Equipment: LXD75 SN8; DSI IIc & DSI Ic (guide cam); Orion 900mm Guide scope; Filter used IDAS LPSII.

Here is wha is happening. I was attempting to do 5-10 minute subs of M31. On exposures greater than 4 minutes, I get a white screen picture. I go through the auto-exposure routine with auto contrast set. Unfortunately, Envisage uses 1 sec to compute the settings. I have the subtract darks setting enabled. If I use exposures greater than 4 minutes, all I get is a white picture.

Unfortunately, 4 minute subs does not seem to capture much more than the bright core and very faint detail of the remainder of the galaxy. I get the same sort of lack of detail and a low signal to noise ratio of this target with these short exposures after stacking 50 such images. My guess is that with the short auto exposure, the white slider is too far to the left, but I am not sure. It would seem that if the white slider has to go much further right to keep from getting white images, then the black slider should follow. There has got to be a better way than taking hours of preview pictures and moving the sliders by trial and error (and still maybe not getting the correct settings). Has anyone had this problem and what is the easiest way to fix it?

Thanks,

Kaos

Hi, Kaos

You guessed right - the white slider is too far to the left. I just leave auto contrast checked all the time. Usually I find that a setting of 2 or 3 is good, then I run up the shadow enhance to open up the shadows (3 - 6 range seems to work for me).

I don't recommend using auto expose for deep sky objects. It may be useful for lunar & planetary. Here is how I do it:

Using "Preview" mode, take a 4 minute exposure.
Check the auto contrast box & adjust the value to get a reasonable image
Increase the shadow enhance (and try different contrast values)
When you have the best image possible, open the "Color" dialog & click on Auto W/B
Box a suitable reference star, and click "Start' to begin capturing.

HTH,

Chuck

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Chuck Reese
CDIP Certified: Nebula, Galaxy, Solar System, Stars & Clusters Imager
CDIP Mentor: Nebulae & Solar System Categories
For information on the Certified DSI Imager Program, see:
http://autostarsuite.net/forums/1427/ShowForum.aspx

Hey Chuck,

Thanks I'll give that a try. I do like the shadow suggestion. I have been leaving both a 1.

I was paying with a terrestrial daytime image a little while ago and could replicate the same issue (of course with much shorter exposure times). The only way I could get that image to display was to move the gain slider way left (to around 10-20). I then had to move the offset slider down to around 20 (give or take). Could this also be the issue, (the gain too high)? It was at 100 based on the auto-exposure.  I could get the histogram to full display by doing this, but was not sure if I would degrade the result using the much lower gain setting. What is the benefit of using the higher gain setting that Envisage wants to use by default?

Thanks

Kaos