Posted 04/19/2017 10:54 pm
An interesting characteristic of the Numerical Aperture is that it completely defines the depth of field. No information about magnification is required. You are correct that I'm using the 20xMM objective for the 20x images. The 20xMM has NA of 0.4, so from the table below it has a DOF of 3.4um. I generally prefer shooting at a step size of 75% the DOF, so I used a step size of 2.5um, which is 2 steps in my stepper-based stacker.
For reference, below is the table of DOF vs NA for microscope objectives, though it works for any lens with NA specified:
Microscope Objectives
NA DOF
0.1 0.055 mm
0.14 0.028 mm
0.2 0.014 mm
0.25 0.0088 mm
0.3 0.0061 mm
0.4 0.0034 mm
0.5 0.0022 mm
0.55 0.0018 mm
A Nikon 20x 0.4 Mplan objective has reasonable working distance and is very sharp. It's not telecentric, but that's not a huge negative. They can be had for $100-$200 if you are patient. I have been using one for imaging turntable styli:
https://www.vinylengine.com/turntab...f=19&t=92996
For reference, below is the table of DOF vs NA for microscope objectives, though it works for any lens with NA specified:
Microscope Objectives
NA DOF
0.1 0.055 mm
0.14 0.028 mm
0.2 0.014 mm
0.25 0.0088 mm
0.3 0.0061 mm
0.4 0.0034 mm
0.5 0.0022 mm
0.55 0.0018 mm
A Nikon 20x 0.4 Mplan objective has reasonable working distance and is very sharp. It's not telecentric, but that's not a huge negative. They can be had for $100-$200 if you are patient. I have been using one for imaging turntable styli:
https://www.vinylengine.com/turntab...f=19&t=92996
Contact me for photographic equipment or visit my home page at:
http://macrocoins.com
http://macrocoins.com
