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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