Foto Dono's 2021 Milky Way Season - Part 2 - The Exposure
Updated: Jan 3, 2021
This is the second part of a series of posts about planning for the upcoming Milky Way Season in 2021. In the previous post, I wrote about equipment. I pointed out there are many choices, but the lens was the most critical part of the setup. The kind of lens you have will help determine the baseline for the exposure to the Milky Way. As a rule, the lens should take up a considerable amount of your equipment budget. It doesn't mean you should go nuts and buy the most expensive thing either. Shop around, and see what's out there.
Here are my closing thoughts on equipment purchases. Before you go out and buy new stuff, really look at what you already have and see if you can make it work. If you are starting with nothing, you might want to rent the gear first. You might discover as you go that you don't enjoy chasing the Milky Way. $3500 to $4000 is what I'd expect to pay if I needed to replace what I have. However, I'd recommend that you practice with what you have and rent what you need first. You should only buy it if you intend to use it frequently all the time. I don't own a lot of gear; however, I do rent the equipment I need for an assignment if I don't already have it. For example, I don't use strobes in the majority of my work. I use either the available light or a flash I own. I only rent the strobes I need for the occasion.
I'm sure that many photographers will disagree with that statement. I want to point out that no one remembers that camera, the lens, or the light you used. They only remember the pictures.
When it comes to setting the exposure, it depends on the equipment I'm using, particularly the lens. The ISO is set between 1600 to 3200, with an aperture of f/2.8. If you aren't using a "fast" lens, like one with an aperture of f/4, you'll need to increase the ISO setting accordingly. The higher the f/stop, the more ISO you'll need. Higher ISOs mean more noise, which can be indistinguishable from the stars.
I'm assuming; if you have gotten this far, you have a basic understanding of exposure. If you need further help or reference material, I wrote an exposure reference guide available as a PDF available for download below. I use it for the classes I teach at Johnson PhotoImaging and elsewhere.
The focal length of the lens also determines the shutter speed. You find the maximum shutter speed by using The 500 Rule. The 500 Rule is an excellent guide for beginners. You divide the focal length into 500, and the result equals your shutter setting. The rule works great for cameras that have Full Frame sensors. If you have a Crop or Micro 4/3's, you'll need to modify the formula. Use 500 for full-frame sensors, 300 for crop sensors, and 250 for micro 4/3 sensors. You then round to the closest second.
24mm/500 = 20.83 seconds - round to 20 seconds
16mm/300 = 18.75 seconds - round to 20 seconds
12mm/250 = 20.83 seconds - round to 20 seconds
The 500 rule isn't a perfect solution. Different sensor types and megapixels also can affect shutter speed. Still, it's an excellent place to start for getting some fantastic images.
Let's look at some examples—the general rule when figuring out camera settings is to round the nearest whole or half. Also, every time you double or half a setting, it's called a stop.
Example of gear and settings with an Olympus O-MD EM-1 Mk II body with an M. Zuiko 7-14mm f/2.8 PRO and a MeFoto Globetrotter tripod. The camera has a micro 4/3 sensor. This is some of the gear I currently own. The settings here are the baseline for any exposure I use for most of my Core image captures. If I switch to a different lens, I will modify the settings. Settings - Aperture f/2.8 - ISO 1600 - Shutter Speed 7mm/250 = 36 seconds.
Suppose I switch the gear around and use an Olympus O-MD EM-10 Mk II body with an M. Zuiko 14-150mm ED f/4 to 5.6 and a MeFoto Globetrotter tripod. The only two pieces I've switched out here is the camera and the lens. The tripod doesn't matter long as it doesn't move or vibrate. Settings - Aperture f/4 - ISO 2500 - Shutter Speed 14mm/250 = 18 seconds. With an f/4 aperture, I'm losing about 1.5 stops of light compared to f/2.8. Here is the formula for that - f2.8/f4=1.5 stops. To compensate for less light, I need to increase the sensor's sensitivity, the ISO, by that same amount - 1600x1.5 stops = 2500.
With either system, the camera records the Milky Way. However, the details captured between the two systems are different. The trade-off between the two isn't other cameras; it's in the lenses. The Milky Way is a very faint light in the sky, and the system needs to capture as much light data as possible. The more light data captured, the more I can use it in post-production. Increasing the ISO doesn't increase the amount of light, just the sensitivity to recording it. The details can get lost in higher ISOs. A "fast" lens that captures the most light is preferred overall.
The guiding rule in creating single captures of the Milky Way is to open the aperture as much as possible. Start with an ISO of 1600 and keep increasing the setting until you can make out the Milky Way outline. Use the 500 Rule to find the shutter speed — round all fractions to the nearest setting.
Depending on the light pollution in your area, you are looking for the Milky Way outline.
In the image above, you can see a faint outline of the Milky Way. It might be mistaken for a cloud. The photo here approximates how the naked eye perceived the Milky Way as recorded by the camera. The Core is just to the left of that bright star. A small amount of illumination is provided by Sharky's Restereaunt, next to the Venice Fishing Pier.
I captured it with a Nikon D610 and the Tamron 24-70mm f/2.8 G2. The settings were - ISO 1600 - Aperture f/2.8 and Shutter 15 seconds. However, I did photograph it with a 24mm focal length. I modified the shutter to run slightly shorter than usual to deal with the restaurant's overflowing light in this capture. Remember, the 500 Rule is the maximum shutter speed. I can always shorten the shutter speed if I need to.
Captured in Duette, FL Nikon D610 with the Tamron 24-70mm f/2.8 G2. Settings - ISO 1600 - Aperture f/2.8 and Shutter 20 seconds. Shutter speed = 500/24mm = 20 Seconds. The house and foreground were lit up by passing cars.