Monday, October 5, 2009

Taking photos at aquariums and exhibits

Taking photos at aquariums is easy once you know a few basic concepts.  Note: I used aquarium photos here but the concepts are the same as those for museums or other exhibits with glass displays.

Disclaimer: be sure to check if taking photos is allowed, and whether flash is allowed. For museums, be aware of copyright laws.

Goals of a decent aquarium photo:
1. Aquarium looks natural (similar to how you see it with your eyes).
2. Subject (your spouse or kid) is adequately lit.
3. No distracting reflections.

Aquarium photos pose these challenges:
1. aquariums tend to be dimly lit, making it hard to take pictures of your spouse or kids without using a flash.
2. aquarium glass often shows the reflection of the camera flash instead of the fish.
3. the ambience of the aquarium is usually lost in the photo.  Taking a shot in auto mode will usually result in an overexposed, washed out subject with a deer-in-headlights look, and a bright reflection of the flash on the aquarium, with the water appearing black or navy blue and the colorful fish nowhere visible.

There are just three basic concepts you need to take proper aquarium photos:

Concept 1: Balancing ambient vs. flash.
The key to showing the colors of the fish is to meter for the aquarium's existing light (instead of metering for the subject, such as your spouse or kids), and then let the flash adjust accordingly.  To learn how, check out this tutorial.

Concept 2: Understanding reflections.
To avoid unwanted flash reflections on an aquarium or other reflective surface, you need to analyze the range of angles where the flash will be visible as a reflection.  The basic tool for such analysis is a diagram (until you get to the point where you intuitively know which reflections will be visible).
1. Draw the camera and the surface of the aquarium that is within the camera's field of view.
2. Draw the position of the flash (if the flash is on-camera, the flash is of course in the same position as the camera).
3. Draw a line from the flash to the left edge of the aquarium.
4. Draw the reflection from the line in step 3.
5. Draw a line from the flash to the right edge of the aquarium.
6. Draw the reflection from the line in step 5.
If the camera is between the lines in step 4 and step 6, then the reflection will be visible in the shot.  If the camera is not in between those lines, the reflection will not be visible in the shot.
In the diagrams below, the blue bar represents the aquarium surface visible within the camera's field of view. The dotted blue lines are imaginary lines perpendicular to the edges of the visible aquarium surface.  The red lines represent the lines in steps 3 and 5.  The green lines represent the lines in steps 4 and 6.
In the top diagram, a camera with on-camera flash is squarely facing the aquarium.  The camera is in between the green lines, thus the flash will be visible.
In the middle diagram, a camera with on-camera flash is facing the aquarium at an angle.  The camera is not in between the green lines, thus the flash will not be visible.
In the bottom diagram, a camera is squarely facing the aquarium, but an off-camera flash is off to the side.  The camera is not in between the green lines, thus the flash will not be visible.

An alternative way of doing a reflection analysis is to diagram the camera in the same way as you would for the flash.  If the flash (or any other object) is outside of the green lines from the camera, the flash reflection won't be visible.

As an exercise, how does the focal length of the lens affect the visibility of a flash reflection (assuming that the camera distance is adjusted so that the same amount of the aquarium is visible)?  Hint: A tele lens will more easily avoid reflections.

Concept 3: Controlling flash intensity.
With TTL, flash is adjusted by flash exposure compensation.  See the TTL Flash FAQ and this tutorial.

Specific strategies:
1. For cameras with on-camera flashes:  Change the angle of the aquarium to avoid a flash reflection within the cameras field of view.
Sample photo (from a point and shoot camera):

In this shot, I avoided a direct flash reflection by shooting the aquarium at an angle (like the middle diagram above). (As for the reverse letter C-like reflection on the upper right of the image, I think it's a reflection of the retroreflective band on our stroller.  That shouldn't show up in normal situations.)

2. For off-camera flash: Take a photo directly facing the aquarium, but position the off-camera flash to the side and angle it greater than about 45 degrees (the exact minimum angle varies with your field of view and focal length).
Sample photo:

In this shot, the flash was at camera right, aimed at about slightly more than a 45 degree angle.  In retrospect, I should have tried aiming the flash at an even sharper angle so that the reflection on the bottom left would not be visible but at least by aiming it at an angle, it is much less distracting than a direct flash glare.

3. Ambient-only: some aquariums don't permit flash photography.  In addition, sometimes it is feasible to avoid using the flash if the aquarium is large enough and emits enough light to be used as a light source for your subject. Keys to making the shot work:
a. shoot in RAW if you want to correct the white balance.
b. use noise reduction software. For the examples below I used Neat Image.
The photo at the top of this blog entry was taken ambient only.  Here's a similar shot where white balance was adjusted. If I had taken the shot in jpeg, it would have been impossible to get an acceptable output with this extreme white balance adjustment (the color temperature of the bluish light from the aquarium was over 50,000K).
Sample:


Of course, the foregoing strategies can't address every conceivable situation.  However, I hope that by discussing lighting concepts (including samples of applying those concepts), I can help you can generate your own solutions.  For example, here's a different kind of situation: at Legoland SeaLife in California, they have aquariums with glass domes in them from which you can get an immersive view of the fish while people looking at the aquarium can see you.  Taking an ambient-only shot, we got the following picture:


There was room for improvement in that shot.  The aquarium looks natural enough, but the subject was not easy to see through two layers of reflective glass and the water in between.  One solution is to use an off-camera flash, which I placed under the glass dome, aimed upward at the subject, then triggered via CLS:


Other resources:
Here is a related post about how to avoid reflections on eyeglasses.
If you liked the discussion about analyzing reflections, check out: Light: Science and Magic.
If you are interested in reading about balancing existing light with flash, read: On-Camera Flash or the TTL Flash Tutorial.
To learn more about wireless flash, read: Nikon CLS Practical Guide, Strobist.com, and this blog.