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Aurora Flatfield Panel help !!!


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Hi all.. not really sure if is the right section for this topic so please if you could point me to the right direction would be much appreciated  :)

 I'm quite new to astrophotography and not to technical processing and dealing with programs ...   I'm using  a 4" refractor on a Heq5 pro mount and a Atik 460ex color camera with the Artemis Capture Software provided with the camera . I was advice to do flats ,darks and bias to improve my images and that's why recently i bought a Aurora Flatfield Panel ( seems that my camera does not need darks ) and i would like to ask other users who might have the same camera as me how many seconds should i aim,for perfect flats or bias  ? Any help on would be greatly appreciated.

thx Dan

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For the bias you want as short an exposure as possible so that there is no time for any 'dark' noise to build up and you're only getting the 'readout' noise from the camera, I believe 0.001s is the shortest you can go on the 460ex.

For the flats you want the histogram peak to be about 1/3 to 1/2 way across, about 20000 - 30000 ADU. It's not critical, you just want the edges of the histogram peak to be well away from the top or bottom clipping point. You want the exposure to be short enough that 'dark' noise is insignificant but long enough that any flicker or other effects on your light panel don't cause a problem. Aim for around 0.5 seconds or so. If your image is overexposed at that exposure put some sheets of white paper in front of the light panel to reduce its intensity.

You might think that when putting sheets of paper in front, it's no longer an 'even illumination' light source as the grain of the paper is visible, but at that distance the paper is so out of focus on the sensor it's not a problem. :smile:

You're right in that it's not necessary to take darks for the 460EX. Use your 'bias' as a 'dark' when calibrating your images.

Alan

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Thx for the quick reply Alan ... So 0.5 seconds should be fine .... not really sure what ADU means but I will google a bit when I have the chance ?. I’m using pixinsight for processing and I’ve seen on a tutorial that 100 frames  each ( bias and flats) should be enough to create a master file is that right ? 

I just uploaded one of my recent target and  not sure why there’s a bright circle probably because I used a reducer I was told that flats should eliminate that so I’m looking forward to test and come back with the results. Thx again Dan 

2D3F7752-0B40-4573-8663-25EF7A442AEA.jpeg

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ADU means 'Analog Digital Unit' (US spelling of analogue is the norm in this context) and refers to the smallest digital division that your analog signal voltage (as read from the CCD pixel 'well') can be converted into. The 460ex is a 16bit camera so the digital value of each pixel can be one of 2^16 or 65,536 states (actually 0 to 65,535). They used to be called 'bits' or 'LSB' (Least Significant Bits), but that was confusing so ADU is now commonly used. So 20,000 to 30,000 ADU is roughly one third to one half 65,535. :smile:

100 bias and flats is certainly a good number to take, the more the better, although the actual improvement in signal to noise gets less and less the more you take until it's not really worth taking any more. I've found that 40 flats is sufficient though other people will have different opinions. As the bias images can be taken very quickly 100 is no problem.

I'm sure you know but when taking the flats ensure all the elements in your imaging train haven't moved since you took you 'lights'. Camera still in the exact  same position and focus still at infinity so that your vignetting areas appear in the same position as your 'lights'.

The darker outer ring has quite a distinct outline, so the vignetting source causing it is fairly close to your sensor  so the Reducer is a good bet. And yes the flats you take should remove that no problem. Good luck with your processing Dan. Your image even without flats or bias looks pretty good. :thumbsup:

Alan

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