Originally posted by clark if money was no object (canon mpe-65 not withstanding), what's the best way to get high magnification with decent light getting into the viewfinder and retaining full or at least partial control over aperture
and giving a decent (i.e. more than 1") working distance with suitable depth of field at f16...
I have the tamron 90mm macro, used a reversed 28mm on it, but mag was only about 3.5:1 and the working distance was about an inch, viewfinder was very bright still. So what combination of extension tube, teleconverters and reversed lenses will give the most magnification with decent optical quality?
(1) Regarding
image brightness, simple theory says (and practice confirms):
(1.1) Stacking a large aperture close-up or reversed camera lens in front of a primary lens to get higher magnification has no effect on image brightness.
(1.2) If the added lens has a smaller aperture than the primary lens, image brightness will decrease (the lens with smallest aperture controls brightness.)
(1.3) A teleconverter behind the primary lens decreases image brightness with the square of the teleconverter's power (in effect the TC moves the primary lens away from the camera.)
(1.4) Increasing the distance between lens and camera with tubes, bellows, etc., causes image brightness to fall with the square of distance.
(2) Regarding
image quality as measured by diffraction spot size for perfect lenses:
(2.1) Stacking lenses to increase magnification has little effect on resolution (because absolute aperture and distance to the image plane don't change).
(2.2) Increasing the distance between lens and camera with tubes, bellows, etc., decreases resolution in proportion to distance.
The above considerations indicate that with perfect lenses, stacking to achieve magnification is preferable to extension as far as brightness and resolution are concerned (although diffraction resolution is seldom a practical macro problem.)
Unfortunately, perfect lenses are hard to find, so you'll have to experiment with the lenses you have.
Dave
PS Depth of field at constant macro magnification depends only on f-stop. For long working distances you are best off using extension with long focal length lenses.