-
there is a tool in Tangra that allows one to extract a short video from a long one.
Tools –> ADV/AAV Tools –> FSTS File Viewer –> Tab “Tools”
-
How to define FITS timestamps in Tangra – QHY174M-GPS
Basically Tangra needs to know the header field for the “Date of Observation” and the format of this Date.
Choose “DATE-OBS” field of the FIT image and Tangra will show you this field bellow. Then you can compare the content of this field with the Format (where you can write freely.) Pay attention to the figures at right of the comma (decimals of second)
And choose the Type of time –> At Start, Mid or End of Exposure.
After Tangra needs to know the header field for the “Exposure Time” and the unit used (usually seconds).
- DARK , FLAT, BIAS…(going to calibrate PHEMU light-curve with Tangra and bias,dark, flat
frames.)
I would like to test bias, dark and flat processing with Tangra.
1- After the phemu recording with OccuRec, i record a short video with telescope covered. Have i to disable the time inserting ?
2- i record a short video with a halogen lamp in front of the scope + tracing paper. What about the video camera gain ? The same as phemu and dark video recording ? Is bias gain dependant ?
3- With Tangra, i load the dark video, then – > Reduction -> Produce dark, bias,… -> check Master bias and run “Produce averaged frame”
4- With the same dark video – Reduction -> Load calibration frame -> Master bias -> check Master dark and run “Produce averaged frame”
5-i load flat video, then -> Reduction -> Load calibration frame -> Master flat -> check Master flat and run “Produce averaged frame”
6-finally, i load phemu video and run the usual process ; does Tangra automatically use the 3 fit files (bias, dark and flat) ?
So i tried the following procedure :
1- With Tangra, i load the dark video by File -> Open video, then – > Reduction -> Produce dark, bias,… -> check Master bias and run “Produce averaged frame”
2- With the same dark video -> Reduction -> Load calibration frame -> Master bias -> check Master dark and run “Produce averaged frame” with 0.04s and 100 frames.
First of all, i don’t use flat correction as camera gain is not the same for phemu and dark videos.
3- Now i load the phemu video by File -> Open video, then i load the master dark by Reduction -> Load Master Dark.
4- I run the photometry process (AstroAnalogVideo-Dark) and get the light-curve.
Result : i don’t see any difference between the “raw” and “AstroAnalogVideo-Dark” light-curves…
5- Now despite the different gain of the flat video, i produce Master Flat (0.04s and 100 frames).
6- I run the photometry process (AstroAnalogVideo-Dark/Flat) and get the light-curve.
Result : Now the final light-curve “AstroAnalogVideo-Dark/Flat” is quite different, but is it a good one ??? That’s the question…
Odp Hristo:
If you are using same exposure dark frames you should be creating the dark frame as “Dark” rather than “Master Bias”. You should be then loading this dark frame as “Dark (Same Exposure)”. Loading ‘Master Dark” assumes that a bias frame has been already subtracted (which hasn’t been in your case). Using a “Master Bias” as same exposure dark would probably work as far as numbers are concerned but is otherwise incorrect procedure. I am in the process of preparing a guide about how to take and apply bias/dark/flat frames with video.
A flat field does not have to be with the same exposure time or gain as the science frame. Darks and flats have to be with the same characteristics. But if your flat field has different characteristics, then you will need a separate dark frame for your science frame and for the flat field .But I am surprised that when you divide by the flat field, the noise increases. Well, in reality the noise will increase, but the division by the flat field should remove something that in fact is not noise but does look like noise.