I found this nearly perfect Dahlia growing my garden, in one of the protected side-yard raised beds that I use for growing flowers. To make this image, I positioned the flower in a vase in front of a west-facing window.
My plan was to use the strong late afternoon sun as my sole light source. I hung a piece of translucent white tracing paper to act as a diffuser between the window and the flower. Papaver Rhoeas Portrait and Light of the Poppy were shot the same way.
Since this Dahlia is relatively opaque, the front of the flower was in deep shadow because the backlighting from the sun didn’t reach it. I used a small piece of white cardboard as a reflector to add a touch of fill light to the front of the flower.
To make the background appear truly white, I shot a series of images at bracketed exposures, all biased to the high key (or over exposed). All other variables were the same for each capture, with exposure times ranging from 10 seconds to 1/30 of a second. I used a 200mm telephoto macro, at f/32 and ISO 100, tripod mounted. I made sure that neither camera nor flower moved between exposures.
In Photoshop, I started with the lightest exposure (10 seconds). In this version, the background was completely white and you could hardly see the flower. Using darker versions, layers, masks, and the Paint Brush Tool I layered in the details in the flower.
After merging down the layers in Photoshop, to enhance the color rendition, I selectively blended the flower with a monochromatic version of itself. I know this sounds paradoxical—but sometimes color can be improved by taking color out.