Hi there, recently I got another guest post published at DPS (Digital Photography School) website. Please check out Tips for Using Neutral Density Filters for Cityscape Photography at Blue Hour if you haven’t yet. Today, I’m going to answer a reader question. It’s probably a problem very familiar to us cityscape photographers shooting long exposure photos at blue hour.
My photos shot at dusk are often underexposed. Am I doing anything incorrectly?
Question came in from Karen
Probably you’ve had the same experience and had to lighten images up in post-production. I’ve experienced the same, too, and a key solution for this seems like exposing one stop longer.
Unedited RAW image (left) and final image after post-production (right). As the RAW image was severely underexposed, I had to lighten it up quite aggressively in post-production.
Let me unpack this. Let’s say I’m shooting with f/11 (Aperture Priority mode) and waiting for a base shutter speed to come down to 2 seconds (which extends the exposure to 128 seconds with 6 stop ND filter attached, according to Long Exposure Calculator app ; similar apps can be found here for Android users). In such a scenario, I used to wait until the shutter speed shown on the display is stabilised at 2 seconds first, then started with 128 seconds of exposure by attaching 6 stop ND filter.
The Very Reason Why We’re Getting Underexposed Images
The problem here is that the sky at blue hour is constantly getting darker with every single minute passing by. 2 seconds of base shutter speed should be sufficient at the beginning of 128 seconds exposure, but falls too short if measured at the end of the exposure cos the sky has gotten darker even during these 128 seconds. This is the very reason why we’re getting underexposed images.
In the scenario above, instead of shooting with 128 seconds of exposure, try shooting with 160 seconds of exposure (which comes from a base shutter speed for 2.5 seconds, a stop longer than the “actual” base shutter speed, i.e. 2 seconds). Although this method doesn’t always guarantee a perfectly exposed image, it helps prevent images from being underexposed to some extent.
By default, a base shutter speed of 2 seconds can be extended to 2 minutes and 8 seconds (128 seconds) with 6 stop ND filter attached (left). Considering the shift in the darkness, try shooting with a base shutter speed of 2.5 seconds, which extends the exposure to 2 minutes and 40 seconds (160 seconds) (right).
“Get It Right in Camera” Rather than “Fix It Later”
If you haven’t tried this “one stop longer” method, let’s give it a try and see how it goes! I’m a firm believer of “get it right in camera” (rather than “fix it later”) and shooting long exposure photos with correct exposure is a case in point. As always, feel free to Contact Me if you have any questions!
Unedited RAW image (left) and final image after post-production (right). By adopting the aforementioned “one stop longer” method, the exposure was almost spot on, requiring very little tweak in post-production.
N.B. At the end of the day, underexposed images are still forgiving, as they can be recovered in post-production, unlike blown-out overexposed images (which aren’t quite recoverable). That said, it’s always good to keep post-production to a minimum because over-editing is like hurting pixels and brings out ugly noises in the photos.