for distant subjects, (more than 10 x focal length
image size = oject size * focal length / subjet distance
when you get close this becomes much more complex but note
1:1 is always when image distance = subject distance = 2x focal length.
If you put close up lenses on, you modify focal length and focus point.
effective focal length 1/(1/focal length in meters + diopter)
1 diopter is 1 meter focal length, 2 diopters is 0.5 meters focal length etc.
maximum focusing distance with a close up lens = 1/diopter in meters
In re reading your post, if you want to get 1/8 inch across the sensor you are really discussing 6x magnification.
I am not sure how easy this will be to achieve at 6 inch working distance
For example you would need about 300 mm of extension tubes on a 50mm lens, but focusing wouldbe at 60 mm from the front element, less than 1.2 your desired distance.
you could put your 24mm lens on a bellows and get a good magnification but with probably a working distance approaching the focal length of the lens
I don't know how reversing rings would work.
Last edited by Lowell Goudge; 02-16-2010 at 04:35 PM.
|