I shoot many of my night and golden hour images using a 70-200mm f/4L IS lens. I often like to stop down for the resultant star shapes from point source lights.
At f/32, I get very definite and specific star shapes. I was able to shoot this at f/32 because there was still a decent amount of light at golden hour. f/32 @ 1/20 second...
My Canon 7D allows a maximum of 30 seconds exposure. This shot was done at ISO 160 using f/14 @ 30 seconds. There are some star shapes but, not the definite stars produced at f/32. However, I could not have shot this at any smaller aperture unless I wanted to boost my ISO...
I have solved the long exposure problem by purchasing a remote release with a self timer that allows very long exposures. It seems to work quite well and was very inexpensive..
http://www.ebay.com/itm/Intervalomet...item33894b1716
I will use it the next time that I am shooting night shots and want very long exposures...
Another thought is a star filter. I have a 4-pointed star filter and will use it the next time that I shoot at night...