Can't see anything on focus screen

[thibaut.bouculat1@9online.]

Hi,

I have sometimes an issue when my D800 is connected to my laptop and when I want to use the focus screen. I can't see any star. It doesn't happen always but more than 50% of the time. The other times, I see easyli the stars.

It is annoying as I can't fine tune the focus precisely.

 

Do you think there is something I miss?

Thanks in advance for your help.

[s3igell]

If by "focus screen" you mean the Frame&Focus mode main Image Display...

1. Select a decently Bright Star in the same general direction as your Target for use in Focusing (Dim Stars don't provide enough feedback to Focus).  Don't attempt to "Force" the Focus operation within the FOV of your Target, as it is neither required nor likely suitable (Dense Clusters don't provide enough Distinction, Nebulae mask Detail, etc).
2. Ensure that you are starting from a position of "Near-Focus" - when Far from Focus, the Starlight is so diffused that you may well "see nothing".  Make a habit of recording the Focuser Scale position once you have your Camera (and rest of Optical Train) In-Focus, to use as starting point for Next Imaging Session.  If no Focuser Scale, consider making a Mark on the Focuser Drawtube with a Permanent Marker (Yellow or Orange for Visibility under Red Headlamp).
3. If you must start a Focusing Effort in an area without a Useful Bright Star, start by taking a few quick Snap Images using High ISO and a 1-2 sec Exposure.  These will do better at capturing Out-of-Focus Moderately Dim Stars.