could be a real problem with thick CCDs for the red channel (still a problem for thinned CCDs).

Mechanical

Tom has assembled the first 3 tip/tilt actuators for the collimator mirror system. The collimator frame and cell support with actuators went together nicely last week. We are scheduling the shop to make another cell and a bunch more flexures for testing. The goal is to fully characterize the linear actuators to quantify repeatability etc. These are challenging because they are push/pull, so we can tolerate very little hysteresis in the system. Initial indications are good (hystersis is very small - virtually immeasurable). Our design is counting on these two commercial components (lead screw and harmonic reducer), and both look real good. We're hoping for few x 0.1-micron repeatability.

Tom is setting up the prototype collimator assembly to qualify the tip/tilt mechanism. Step 1 is to qualify actuators, then do optical evaluation in a full-up configuration of the platform and use source laser and a quad-cell receiver to do repeatability tests at highest level - all critical flexure and actuator issues will be revealed by these tests. Tests should start at the end of February and run thru March.

Mark Derwent reported on the results of tests of the prototype Filter Wheel assembly.

The first test went very well, basically the filter wheel is about as close to done as we can get. Mapped out sensors with a test setup. All went quite good. Designed cover to go over it (light shield). Will be getting gears anodized and will assemble a second one. A little re-work, changed margins on code bits. Mark added feature to make polarity of filter cells in the wheel more obvious (inspired by a compact flash card for an MP3 player). He does it with different length slots. This will prevent a person from accidentally trying to load a filter into the wheel upside down (e.g., relative to any bar codes or labels on the outer rim of the cell).

In-position, he tested for how much play there is in the system before you lose track, and how quickly it registers the fact that the whell is in position. The pause interval for the anti-bounce system looks to be 50 milliseconds.

Mechanical docking repeatability is about 5-10 microns (due to random noise in the detent bearing, and random runout in bearing). Should work very well. Everything came in right as calculated. All forces etc. right on. Should be a real sweet filter wheel mechanism.

In other work, the shop has finished the test grating cells. It was a tough part to fabricate, involving a lot of material removal, but going OK now. Will need to test with flats, flexures, etc. after they are done to qualify the grating mounting design. This needs to be done before we can finally order the gratings. Goal is to get these done now so we can initiate the R=2000 grating order. Flats have not come in from the vendor, delaying the tests.

Tom got a free bypass grating for the flexure compenstation system in a Nestle's Quick container. It was a free prize, a little treasure map including a cylindrical lens array with 3 lens/mm, which is a nice crude grating. We need 7 line/mm for our current FCS bypass grating design, but if we get time, we'll aluminize it and play with it and try out some ideas.

This Friday, the department lunch talk will be a general review of our instrumentation efforts for the department. Darren will give and overview, and Rick will follow with an update on the MODS project (an updated version of the December SAC presentation). A lab tour will follow afterwards.

The next meeting will be Feb 14 (Valentine's Day).

R. Pogge, 2002 February 28