Getting ISO Right in the Digital Camera II
I know that I’m in trouble when I insist at the beginning of a blog that
“This will be a short one”. It usually means that it will go on for pages, but
this time, I am committed. I have a talk to prepare for the Worcester Camera
Club and I have much more to do. I could always dust off one of my old talks, but my plan has been to do a new presentation covering a lot of the
“Getting It Right in the Digital Camera” articles that I have been publishing of
late. So, HONESTLY, this will be a brief extension of my recent “ISO Control” article.
Two week ago I discussed the use of the expanded ISO range in many of our
newer digital cameras and the benefits of being able to control ISO with the
turn of a dial. The capability to adjust ISO as shooting situations change has
provided an important new control over exposure. I have talked previously about
the benefits of bracketing photos including both exposure and focus. ISO can
also be bracketed in some challenging situations.
|ISO 100 Moving Foliage|
In my landscape photography, I am often faced with trying to get broad
depth of field in situations where the wind is moving the foliage.When I stop
down to expand the depth of field the resulting long exposure usually leaves the
foliage a blurry mess, especially in the foreground.
|ISO 100, 1.3 Seconds|
One approach, which I have
discussed before, is to focus bracket or stack, using
|ISO 1600. 1/8 Seconds|
multiple images with a
wider aperture to allow faster shutter speeds, but sometimes this isn’t enough
to freeze the gyrating greenery and the shallow depth of field of each image may
not fully overlap leaving gaps of soft focus. Another strategy is to capture an image with the
aperture and shutter adjusted to freeze the motion with acceptable depth of
field and then adjust the ISO to balance the exposure. This may only be
required in the foreground image(s) where the motion is most noticeable.
Greater noise reduction may be required for these slices, but they can then be
stacked with the images taken at lower ISO to construct a complet
|Stacked Image with Foliage Motion|
e picture with
full DOF and sharp leaves, horses or whatever else was moving.
For my example I am using the same image that illustrated my first ISO Control article. The picture taken at ISO 100 and 1.3 seconds had the best image quality, but with blurred foliage, both on the foreground tree and in the background. ISO 1600 gave me a shutter speed of 1/8 second which was sufficiently fast to freeze the movement and had good DOF at f20. I simply stacked the ISO 1600 above the ISO 100, aligned the two with Auto-Align and then painted a mask to reveal the sharp foliage over the areas of blur. With the use of noise reduction and the application of the high ISO image only where needed the final picture retained high image quality.
That’s IT. I told you this would be short. In this case the "best image from the camera" was actually two images at different ISOs. Give it a try and let me know
how it comes out.
OK, I can’t resist. Just one more point while we are talking about moving
foliage. Another technique I use occasionally to freeze motion is based on the
fact moving foliage does not all move at the same time. If you take a number
of images at the same focal length you can often combine parts of each to
isolate times when each region is relatively still. This is inevitably a
tedious process of selective masking, but the results can be quite effective.
That’s it, I promise. Now off to Powerpoint.