Stopping down a lens with a CCD?

[Adamar98]

I Managed to link my Canon 200mm lens to my CCD lastnight. Took a few images but my stars are looking rather pants. How do I stop down the lens so it stays at a certain aperture? If I set it on the dslr will it stay at that aperture once I take the lens off and put it on the CCD? That's what I tried but I don't think it did.

Thank you

Adam

[StuartJPP]

There is a fiddle you can do to keep the aperture stopped down. Attach the lens to a camera in Av mode and set the aperture to whatever you want, for instance f/5.6 and press the DOF button to stop the lens down. With the DOF button depressed dismount the lens and it will stay at f/5.6. However this produces diffraction spikes which personally I don't like.

Best bet is to stop the lens down with a front aperture mask or a step down ring like these:

DIY - http://stargazerslounge.com/topic/183308-spiky-stars/?p=1903395

Step Down - http://stargazerslounge.com/topic/183308-spiky-stars/?p=1904104

[Adamar98]

Cheers Stuart.