"Neuman - Ruether"
news:3dee84df.4266616@newsstand.cit.cornell.edu...
> >"Neuman - Ruether"
> >news:3dea5e8d.1288930@newsstand.cit.cornell.edu...
> > On Sun, 01 Dec 2002 18:35:39 GMT, "Tony Spadaro"
> >
> > > I don't know what brand you are talking about but I've used 2x
> > >converters
> > >on several and they work without stop down metering.
> >> Then you were using color negative film with the f1.4 lens
> >> and 2X converter, or you were using lenses around f1.8 or
> >> slower... The coupled-metering of the combo cannot be
> >> correct due to the inability of the converter to pass all
> >> the light of an f1.4 lens... If you compare the exposure
> >> with stop-down metering with the lens at f1.4 and at f2 with
> >> the 2X converter, you will find the shutter speed stays
> >> nearly the same, though the lens passes nearly twice the
> >> light at f1.4 as f2...
> >> David Ruether
> On Sun, 01 Dec 2002 21:59:07 GMT, "Tony Spadaro"
>
>
> > I think you have a defective meter. I've used 2X converters with
f1.4s,
> >f1.8s, f2.0s, f2.8s, and variable aperture zooms and on several different
> >brands of camera. The meter has remained accurate - although obviously
> >reporting the wrong aperture by two stops - in all cases.
> I have checked this with multiple cameras - and Nikon
> also states that using lenses faster than f2 on converters
> will result in inaccurate metering (accurate if the coupling
> is disabled and stop-dowm metering is done, since this
> meters the light actually reaching the meter, and not a
> substitute). F1.8 is close enough to "slip by", but f1.4/1.2
> isn't - unless your converters have unusually large-diameter
> glass...;-)
> David Ruether
On Mon, 02 Dec 2002 18:45:48 GMT, "Tony Spadaro"
> This may be true with some Nikons, it was not true with my F2 or Ftn, and
>it was no one has ever mentioned having the slightest problem on any of the
>Nikon sites. It is certainly not true with Canon EOS gear, or Konica
>Autoreflex T2s, or any one of a number of other cameras I used in the 60s
>and 70s, most of which had 50mm f1.4 lenses. I used B/W film and slide film
>only through most of the 60s, 70s, 80s and 90s, and have only gotten into
>using CN seriously since getting a better scanner this year.
> Is there any logical explanation for this inaccuracy or has it got
>something to do with a lack of chip in the electronic mount?
The explanation is simple: the 2X converters become part of
the optics of the lenses they are attached to, and the glass
diameter of all I have seen is insufficient to make a
combination pass enough light to be much faster than about
f4 for the combination... The metering of manual lenses uses
analogue substitutes for the exposure info unless stop-down
metering is used (the true amount of the light passing
through the optical combination is then measured, rather
than a "representation" of it), resulting in exposure error
(the camera thinks the combination is f2.8 with an f1.4
lens on a 2X converter, but it is actually closer to f4).
With electrical representations of the aperture used on the
lens, I would expect the same problem, since the "info" used
for the exposure is different from the real speed of the lens.
If the lens is shot at f 1.4 and then at f2, the
camera "thinks" a one stop change has been made in exposure,
but in reality there is very little change in the amount of
passed light. Try this: use stop-down metering with the
F2 or Ftn and meter a plain tone area at the same angle
while moving the aperture between f1.4 and f2 with the
lens on a 2X converter. I suspect that the shutter speed
change needed to indicate "correct" exposure will not
change the expected whole shutter speed (or anything like
it), indicating that the combination is about the same speed
at the lens marked aperture of f1.4 or f2, and therefore
there is metering error when not using stop-down metering...
> I ask this because if you use a T mount lens (any T mount lens, not just
>teleconverters) on an EOS body, you do have to use stop down metering as the
>camera will report an aperture of "00". Then you stop down the lens in more
>or less the match needle style of cameras like my Pentax Spotmatic.
These stop-down meterings will produce the correct
exposure - but methods using analogue hookups to the
lens will not...