By Tony George for 2013 IOTA Conference

Issues:  Many IOTA members are purchasing integrating CCD video cameras to expand the range of occultations they can observe  CCD video cameras have a variety of ‘settings’, not all of which are appropriate for getting good video data  Establishing a set of ‘guidelines’ will help IOTA members get the best possible results from their integrating CCD video camera observations

Cameras most commonly used:  WAT 120N+  PC165DNR  Mintron  Mallincam Note: It is the observers responsibility to understand the operating characteristics and controls of their camera. Too many times we receive videos with compromised data due to incorrect settings or operation. If in doubt, ask for advice from experienced observers prior to your observation.

Important settings:  Shutter – fast and/or slow  Gain – manual and/or automatic  Gamma – off/LO/HI (if applicable)  Color mode (if applicable) – B/W or color

WAT 120N+ Control Box

PC165DNR Control Menu

Shutter (integration) guidelines:  Operate the shutter at the fastest possible speed setting necessary to get a ‘stable’ target star image. The target star doesn’t have to be constantly visible if there is atmospheric instability, but it should only blink out occasionally. Operating at the fastest possible shutter speed gives the best time resolution for disappearance and reappearance timing, as well as for capturing other photometric phenomena such as double star step events

Shutter (integration) guidelines (cont.):  Avoid sub-frame shutter speeds. Some cameras allow a setting that will give exposures at less than 1/60 th second. Observers have used short-speed settings to reduce star brightness. However shorter exposures give no information during the field when the shutter is closed and valuable timing information can be lost. The fastest setting that should be used is 1/6oth setting (field level timing).

Shutter (integration) guidelines (cont.):  Operate the shutter in ‘manual’ mode. Some cameras (Mallincam) adjust the shutter speed (integration rate) automatically if not set manually. This is very problematic for the proper analysis of the light curve.

Gamma guidelines:  Gamma is the relative brightness of faint objects compared to bright objects. No gamma means that the relative brightness is ‘linear’, which is preferred for observations where relative magnitude photometry is an important objective – such as NEO photometry  Cameras with manual gamma settings should be set to gamma off (1.0 gamma) as a first choice. This gives the best photometry for analysis of the light curve.  WAT 120N+ can also be set to gamma LO (0.45) or gamma HI (0.35), if needed to enhance the visibility of the target star for a given shutter setting.  Use the combination of gamma and shutter speed that gives a stable target star image (if possible) at the fastest possible shutter speed.  Don’t set gamma off if it means you have to integrate at ¼ second, if instead you can set gamma HI and integrate at 1/30 th second.

Gain guidelines:  Cameras with manual gain control should be operated in manual mode.  Set gain to MAX to allow using the shortest possible shutter (integration) speed  Use gain control (adjust downward) to reduce target star brightness to avoid image saturation if the shutter is already set as fast as possible (1/30 th second)  Mallincam AGC should always be OFF. This camera allows for variable shutter settings under AGC and therefore proper event timing cannot be assured when analyzing the light curve.

Color mode guidelines:  B/W cameras are preferred over color cameras. On-chip resolution is better. Photometry is better. If color information is desired, filters should be used.  Color cameras, if possible, should be set to B/W mode.  Recording in color can result in odd results when the data is captured to a PC, as some capture programs only capture one of the three color channels

Observation object guidelines:  Asteroids: events are typically short – maximum time resolution is preferred – use lowest possible shutter speed consistent with getting a stable combined asteroid+target star image – asteroid does not need to be visible.  Lunar double star: step events are expected – maximum time resolution is preferred – use lowest possible shutter speed.  TNO’s: events are typically longer duration – target stars are typically faint with the TNO even fainter – use integration as needed to get stable combined TNO+target star image – TNO does not need to be visible.

Conclusions:  Integrating CCD video cameras allow IOTA observers to attempt a broader range of event magnitudes  Proper camera settings are important to getting good light curves  Use of these integrating camera guidelines will help to get the best possible light curve  If in doubt, ask an experience observer for advice before investing time and energy into your observation