Hi Tom,
I just checked my test shots so far, and the combination of FA 50/1.4
and A*200/4 macro produce no vignetting at all at f/16 when the 50 is
set to f/2 or wider.
Curiously, I just emerged from a test session using a very unlikely
combination: A*200/4 macro, and 645A-45/2.8 reversed. The
magnification is roughly the same as with a 50mm, and the image circle
of the 45 is much larger. But guess what... there was bad vignetting
at f/16 and slight vignetting at f/32 with the 45 set to full opening.
This surprised me a bit, but I suppose the limiting factor is in the
optical construction rather than the size of the image circle. :-)
The experience was interesting nonetheless. A reversed 645 optic gives
a longer working distance than a reversed 35mm optic, which may be
very valuable in the field.
Cheers,
Jostein
Btw, according to some, I already classify as the Nutty Norwegian even
before taking to stacking lenses...
----- Original Message -----
From: "Tom Reese" <[EMAIL PROTECTED]>
To: <pentax-discuss@pdml.net>
Sent: Monday, December 19, 2005 5:09 PM
Subject: Re: Re: Stacking lenses for macro.
It was always my understanding that the stacked lens functioned as a
multi-element very high quality close-up lens with a high diopter
value. A 50mm lens has a diopter value of +20.
My experiments with stacked lenses have convinced me that the
stacked lens needs to have a very wide aperture to minimize
vignetting. I've used an
A 50/1.4 stacked on an A 200/4 with some success. I still needed an
extension tube behind the 200mm to avoid vignetting. The viewfinder
gets awfully dark, depth of field is extremely shallow and exposures
are long enough to make you wish you were never born if there is any
breeze at all.
Stacking lenses is an excellent way to drive yourself nuts.
Tom Reese
