Interesting discovery. I don't often use stacked lenses but the time I
do I'll give this a try. How far down did you close the aperture? I
assume that at some point it would be effectively be stopping down both
lenses (the one stacked on front and the one attached to the camera.)
I have not tried any digital medium format macro but experimented a bit
with 1.5 - 2x lifesized on the Pentax 6x7, using a combination of
extension tubes and a Raynox DCR-250 converter, which worked well.
Completely agree with you on "Closeups In Nature" - its a great resource
for macro techniques and some of the math. Another is the old Kodak
Workshop Series book "Closeup Photography" which gets a little more into
the math regarding DOF and exposure compensation for extension, etc.
Between the two books the math is pretty well covered, but in the
digital era figuring out exposure settings is (thankfully) unnecessary -
a few test shots and adjustments gets the correct exposure very easily.
Mark
On 9/4/2016 6:38 AM, Jostein wrote:
We have tradition for calling new gear aquisitions for enablement, but
since this is about knowledge aquisition, it didn't seem right even if
it feels like enablement.
The 645D is a bit cumbersome to work with for macro, because of its
sheer size. The motivation to do so is of course image quality, like
when using the 645FA 120mm f/4 macro. However with so much CCD real
estate, it's tempting to seek more magnification with extension tubes,
reversed lenses or most of all; stacked lenses.
I've used the optics involved before, with a K-mount adapter and
various APS-C cameras. So I know the drill, and I have had high
expectations based on earlier results with subjects as different as
snow crystals and freshwater plankton. One of the best combinations
seems to be a 645FA 150mm f/2.8 with a reversed 75mm f/2.8 stacked in
front, giving 2X lifesize magnification.
But not on the 645D. All sorts of weird colour fringing popped up, it
was like watching an old 3D film without the coloured glasses.
My guide to the chaos of macro photography has always been the
venerable book "Closeups in nature" by John Shaw. It's nearly fourty
years old, but still relevant and with many wonderful images to
illustrate his text. On the subject of stacked lenses he explicitly
states that the reversed lens should be used wide open.
It shouldn't. That's my enlightenment. With the camera-mounted lens on
full aperture and the reversed lens stopped down, all the weird
fringing disappeared. I tested the same with K-mount lenses too, of
course, and with the same eye-opening and jaw-dropping result.
So, that's my little eureka moment for the week and I'm proud of it.
Carry on. :-)
Jostein
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