Interesting. So must we call you Archi now? I tried sourcing John Shaw's
book locally - you won't believe how much they want.
Alan C
-----Original Message-----
From: Jostein
Sent: Sunday, September 04, 2016 12:38 PM
To: Pentax-Discuss Mail List
Subject: Enlightenment
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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