dbk21au04.as setting question, gain vs. exposure
Posted 20 November 2012 - 08:02 PM
I am currently imaging with a Nexstar 8SE OTA on an Orion Sirius mount. I have had a few imaging runs with the above camera, and have noticed some excessive noise after processing. I don't know if this is the result of more gain or what. I know that if I increase the gain and keep exposure around 1/30 of a second I can keep my framerate at about 30fps, but of course the framerate drops when I increase exposure and dial down the gain. Which is preferrable, more exposure or more gain? Is the increased gain the reason for the noise in my images?
Posted 20 November 2012 - 09:29 PM
With gain you can overcome noise by using more frames in the stack to reduce the noise. If the planet is moving around the capture area at all noise patters will also be eliminated by a large number of frames, if the planet does move much or stays on the same exact stop, noise patters on the chip will be noticed in your final image. I use a high gain setting and faster frame rate when the seeing is average or below, I also will move the planet around the chip a bit while imaging.
Longer exposure times will allow blurring in the image during times a bad seeing, but when the seeing is very good increasing the exposure time will not has as much an adverse effect on the final image. A shorter exposure time even when the seeing is good will probably produce a clearer final image. I will use longer exposure times when the seeing is above average and reduce the gain. An image with lower gain will require fewer frames to get a smooth image.
So as I say yes you want low gain, and you also want a short exposures and low gain. It's a balancing act. What I have done is found the highest gain that I find "workable" in post processing and then use that to figure out what exposure to use that evening. What I want is the highest number of frames per second and shortest exposures with a gain low enough to produce a smooth image.
I am sure others on this site have different strategies and they may work well, but that is mine.
Posted 20 November 2012 - 09:45 PM
again much thanks for the info, can't wait to apply it.
Posted 20 November 2012 - 09:49 PM
thanks in advance,
Posted 20 November 2012 - 10:06 PM
With IC Capture, the button is on the upper left of the toolbar. If you adjust gain until 50%, or "127" along the intensity axis (0 - 255) you have a reference point for comparing all future videos and images.
Posted 20 November 2012 - 11:11 PM
Posted 20 November 2012 - 11:54 PM
I can't wait till this weekend to try these tips and thank you all for the advice.
Posted 21 November 2012 - 12:11 AM
Posted 21 November 2012 - 12:17 AM
Posted 21 November 2012 - 06:14 AM
Depending on image scale, Jupiter can rotate quite a bit in those 3 minutes, but the stacking programs do a really good job of avoiding smearing. You might want to experiment some to find out what works best for you.
The below image is from a 3 minute capture, and 1000 out of 3400 frames were stacked. (Used an 8SE OTA + 3x barlow)