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I want to photograph the milky way but have had troubles with ambient light. The first attempt suffered from streetlights. The second attempt away from streetlights suffered from full moon which I found is surprisingly bright, as I had to photograph in the moonlight shadow of a building. I will try again when I get a chance to work outside of moonlight hours.

I have used the following exposures:

  • ISO 6400, 5 s, f/2.8 (on a 24mm prime)
  • ISO 1600, 15 s, f/2.8 (wide open on this 17-55mm lens @ 17mm)

...mainly because higher ISOs with longer exposures result in too much ambient light. Nevertheless, I don't see milky way in the pictures I have taken. The pictures, however, have lots of ambient light which I believe is my problem.

I have seen some mutually contradictory information about setting the exposure for milky way. One answer tells that ISO should be 6000*Fstop^2/shutter. Another source recommends ISO 1600, f/2, 30 s (or equivalent). There's a factor of 2 (one full stop) difference between these recommended exposures.

At least shutter speed (or should I say exposure time) seems to be pretty agreed-on: the first answer recommends 600 / 35mmEquivalentFocalLength, whereas the other source recommends 500 / 35mmEquivalentFocalLength, and there's only 20% difference in these two sources (or in terms of stops, only one quarter stop).

On this 17-55mm lens @ 17mm, I can go as long as 18-22 s according to the 500/f or 600/f rules. What would be the optimal ISO for this? Should I go for:

  • ISO 3200, 20 s, f/2.8, which is slightly underexposed according to the second source but slightly overexposed according to the first source, and which is valid according to the 600/f rule but not according to the 500/f rule
  • ISO 6400, 15 s, f/2.8 which is correct exposure according to the second source
  • ISO 3200, 15 s, f/2.8 which is correct exposure according to the first source

...or something else? The camera is a low-end crop sensor one, so I believe ISO 6400 could be a bit too high (it's the maximum non-extended ISO on this camera), and I may even have to downscale the 24 Mpix images to 6 Mpix for reduced noise even at ISO 3200, which would give preference for ISO 3200, 20 s, f/2.8. Manual ISO works on this camera only using full stops.

  • Keep in mind that the Milky Way moves in the night sky like everything else! If your camera isn't pointed in the plane of the Milky Way you're not going to image much regardless of your exposure settings or how dark it is. Also you will get a much more dramatic view in the summer as that's when the night-side of Earth will be facing the galactic center. – Gene Apr 19 at 22:47
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I want to photograph the milky way but have had troubles with ambient light.

Then don't shoot in areas with any ambient light.

... full moon which I found is surprisingly bright

Then don't shoot when the moon is up.

If there's anything in the sky as bright as or brighter than the Milky Way, you're not going to be able to capture the Milky Way. It will be lost in the brighter light from ambient sources or from the moon.

Whats the "most amount of moon" acceptable for astrophotography?
Is astrophotography basically pointless with a moon in the sky?
How to get the best results for landscape and stars photographs?
How to have colors in Milky-way?

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