Still learning the ropes of deep sky photography. My earlier attempts a few years back were not very successful, so I upped my game by (a) buying a collimator tool for my 6" Newtonian and doing a proper collimation job, and (b) doing a very careful job with polar alignment of my mount. At the end I improved substantially quality of my un-guided deeep sky photos (in the prime focus of the telescope): now 30 seconds exposures are good most of the time.
Here are the two examples from the night before: globular cluster M13 and planetary nebula M57:
[IMAGE'S LINK: https://flic.kr/p/J2UT1C]Space fluorescent bulb by SyamAstro (500,000 views - thank you!), on Flickr
I used multiple 15-second exposures at ISO 3200 on my Canon 50D. The M13 shots was stacked from 20 exposures, the M57 shot - from 100 exposures. I used electronic shutter (FRSP) under Magic Lantern for shake-free shots. (And hence the 15-second exposures: unfortunately FRSP doesn't work at >16s.) I used 20-shot dark frames, and did the stacking in DeepSkyStacker.
What was surprising that both shots have the same limiting apparent magnitude - 16.2m, despite the factor of 5 difference in cumulative exposure. I realized I still have to learn quite a bit about DSLR usage in astrophotography (my prior astrophotography experience was from the old film days.) From reading a couple of articles (like http://dslr-astrophotography.com/iso-dslr-astrophotography/ ) I realized that my choice of ISO (3200) is likely the worst possible for my camera; ISO 1600 should be much better. I'll give it a try next time. Also, the 15 second exposure could be the fundamental reason I can't go beyond 16 magnitude, regardless of the number of shots, as there are simply not enough (or none at all) photons in many short exposure shots, so stacking won't increase the sensitivity anymore. The proper solution would be longer exposures, which might mean the need for an auto-guider and for a better location (my city has really bad light pollution problem; I can do maximum 30s at ISO 3200 at f/5 before the background overwhelms the photo.)
Here is a specific quote (http://www.covingtoninnovations.com/dslr/newdslr/):
"The best ISO for deep-sky work with most Canon DSLRs, and indeed most DSLRs of all brands except the very newest, is around 1600. ... With most Canon DSLRs (such as the 60D) that is around ISO 1600. Shooting at more than ISO 1600 does not record any more light; it just loses dynamic range."