On Thu, 20 Mar 2003 07:33:00 GMT, dhaynie@jersey

On Thu, 20 Mar 2003 07:33:00 GMT, dhaynie@jersey.net (Dave Haynie) wrote:

>On Thu, 20 Mar 2003 00:32:22 GMT, d_ruether@hotmail.com (Neuman - Ruether)

>wrote:

>>On Wed, 19 Mar 2003 15:42:40 GMT, "ralford"

>><ralford@bigfoot.com> wrote:

>>>Not to diminish your post, however, the link from Dave (I think) ,

>>>http://www.mav-magazine.com/Apr2000/page22.html does a nice and easily

>>>available job of discussing most of what you describe.

>>[...]

>>Ummmm, actually, I describe so very, very much more,

>>below...;-)

>The MAV article was only really addressing aperture, which was the

>thing you all forgot from the on-going debate. You'd certainly need a

>casual acquaintance with the basics before reading that. Given the

>level of the discussion, I assumed that had either been covered, or

>was implicit, when I jumped in.

Ummm, I think I covered this, with (among other things):

>> "Most lenses are fitted with a "diaphragm", which allows

>> adjustment of the amount of light passing through the

>> lens, and this is calibrated so that as its area is

>> changed, a commonly-used set of names ("f-stops")

>> is used to describe the changes. These are based on

>> the same formula, FL/diam.=f-stop (example: 100mm

>> f2 lens has its diaphragm diameter cut in half, so now

>> 100mm/25mm=f4). This specifies the brightness of

>> a given light that passes through the lens, *regardless*

>> of all other factors (f4 is f4 is f4, regardless of lens

>> FL or maximum clear aperture [with exceptions

>> occurring if transmission is unusual, if illumination

>> isn't even, if the lens does not open as wide as f4, and

>> especially if focus is radically changed from infinity

>> to very close - but in this last case, reworking the

>> figures by adding the FL to the increased lens-center-

>> to-sensor distance needed to change the focus gives

>> you the correct new "effective aperture" {example:

>> 100mm f2 lens is focused very close, requiring 50mm

>> of extension to achieve correct focus, so then

>> 100mm+50mm/50mm=f3, vs. 100mm/50mm=f2}])."

And, I repeatedly added in the discussion that the

lens characteristics (including f-stop used, of course)

were specified as equal (the only reasonable thing to do

in a comparison of CCD sensitivity...). I also repeatedly

pointed out that the lens really is irrelevant in

the discussion, which is still true...;-)

>>>> which is limited by (but not to!) the lowest resolution

>>>> part of the system. The resolution product is always

>>>> lower than the lowest part, but can be improved by

>>>> improving any part, including ones that are already

>>>> far higher than the lowest.

>And conversely, in the effective resolution convolution, the weakest

>link predominates. Which is, I suspect, the big reason that lens

>quality has only recently become a selling point in consumer digital

>photography. And in video, it's still largely just a high-end issue --

>folks rarely pick their fixed-lens camcorder based on lens quality.

>It's not that it doesn't matter, but that, even when you're at 25:1

>zooms (crazy range, to a guy who grew up in 35mm land and didn't even

>own a zoom until I bought my first camcorder), the weak link is the

>imager.

This is true. But, oddly, as I pointed out above, improving

the already-better part does improve the product. You can

actually follow image degradation due to diffraction with

the better small camcorders, for instance, though the

effects are subtle compared with possible imager

characteristics changes... (see:

www.David-Ruether-Photography.com/diffraction.htm).

>In film photography, the weakest link has increasingly not

>been the film. In digital still photography, the growth from 2 to 4 to

>6 and now, up to 16Mpixel sensors has that technology converging on

>the same issues that film photography has had to deal with: a good

>lens can be expensive, even in the day of CAD and rare glass optics.

>Dave Haynie

This is not necessarily true. In the diffraction test

with the VX2000, the lens included in the "package"

(presumably a not very expensive part) is quite good,

having very good resolution to the corners of the TV-safe

area even wide open - and it reaches diffraction-limiting

fairly early as it is stopped down (and no lens of any price

can exceed this limit...), it shows good brilliance and

freedom from flare and ghosting, so...;-) It is not as low

in linear distortion as a more expensive lens (which would

likely be slightly faster, with diffraction-limiting

reached at a wider stop - and with better manual zoom

and focus controls). This brings up another issue with

lenses (it is never simple...;-) - lens performance varies

(both center and edge/corners) with f-stop used, focus

used, and with angle-of view selected. One cannot refer

to "lens performance" as a single quantity... And by

mid-stops, a cheap lens *can* about equal a very expensive

lens in most important respects... And, BTW, I have a

still-photo background in lenses, too - see: