D810: Difficulty in focusing on Deep Sky Objects

[hdnathan]

When attempting to photograph Deep Sky objects with my Nikon D810 the Live View in BYN is so noisy and seemingly not sensitive enough to resolve stars.  I am having to swing away from the session and go to a very bright object elsewhere in the sky to check focus and even then the picture is so noisy the focus numbers just "dance around"up and down in radical swings that all I can do is just make a "best guess" as to where focus is.

 

What am I doing wrong and/or is there a work-around?

 

Thanks,

 

Nathan 

[s3igell]

Sounds about right!!

 

Most of that "Bouncing Around" is due to your Local Seeing Conditions - Turbulence in the Upper Atmosphere plus any Near-Ground Heat Turbulence.

 

You didn't provide any details about what type of Scope or Camera Lens you are using - nothing to indicate how much Focal Length you are dealing with...

Obviously, More Focal Length = Smaller Field-of-View = Greater Impact by Seeing...

 

If you are unable to resolve any but the Brightest Stars, then it sounds like you might be using a rather Wide Lens or a Scope at a Slow Focal Ratio...  If a Lens, ensure that you Open the F-stop as Wide as Possible without getting Too Soft and Distorted a resulting Image...

Also, ensure that you have your LiveView "Maximum Sensitivity" checked in the Settings screen...

 

Otherwise, you are experiencing what most of us deal with for Focusing Efforts...  You'd benefit from the addition of a Bahtinov Focusing Mask (for all but the Wide Zoom Lenses), but everyone finds that they have to Focus on the Brightest Nearby Star...

 

The only other suggestion:  Contact your Local Astronomy Club for suggestions about any regional Observing Areas which might have "Better Seeing"...

[admin]

Hi Nathan,

 

That is a physical limitation of the camera and live view itself.  Live view is only a few milliseconds of data and will only work on bright stars.

 

Alternatively you can snap images of several seconds in F&F if that helps.

 

Keep us posted,

 

Regards,

[hdnathan]

Thanks to both of you on the response, got it!

 

BTW: Scope is a SkyWatcher Esprit 80ED APO triplet, f5 with .85 flattner, Nikon D810 in prime focus 

 

Thanks again,

 

Nathan