Roger Clark
03-09-2008, 10:30 PM
Hello,
I need to get images at as high a magnification possible of a subject about16-inches or greater from the front of the lens. When I say as much magnification, I mean 2x (minimum), 5x (better).
I've tried combinations like (canon lenses and bodies):
180 mm f/3.5 L macro lens:
180mm + 2x TC 16-inches from front of lens = 1.0x
300 mm f/4 L IS:
300mm +25mm extension tube + 25mm extension tube + 2x TC =1.0x at 30 inches (the closest I can focus the lens.
I could buy more extension tubes; if I can get the 300mm down to 16 inches,, I could
approach 2x magnification.
Further, I'm looking through a window (at some ice samples at about -400 degrees F, -250 C).
My resolution on the target will become diffraction limited (60mm aperture) as I increase magnification and I may not resolve more on the subject.
I've been using a 20D, but will likely switch to a 40D to get live preview for focusing.
So, does anyone have any advice on how to achieve the magnification I need?
Another lens, in the 300 mm range with closer focusing ability? I obviously
do not need a wide aperture lens, nor AF, so other brands will be considered.
But I can't get closer than 16-inches.
Roger Clark
I need to get images at as high a magnification possible of a subject about16-inches or greater from the front of the lens. When I say as much magnification, I mean 2x (minimum), 5x (better).
I've tried combinations like (canon lenses and bodies):
180 mm f/3.5 L macro lens:
180mm + 2x TC 16-inches from front of lens = 1.0x
300 mm f/4 L IS:
300mm +25mm extension tube + 25mm extension tube + 2x TC =1.0x at 30 inches (the closest I can focus the lens.
I could buy more extension tubes; if I can get the 300mm down to 16 inches,, I could
approach 2x magnification.
Further, I'm looking through a window (at some ice samples at about -400 degrees F, -250 C).
My resolution on the target will become diffraction limited (60mm aperture) as I increase magnification and I may not resolve more on the subject.
I've been using a 20D, but will likely switch to a 40D to get live preview for focusing.
So, does anyone have any advice on how to achieve the magnification I need?
Another lens, in the 300 mm range with closer focusing ability? I obviously
do not need a wide aperture lens, nor AF, so other brands will be considered.
But I can't get closer than 16-inches.
Roger Clark