Having just returned to Astro Imaging, after being out of the hobby for eight years, I find that things have moved on with both hardware and software.
After 12 years of imaging with a variety of Starlight Xpress CCD cameras, CMOS now seems the be the defacto standard, and introduced the need to set things like Gain and Black Level.
This is where confusion creeps in, as different software packages use different numbers, to represent the same setting level.
In the case of Sharpcap Pro, the Gain Setting scale goes from 0-72000, whereas in Astroart, and others for example, the scale is different.
The same goes for Black Level, in Sharpcap Pro, it goes from 0-1984.
I have an Altair Hypercam 294c, and its has been suggested that the Gain setting is in the order of 450, and the Black Level 30, but do these numbers relate to Sharpcap?.
I am used to working with FITS files, and to save captures in FITS format, requires the LX Mode to be 'ticked'. What doe LX Mode mean in Sharpcap?. I had a variety of Meade LX series SCT's over the years, is Sharpcap's LX Mode related to these?.
Finally. the 294c camera is USB 3.0 enabled, but in Sharpcap, the USB speed only goes up to 2.0.
Apologies for the number of questions, but I would like to understand the software better.
Dave
Settings in Sharpcap Pro
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Re: Settings in Sharpcap Pro
Hi,
yes, unfortunately gain is a bit confusing as each camera manufacturer has dealt with it differently. To begin with, I just made SharpCap use the same values that the camera manufacturer uses, although now I do try to standardise for new brands of camera (I don't change how the gain works for existing brands as that risks confusing existing users).
Right... Altair camera gain - This is expressed as a percentage of minimum gain, so it starts at a minimum of 100 and goes upward. 200 gain is 2x as bright as minimum (100). 400 gain is 4x as bright, etc. 72000 gain is 720x as bright! In some other applications, the gain for Altair cameras is given in a range that starts at 1 for minimum gain - that would have a range of 1-720 corresponding to SharpCap's 100-72000.
Other camera brands use gain values that are measured in dB or 0.1 dB. Some brands have gain values that have no true meaning - they are just numbers. Some brands have variations from model to model, which is even worse... At least Altair is consistent across all models!
Black level - this just offsets the image pixel values upward by a constant amount. It's best set by trial-and-error. Setup your camera for exposure, gain, temperature, etc and then take dark frames (of the duration you intend to use) in the highest bit depth mode. Show the histogram then turn up the black level just enough to make sure that the histogram peak is just separated from the left hand side of the graph (practically no pixels at zero pixel value).
LX mode (long exposure) - in SharpCap this just changes the range of the slider for the exposure - with it checked the range is from 1s up to the camera maximum. With it unchecked the slider runs from the camera minimum exposure up to 5s. The reason behind this check box is that it is dreadfully difficult to control the exposure correctly if the slider goes from 0.1ms up to 1000s. Just to make it clear - this tick box does nothing to the camera, just changes the range shown in the UI. You can get FITS images at 100ms exposure if you want - just turn off the option for auto selection of output format and select the output format manually - see https://docs.sharpcap.co.uk/4.0/#!2!Cap ... and%20Area, https://docs.sharpcap.co.uk/4.0/#Configuring%20SharpCap
USB - the value of zero to two for the USB speed is not related to USB2/USB3 - instead it is an arbitrary number that controls how hard the camera will try to get maximum data rate through the USB system. Turning it up will usually increase frame rates for high speed imaging, except when sometimes turning it up too high will stop the whole camera working - see https://docs.sharpcap.co.uk/4.0/#Altair ... 20Controls
Finally, recommended gain... With the 294C you may wish to consider gain 900 as a starting point - at gain=900 the camera switches mode from 'low conversion gain' (gain <900 in SharpCap) to 'high conversion gain' (gain >=900 in SharpCap). This switch dramatically reduces the read noise of the camera, which allows shorter sub exposures to be taken, which in turn puts less reliance on great tracking/guiding. SharpCap has built in functionality to help choose a good gain and exposure value - see https://docs.sharpcap.co.uk/4.0/#Smart%20Histogram
cheers,
Robin
yes, unfortunately gain is a bit confusing as each camera manufacturer has dealt with it differently. To begin with, I just made SharpCap use the same values that the camera manufacturer uses, although now I do try to standardise for new brands of camera (I don't change how the gain works for existing brands as that risks confusing existing users).
Right... Altair camera gain - This is expressed as a percentage of minimum gain, so it starts at a minimum of 100 and goes upward. 200 gain is 2x as bright as minimum (100). 400 gain is 4x as bright, etc. 72000 gain is 720x as bright! In some other applications, the gain for Altair cameras is given in a range that starts at 1 for minimum gain - that would have a range of 1-720 corresponding to SharpCap's 100-72000.
Other camera brands use gain values that are measured in dB or 0.1 dB. Some brands have gain values that have no true meaning - they are just numbers. Some brands have variations from model to model, which is even worse... At least Altair is consistent across all models!
Black level - this just offsets the image pixel values upward by a constant amount. It's best set by trial-and-error. Setup your camera for exposure, gain, temperature, etc and then take dark frames (of the duration you intend to use) in the highest bit depth mode. Show the histogram then turn up the black level just enough to make sure that the histogram peak is just separated from the left hand side of the graph (practically no pixels at zero pixel value).
LX mode (long exposure) - in SharpCap this just changes the range of the slider for the exposure - with it checked the range is from 1s up to the camera maximum. With it unchecked the slider runs from the camera minimum exposure up to 5s. The reason behind this check box is that it is dreadfully difficult to control the exposure correctly if the slider goes from 0.1ms up to 1000s. Just to make it clear - this tick box does nothing to the camera, just changes the range shown in the UI. You can get FITS images at 100ms exposure if you want - just turn off the option for auto selection of output format and select the output format manually - see https://docs.sharpcap.co.uk/4.0/#!2!Cap ... and%20Area, https://docs.sharpcap.co.uk/4.0/#Configuring%20SharpCap
USB - the value of zero to two for the USB speed is not related to USB2/USB3 - instead it is an arbitrary number that controls how hard the camera will try to get maximum data rate through the USB system. Turning it up will usually increase frame rates for high speed imaging, except when sometimes turning it up too high will stop the whole camera working - see https://docs.sharpcap.co.uk/4.0/#Altair ... 20Controls
Finally, recommended gain... With the 294C you may wish to consider gain 900 as a starting point - at gain=900 the camera switches mode from 'low conversion gain' (gain <900 in SharpCap) to 'high conversion gain' (gain >=900 in SharpCap). This switch dramatically reduces the read noise of the camera, which allows shorter sub exposures to be taken, which in turn puts less reliance on great tracking/guiding. SharpCap has built in functionality to help choose a good gain and exposure value - see https://docs.sharpcap.co.uk/4.0/#Smart%20Histogram
cheers,
Robin
Re: Settings in Sharpcap Pro
Hi Robin
Thank you for taking the time to write such a comprehensive reply, it is much appreciated, and I now have better understanding of what the numbers in Sharpcap mean.
Clearly the astro camera manufacturing industry, needs some standardisation, which would make life much easier for software developers, such as your good self.
I can understand the logic in why the LX mode is there, and the difficultly that would arise without it. As an 'old timer astro imager' ,who had several Meade LX series SCT's, over the years, it had me wondering, but you can put that down to a 'senior moment' (lol).
I do like the user interface of Sharpcap, and look forward to "putting it to work".
Thanks again
Dave
Thank you for taking the time to write such a comprehensive reply, it is much appreciated, and I now have better understanding of what the numbers in Sharpcap mean.
Clearly the astro camera manufacturing industry, needs some standardisation, which would make life much easier for software developers, such as your good self.
I can understand the logic in why the LX mode is there, and the difficultly that would arise without it. As an 'old timer astro imager' ,who had several Meade LX series SCT's, over the years, it had me wondering, but you can put that down to a 'senior moment' (lol).
I do like the user interface of Sharpcap, and look forward to "putting it to work".
Thanks again
Dave