Following Saturday’s post (Getting Close), I have spent a bit more time experimenting with how close I can get using my camera set up. With this shot, I used my Nikon D40 attached to my Vivitar 90mm lens (including extension section, which takes it to a 1:1 ratio), my Raynox DCR-250 and a reversed 18-55mm at 18mm (aperture held open). I have brightened the image with Picnik so you can see the markings (about 8mm across the ruler). My sensor is about 24mm wide so that works out at about a 3:1 ratio. The gold standard is 1:1 (1mm in real life equals 1mm on the sensor) so I have surpassed that.
A 1mm wide section is 320px wide, so 1px must be is about 3μm across. Therefore, given better lighting, I should be able to see plant cells and pick out details of the larger ones as, according to my online searches, plant cells vary between 10-100μm wide.
Magnification depends on the size of screen the image is viewed on. On my monitor at 100% image size, 1mm on the ruler takes up 12cm (120mm) so magnification is x120. That is not as much as some of the relatively cheap USB microscopes boast but I suspect the image quality is much higher.