American Association of Variable Star Observers (AAVSO)
Fri, 03/29/2024 - 17:30

OC61 is the 24-inch telescope at Mt. John University Observatory, New Zealand (South Island) that we run in partnership with the University of Canterbury.  Mt. John can have some spectacular seeing conditions and is very dark.  It also has a lot of cloudy or windy weather.

Recently, we upgraded OC61 with a new QHY600 camera and a new control computer.  It has been having startup problems, with details given below.  We apologize to researchers obtaining images from OC61, and ask that you bear with us through this period.


While the QHY600 is a 61Mpix camera, we operate it in 4x4 binning mode, so the images are about 4Mpix in size.

New images with the QHY600 started on 2024/02/03.  Unfortunately, Walt Cooney has found that the darks used to process images from 20240203 until 20240323 were taken with the wrong camera gain and offset values.  We've obtained new darks with the correct settings, and will be reprocessing the images in this period.  You will get new images loaded into VPHOT or the ftp site, along with notifications as they become available.

The new camera has a reduced field of view.  The original camera was 14x14arcmin; the new camera is 14x9 arcmin.  For most projects, you will still have sufficient comparison stars, but you may wish to request a new field center to pick up additional ones as needed.

The new camera is causing problems with plate solving.  We're still trying to find the right balance of star density in the astrometric catalogs to solve these images reliably.  Not only do you have fewer images with WCS in the FITS headers, but on many occasions, the telescope does not blindly point well enough and your target may be out of the field of view.  The obvious solution is to put a focal reducer into the system, which we are considering.  There are no focal reducers on the market with sufficiently large field of view and that work with f/15 beams.

During the period 20240311-20240315 inclusive, the filter wheel malfunctioned.  This is demonstrated by a peculiar background on all images, caused by an error condition LED on the wheel.

The mount continues to have an RA "flop", where some images, especially the first after a slew to a new field, will have barbell-like stars because the mount is moving between two positions.


I am in the process of sending new science and guide cameras for the eShel spectrograph.  Along with its focal reducer, we should be able to go much fainter with this spectrograph.  A group of Australian/New Zealand amateurs have offered to test and commission the spectrograph.  I'll pass along details when it is sufficiently stable for accepting observing proposals.

I'm very sorry for the problems with OC61, and even more sorry for not communicating the issues sooner.  I'll try to do better in the future.