Camera Gain Values?

james1ca

Can you explain how you determine the gain value settings that you use in your drivers? What I mean is how do you go from a gain of 1 (e-/ADU) on the ASI174MM to a recommendation of a unity gain setting of 189 (in 0.1 db) in the driver?

I've tried to search for this information within the forums but unfortunately your search engine rejects searches for the term "gain" as being too common of a word.

Sam@ZWO

you can find out in this image

you can calculate this image yourself too, follow this:

http://www.cloudynights.com/page/articles/cat/fishing-for-photons/signal-to-noise-part-3-measuring-your-camera-r1929

it's very important to get the GAIN (e/ADU)

james1ca

Thanks, but that is not what I really wanted. I know that I can calculate the gain myself (there are various methods, some more accurate than others) and I'm familiar with the graphs that you supply for your cameras, but I want to know how you came up with the driver gain settings in decibels (dB). Are those values based upon internal sensor settings or can they be calculated from the actual gain values in e-/ADU?

Like I asked earlier, if unit gain is 1 e-/ADU then why does the ASI174 driver use a value like 189 to represent that setting? Obviously, 189 (or even 18.9 dB) is not equal to 10 log (1/1).

I think in a previous post (somewhere) you showed how the driver gain settings were calculated based upon a set of values taken from the camera, that's what I want to know. Unfortunately, I can't find that post using your site's search feature (if the post even exists).

I'd like this information for the ASI178MM-Cool, which apparently has a unit gain near 0bB which makes some sense as 10 log (1/1) = 0, but then why is the gain at 0.25 e-/ADU represented by a driver setting of 100? A change like that in decibels should represent a factor of 10, not just 1 to 0.25 or a ratio of 4.

Since you indicate that the driver values are in 0.1dB units I'd think that they must represent some actual measurement or setting in the camera, they can't just be numbers picked along some meaningless number scale.

Sam@ZWO

the gain is set through sensor in 0.1db unit

take 174 for example

the GAIN=8e/ADU when gain is set to 0 which means 1X at default

so you need around 8x gain to drop the GAIN to 1e/ADU

8x=20*log(8)=18db

that's how this value 189 comes

I don't know if I understand you and descripe it clear?

thanks

james1ca

Sam, thanks, that should get me started.

jmgoldba

The CloudyNights link posted is for CCD cameras. Does the same hold for CMOS? I'm trying to calculate the read noise and gain for our 6200MM and my CCD based software equations (which work with our CCD cameras and match AIP4WIN results) aren't matching the EGAIN in the FITS header.

On a related note, I've seen that there is a different method for calculating read noise for CMOS (since each pixel has its own amplifier) which is based on a histogram plot of frequency (# of pixels in a bin) vs. read noise (bin) where either the median or RMS value is used. How does ZWO determine the published read noise for their CMOS sensors?

Jesse