My first experience with The Brain on Hydrogen Alpha

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oopfan
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My first experience with The Brain on Hydrogen Alpha

#1

Post by oopfan »

Hi Robin,

Last night I may have bitten off more than I could chew! I attempted to use The Brain with Hydrogen Alpha for the first time on the Crab Nebula with the Full Moon just one constellation away.

One big mistake I made with The Brain was not selecting a region devoid of stars and nebulosity. In other words I didn't read the "fine print" in the instructions. The result was that it used the entire frame so all I got was a lot of noise and the faintest hint of stars. For new users like me perhaps you could draw a default region if one was not previously defined just as a visual reminder that this is serious business.

So I ended up running The Brain twice which was a good learning experience to see the difference in recommended exposure settings. Both times it recommended a gain of 187. The exposure time increased from 21 sec to 41 sec after I properly defined the region. Good. The thing that I found a little troubling, however, was that the Black Level was zero. I don't know but I was expecting some sort of difference. I guess due the high level of "light pollution" generated by the Moon that no offset was needed.

Lastly, I had trouble with the "Display Histogram Stretch" tool on the control panel. (By the way this was with the Altair 290M camera.) I turned on the "stretch" so that I could better see the stars and nebula on each frame as it was collected. Later, after I brought my kit inside, I looked at the data and discovered that the stretched data was being saved to the FITS file. I could clearly see this in FITS Liberator, and with Star Tools complaining about giving it non-linear data.

I don't have the version number of beta SharpCap 3.1 with me right now, but it was the latest one as of January 2, 2018.

Thank you,
Brian
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Re: My first experience with The Brain on Hydrogen Alpha

#2

Post by admin »

Hi Brian,

thanks for the feedback - just tested and as far as I can see the display stretch is not affecting the saved files - please can you share one of your captured files with me so I can investigate.

cheers,

Robin
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Re: My first experience with The Brain on Hydrogen Alpha

#3

Post by oopfan »

Sure, there are two FITS files for a total of 8MB. Can I simply attach them to this post or is there a SharpCap dropbox that I can use?
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Re: My first experience with The Brain on Hydrogen Alpha

#4

Post by admin »

Thanks for sending the fits files to investigate. Both are 12 bit data scaled up to 16 bit (ie all data values multiplied by 16), which is what is expected - this means that all the pixel values in the fits files are multiples of 16.

In the first file, the maximum pixel value is 27000 odd, but there are only 3 pixels with a value above 2500, and only 100 pixels or so with values above 800.

In the second file, the maximum is only 2700, but aside from the missing 3 pixels with high values the distribution of the bulk of the pixels values is much the same.

When you load a file into FitsLiberator, it scales the histogram horizontal axis automatically between the minimum and maximum pixel values in the file, which explains the differences in look of the two histograms, but actually there is not much difference between the two images as you can see below (I set the black and white levels for both manually to 0 and 750 to give them an equal stretch in FitsLiberator).

cheers,

Robin
Capture.PNG
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