8 replies to this topic

[tfulks]

Say you're imaging a Broadband Target with a OSC camera and using a Broadband filter or an SII+OIII filter. When doing calibration frames, do you capture your calibration frames with the filter in or not? If so, which calibration frames require the filter and which ones can be acquired without the filter?

[Dynan]

Your flats need the filter. No others.

[Jim Waters]

Flats - The optical train must remain intact when taking Flats.  All filters must remain in and at the same focus point used during imaging.

Darks - Just cover the opening of imaging camera (see below).

BIAS - Just cover the opening of imaging camera and take as fast an exposure that you can.

 

My Dark library for -15c, -10c, 0c, and 10c

• 30 seconds
• 60
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Welcome to Cloudy Nights.

[tfulks]

Thank you for the info, much appreciated.

[PirateMike]

To add to the topic...

 

Flats... should also be taken at the same camera rotation, and should be taken anew at imaging every session. Some cameras don't like very short exposure times, some others don't mind. I always try for 3 seconds.

 

Darks... are good for quite a long time, maybe three months or more. A library can be made (as Jim Waters suggested) of all the expected exposure times and temperatures.

 

Bias... some cameras don't like very short exposures, just like flats. I don't use bias frames anymore.

 

Dark Flats... these should be taken at the same time and temperature as your regular flats, but without any light getting to the sensor.

 

This might help you understand frame calibration better... https://www.youtube....&index=3&t=584s

 

 

Pirate Mike

 

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Edited by PirateMike, 12 May 2025 - 09:36 PM.

[tfulks]

TY Pirate Mike, much appreciated.

[bignerdguy]

To add to the topic...

 

Flats... should also be taken at the same camera rotation, and should be taken anew at imaging every session. Some cameras don't like very short exposure times, some others don't mind. I always try for 3 seconds.

 

 

Pirate Mike

 

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To add to this, short exposures don't work well for flats, especially if you use an LED light source.  This is because the LED is pulsed due to the way they are powered and not steady so at extremely short exposures you can actually get varying ADU levels for each sub exposure which will throw the flats off.  Best solution is to reduce whatever light source you use to a low enough level that you can take a 1-3 second image and get the ADU where you want it in that time.

Dark-flats or bias frames are needed as the Flats need to be calibrated to remove any pedestal to prevent negative values for pixels, If you don't the flats wont work correctly.  Bias frames are taken at the shortest time possible for a given camera exposure and yeah, some cameras don't do well on such short exposures.  Best option is Dark-Flats.

[AstroFromHome]

To add to this, short exposures don't work well for flats, especially if you use an LED light source.  This is because the LED is pulsed due to the way they are powered and not steady so at extremely short exposures you can actually get varying ADU levels for each sub exposure which will throw the flats off.  Best solution is to reduce whatever light source you use to a low enough level that you can take a 1-3 second image and get the ADU where you want it in that time.

Dark-flats or bias frames are needed as the Flats need to be calibrated to remove any pedestal to prevent negative values for pixels, If you don't the flats wont work correctly.  Bias frames are taken at the shortest time possible for a given camera exposure and yeah, some cameras don't do well on such short exposures.  Best option is Dark-Flats.

They work well with IMX571 sensors. The frequency of the LED Panel just needs to be high enough that sub-second flats don't Show any flickering effect.

 

Depending on the camera either Bias or Dark-Flats work better to calibrate the flat frames.

 

I would have expected the question of the topic starter more in the Beginning Deep Sky Imaging forum.

[MichaelACG]

Flats - The optical train must remain intact when taking Flats.  All filters must remain in and at the same focus point used during imaging.

Darks - Just cover the opening of imaging camera (see below).

BIAS - Just cover the opening of imaging camera and take as fast an exposure that you can.

 

My Dark library for -15c, -10c, 0c, and 10c

• 30 seconds
• 60
• 90
• 120
• 180
• 240
• 300
• 360
• 420
• 480

Welcome to Cloudy Nights.

My understanding is

• Darks: Also per gain/offset ... if you use different gains/offsets.
• Bias: Must be also per temperature. And per gain/offset, if you use different gains/offsets.