Using a T adaptor.

Loving learning the features of my new D5100......still a long way to go though. I've bought a T adaptor and mount to be able to connect my Celestron telescope to it but I find that I get the "Lens not attached" error in the live view and can't operate the shutter....is there a setting I need to be able to do this ?
thanking you.....

I think 'M' - manual mode will be the only mode that will work without a lens attached.

Just tried your suggestion and you're quite right...it does work in the "M" setting....easy when you know how isn't it? I really appreciate your help. Thank you.

Yes all non CPU lense can only be used in the "M" mode in the D3xxx and D5xxx series, you may have to try out with different exposure speeds to get it right.

Another thing that may be useful is photo stacking.
Astrophotography: Star Photo Stacking