Using a QHY600M (16-bit) camera, I'm trying to do photometry using SharpCap with Gain=0 and Offset=10, and writing FITS files. A histogram of the ADU values in the FITS images shows that the ADU values in the pixels are being changed, i.e., "stretched" (for astrophotography folks). What SharpCap parameters must I set to ensure that the ADU values in each pixel remain unchanged, i.e. not stretched?
Under "Image Controls" I see parameters "Gamma", "Brightness", and "Contrast". Do these affect the ADU values in the stored FITS image?
Thanks,
Geoff
Photometry
Re: Photometry
Geoff
Under File > SharpCap Settings > General tab see:
Checking this should provide what you need.
The settings under 'Image Controls' only affect the displayed image and nothing from here finds its way into the FITS files. I fell for that one a long time ago.
Dave
Under File > SharpCap Settings > General tab see:
Checking this should provide what you need.
The settings under 'Image Controls' only affect the displayed image and nothing from here finds its way into the FITS files. I fell for that one a long time ago.
Dave
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Re: Photometry
Thanks. I tried checking that box, but it didn't help. The histogram of ADU values were still stretched. But I will try again, using a different Gain setting.
Re: Photometry
Geoff
I am sure Robin will be able to throw more light on this.
Dave
I am sure Robin will be able to throw more light on this.
Dave
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Re: Photometry
Hi,
if you already have a 16 bit sensor then that check box should be irrelevant, but do make sure you are capturing in MONO16!
Gamma, Brightness and Contrast should be left at default values (1.0, 0.0, 0.0) to avoid stretching. The same for the colour balance controls on a colour camera. You should be safe adjusting exposure, gain and offset.
cheers,
Robin
if you already have a 16 bit sensor then that check box should be irrelevant, but do make sure you are capturing in MONO16!
Gamma, Brightness and Contrast should be left at default values (1.0, 0.0, 0.0) to avoid stretching. The same for the colour balance controls on a colour camera. You should be safe adjusting exposure, gain and offset.
cheers,
Robin
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Re: Photometry
I use a QHY600M camera (16-bit) to take images that enable photometry.
1. I check that box about “Save 10/12/14 bit images in FITS files without scaling . . ."
2. I set "MONO16".
3. I set gamma, brightness, and contrast to (1.0, 0.0, 0.0), because Robin states it avoids stretching.
4. Set Gain = 0 and Offset = 0.
That Gain=0 gives Full Well = 51k e- and read noise = 3.7 e-.
(Alternative: At Gain=57, one gets full well = 23k but lower read noise of 1.7e-, useful for faint sky and objects.)
1. I check that box about “Save 10/12/14 bit images in FITS files without scaling . . ."
2. I set "MONO16".
3. I set gamma, brightness, and contrast to (1.0, 0.0, 0.0), because Robin states it avoids stretching.
4. Set Gain = 0 and Offset = 0.
That Gain=0 gives Full Well = 51k e- and read noise = 3.7 e-.
(Alternative: At Gain=57, one gets full well = 23k but lower read noise of 1.7e-, useful for faint sky and objects.)