Dragscript for acquiring flats

I’ve been trying to come up with a good way to acquire flat frames for my CMOS camera. I used the Voyager flat wizard to determine appropriate exposure times for each filter. To calibrate out the amp glow, I separately created a master dark for each exposure setting. Since I have a portable setup, I have to take flats at the beginning of each night.

Voyager has made this really easy and convenient: I’ve written a dragscript that cools the camera, opens and turns on the flat panel, acquires flat frames, and then turns off and closes the panel. I kick off this dragscript at the beginning of the evening, just before I start the main imaging sequence. All of this is working great.

But there’s one minor issue: I like to put each night’s flats in a separate directory, which makes it easier to keep track of the files. Currently, the exposure block in the dragscript stores the flats in a folder that reflects the current date, but this requires me to edit the dragscript at the beginning of each session.

Is there a way to avoid editing the dragscript? I couldn’t see a way to generate folder names from the current date in a dragscript. Is that possible?

One alternative would be to write a sequence for the flats, since I can save files in a folder with the current date from a sequence. But from what I understand, this would require creating a sequence with a dummy target, and is generally not the preferred way to take calibration frames with Voyager.

Does anyone have a suggestion for a better solution?

Thanks,

  • Rajeev

I do this from a DragScript by running an Auto Flat sequence.
Check the box that says “Create Logical Data Subfolder…” under the Flat Base Directory field.
This will create a new folder named with the date of the evening you started imaging.
https://voyager.tourstar.net/index.php?title=OnTheFly#Taking_Automatic_Flats

Cheers,
Rowland

Hi, Rowland,

Thanks for the suggestion. But Auto Flat computes exposure from the median values in the image, right? So the exposure times would vary each time? From my CMOS cameras, the only way to properly calibrate out the amp glow is to avoid dark scaling, so I need matching darks. So I used Auto Flat once to figure out the exposure settings that give me a good median value, for each filter. That way I use the same exposure settings each time, so I can reuse dark frames for calibrating the flats.

Cheers,

  • Rajeev

Sorry Rajeev, but i used a different ASI camera for some targets , i done flat with skyflat and i dont found problems on calibrate the target data. Dark scaling for flat is not a real problem and i used only bias. Anyway you can use min and max exp really closest or equal in autoflat sequence just use a tollerance that avoid mean reject.

All the best
LO

Hi, Leo,

Oh, great - that looks like it should work. Thanks. I’ll try it out,

Cheers,

  • Rajeev

Hi, Leo,

A quick update: I tried Leo’s solution (creating an AutoFlat sequence with min=max=injitial exposure, and setting a high tolerance, and it works great!).

Thanks for the suggestion,

Cheers,

  • Rajeev

Great news Rajeev

All the best
LO