In the previous post about front-curtain and rear-curtain sync modes, I used a two-exposure model to describe the final image created by the contribution of both ambient and flash lights. In this post, I will go into details about the shooting parameters that affect both exposures and the most effective techniques of balancing flash and ambient exposure. I will mostly speak in Nikon terms since that’s the only brand of DSLR camera I have access to.
Four parameters
The four camera parameters that affect the final exposure are: ISO, aperture, shutter speed, and flash output amount. If the camera and flash are in full manual mode, all four parameters can be freely adjusted by the photographer. In the chart below, a check mark is used to indicate that the particular camera or flash parameter affects ambient or flash exposure. “–” means it does’t. An important assumption is made here: Flash duration is so short compared to shutter speed that shutter speed does not affect flash exposure. This excludes the FP high speed sync flash mode from our discussion to avoid complications. Read More…
Posted in
Flash photography on January 1st, 2010.
2 Comments.
Many new digital SLR cameras now come with a feature called Auto ISO, which automatically adjusts the ISO sensitivity of the camera based on pre-programed algorithms and user preferences such as maximum allowed ISO and minimum shutter speed.
Is this feature useful?
The typical support argument for the Auto ISO feature goes like this: Camera lenses have the maximum aperture limitation. At a given ISO, the required shutter speed to achieve proper exposure may be too slow to stop motion or avoid camera shake even when the aperture is at its maximum setting. In this case, the ISO setting of the camera needs to be raised until a usable shutter speed can be obtained. This previously human-involved process can be automated by the Auto ISO feature.
Still need to see some more convincing arguments or have some questions answered about the usefulness of the Auto ISO feature? Professional photographer Steve Simon shared his thoughts on the Auto ISO feature in Nikon DSLR camera in two discussion threads on Flickr:
In the article titled Understanding Flash Sync Speed, I discussed in details how focal plane shutter works and what maximum sync speed is. What was left out was the two different flash sync modes: front-curtain vs. rear-curtain sync.
In front-curtain sync, the flash fires immediately after the first (front) curtain opens completely; in rear-curtain sync, the flash fires just before the second (rear) curtain starts to close. To understand the differences they make, let’s use a simple two-image model.
The image sensor continuously capture the image formed by the lens on the sensor surface when the shutter is open. There is one image captured by the camera in each exposure but you can imagine the sensor captures two images: one image formed by ambient light and one image formed by the flash. The two images are then superimposed together. In front-curtain sync, the flash image is captured first followed by the image of the ambient light; while in rear-curtain sync, the flash image is captured after the image sensor captures the ambient image. Read More…
Nowadays, camera manufacturers want you to believe their cameras are very sophisticated precision digital instrument that can take great photos effortlessly. There is some truth in the marketing literatures, but they don’t typically tell you at the same time that their cameras can also produce garbages if the users fail to use them properly. I admit, this is really not necessary for them to do so in the marketing materials and most camera manuals do come with such warnings. The matter of the fact is that many people have some unrealistic expectations from their cameras that cost them hundreds if not thousands of dollars. Read More…
Question:
When I use flash for indoor pictures, will a manual setting of shutter speed 1/60s and aperture f/4 give the same exposure as shutter speed 1/240s and aperture f/2, assuming the focal length and ISO are the same?
Answer:
The two different shutter speed and aperture combinations should give you equivalent ambient/background exposure but for subject exposure, the answer can vary depending on the exact shooting situation. Read More…
Posted in
Q & A on September 27th, 2008.
No Comments.
The Tamron AF 17-50mm f/2.8 SP XR Di II LD Aspherical IF lens has received some good reviews (see review by PhotoZone.de) and appear to be a nice low-cost alternative to more expensive offerings from larger camera and lens manufacturers like Canon and Nikon. However there have been quite a few complains (including myself) of the lens overexposing in flash photography, especially in Nikon TTL-BL mode. Here are some threads I found on the Internet. Read More…
Posted in
Flash photography,
Lens on October 24th, 2007.
10 Comments.
For some unknown reasons, Nikon decided to skip the automatic exposure bracketing feature on the D40 and D40X DSLR cameras. For people who are interested in high dynamic range (HDR) photography using D40/D40X, this is a convenient feature that is missing. However you can still do HDR photography without it using D40/D40X. Here are two ways of doing that. Read More…
Posted in
Beginner Tips on October 21st, 2007.
9 Comments.
The photo below shows a typical example of a landscape photography situation with challenging dynamic range. Taken at ISO100, f/8, and 1/180sec, the multi-pattern (matrix) metering on the Nikon D200 choose to expose the clouds properly but most of the scene below the sky was under exposed. Should I blame Nikon for making such a bad camera? Nope, you may get similar result, if not worse, from just about any camera. Thanks to the camera’s decision not to properly expose the field instead, or I would be left with over exposed sky that I could not fix with post-processing. It is really a easy fix in Nikon Capture NX. Follow the link below the photo to read more.
Read More…
Posted in
Photo editing on October 8th, 2007.
5 Comments.
