From: Chris Malcolm on 12 Mar 2010 08:39
In rec.photo.digital stephe_k(a)yahoo.com <stephe_k(a)yahoo.com> wrote:
> My point was that pixel pitch below a certain level with most MF glass
> is pointless other than for marketing reasons. And is likely to have a
> threshold different from what could be useful with 35mm based Dslrs.
My point is that you're mistaken in thinking there is a threshold. At
one extreme of a very good lens and a small resolution sensor all the
image resolution comes from the sensor. At the other extreme of a very
large MP sensor and a poor lens all the resolution comes from the
lens. There's a point in the middle where the contributions of sensor
and lens to image resolution are equal. At that point improving lens
resolution is subject to ever diminishing returns because the sensor
exerts an increasingly larger effect on the combined resolution. Vice
versa for increasing sensor resolution.
So around what is usually taken to be the "threshold" there is an area
of wiggle room where although you get diminishing returns from
improving either lens or sensor resolution there still are returns.
If it can be done cheaply enough they're worth pursuing. And
because it's the square root of MP which is proportional to linear
resolution that gives quite a large amount of MP wiggle room around
the so-called "threshold".
What is currently considered the threshold is also in part dependent
on costs. When increasing MP keep diminishing in their contribution to
resolution (and other aspects of image quality) there comes a point
where it's simply not worth the money to push MP any higher even
though there are still some gains to be made. But as higher resolution
sensors get cheaper that point shifts.
So yesterday's MP "threshold" for APS-C, or for 35mm full frame, or
MF, will tend to keep drifting up as technology improves because
there's still some extra image quality to be got. Also sensor
technology in terms of noise, of exposure bleeding, and so on, keeps
improving. So some of the increasing MPs at each format is actually
delivering improved quality. Not all of it is pure marketing nonsense.
Words are good at arguing about logical relationships. They're rubbish
at arguing about numerical relationships. That's why we had to invent
mathematics. The much bruited "thresholds" of image quality with
respect to sensor and lens parameters are artefacts of the inevitably
Procrustean translation of the mathematics of resolution to words.
From: Michael Benveniste on 12 Mar 2010 08:52
"David J. Littleboy" <davidjl(a)gol.com> wrote:
> The general opinion over here is that Pentax 645 glass is sharper than
> Mamiya 645 glass, and as I demonstrate in my other note, Mamiya 645 glass
> is more than adequate for this density of a sensor.
I've never done a comparison, but I have tried two different Pentax 645
lenses on my D200 -- a 120mm f/4 Macro and a 45mm f/2.8. Like
most lenses, there was some softness wide open but each firmed up
quickly while stopping down. IIRC the D200's pixel density is about
the same as this new 645D.
So that leaves the question of how well sharpness holds up across
a 33mm x 44mm sensor. Well, my latest Pentax 645n project just
got back from the framers. It's two macros shot of a 27mm coin,
using the 120mm and an extension tube to get the needed magnification
to fill the frame. The shots hold up extremely well when printed at 20".
> So I don't have a clue as to what they'd come out with a new 55mm lens.
> Maybe gunching up performance wide open? Ah, I see. Pentax lenses are also
> known for their horrible bokeh, and this one has a rounded diaphragm.
Their 75mm f/2.8's bokeh is nothing to write home about, but I
don't think that's the main reason. Pentax needed a lens to sell with
this camera, and at least according to Pentax Canada all 645 lenses
But even if they had a warehouse or two of "new old stock," none
of those lenses would be a traditional "normal" lens for this new
camera. While there was a 55mm manual focus lens in P645 mount, they
didn't make an autofocus version. The 45mm lens is a bit too wide for
the role (35mm equivalent of a 36mm lens), and the 75mm a bit long.
The only other obvious candidate was the 45-85mm zoom, but even
ignoring the issues of price point, I suspect that's not what the
target market was looking for.
Mike Benveniste -- mhb(a)murkyether.com (Clarification Required)
Amo conventum instituti. -- Artifex Hannibal
From: David J. Littleboy on 12 Mar 2010 09:18
"Michael Benveniste" <mhb(a)murkyether.com> wrote:
> "David J. Littleboy" <davidjl(a)gol.com> wrote:
>> The general opinion over here is that Pentax 645 glass is sharper than
>> Mamiya 645 glass, and as I demonstrate in my other note, Mamiya 645 glass
>> is more than adequate for this density of a sensor.
> I've never done a comparison, but I have tried two different Pentax 645
> lenses on my D200 -- a 120mm f/4 Macro and a 45mm f/2.8. Like
> most lenses, there was some softness wide open but each firmed up
> quickly while stopping down. IIRC the D200's pixel density is about
> the same as this new 645D.
> So that leaves the question of how well sharpness holds up across
> a 33mm x 44mm sensor.
Since I have a shift adapter, I could test that as well. Doh! (Of course,
this would only be a proof of concept sort of thing since the lenses are
Mamiya not Pentax.)
>> So I don't have a clue as to what they'd come out with a new 55mm lens.
>> Maybe gunching up performance wide open? Ah, I see. Pentax lenses are
>> also known for their horrible bokeh, and this one has a rounded
> Their 75mm f/2.8's bokeh is nothing to write home about, but I
> don't think that's the main reason. Pentax needed a lens to sell with
> this camera, and at least according to Pentax Canada all 645 lenses
> were discontinued.
> But even if they had a warehouse or two of "new old stock," none
> of those lenses would be a traditional "normal" lens for this new
> camera. While there was a 55mm manual focus lens in P645 mount, they
> didn't make an autofocus version.
Oops. There you have it: a real reason. Case closed.
> The 45mm lens is a bit too wide for
> the role (35mm equivalent of a 36mm lens), and the 75mm a bit long.
The 45mm would be fine here as a normal lens. I use 65mm on 6x7 and 40mm on
David J. Littleboy
From: Bowser on 12 Mar 2010 09:22
<stephe_k(a)yahoo.com> wrote in message news:hnciu9$r2f$1(a)news.albasani.net...
> Bowser wrote:
>> On Wed, 10 Mar 2010 16:42:19 -0500, "stephe_k(a)yahoo.com"
>> <stephe_k(a)yahoo.com> wrote:
>>> Alfred Molon wrote:
>>>> In article <hn7ckt$g4d$1(a)news.albasani.net>, stephe_k(a)yahoo.com says...
>>>>> But is a crop camera 44 x 33 mm vs 56 x 42 mm of full 645 format. Not
>>>>> a huge increase over 36x24mm for the price and what you lose on wide
>>>>> angle $$$ MF glass etc.
>>>> 68% more area, that is a significant increase. It's also nice to have
>>>> 40MP resolution - no DSLR comes close.
>>> A: Is is equal resolution to what a good full frame DSRL has now?
>>> B: Is the MF glass resolving enough to do anything if it does resolve as
>>> highly. i.e. are you actually gaining anything.
>> I've seen these questions before, but back in the "film" days. Testers
>> would *prove* that MF glass has lower resolving power than 35mm glass,
>> but when comparing images from my hassy 500 C/M to those from my
>> Nikon, there was NO comparison. So will the reality that meant "more
>> film means higher quality images" hold true for larger sensors,
>> despite that the glass may, theoritically, be capable of less
>> resolution? I'm guessing yes, but I'll wait and see. Anyway, I'm sure
>> that anyone with a Pentax MF system loves this news. The 645 N II I
>> had (for a short time) was a stellar machine and maybe the best
>> handling camera I've ever owned.
> My point was that pixel pitch below a certain level with most MF glass is
> pointless other than for marketing reasons. And is likely to have a
> threshold different from what could be useful with 35mm based Dslrs. It's
> sorta like thinking how using techpan might be useful with 35mm film
> camera with really good glass, it's overkill for a 120 film camera and no
> way could you ever use the resolution the film is capable of with MF
Here again, my experience with a special B&W file in the Hassy seems to
indicate otherwise. I shot H&W Control film a while back, which was a slow
speed but amazingly fine grained and detailed film. The Hassy lenses seemed
to keep up, but this is all anecdotal, not scientific. I shot a section of
the Maine coast once for someone who wanted a large mural for their home,
and used the Hassy with the 50mm f4 wide angle on H&W Control. The final
print was nearly 12 feet wide and was amazingly detailed. Cost a fortune,
though, since it was all chemical back then; no digital printers. And H&W
was a true pain to process and print. Paper thin negs that require great
care to print. I don't miss it, not at all.
I guess I'll wait and see how the Pentax does before complaining about pixel
stuffing, and hope that it's as good as it looks. What I really liked about
my Pentax was the very simple mechanical controls. Levers, sliders, rings,
and switches beat the hell out of menu commands. You want Av? Move the
apeture ring off the green circle. Tv? Move the shutter speed dial off the
green box. Manual? Move them both. Simple, straightforward, and accessible.
I really with today's designers would revert back to more mechanical
controls for certain camera functions. And yes, give me that damned aperture
ring back. Doesn't have to be a mechanical connection, just something on the
lens that controls the aperture.
> I agree with your film based IQ assessment and still shoot MF film yet
> would never bother shooting 35mm film for the reasons you stated. It's
> also why I made the comment about this being a crop camera and isn't
> taking advantage of the full format. And how the MP count they used was
> likely done for marketing reasons, the "Holy S--- it's got 40MP" reaction.
From: Robert Spanjaard on 12 Mar 2010 10:36
On Fri, 12 Mar 2010 08:34:51 +0100, Alfred Molon wrote:
>> Who are 'they'? Pentax or Kodak? Why do you consider degraded image
>> quality to be an improvement?
> I don't think they need to degrade image quality to provide live view.
> There are so many high end DSLRs around with live view.
And how many of them use full frame CCD's? How do you switch from full
frame CCD to CMOS without losing image quality?
Regards, Robert http://www.arumes.com