PDA

View Full Version : Gain settings



darbyvet
April 4, 2011, 19:11:36
Hi
I have a question for planetary imagers.
I have a celestron 8SE and a DFK 21aus camera and a Televue 2.5 powermate image amplifier.
I am a beginner planetary imager
I was imaging Saturn last week.I had an exposure setting of 1/23s and I left the gain setting on auto.I got some nice pics with good color, but I couldnt get good detail on the bands on the planet.Seeing was poor though.

I tried again this week and this time I played with the gain setting.I reduced the gain setting to 500 and increased the exposure time to 1/5 sec.Again I got some fairly good images, but Saturn was reddish pink instead of being a nice yellow.Seeing was poor and there were some thin high clouds

So my questions are;
1. Do you normally try to adjust the gain setting on the DFK camera to get better detail? It seems to me that decreasing gain did not help -Maybe because seeing was poor?
I have read that decreasing gain can help with improving fine detail on planetary imaging.

2. Why was Saturn a different color.Was it due to the high clouds or the reduced gain?

I imaged using Y800 codec and used registax5 with debayering so stack and process the images.

I am trying to get a web page set up so I can upload the images.

darbyvet
April 4, 2011, 19:32:47
http://www.senecafallsvet.com/site/view/194286_astropics.pml


this was the image with 1/23 exposure and gain left on auto

darbyvet
April 5, 2011, 02:37:06
1/23s exposure gain setting auto.poor seeing.

darbyvet
April 5, 2011, 02:40:35
gain reduced to 500.exposure 1/5 sec.again seeing poor (probably a little worse than the other image taken a few days earlier).Very fine high clouds.Anyone know why the color is so different

Stefan Geissler
April 5, 2011, 08:22:12
The colors are different, because you run the camera on auto white balance. You should set the white balance manual to appropriate values.

darbyvet
April 5, 2011, 14:56:37
Thanks Stephan,
what settings would you use for white balance? Do you switch from the y800 codec so you can see the live image in color and then adjust the white balance until you get the correct color and then swtich back to y800 to record the images?

Stefan Geissler
April 5, 2011, 15:33:55
No. I would set the default values or what ever looks fine.
You can change the video format to YUY2 and set the white balance properties. For AVI Capture your set the video format back to Y800.

darbyvet
April 5, 2011, 19:40:51
Thanks Stephan,
I will try that when the skies clear.
Can I ask what imagers are doing as far as gain.Do most people adjust the gain down if the seeing is OK to improve detail.

It seems to me that if seeing is poor higher gain may be necessary or the images gets so dim that you need to increase exposure.When you increase exposure you decrease the number of frames you take so you will get fewer good frames.
I think that is why my high gain image is clearer and brighter.Although seeing was poor I got enough good frames because the exposure time was short.

With the second image I reduced the gain too much and the increased exposure time meant that I didnt capture enough good frames for a detailed image

Does this make sense?

Stefan Geissler
April 6, 2011, 13:00:01
You are right. Long exposure, especially if longer as the frame rate's time intervall reduces the frame rate of image at all. Also high gain produces a lot of noise. Therefore you must find the best setup for your light conditions.

darbyvet
April 6, 2011, 15:16:08
Thanks Setphan,
It was clear last night so I went out experimenting.I turned off auto white balance and I got a nice yellow saturn.I turned the gain to auto and was able to expose at 1/54 and get several thousand images in 5 minutes.When I processed I got a pretty good image even though seeing was very poor.

I then turned the gain way down (500) and increased the exposure to 1/5 s and got much crisper individual frames, but because I only captured a few hundred frames in 5 minutes the processed image was not too much different than the high gain with many frames.

I am waiting for a good night of seeing to see how much detail I can get

JKr
April 6, 2011, 15:32:14
Thanks Setphan,
It was clear last night so I went out experimenting.I turned off auto white balance and I got a nice yellow saturn.I turned the gain to auto and was able to expose at 1/54 and get several thousand images in 5 minutes.When I processed I got a pretty good image even though seeing was very poor.

I then turned the gain way down (500) and increased the exposure to 1/5 s and got much crisper individual frames, but because I only captured a few hundred frames in 5 minutes the processed image was not too much different than the high gain with many frames.

I am waiting for a good night of seeing to see how much detail I can get

I believe a good approach is to:
- use the highest frame rate you can without underexposing too much
- use the longest exposure available for that frame rate (e.g. 1/16th sec for 15 fps)
- Increase the gain until the exposure is good. If you use a high focal ratio (~ f30-35) you may need to use max gain; if you use a lower ratio you can get good exposure without resorting to high gains.

To get a good result is seems a high frame rate and short exposure times is more important than low noise. If you stack 1000 - 2000 frames the noise will largely be averaged out.

darbyvet
April 7, 2011, 17:21:19
Thanks JKr

darbyvet
April 17, 2011, 02:25:03
Here is another attempt at Saturn using manual white balance settings in average seeing

Stefan Geissler
April 18, 2011, 16:38:16
Hi,

Nice details in the image, but it looks for too much blue. What have been your white balance settings?

darbyvet
April 18, 2011, 18:34:00
Thanks Stephan,
What I did was lower the red and blue color setting until the histograms for all three colors looked the same and the image looked OK when I enabled debayering in live view.I then turned off debayering and recorded as Y800 and used registax to stack the image. I could only get the three color histograms to go to about 128.The moon was very bright in the sky and quite close to Saturn so I dont know if that is why the image is a little blue.I did alter the color balance a little in registax to try to bring out the line of storms in the equatorial band. I did record the red and blue settings in a log book-BUt I cant find the log book!

darbyvet
April 19, 2011, 02:47:15
here is another attempt after processing with the gimp

darbyvet
May 2, 2011, 03:29:38
new attempt at saturn with 5/10 seeing.better color balance

donwaters
May 14, 2011, 17:13:44
How do you turn off debayering? I have a new camera and do not see this anywhere on the menu.
Don

Stefan Geissler
May 16, 2011, 08:55:56
Don

Use "Y800" video format. Not BY8 or UYVY.