I just wanted to shoot pretty pictures in a fast and easy way without the need to spend a lot of money. Hence, I decided to attach my unmodified Nikon d3100 DSLR on the lenses I had at that time.
I used the optional remote cord to take the pictures.
Although the Nikon (as every consumer camera) has no active cooling, its sensor is known for its low dark noise, i.e. typical deep sky exposures of 3..5 minutes at ISO 200 are no problem in the cold winter nights. During imaging of the Moon or the Sun you may however notice mirror vibrations, especially when you are firing at long focal lengths (>1000mm). A workaround is to work with a remote cord, in silent mode settings, at ISO800.
If deep sky photography is your only application area, you can modify your Nikon at special shops like Optic Makkario in Germany. They set your Nikon in a so called "undefined state" by removing its internal daylight filter and making it able to register all frequencies. An IDAS LPS D1 light pollution filter is mandatory then. It is available in numerous sizes at TS.
Nikon also excels in the photography of planetary nebulas, the moons of the outer planets, and dark nebulas. An apochromatic refractor with 800..1400mm focal length and 100..150mm aperture are perfect for doing this. Example: the moons of Uranus.
My astro images are usually taken under heavy light pollution (LP). Since, I initially did not own a LP filter, I had to reduce the exposure time, increase the ISO (>400) and to process the results harder with Aperture 3 on my Mac. I captured all astro photos in NEF (Nikon's RAW) format in order to prevent data loss, a well known problem of JPG files. Nikon's NEF format offers more processing options and greater dynamics in later stages. Apple's Aperture 3 fully supports Nikon's NEF format. You can see an example here (size 3,5MB). A cropped version of M13 is shown below:
Photoshop users: NEF files must be converted in DNG format to be further processed in Photoshop. A good converter is here: http://www.adobe.com/support/downloads/detail.jsp?ftpID=4923
Nikon's ViewNX software can also convert the NEF files in a photoshop readable format.
Many findings in this review can be more or less also implied on newer Nikon models. Hence, if you want to buy one, you could go for the newest model as well. The Nikon D5500 was introduced in January 2015.
Thanks for reading