I chose the above blue hour photo to celebrate, with France, the restoration and reopening (last week) of the Notre-Dame Cathedral, after the devastating fire in 2019.
I took this blue hour photo a few years before the fire, from a bridge over the Seine River, while teaching a European photo workshop (single exposure • Canon 5D Mark III + EF24-70mm f/2.8L USM @ 35mm • 10 sec, f/8.0, ISO 100).
Blue Hour SINGLES vs. Blue Hour BLENDS: Many of you have used blue hour exposures in you astro-landscape photography for doing "Blue Hour Blends," (pages 122-124 of my "Milky Way NightScapes" eBook, version 2.0) where you use a blue hour exposure to blend with an Astronomical Dusk exposure in order to increase foreground detail.
In this tutorial we are not talking about blending two exposures to extend our dynamic range, but we are using the magic of the blue hour to enable us to get more detail in the foreground AND the night sky with just ONE exposure! Of course, we cannot get maximum star details during the blue hour, but there are still beautiful night sky features to be had in this period of the night.
What is the Blue Hour? According to Wikipedia, "The blue hour is the period of twilight (in the morning or evening) ...when the Sun is far enough below the horizon so that the sunlight's blue wavelengths dominate... Since the term is colloquial, it lacks an official definition such as dawn, dusk, or the three stages of twilight."
When is the Blue Hour? Even though Wikipedia does not list an official twilight period for the blue hour, PhotoPills places the blue hour within the Civil Twilight, where they have it occurring during the period when the Sun is between 4º and 6º below the horizon:
That time period where the Sun travels those 2 degrees (from -4º to -6º, after sunset, or from -6º to -4º, before sunrise) can last anywhere from less than 10 minutes to about an hour, depending your latitude and the time of the year. Here are some examples:
Blue Hour Periods on June 21, at different latitudes - shown in minutes (')
40º N ~ starting 32' before sunrise & starting 20' after sunset | each period lasting for 13'
20º N ~ starting 25' before sunrise & starting 16' after sunset | each period lasting for 10'
0º ~ starting 22' before sunrise & starting 14' after sunset | each period lasting for 8'
60º N ~ starting 107' before sunrise & starting 52' after sunset | each period lasting for 55'
As you can see, between 0º and 40º N blue hour periods are pretty consistent. The same thing applies in the Southern Hemisphere (0º to 40º S). However, when you travel further north (i.e. 60º N) and south (i.e. 60º S) the blue hour periods stretch out and become longer — especially during the summer months.
Planning Your Blue Hour Shots. In many situations you can plan on starting your evening blue hour shooting about 15 to 20 minutes after sunset. In the pre-dawn, you can typically begin shooting your blue hour about 25 to 30 minutes before sunrise. In both situations, that sweet spot of blue hour shooting will last for about 10 to 12 minutes.
For more precise blue hour planning, I like to use PhotoPills. The following example is planned around the Heceta Head Lighthouse on the Oregon coast. My first step is selecting the PhotoPills "Planner", where upon I located the lighthouse on their map and dropping the pin near the lighthouse. I then choose the date (June 21st) to plan my photography and slid the top menu bar until I located the Blue Hour times. PhotoPills indicated that the evening blue hour will begin at 9:26 PM. Sliding the time line at the bottom helps you to visualize your scene — as you slide the time line towards 9:26 PM, your scene changes from normal daytime tones, to the "Golden Hour" (warmer color), to then to a cooler tone "Blue Hour" tone:
Sliding the top menu bar to the 4th menu (Rise/Set times for the Sun and Moon), you can see that the Sun will set at 9:04 PM...
...and that the evening blue hour begins at 9:26 PM (22 minutes after sunset), and that the blue hour period will last for 14 minutes (from 9:26 thru 9:40 PM).
Taking Your Shot. I start taking my blue hour shots right at the beginning or just a few minutes before the START of the blue hour, and CONTINUE to take additional images about every one or two minutes until the blue hour is over — and even a few minutes past (into the Nautical Dusk).
MAGIC of the Blue Hour. What you are looking for in your blue hour photography is that perfect TIMING when the sky is as dark as it can possibly be — giving a "night" look to your scene — yet still having enough ambience to give detail to the foreground — all in ONE exposure! This is why you need to take a series of exposures throughout the blue hour, where you are seeking to find that time when the scene perfectly matches your camera's dynamic range.
Bracketing: If you are shooting in RAW, you shouldn't need to do much bracketing with your exposure, as you will be able to pull out most of what you want within Photoshop's Adobe Camera Raw or Lightroom's "Develop" by increasing shadow detail and reducing bright highlights with the appropriate sliders.
Starting exposures: At the beginning of the blue hour, start with a basic exposure of about f/8, 1-second, ISO 100. As you get near the end of the blue hour, you'll typically need to increase your exposure time to about 10-seconds. Stop down if you need more depth of field, and adjust your shutter time accordingly. You may need to increase your ISO to 200 because of clouds or other atmospheric conditions. It's also okay to increase your shutter time to as long as 30 seconds, but don't go any longer, or you'll risk taking fewer images during the blue hour window — one of which may produce the perfect that balance of highlight and shadow detail.
If you have to go to ISO 400 or higher, you've probably drifted into the Nautical Dusk period, but that isn't always a bad thing — it all depends on the effect you're trying to create. This shot of the Heceta Head Lighthouse was taken at the end of the evening blue hour and purposely left in a cool "blue" tone...
...while this photo of the same lighthouse was taken at the beginning of the morning blue hour, and I purposely shot the photo with a warmer White Balance (7500º Kelvin) to help cancel the cooler tones that typically come with a image taken during the blue hour:
