SharpCap Forums

Hi Robin:

I am getting good results with the July 2022 and August 2022 of Ascom Mallincamsky software however even though I understand how to use the sensor analysis tool I dio not know how the results in https://docs.sharpcap.co.uk/4.0/#Smart%20Histogram bottom of the page were arrived at.

Is there any connection between the information here and what I may plug into the calculator at this link https://tools.sharpcap.co.uk/?

I love the resources here and I did run SA then smart histogram for ASCOM Toupcam. I intend to run Sensor Analysis on all my cameras.

Many thanks,

Dan Kahraman

Hi Dan,

the thing that links the two is the (approximate) formula for minimum sub exposure time, which is

10 * read noise squared / (light pollution rate in e/pix/second)

So, if you are using your camera at a gain where the read noise is 2e, and your local light pollution is 0.6 e/pix/s, you calculate 10 * 2 * 2 / 0.6 and get a minimum exposure of about 66s.

Note that the constant of 10 corresponds to accepting that read noise will be allowed to raise the total noise in the stack by 10% compared to the level you would have for a single, extremely long exposure that takes the same amount of time as the entire stack.

cheers,

Robin

Robin:

I am getting much lower sub exposures as my read noise at Gain 123 for the IMX410 teamed with f/4 system, Bortle 4.9, Q.E. 85%>>>>~1.8 seconds..Read noise is quite low at this Gain with this sensor
With the IMX571 at Gain 100, read noise is 1.03e, f/1.8 Hyperstar, same Bortle, Q.E. 80%>>>>1.53 seconds

Are these values correct? Maybe my local light pollution electron number is too high?

Dan Kahraman

Hi Dan,

I think so... what the numbers are saying is that in these conditions there is no final image quality benefit from taking longer exposures. On the other hand, you may decide to go longer (say 15 to 30s) to reduce the amount of data you collect, shorten processing times, etc. Remember that the number calculated is the *minimum* sub exposure time. There's also a maximum value that depends on how good your guiding/tracking is, how quickly the sensor becomes saturated on the brighter parts of the image, etc.

cheers,

Robin