Quote:
Originally Posted by gb44
Thanks for the tip Leo. I got one so I can replace the bulky lightbox I,ve made years ago.
It works well for my 12inch Meade. I was easily able to get the right histogram in SharpCap and the APT flat aids routine went smoothly.
I have one area of concern. The white balance is very different from my previous light box where G was dominant. This pad gives a B dominant histogram.
I can adjust the WB balance in SharpCap but not in APT. I dont know if I need to adjust the WB either. WHat do I do?
TIA
GlennB
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Glenn,
I’m assuming you’re using a OSC camera to take Flats with the new LED light pad ?
Don’t worry too much about colour balance or white balance as all LED panels emit different wavelengths of colour depending on the configuration, the coatings on the RGB leds and the driver that’s controlling them, some more towards the blue spectrum and some more towards the red spectrum.
Ideally you want an LED light panel with a colour temperature around 6500K to 8000K so in essence Daylight. Also a colour rendering index (CRI) of at least 80 to 90 to ensure an even spread of light source.
As long as you expose your Flats long enough so your 3 peaks are off the left side of the Histogram and right side towards 1/2 way then you should be Ok
Also take at least 20 to 40 Flats when using an LED light pad as some do oscillate ( flicker ) at low brightness levels due to Pulse Width Modulation control. When stacked any minor banding will be eliminated even at short exposures of 0.1 sec. This slight flicker or oscillation cannot be picked up by the human eye.
I found that another layer of opal acrylic diffusers taped to the light pad worked much better than a white T shirt for diffusing the light slightly especially at when you require lower brightness levels.
Your stacking software should take care of the background, I know DSS and ASTAP does it automatically for you. I suspect APP , Pi also takes care of your background as well.
I use APT ( CCD Flats Aid ) to take Flats with my ZWO 2600 series cameras
For my OSC 2600MC camera
Broadband ie: only with internal UV/IR cut window my Target ADU is set to say 20,000 which generally gives me a Histogram range ( 3 peaks ) of 8000 to 33,000 at an exposure of between 0.15 sec and 0.9 sec. I just adjust either brightness on the light pad or adjust target ADU or both to achieve this result.
Narrowband ie: L Extreme or Antlia ALPT dualband filter again my Target ADU is set to 20,000 which generally gives me a Histogram range ( 3 peaks ) of 8000 to 33,000 at an exposure of between 2 sec and 5 sec. I adjust either brightness on the light pad or adjust target ADU or both to achieve this result.
For my Mono camera 2600MM I stick to the above scenario but the Target ADU’s and brightness levels on the pad differ greatly from filter to filter to achieve similar results. Target ADU’s can be from say 18,000 to 26,000 depending on filter
I still try to achieve flats exposure times of 0.15 sec to 0.9 sec for Luminance, Red , Green and Blue filters and flats exposure times of 2 sec to 5 sec for Ha , Oiii and Sii filters
ZWOASI2600 series cameras have a 16bit ADU which equates to ( 2 to the power of 16 = 65,536 then divide by 2 or 50% ) = 32,768 ADU which is your maximum ADU range or roughly 1/2 way along the Histogram
NB: I found that if I start with a Target ADU in APT between 20,000 and 22,000 ADU this works best for starting the search for the correct exposure times.
The above settings and results are based on the ZWO 2600 series cameras and my Newts. You have to customise settings for your particular camera.
Also all Flats for all filters have same Gain and Temperature as my Lights.
I calibrate my Flats with Flat Darks ( gold standard ) however Bias work as well and use Darks to calibrate my Lights , so full calibration suite.
I’ve used the A3 Huion and Huion A2 dimmable light pad for over 4 years now and never had an issue with Flats.
Hope the above information helps
Cheers
Martin
