On Thu, October 15, 2009 22:14, karl shah-jenner wrote:
> What I suspect is the manufacturers were having the marketing guys write
> up
> whatever they liked to convince buyers that they needed new lenses - aside
> from the obvious problems of using lenses designed for 35mm on what is
> often essentially a competitor to 110 - and this is no different from the
> issues one would experience using a Pentax MF lens on a 35mm camera.
I'm allergic to "conspiracy theory", and this has all the hallmarks of
that to my ear. However, I'm not an expert myself and so I can't exactly
explain everything that's really going on, either. I just don't believe
that there aren't experts who would blow the scam writing blogs on the
internet. Eventually this would become news at a level I would see it.
>>I won't for a moment disagree that the designation "digital" on lenses
>> has
> been thrown around somewhat randomly and hasn't always meant anything, and
> that it has no very specific definition. However, I do think that as
> we've learned more about digital photography, we've found some issues with
> how image-forming light coming out a lens interacts with film vs. digital
> sensors, and that some changes to lenses and some changes to sensors (or
> the microlens arrays over the sensors) have been made to make things work
> better. These issues include how the sensor reacts to light at shallow
> angles (considerably differently from film), and the fact that the sensor
> is shiny and thus can make sharp reflections, in addition to the fact that
> many DSLR cameras use smaller-size sensors than 24x36mm
>
>
> Shiny is another one that gets me. Some film surfaces have been *very*
> shiny, and atop that, some very pale - reflecting a *lot* of light around
> inside cameras.
None of the film I've used has had shiny surfaces that I can recall;
particularly not on the emulsion side. And I was making the point that
that meant it could reflect actual images, rather than just blurs. My
point was that people are more likely to notice actual ghost images than
mild flare blurs, and hence were more likely to complain about them,
making it perhaps worth worrying about improving some aspects of the lens,
that being the part the lens-makers can control.
I did have a fascinating experience involving TTL flash and a film with an
unusual reflectivity. It was the Polachrome slide film. I was using it
on-stage at the World Science Fiction Convention in 1989 (in Boston). I'd
been in charge of photography for a retrospective slide show on the
convention, to be shown at closing ceremonies. This was pre-digital, so
presenting slides at the end of the convention was a slight financial
challenge -- we had to pay a lab for extra hours and special courier
service.
To carry through the theme of "immediacy" we planned to have me take a
photo on-stage at the beginning of the ceremony, which would appear at the
end of the slide show. Hence, Polachrome.
I'd done a test run with a previous roll, so I was slightly familiar with
the processing mechanics. It hadn't occurred to us that exposing the film
would turn out to be a problem, and the test roll didn't show a problem
(it was done by available light). Here's your case for making your test
conditions as close as possible to real conditions, and losing sleep over
any differences at all :-).
Speaking of losing sleep, I was also running on two hours of sleep the
previous night, due to having been up all night processing film (the last
night we didn't have time to send it to the lab, so we processed 65 rolls
ourselves) and marking and sorting the rolls (I did the initial technical
quality control before handing it over to the people who did the final
slide show; I was also responsible for the photo team and handing out
assignments).
I was very lucky. When I started shooting pictures on stage before the
ceremony begin (I had 36 to play with, after all), the flash reported
inadequate light under conditions where this was not believable. If the
problem had been slightly different, I would have had no symptoms until
the roll came out of the processor horribly overexposed. Luckily, I had a
symptom, and I got as far (at the time) as figuring out that there was
something wrong with the TTL exposure system. I switched to A mode, and
the symptom went away, and I got a usable slide for the show.
Later, after some sleep, I realized that the Polachrome film was visibly
very much darker than "ordinary" color and B&W films. Doh! I should have
noticed that earlier, of course. Just like I should have done a test
using exactly matching conditions, meaning TTL flash, before the night of
the actual use.
> If you recall many years back me describing here how I built an
> infrared-lit film changing cabinet with a CCD camera inside? it made
> loading troublesome cameras, spools and sheet film holders very easy and
> was extra handy if I wasn't sure if a double dark was loaded or not ;)
Oh, very cool. I think I'd remember if I'd read it at the time. Neat idea!
> As I was doing a lot of IR photography I popped a bunch of cameras and
> lenses under the IR to have a peek and see how reflective the inner
> workings of the cameras were.. which is when I discovered deep black
> anodised aluminium reflects IR light like chromework - at the end of the
> day I found old British lenses with black painted interiors reflected the
> least and mirrored what I had been experiencing when using various lenses
> -
> a much sharper, contrasty image than with any other lenses. And another
> surprise was the cameras - the Canon T70 ( a dog by anyone's definition)
> was by far and away the darkest camera internally for IR light. It was
> also the *only* camera with a dark film pressure plate. Since Kodak
> weren't using an antihalation layer in their IR film, the T70 was the best
> camera to use for IR if one didn't want the dreamy, flared results we were
> used to seeing in pictorial photography. - Adding black paper from 120
> roll film to cover the pressure plate of other cameras helped to a degree,
> but the internal reflections were still there.. My point - reflections
> occurred and most people didn't notice a jot.
Fascinating! I wonder if other infrared photographers had figured this
out. They must exchange arcane knowledge somewhere!
> The Olympus cameras equipped with off the film metering were a lovely
> design, and for 90% of users performed faultlessly - but there were still
> that 10% who found a niggling problem - and for those using photography
> for
> critical applications, they came to realise the levels of light reflected
> from differing films caused differing exposures. Again, few people
> noticed
> anything.
Yep. After my experience with the Polachrome, I thought about the visible
brightness differences of other films I used, and wondered.
> Another gadget I built was intended for testing film speeds - a panel of
> ND
> squares I could photograph ensuring a full range of exposures in 1 stop
> intervals across a single frame of film :) Except it didn't work. The
> reason as I reported here was that different lenses produced quite
> different contrasts. What I didn't report was that when using the same
> lens and switching films, different films had different contrasts. This
> was not just a development issue as one would expect, as I had controlled
> for that by establishing reference development times from direct exposed
> and developed film. This again suggested refection of the film surface
> played some part. mhey - I gave all this experimenting up and worked with
> what I had ( I decided while it was a nice mental exercise, *I* didn't
> really care either ;)
Some of Ctein's work on brightness ranges I remember as coming to the
conclusion that flare was the limiting factor in anything short of very
extreme controlled conditions.
> Digital sensors - there is some interesting mechanics at play there!
>
> microlenses. Firstly we know it's not a straight sensor by sensor
> conversion to image. We don't *need* super highly resolved light falling
> on each individual sensor, in fact it's undesirable as it causes all
> manner
> of problems like moiré - subsequently an antialiasing filter is added to
> 'blur' the light. We use 3 or more sensors to determine the colour of the
> light then we interpolate that back into three separate pixel colours and
> locations. Microlenses are needed though to gather the light hitting that
> part of the sensor and focus it tightly onto the phototransistor it's
> self.
>
> Now we all know a bit about lenses, and we all know how a dome shaped
> hemispherical lens sitting above something will work - pretty much
> whatever
> angle the light strikes the hemisphere will be focussed pretty much dead
> centre - where the phototransistor sits ..just as it's designed to do to
> prevent the light falloff from reflection that would occur if the dome
> were
> not there and the surface were in fact flat. ..(if you didn't know this,
> think how a wide angle works)
Note that Leica has published diagrams and photos (and I think there are
third-party photos) showing an offset micro-lens placement (varying across
the frame, centered in the center, offset at the edges) in their M9 and I
believe M8 cameras, which they say are specifically to make them work
better with old rangefinder wide-angle lenses (and new ones, designed for
film).
I don't feel I have any reason to doubt that oblique rays are an issue for
digital sensors. It's been repeatedly said by experts from a wide range
of companies, and the outside experts aren't calling them on obvious
mistakes. This is of course very different from being an expert qualified
to really argue the question, from either side, myself!
> So we have microlenses and a fuzzing filter, we have algorithms playing
> with the data collected from the photosites - we even know now that
> fringing is correctable by firmware (the Sony F828 was widely criticized
> as
> having poor optics due to purple fringing - the fact is such fringing was
> a
> reality even for film but few people ever enlarged film images to the
> extent they do when simply viewing digital pictures and subsequently never
> saw it)
Yes, it's much easier now to "pixel peep", and people often demand levels
of quality that are irrelevant to the size prints they make.
Then again people make 4x6 foot prints from DSLR output a lot more
frequently than they did from 35mm film output! Some people are really
benefiting from the higher quality images we get today.
> When we have all this, what need is there for anything faintly resembling
> a
> requirement for light rays to be collimated, even partially?
>
> Maybe an argument could be presented for such a thing but then where are
> the real world examples?
>
> I'd imagine that in its infancy when DSLRs were first hitting the market
> and sensors were still being refined we'd have seen an uproar from people
> buying into these systems who used their old film camera lenses only to
> find vignetted dark corners, blurry images and colour fringing. It didn't
> happen.
It seems to me that people WERE complaining about that, in the early days.
But some things, like micro-lenses, were in place before it became a
consumer pass-time at all.
> So what the heck is all this in the manufacturers blurb about telecentric
> or near telecentric lenses, parallel light, etc?
>
>
> Again, I'd love to hear from anyone who owns a 'digital' lens made by a
> manufacturer who claims any such thing who can look through the lens and
> see if the aperture look *really* far away (like infinity?)
I've got a Sigma 12-24mm F4.5-5.6 EX DG ASPHERICAL HSM lens. That "DG" is
their "for digital" mark ("DC" is their mark for lenses for small-frame
digital, that won't cover the full 35mm frame; this lens covers the full
frame and hence is DG rather than DC). So I'll look when I get home.
I've also got the AF-S NIKKOR 24-70mm f/2.8G ED. They say "Fast-aperture,
high performance wide-angle zoom optimized for FX and DX-format sensors
and features Nikon?s ED Glass and Nano Crystal Coat." Does that count as
sufficiently "digital" for you? I can check it, too
Unfortunately I no longer have the 17-55/2.8 DX, I sold it off when I got
my D700.
--
David Dyer-Bennet, dd-b@xxxxxxxx; http://dd-b.net/
Snapshots: http://dd-b.net/dd-b/SnapshotAlbum/data/
Photos: http://dd-b.net/photography/gallery/
Dragaera: http://dragaera.info
