For film there was an APS-C standard, and it was rigidly adhered to, if
you wanted to sell a camera that used APS film cartridges. Digital is a
close enough for horseshoes proposition, even FF sensors aren't exactly
the same size as the original 35mm film gates. Not surprisingly all
digital sensors are bit smaller than the old film specifications.
On 9/10/2013 1:43 PM, John wrote:
APS-C stands for "Advanced Photo System" - C for "Classic" - 25.1 × 16.7
mm; aspect ratio 3:2, so there actually IS a standard, even if it's
universally ignored.
On 9/9/2013 4:50 PM, Zos Xavius wrote:
Yuh. k-7 and k20D have the same sensor. A samsung sensor. Its true
there is no standard for aps-c. Generally canon is a 1.6x crop and
nikon/sony/everyone else is a 1.5x crop. I don't know about you, but
I'm rather glad I'm not a canon crop-sensor user and not just because
of the reduced FoV.....
On Sun, Sep 8, 2013 at 10:10 PM, P.J. Alling
<webstertwenty...@gmail.com> wrote:
DPReview seems to think that the K-5 and K-7 have exactly the same size
sensor. I don't remember where I got those numbers from but IIRC
they came
from the Pentax web site when I first bought my K20D. When the K-7 was
released the sensor was reported to be the same as the K-20D. I
could be
wrong in the particular. However there is no generally accepted
standard
specification for the dimensions of APS-C sensors.
On 9/8/2013 8:31 PM, Zos Xavius wrote:
Hmmm....according to dxomark:
K-7 - 23.4x15.6mm
K-5 - 23.7x15.7mm
If those numbers are right, the k-7 is exactly 3:2 while the k-5 is
slightly wider.
Comparing pixel dimensions I get the following aspect ratios:
K-5 - 2:3.02
K-7 - 2:3.01
Fairly negligible if you ask me.
On Sun, Sep 8, 2013 at 8:11 PM, P.J. Alling
<webstertwenty...@gmail.com>
wrote:
The Samsung sensor family used in the K20D and K-7 has a slightly
smaller
footprint on the order of 10ths of a mm than the Sony sensors used
before
in
the *ist-D and all the other Pentax DSLRs. It seems like a small
enough
difference. but that can mean a huge difference in AOV when
dealing with
wide angle lenses.
The K-20D and K-7 use a 16x23mm sensor with a ~28.02mm diagonal.
The other Pentax DSLRS, (and Nikon DX DSLRs) use a 15.7x23.7mm sensor
with a
~28.4mm diagonal.
Besides being slightly smaller the Samsung sensor isn't exactly
the 2:3
aspect ratio ratio either. When switching between my *ist-Ds and
my K20D
I
actually notice the difference in aspect ratio quite noticeable
especially
when printing.
Canon uses a 14.9 x 22.3mm sensor for it's APS-C sensor cameras
with a
diagonal of ~26.8mm
So there is a much larger difference between Canon and any of the
Samsung
or
Sony sensor cameras, but if you buy a say a 10mm fisheye lens from a
third
party manufacture that comes in multiple mounts, it may be
actually be
180°
over the diagonal of one of those sensors or none of them.
On 9/8/2013 7:11 PM, Zos Xavius wrote:
Correct me if I am totally wrong, but isn't the k-7 sensor size the
same as sony sensors with a 1.5x crop? Canon is the only oddball I
know of with their slightly smaller 1.6x crop sensor. Ok....I just
googled it. The difference is .1mm horizontally between the k-7 and
k-5. Not enough to even noticable.
On Sun, Sep 8, 2013 at 1:54 PM, P.J. Alling
<webstertwenty...@gmail.com>
wrote:
That's true, it's "around" 7.5mm. However almost all of this is
pretty
fuzzy. A full frame fisheye is supposed to cover 180° across the
diagonal
of the format.
Depending on the curvature that the lens imparts that can be
done with
a
number of different focal lengths in the same ball park can be
designed
to
do that.
Then when you get to APS-C, well, there's Canon's standard
sensor size,
the
Sony sensors which are slightly larger, the K20D/K-7 with a sensor
that's
intermediate between them, and whatever Samsung is using these
days.
Hell, even "full frame" digital sensors aren't exactly the same
size as
the
standard film gate for 35mm film cameras.
So it's unlikely that a full frame fisheye will actually fit the
classical
definition on any format. Though it would be easiest to do for
m4/3
and
4/3
system cameras since the sensor dimensions are fully specified.
On 9/8/2013 1:31 PM, Dario Bonazza wrote:
Fisheye for m4/3 is around 7.5mm. This is what I have:
http://www.ephotozine.com/article/samyang-7-5mm-f-3-5-umc-fisheye-lens-review-19847
Dario
-----Messaggio originale----- From: P.J. Alling
Sent: Sunday, September 08, 2013 7:12 PM
To: Pentax-Discuss Mail List
Subject: Re: Which second party camera system do you like?
Mini-survey
With rectilinear lenses doing format translations is easy. AOV is
AOV,
but Fisheye lenses make hash those kinds of comparisons. I have a
Pentax
17mm fisheye, and an old 12mm semi circular, (on film), fisheye
made
by
Sigma in the early 60's. I don't have any examples currently,
(and
don't even have my film scanner attached to my current
machine), but
the
12mm on APS-C digital actually seemed to cover more than the
17mm did
on
film even though the 12mm was 18mm/e. I'm pretty sure that
comparing
fisheye lenses, AOV, by focal length is a fools errand.
On 9/8/2013 12:53 PM, Aahz Maruch wrote:
On Sun, Sep 08, 2013, Godfrey DiGiorgi wrote:
On Sep 7, 2013, at 9:43 PM, Aahz Maruch <a...@pobox.com> wrote:
Sure, but there's nothing like the 8mm fisheye you can get for
APS-C
for
12mm/e. For most purposes, you're correct that's
sufficient, but
people
who really care about extreme wide-angle are likely to be less
satisfied
with m4/3.
"For most purposes ..." Don't be ridiculous.
A fish-eye lens is a specialty lens, and the ONLY wide-angle
lens
focal length not listed in native Micro-FourThirds mount.
Perhaps
that's because there's a superb fish-eye lens in FourThirds SLR
mount,
which work on mFT bodies with any of the four available,
dedicated
Panasonic and Olympus FourThirds to Micro-FourThirds mount
adapters
for 100% full function operation.
The point is that m4/3 8mm is 16mm/e.
Your comment sounds like it fits one of the categories in
Ctein's
most
recent column on "The Online Photographer":
http://theonlinephotographer.typepad.com/the_online_photographer/2013/09/bad-science-vs-good-science-a-guide-for-the-layperson-part-1.html
Check out the "God of the Gaps" category. ;-)
<shrug> Some people regularly claim that they want FF over
APS-C due
to
wide-angle versus crop-factor -- given that Marnie didn't even
know
that
m4/3 has 2x crop factor compared with APS-C's 1.5x, I think it
was
entirely reasonable to mention the wide-angle issue. I certainly
don't
think it'll play a significant role in her decision given her
telephoto
preference (or if it does, it'll have a reverse significance).
Side note: most of my shooting is also telephoto (except for
macro),
so
I'm definitely not grinding any axe favoring wide-angle and I
consider
the m4/3 crop factor a plus myself because it makes for
lighter and
smaller telephoto lenses.
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