Difference between lenses for film and lenses for digital?

On 6 Jan 2007 17:01:13 -0800, "bluezfolk" wrote:

>
>One4All wrote:
>> Is there a difference between lenses made for photographing with film
>> vs. digital photographing? I've read that there is. I ask because I
>> want to buy one of the new Pentax K cameras that will allow me to use
>> my film lenses. If there is a difference, is it so small as to make the
>> issue irrelevant?
>
>
>AFAIK they are the same, but the film lenses focal lenghts are based on
>the diagonal of the film size which may not be the same as the sensor
>size (then again it may) so there may a discrepsancy in the focal
>length. Thats why you always see digital zooms showing their 35mm
>equivalant (which is what people are used to). If I were you I'd use
>my film lenses on the digital.
>
>
> Eric

Are you sure?
Since the OP is speaking about DSLRs, he's asking about the difference
between older lenses that aren't defined as being designed for DSLRs,
as opposed to those that are labeled as designed for DSLRs.
In that case, the focal lengths are the same, and (except for the case
of Canon's EF-S lenses) can be used on film SLRs, but many will
vignette. The focal lenght, though is the same, whether the lens is
designed for DSLRs or not. Thus, a 50mm lens designed for a DSLR is
the same focal length as a 50mm lens not designed for a DSLR.
Where you see 35mm equilivents are in cameras with fixed (not
removable) lenses (such as P&S cameras) which actually have lenses
with (usually) shorter focal lengths suited to the smaller sensers
these cameras have.

--
The Coney Island Polar Bear
Club hosted its annual New
Year's Day swim in the frigid
waters off New York City Monday.
It wasn't completely successful.
Paris Hilton and Britney Spears
came out of the water just as
drunk as when they went in.
 >> Stay informed about: Difference between lenses for film and lenses for digital? 

stephen.RemoveThis@stevedunn.ca (Stephen M. Dunn) writes:
> The other is that digital sensors tend to be more reflective than
> film.

http://photonotes.org/articles/eos-flash/ says:

TTL flash metering works by measuring the pulse of flash-generated
light bouncing back off the subject and entering the lens. It
actually measures this light reflecting off the surface of the
film itself, in realtime, by using an off the film (OTF) sensor.
The light from the flash bulb is quenched when the sensor
determines enough light has been produced to achieve a
satisfactory flash exposure to get a mid-toned subject. Since
digital cameras do not have film, digital EOS cameras do not
support TTL.

So given digital sensors are more reflective than film, why is the
same trick not used for flash metering?

--
http://www.greenend.org.uk/rjk/
 >> Stay informed about: Difference between lenses for film and lenses for digital? 

On 6 Jan 2007 23:29:07 -0800, "Rich" wrote:

>
>One4All wrote:
>> Is there a difference between lenses made for photographing with film
>> vs. digital photographing? I've read that there is. I ask because I
>> want to buy one of the new Pentax K cameras that will allow me to use
>> my film lenses. If there is a difference, is it so small as to make the
>> issue irrelevant?
>
>Properly designed lenses for sensors differ from film lenses. They are
>telecentric, meaning the light rays enter the sensor surface as
>perpendicular as possible.

Supposedly, the "digital" lenses are telecentric, yet they also have a
close backfocus. IMHO those are conflicting requirements.

KS
 >> Stay informed about: Difference between lenses for film and lenses for digital? 

In article Richard Kettlewell writes:
$http://photonotes.org/articles/eos-flash/ says:
[...]
$ Since
$ digital cameras do not have film, digital EOS cameras do not
$ support TTL.
$
$So given digital sensors are more reflective than film, why is the
$same trick not used for flash metering?

Some did; the first few EOS DSLRs (sold under different names as
Canon and Kodak products) did their flash metering the same way as
the EOS 1N film body upon which they were based: using a sensor
looking at the light reflected off the "film" (OTF).

Since Canon started making DSLRs on its own with the D30, this
has been dropped; all Canon DSLRs starting with the D30 have used
only E-TTL (or E-TTL II) flash metering, which uses the same
evaluative metering sensor used for ambient metering, and don't have
the OTF sensor.

Why the change? I don't know. Canon has also been using E-TTL
or E-TTL II for film bodies for over a decade now, though until
relatively recently their film bodies also retained the OTF sensor
and supported the older A-TTL and TTL flash metering systems which
used the OTF sensor.

I can make a couple of guesses. One is that the reflections
off the digital sensor may be more directional than those off film,
and perhaps this messed up flash metering. The other is that
there are some pretty clear advantages to E-TTL/E-TTL II over
A-TTL/TTL; the flash metering zones are much smaller, which offers
the same advantages that smaller zones offer to ambient metering,
and since the zones are the same for ambient and for flash, the
amount of light added to a particular zone by the flash can easily
be determined. So maybe Canon felt it would be wise to make a clean
break here (and since many of Canon's film bodies since then have been
relatively minor reworkings of older film bodies, perhaps they didn't
feel that excising the OTF sensor from these was worth the bother).

And just to be perverse, here's one reason why OTF metering
could be *better* for digital than it was for film: it can be
designed to know exactly how reflective the digital sensor is.
With film, there's no guarantee that every film, past and future,
from every manufacturer will reflect light the same way, so the
flash metering system could come up with different answers for
exactly the same scene depending on what film was used. But
every body of the same model should have a sensor with exactly the
same reflective characteristics; measure it during development
and you're done calibrating the flash system for that model.
--
Stephen M. Dunn
>>>----------------> http://www.stevedunn.ca/ <----------------<<<
------------------------------------------------------------------
Say hi to my cat -- http://www.stevedunn.ca/photos/toby/
 >> Stay informed about: Difference between lenses for film and lenses for digital? 

[A complimentary Cc of this posting was sent to
Richard Kettlewell
], who wrote in article :
> stephen.DeleteThis@stevedunn.ca (Stephen M. Dunn) writes:
> > The other is that digital sensors tend to be more reflective than
> > film.
>
> http://photonotes.org/articles/eos-flash/ says:
>
> TTL flash metering works by measuring the pulse of flash-generated
> light bouncing back off the subject and entering the lens. It
> actually measures this light reflecting off the surface of the
> film itself, in realtime, by using an off the film (OTF) sensor.
> The light from the flash bulb is quenched when the sensor
> determines enough light has been produced to achieve a
> satisfactory flash exposure to get a mid-toned subject. Since
> digital cameras do not have film, digital EOS cameras do not
> support TTL.
>
> So given digital sensors are more reflective than film, why is the
> same trick not used for flash metering?

My conjecture is that the reason is the same as with "stealth"
aviation: AFAIU, the principal feature of so called "stealth" aircraft
is not that they reflect radiation much less (THIS holds too, but is
not the MAIN reason for hard detection), but that they reflect is much
less *in random direction*. A stealth aircraft is essentially a giant
"flat mirror": it reflects the radar radiation via more or less in one
direction; so the probability is much low that in any particular time
it would reflect anything back in the radar direction.

I would assume that the same holds for digital sensors: film reflects
more or less diffusely, but sensors reflect "mirror-like". So what
reaches the flash sensor is not very much related to what it *wants*
to see.

[All this is just a random musing, I have never seen any explanation.]

Hope this helps,
Ilya
 >> Stay informed about: Difference between lenses for film and lenses for digital? 

Stephen M. Dunn wrote:

> And just to be perverse, here's one reason why OTF metering
> could be *better* for digital than it was for film: it can be
> designed to know exactly how reflective the digital sensor is.
> With film, there's no guarantee that every film, past and future,
> from every manufacturer will reflect light the same way, so the
> flash metering system could come up with different answers for
> exactly the same scene depending on what film was used. But
> every body of the same model should have a sensor with exactly the
> same reflective characteristics; measure it during development
> and you're done calibrating the flash system for that model.

Yes, very true. The Polachrome instant slide film was *much* less
reflective than normal films, and really screwed up my flash
auto-exposures. Luckily, the error was so big I noticed the flash
running out of power when it shouldn't, and changed to A mode, and got
the pictures anyway.

I'm very annoyed about DSLR flash. Even my D200 with SB800 flash
doesn't do anywhere near as well at flash exposure as my N90 and Sunpak
555 in 1994.
 >> Stay informed about: Difference between lenses for film and lenses for digital?