Hmmmmm... this is going to be touchy, pls see last comment even if you
already hate the thread...
Internal reflections are problem, to be avoided. One step is restricting
the image circle, the other is that fancy irregular almost perfectly
black painting inside the mirror box - oh, forgot some funny shaped
surfaces too. But then, the last two are functions of the camera and we
may forget them for the moment.
The lens is a piece of design, dreamed by a photographer, converted to a
project by an engineer, calculated by a computer, aproved by a market
wizard, vetoed by masked persons who won't spend that much... return to
step 2, now to be downsized in cost and quality, then down the line
again until one of them fails and the lens is either scraped or
produced. Hint: there are far more good projects than existing lenses.
In the process of cutting down the big, bad cost, some design
compromises are made - so at one point they reduce the amount of glass,
plastic, metal and sorcery to the minimum. That means any lens produced
would perform better, at a higher cost. In a good world, not much better
a lens, by a huge price difference - the last 2~3% to be achieved in
quality could cost more than 60% of a product.
Possibly one of the compromises made by Pentax was re-issuing the 200mm
2.8 under a new name, with more eletric paths and a new price tag but
with the same optical design and parts. To reduce the costs. Now get
that cost reduction one step away and the last shaving you get is not
optimizing the baffling system to the (hipotethic) smaller image circle.
Why hipothethic? For a time Pentax wouldn't state as clearly as today
the fact they would not release a FF Digital Pentax - so the DA* 200mm
2.8 could be left almost untouched so it would possibly be used by the
possible FF camera. AND keep it cheaper to produce. After all, internal
reflections can be fought in the camera too... And in order to prevent
light falloff and improve quality at the corners you give the image
circle some (small) slack. Then you place that lovely black curtain with
almost rectangular cutout at the end of the lens... That will keep the
light where it's supposed to be.
The issue may be discussed for a good time but the proof is the testing.
So far the tests made and discussed indicate some of the lenses deserve
a full test, many of them will fail, but possibly one or three will
pass. Is [place your your pet lens here] FF-capable? Touchy subject
indeed, and right now I'm willing to do and read tests. Call me a
material, grumpy, old fool. Yes, and I hate imposed limits too. :-)
LF
ps: hope you don't mind my trimming of the empty lines and the original
message down the page.
JC OConnell escreveu:
This is undesireable for DA lenses. Why? Because you
really dont want your lenses to create image circles
way larger than your format on a fixed format ( no
swings, tilts, or shifts ) camera. The reason is
bright objects outside the recorded field of view
bounce around inside the camera and can create or
add unwanted image flare as a result. Its better
to have the image circles just large enough for the
job ( some margin for shake reduction) but not way
larger than needed.
JC O'Connell (mailto:hifis...@gate.net)
"Honesty is the first chapter in the book of wisdom" - Thomas Jefferson
-----Original Message-----
From: pdml-boun...@pdml.net [mailto:pdml-boun...@pdml.net] On Behalf Of
Joseph McAllister
Sent: Wednesday, April 29, 2009 6:09 PM
To: Pentax-Discuss Mail List
Subject: Re: image circle of DA lenses: how much smaller than FF?
Slapping some of my DA lenses on an LX I have not found any that
didn't cover the entire screen, with no apparent vignetting except at
a zoom's widest angles. Not scientific. Not all inclusive. Just an
observation.
If I had the time, and I cared, I'd shoot a few rolls of film to test
each of my DA lenses. But I don't, so I won't. Maybe some other time.
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Luiz Felipe
luiz.felipe at techmit.com.br
http://techmit.com.br/luizfelipe/
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