On Oct 11, 2005, at 6:33 PM, Rob Studdert wrote:
Question: I have a set of extension tubes, a 2x-S teleconverter, and
the A50 Macro. I'm trying to make the greatest magnification possible
out of the set. I presume the way to do this is to assemble
Camera->Tubes->Converter->Lens
... eh?
from the distant past:
On 13 Jan 2004 at 6:58, Christian Skofteland wrote:
Rob, John Shaw in "Closeups in Nature" says to put the TC on the
camera
body, the tubes in front of it and the lens in front of that.
This way you
multiply your extension, thereby allowing you to focus closer and
increase
your magnification.
If you put the tubes on the body and the TC in front of the tube
you are
multiplying the lens focal length but the extension is the same.
Therefore
your magnification would be lower than using just the tubes.
OK I performed some practical tests with various combinations of
lens TC and
tubes. In all cases I used the full 57mm 3 tube set with the lens
set wide open
and set at its minimum focus distance, the AF TC was set at its
infinity focus
position. The exposure factor quoted below is relative to 200mm at
minimum focus
distance.
The 200 alone gave me 1:1 (23.5x15.7) on the sensor.
The 200 +1.7AF gave me 1.75:1 (13.4x9mm), exposure -1.58 stops
The 200 +1.7AF+tubes gave me 2.85:1 (8.2x5.5mm), exposure -2.74 stops
The 200 +tubes +1.7AF gave me 2.42:1 (9.7x6.5mm), exposure -1.77 stops
My quick test with the 50mm seems to indicate the same thing.
Camera->tubes->converter->lens
nets greater magnification than
camera->converter->tubes->lens.
Hard to say without setting up the jig in the copystand and doing the
appropriate testing, but I would suspect that keeping the converter
closer to the lens also nets better optical performance.
thx
Godfrey
