hi, i am trying to use astap but no matter what i seem to try when i stack colour raw images, the resultant stacked file is greyscale. What am i doing wrong please?!
In tab alignment you have to check mark the option "Convert OSC images to colour". Prior to that you also have to set the debayer pattern correctly. Test one of the four debayer pattern with the test button. Han
I have one question. I use a Johnson V filter. But I don't understand how I can calibrate the fact quantum efficiency of my sensor could be different from a wavelenght to an other into this pretty broadband filter. Let's take an extreme example : if the filter transmission is from 500 to 600nm, equal transmission for each wavelenght. Let's take 5% quantum efficiency at 520nm and 95% at 580nm. Let's take 2 stars in this example : one is strongly emitting light around 520nm and the other one at 580nm. The fluxes are equal for these 2 stars between 500 and 600nm. But, I will find very different magnitud in V Johnson band because quantum efficiency are very different. I will find that the the star which emits light at 580nm is brighter. Maybe this is a parameter we can't controlate when doing absolute photometry and we accept the the quantum efficiency is pretty constant along the spectrum of my filter. Thanks by advance
The spectrum of stars is pretty wide. They emit in a spectrum from red to blue and your camera efficiency will be pretty constant in the range 500 to 600 nm. The algorithm works pretty simple. It measures for each star the ratio between the magnitude from the database and the measured star flux. From all those ratios is will take the median value (median not mean) and use that to calculate the magnitude of each object based on the measured flux. So it will use 10, 100 or 300 stars stars for calibration. Variable stars will be outliers and will not have any real influence. If you use the star database with the Johnson-V mangitude (now called V16 or V17) the accuracy is pretty good. Han
@@hank3327 Thank you very much for your answer ! We assume the efficiency is pretty the same all along the range. I didn't know your software, but it seems to be very efficient :)
In general the AAVSO want's to document for any report the reference stars used. So if a reference star has an updated magnitude, they can correct all reports. It's all a manual labor intensive operation. With Gaia stars with a magnitude value in unprecedented accuracy (error in milli magnitude), I'm of the opinion that this is no longer required. I assume many AAVSO members will disagree. This will takes years to change.
@@hank3327 Ok, I understand the problem. I think we can evaluate the best method by calculating type B uncertainty and yes, you're right, take the whole field of stars as reference is an unbeateable method...
Hello Hans, just to say i am learning this great and very powerful program. thankyou for all the videos you put up
hi, i am trying to use astap but no matter what i seem to try when i stack colour raw images, the resultant stacked file is greyscale. What am i doing wrong please?!
In tab alignment you have to check mark the option "Convert OSC images to colour". Prior to that you also have to set the debayer pattern correctly. Test one of the four debayer pattern with the test button.
Han
@@hank3327 thanks i will try
I have one question. I use a Johnson V filter. But I don't understand how I can calibrate the fact quantum efficiency of my sensor could be different from a wavelenght to an other into this pretty broadband filter.
Let's take an extreme example :
if the filter transmission is from 500 to 600nm, equal transmission for each wavelenght.
Let's take 5% quantum efficiency at 520nm and 95% at 580nm.
Let's take 2 stars in this example : one is strongly emitting light around 520nm and the other one at 580nm. The fluxes are equal for these 2 stars between 500 and 600nm.
But, I will find very different magnitud in V Johnson band because quantum efficiency are very different. I will find that the the star which emits light at 580nm is brighter.
Maybe this is a parameter we can't controlate when doing absolute photometry and we accept the the quantum efficiency is pretty constant along the spectrum of my filter.
Thanks by advance
The spectrum of stars is pretty wide. They emit in a spectrum from red to blue and your camera efficiency will be pretty constant in the range 500 to 600 nm.
The algorithm works pretty simple. It measures for each star the ratio between the magnitude from the database and the measured star flux. From all those ratios is will take the median value (median not mean) and use that to calculate the magnitude of each object based on the measured flux.
So it will use 10, 100 or 300 stars stars for calibration. Variable stars will be outliers and will not have any real influence. If you use the star database with the Johnson-V mangitude (now called V16 or V17) the accuracy is pretty good.
Han
@@hank3327 Thank you very much for your answer ! We assume the efficiency is pretty the same all along the range. I didn't know your software, but it seems to be very efficient :)
@@hank3327 If I understand well, your software choose hundreds of stars for calibration whereas other softwares like AIP4Win choose only two stars ?
In general the AAVSO want's to document for any report the reference stars used. So if a reference star has an updated magnitude, they can correct all reports. It's all a manual labor intensive operation. With Gaia stars with a magnitude value in unprecedented accuracy (error in milli magnitude), I'm of the opinion that this is no longer required. I assume many AAVSO members will disagree. This will takes years to change.
@@hank3327 Ok, I understand the problem. I think we can evaluate the best method by calculating type B uncertainty and yes, you're right, take the whole field of stars as reference is an unbeateable method...