[A. J.]

I come looking for an answer to why my night shots (see here) turned out grainy.

Given the late (or early as it was) hour, I forgot and left my ISO set at 200. Am I correct then in making the leap of faith, that if I set my ISO to 800,1600, 3200 or beyond (my D300 goes higher), that I will be able to clean up my image and significantly reduce the grain?

Is there a point of diminishing returns, meaning going beyond ISO 800, 1600 or even 3200, will not improve the clarity of the final image?

The Zion shot was a 46 min. exposure, shot at f3.5, with a 12-24mm wide angle, taken between 2:30-3:16am MST. The Bryce shot was a 35 min. exposure, same lens, same ISO, relatively same time. I was looking to get the star trails.

Suggestions on improving the final image, in-the-field (e.g., different f value, longer/shorter exposure, ISO setting, etc)?

Oh, BTW.....

maybe 46 min. was a tad bit too long for the exposure. Thus, another question, how can one decide/tell what IS a proper length of time (exposure) for such a shot?

Too short and the trails do not appear, too long and too much light enters the image. Maybe if I started closer to midnight, I would be less impacted by the coming twilight/dawn. I just won't sleep any more.

Also the evening was super clear, altitude was at approx. 4000 ft. (+/-) at Zion and 8800 ft. at Bryce, and the sky was just ablaze with stars. Possibly the billions and billions of stars and their associated light contribute to the potentially over exposed image.

When taking such long exposures, there is little opportunity for many multiple shots in one evening before the dawn's light begins to wash out the sky.

Thanks in advance for any insights that can be provided!

I appreciate it.

A. J.