Thu, 08/06/2015 - 18:34
Hi,
in the beginner spreadsheet of Citizen Sky, the calibrated magnitude for the check and target stars are calculated using the parameters (slope, intercept) obtained from only one image.
Then, if I have a set of images, I must measured the instrumental magnitude for all comparison stars from only one image, while for the other images I must measured only the instrumental magnitude for the check and target stars.
Is it right?
Regards,
Luigi
Hi Luigi,
In any case Comp, Target, Check shall be measured in the same image or in the same stack of images. If not any extinction difference between images will generate a systematic error. But the color transformation coefficient could be calculated only one time if the observation conditions are the same, high in the sky. This is maybe the reason for such confusion, but I do not remember the details of that spread sheet.
Clear Skies !
Roger
Hi Roger,
excuse me, but I want be sure that I have understood well.
For example, I take a series of images, say 30, of the same field. Each image has an exposure time of 10 s. Then I stack them in groups of 6. So, at the end, I have 5 images. The interval between the beginning and the end is about 10 minutes, sometimes even 15 minutes, because, during the exposure, I have to adjust the tracking as the camera is mounted on a tripod.
At the first, I though it was necessary to measure the instrumental magnitude for the comparisons and target in all 5 images, doing a separate best fit for each image. Surely this required much work because I have to measure comparisons, check and target in each image. Instead, in the spreadsheet (beginner and intermediate) of Citizen Sky, the best fit is made for only one image (say the first image) and then I have to measure comparisons just once, while for the other images I have to measure only the check and target star.
Do you think that, during the 10-15 minutes, the observation conditions may be supposed constant?
Regards,
Luigi