Venus Amateur Observing Project
Venus is very bright, which permits very short exposures to be made in the visible & near infrared wavelengths with most telescope / CCD combinations. In the near UV, the combination of reduced CCD sensitivity and attenuation by the Earth's atmosphere requires longer time exposures. Nevertheless, exposures in the UV are typically less than 100ms for typical f-ratio used for planetary imaging.
The effective focal length of the instrument should be adjusted so that the image scale per pixel is approximately twice the resolution limit of the instrument (for example: if the resolution of the telescope is 0.5", then the image scale for pixel should be approximately 0.25"). The image scale can be calculated according to the following equation:
Alternatively, the actual image scale can be measured from the image (e.g. by dividing the number of pixels the planet takes up on the screen by the angular diameter of the planet). Typically to achieve the necessary image scale (generally between f/20 to f/40) a 2x to 3x telenegative Barlow lens is required.
The image exposure should be adjusted to ensure a good dynamic range, without saturating the image. The optimal settings for each filter combination will need to be determined experimentally and will vary depending on conditions (for example transparency). For example with a 235mm SCT at f/35 an ATK-1HS camera at 10fps required 1/25s exposure for U-band, and 1/250s for V-band images.
Imaging should ideally be performed under good seeing conditions, although routine monitoring even during poor seeing conditions is often sufficient to record major atmospheric features. Venus is bright enough be observed and imaged in daytime when the planet is generally at higher elevations than during nighttime. Care should be taken that the telescope does not accidentally point at the sun during daytime observing. However, daytime seeing conditions can often be poor, especially if the telescope tube is exposed to direct sunlight. Often around sunrise and sunset seeing conditions can often be good.
Prior to making routine observations the imaging setup for Venus observations should be optimised by experimenting with camera settings, filter combinations and focal ratio.
The observer should be familiar with planetary imaging their instrument and camera. Sky & Telescope magazine (http://www.skytelescope.com) has published several articles on planetary imaging that may be of interest to Venus imagers: