Re: Question about lens F-rating on digital slr
- From: Wolfgang Weisselberg <ozcvgtt02@xxxxxxxxxxxxxx>
- Date: Fri, 25 Aug 2006 03:02:50 +0200
Bill <bill@xxx> wrote:
Wolfgang Weisselberg wrote:
I've wondered about this since I read in an Australian lens review that
putting a full frame lens (like the F2.8L) on a 1.6 crop digital can
actually result in reduced performance over putting a lenses specifically
designed for the smaller sensor.
There is no such thing as special "digital" glass, so no, the results
will not be reduced at all.
Ah, but there is:
- lenses that don't fill out full frame, only the crop frame.
Cheaper, lighter and --- if build well --- just as good.
I understand what you're trying to say, but I'm sorry that's a design
issue, and has nothing to do with special glass properties.
"glass" as in "lens", yes, that's a digital lens, since the
APS format is dead.
"glass" as in "UD elements" or "flourite elements", no,
there's no special "digital elements" stuff.
- lenses that (e.g. by multicoating) deal "better" with light
entering from the sensor's end. Where "better" is probably
when compared to that manufacturers normal methods or marketing.
That one I will "agree" is marketing, nothing more.
At first I thought there might be something to it - seemed somewhat
logical. But after personally using over a dozen different lenses from
both Canon and Nikon that were all designed, coated, and manufactured
before digital SLR came into fruition, I believe it's a load of bunk.
Ah, but did you sample good lenses? These would be designed right
(instead of cutting corners).
Have you also tested them in high contrast situations, e.g.
shots where the sun is near or in the frame, possibly without
using a lens shade?
As I'm sure you remember, some years ago the digital craze really took
off, and anything that had the word "digital" slapped on the side of it
was a hot seller due to brilliant marketing in the new digital age.
It still shows today, but to a lesser degree, when buying something that
is not at all digital, like home theater speakers.
Naah, there are many 'digital' thingies that didn't make it.
Using a FF lense on a 1.6x cropped camera will use the "sweet spot" of
the optics in the lense center, usually resulting in better sharpness
and contrast across the 1.6x cropped frame.
Compared to that FF lens on a FF sensor. A bad FF lens will not
magically become good on a crop sensor.
I didn't say it would.
I didn't say you did.
Obviously they will not become great lenses. But they do produce better
results at the sensor edge than they do at the film edge.
True, unless they were completely broken by design (e.g.
being even worse halfway to the border than at the border).
However, that only matters if the lens itself is good enough
for the pixel peeping possible with todays digital cameras.
Lenses that were made 10+ years ago before DSLR cameras even existed
will function perfectly on cropped sensor cameras and produce the same
The 75-300mm is from 1995 ... and most tests do not test
things like "shooting into the sun", flaring, ...
That has little to do with digital, and a lot to do with lense coatings
and quality of design.
Ay, and there's the rub: does the lens coating handle
light reflected from the film/sensor well?
Quite simply, a well designed and high performing lense made years ago
will work just fine on a digital body.
*IF* used so that it's strengths come into play, not
it's weaknesses. (Every lens has both!) As an example, I
wouldn't like trying to focus a MF lens on today's amateur DSLR
viewfinders, with just a poor excuse for ground glass and no split
screen nor microprism ring --- at least in most circumstances.
(Small apertures and hyperfocal distances come to mind.)
I also wouldn't like a 28mm for WA on a crop sensor.
I also wouldn't like provoking flare and stray light with some
lenses (just look at 30 odd elements of some IS zooms of today),
even if they are near perfect otherwise.
I've read reports of people using Nikon F-mount lenses from the 60-70's
on their digital bodies, and they all work just fine.
And why shouldn't they?
A good lense is a good lense.
 digital sensors reflect much stronger than film (which rather
scatters light than reflecting it, too). Which exacerbates the
problem of in-lens reflections back to the sensor/film. That's
the reason TTL flash metering is done with pre-flash(es),
not with light reflected from the film/sensor.
I'm sorry, but pre-flash TTL came into existence prior to digitals
proliferation, back in 1995 for example for Canons E-TTL.
True --- look up Canon's A-TTL for even earlier use of
But that doesn't invalidate my statement (ok, I was unclear:
"digital sensors reflect much stronger [and don't scatter
light]. That's the reason [for] preflashes]."
From what I understand, because the AA filter over the sensor is flat,
So is the CCD or CMOS chip. It has to be flat and exactly
perpendicular to the optical axis, or you'll have problems with
varying sharpness especially wide open.
any light it reflects goes straight back instead of scattering light the
way film does. So bouncing light to the TTL flash sensor inside the
mirror box was no longer practical with digital bodies.
Yes. Now, the light is reflected, straight back. If the lens was
only coated and designed for light entering from the other side,
that might give problems, like stray light being reflected back
to the sensor, and not necessarily on the same pixel ...
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