Image calibration frames for ASI224MC

[barbulo]

Hi everyone,

I know this is recurrent topic but as it happened to many others, the more I read about, the more confused I am.

What I (think I) know so far:

• My camera (ZWO ASI224MC) is designed for planetary image. However, I’ve read that it works fairly well with DSO.

• Image calibrating makes no sense for planetary imaging but does for DSO.

• Different types of cameras requires different calibration images sets. I’ve read about Darks, Flats, Bias and Flat-Dark.

What I surely don’t know:

• What kind of calibration frames does my camera need?

• Do I need to introduce any software into my current workflow? For planetary I am using PIPP – Autostakkert – Registax – FITSwork – PS.

Further question will arise after your kind and patient answers.

Thanks in advance.

[vlaiv]

11 minutes ago, barbulo said:

Image calibrating makes no sense for planetary imaging but does for DSO.

It does make sense for planetary imaging as well. If you want the best results - you should also do calibration frames for planetary imaging.

12 minutes ago, barbulo said:

What kind of calibration frames does my camera need?

Calibration is always the same - you want to remove any signal that is due to characteristics of the sensor and telescope and leave only light signal.

As minimum set of working calibration frames I suggest you use:

- darks

- flats

- flat darks

13 minutes ago, barbulo said:

Do I need to introduce any software into my current workflow? For planetary I am using PIPP – Autostakkert – Registax – FITSwork – PS.

No, PIPP handles calibration for you.

You shoot those - the same way you shoot your planetary video - as a video, except:

- darks need to be of same exposure length and settings as your lights (don't forget to cover the scope for these - they must be dark - so without any light)

- flats need to hit 75% of histogram - so adjust your exposure length accordingly

- flat darks need to match your flats in settings and exposure length and also be taken in darkness (covered scope)

 

[michael.h.f.wilkinson]

In my experience, flats are far more important than darks in planetary imaging, except in one or two older image sensors which showed clear pattern noise (ASI130MM, I am looking at you). Bias frames tend to be enough in most cases, and even those add relatively little. If the flats need longer exposures (as they do when I use a flat panel), then it makes sense to take dark flats at the same exposure time as the flats. I always use AS!3 to create both flats and dark flats for planetary imaging. The trick is to make the dark flats first, then load the resulting dark flat, to make dark-current-corrected flats. I then unload the dark flat, load the flat, load either the regular dark or bias frame as needed, and process the lights.

 

[barbulo]

Thank you @vlaiv and @michael.h.f.wilkinson
Clear that I need calibration for planetary imaging.
Clear that I need Darks, Flats and Flat Darks (I understand for both planetary and DSO).
Clear that I can use PIPP for that purpose.
I understand the settings explained by @vlaiv, but when I tried to decipher @michael.h.f.wilkinson's trick I got very confused. If I have to make the Flats based on the histogram, maintaining the same setting of the lights (included gain I suppose) and  adjusting the exposure time, and then take the Flat Darks with that same settings, how could I take the Flat Darks first? 

 

[vlaiv]

8 minutes ago, barbulo said:

I understand the settings explained by @vlaiv, but when I tried to decipher @michael.h.f.wilkinson's trick I got very confused. If I have to make the Flats based on the histogram, maintaining the same setting of the lights (included gain I suppose) and  adjusting the exposure time, and then take the Flat Darks with that same settings, how could I take the Flat Darks first? 

I think suggestion has nothing to do with recording time - it has to do with processing time and creating of masters - in which order to create those.

[barbulo]

16 minutes ago, vlaiv said:

I think suggestion has nothing to do with recording time - it has to do with processing time and creating of masters - in which order to create those.

Now it makes a bit more sense to me.

 

3 hours ago, michael.h.f.wilkinson said:

The trick is to make the dark flats first, then load the resulting dark flat, to make dark-current-corrected flats. I then unload the dark flat, load the flat, load either the regular dark or bias frame as needed, and process the lights.

However I am still a bit lost in the calibration frames processing procedure. Those frames I took go directly to the respective tab in PIPP or I have to create the masters. How?

[michael.h.f.wilkinson]

23 minutes ago, barbulo said:

However I am still a bit lost in the calibration frames processing procedure. Those frames I took go directly to the respective tab in PIPP or I have to create the masters. How?

I don't use PIPP except for doing a pre-selection of lights. I do everything in AS!3. If I have dark/bias frames, I first load the appropriate SER or AVI, and stack that as a dark (using the image calibration pull down menu), then do the dark-flats, then load that as a dark reference in AS!3, then select the flats and create a flat reference with that (which will be corrected for dark current because the dark-flat reference has been loaded). I then unload the dark-flat reference, load the dark/bias reference (if I have one), and load the flat reference I have just created. Then I stack the lights. This is roughly my work flow for lunar and solar. 

Again, for planetary work, even flats are not always needed (as log as there are no dust bunnies over the planet), and the following images were obtained with an ASI224MC without calibration

For DSOs I would not use PIPP or AS!3, but Astro Pixel Processor. Which got some nice results with the ASI178MM I have used, in combination with a filter wheel

and just a monochrome M51

 

[barbulo]

Thank you very much @michael.h.f.wilkinson for your advise.

Your examples look awesome and are very stimulating to me.