EXPOSURE DATA

Exposure data details the number of exposures and duration of each exposure for each filter used to create a final image. The data are in the form of:

• filter code ‘:’ exposure count ‘x’ exposure duration ‘;’

As an example, [L:30x30s; TR:30x30s; TG:30x30s;TB:30x30s] would indicate an image consisting of 120 exposures with 30 luminance exposures at 30 seconds each, thirty red exposures at 30 seconds each, and so forth. This combination is known as LRGB imagery. The luminance exposures provide the brightness, contrast and detail. The color exposures provide the color. Typically, most of the available exposure time is dedicated to the luminance exposures. It is also quite common for the color exposures to be taken at a lower resolution.

If the exposure data is prefaced with a “(V)” the camera used was a video camera. Bright objects (Moon, most planets, the Sun, etc.) allow the use of high frame rate video cameras. This allows me to capture many hundreds or thousands of exposures. Software can then analyze the video stream and rank each exposure for sharpness. By using only the best exposures, the affect of atmospheric distortion can be minimized. The quality of the focus and atmosphere determines what percentage of the individual exposures are used to construct the final image.

The following standardized codes are defined by the AAVSO and, although somewhat cryptic, are necessary due to some software processing packages needing the codes instead of a more readable name.

The filters and associated codes that are available for my images are:

• TR – (Tri-color red) Red channel in a DSLR or color CCD camera.
• TG – (Tri-color green) Green channel in a DSLR or color CCD camera.
• TB – (Tri-color blue) Blue channel in a DSLR or color CCD camera.
• CV – (Clear) No filter used.
• L – (Luminance) This filter passes all the above color range but blocks near-infrared and ultraviolet.

• B – (Johnson blue – 445 nm) Broadband photometric filter.
• V – (Johnson visual – 551 nm) Broadband photometric filter.
• R – (Cousins red – 658 nm) Broadband photometric filter.
• SG – (Sloan green – 475 nm) Broadband photometric filter.
• SR – (Sloan red – 620 nm) Broadband photometric filter.
• HA – (Hydrogen Alpha – 656.28 nm) Narrowband filter. This frequency is emitted by ionized hydrogen which is common in nebulae or on the surface of the Sun.
• UV*- (Ultraviolet – 325-381 nm) Broadband filter. This filter is used primarily to image detail in the cloud tops of Venus.

• F* – (Full color) Technically, not a filter. This image is full color without the use of filters. This code will apply to cameras such as DSLRs that take full color images in one step.
• M* – (Monochrome) Technically, not a filter. This image is taken by a full color camera without the color information applied. This code will apply to cameras such as DSLRs that take full color images in one step.
• D1*- (≈325-800 nm) 100 lpi diffraction grating. This device produces a low-resolution spectrum.
• D2*- (≈325-800 nm) 200 lpi diffraction grating. This device produces a low-resolution spectrum.

* – Not a standard AAVSO filter code.