Is ISO 800 too high for 50 second exposures night shots.....I am trying to work out why my HDR images are so noisy.
I have used exposures up to 120 min in my HDR city photos Tony, check out these: HDR City shots
I would recommend you open up the lens a little though, I used f/8 or there abouts and also a much lower 200 ISO.
Experiment with these ball park figures and see how you go.
From almost the same spot I took this image, settings were F/8 ISO800 30sec..
At the time I didnt have a remote shutter cable, and hence was limited to 30sec exposures. with a cable I would have done 1 min exposures at ISO400 or perhaps longer at ISO200...