Part 6 - The relationship between aperture, shutter speed, and ISO

 Dynamic range and HDR

Center image shows bracketed photos, side images different degrees of HDR.

Dynamic range is the ability of a medium like film or digital sensor to capture details over a range of light values.  A low dynamic range, say 5, means that there is about 5 stops of details from black to white; any light values past that are not captured because they end up being either totally black or totally white.  Jpegs have a dynamic range of about 8, meaning that they can captures 8 stops of light shades.  Raw sensor data tends to have a dynamic range of  12 or 13.

HDR stands for High Dynamic Range.  It is an artificial process where several bracketed images are taken and the group combined into a single photo.  It can be done manually, as above, where a series of bracketed pictures are shot and saved on a hard drive where a computer program like Photoshop or Photomatix is used to layer them together.  The advantage of this method is that you can choose exactly how you want them coalesced, allowing for significant variation.  

Many modern DSLR and mirrorless cameras offer HDR in house where the camera automatically takes a few shots in quick succession and joins them together.  The advantage is that you get a jpeg with a wider latitude than what an individual jpeg would do alone.  The disadvantage is that there is little you can do in the way of varying the outcome.

Cell phones automatically do HDR and the option to turn the process off is limited at best.  You can choose, however, to not use HDR when recording video.

Below is an HDR image done in-camera using a DSLR.

Clear Lake, Washington - in-camera HDR done with a DSLR.

The trick to doing HDR by yourself with a DSLR or mirrorless camera is to either use a tripod or do it handheld with the drive mode set to high (6+ frames per second) and auto bracketing set up (Aperture priority mode and bracketing set up to at least 5 frames +/- one to two stops apart).  It is easier using a tripod as you can capture each image at whatever exposure using exposure compensation or manual alterations.

There can be a problem with ghosting where a figure moves in the various photos.  That can be dealt with automatically by some programs while in other situations you have to remove the offending figure in each frame.  A time-consuming process.

I have done HDR using a variety of programs, cameras, and methodologies.  The results are somewhat mixed but always interesting.  It is fun to do.

Thanks for reading.

Eric Svendsen     www.ericspix.com