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

Attendees: Darren DePoy, Mark Derwent, Tom O'Brien, Ed Teiga, Paul Byard, Carrie Lewis, Abiye Lakew, & Rick Pogge

Paul Byard gave a brief report on revised predictions of the image quality of the MODS blue camera. The new calculations are based on inputing the measured surface error maps from SOML and Sagem/REOSC for the completed optics (collimator and camera primary mirrors, and corrector lens). Code-V uses these data under the assumption of perfectly aligned optics to compute D80 values for imaging and spectroscopic modes at various wavelengths.

The Collimator mirror wavefront error is so small (+/-0.07 waves rms) that omitting it from the models makes no measurable difference, so in the interests of computation time it is left out and he can treat the collimators as essentially perfect optics.

When the measured camera mirror and corrector errors are put in, the blue channel performs to our original specification with no noticeable degradation.

Using LightTools, Paul used the Code-V results to simulate monochromatic slit images at various wavelengths, but only on-axis due to the computation time constraints. Wavelengths covered 340-500nm, the nominal working range of the blue camera. Overall, the results are very promising, and MODS will be an excellent Blue/UV spectrometer.

This experience suggests that this is an excellent way to evaluate the optics when completed pieces are ready for acceptance by the project. Of course the models are only as good as the inputs, so some questions remain about how we validate the error maps we receive from the vendors. Paul did not generate spot diagrams for assessing off-axis performance, but will do this for subsequent iterations.

Taking the current results at face value (using data provided by Steve Miller), it looks like the blue optics for MODS are very close to completion. There is still finishing work to be done on the blue corrector lenses, but the camera primary looks like it should be ready for negotiating the final acceptance. Paul will continue working with Steve Miller at SOML on this.