I just wanted to follow up on my question about Dark Frame Calibration for the QHY600 with overscan region. I suppose maybe their are two questions here,
1. Dark Calibration with just the overscan regions.
2. Dark Calibration with overscan regions and MasterDark, Bias frames.
Appreciate the support.
The overscan area used to do the "Overscan Trim" There is some topic on the basic concept of it , You can search "Overscan Trim" and you can find may useful infomation.
And Here I think we can simpfied it for astrophotograhy :
Calibrate results = (L-D)/(F-B)
L: LIGHT FRAME
D: DARK FRAME
F: FLAT FRAME
B: BIAS FRAME
and we always use the dark flat frame (DF) to instead of bias frame . so it is
The overscan calibrate is to correct the "base line" of a image, or we can say that each frame may has a drift . Ths drift can be regards as each pixel been add a constant. Ths constant is the same to all the pixel in one frame, But each frame the constant is not the same. If we calculate the average of the overscan area, we can get this constant of each frame. The goal of the calibration is to let each frame has the same constant .
And I think we do not need to do overscan calibraton for light frame and dark frame. Because they are in numerator of it. It will not cause any problem for astrophotograhy. (but for obsolutely meassurement it will cause something) . What we need to do is for the (F-DF) since it is in the denominator. So we must calbrate the Flat frame and Dark Flat frame to let same has the same constant (overscan value).
So the method is :
Get the master flat frame
get the master dark flat frame
Measure the average of the overscan area of the master flat frame and master dark flat frame. For example , the master flat is 500, the mast dark frame is 600. Then , you can add a constant 100 to the whole master flat . Then , the master flat 's overscan value will become 600. Then you can use (F-DF) to get the calibrated master dark frame.
Edited by QiuHY, 19 May 2020 - 12:38 PM.