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.