I (Bart) wrote:
>>Yesterday I was browsing through the 70-200 manual when I came across
this
>>remark:
>>"when using a 2x extender (teleconverter) with the 70-200/4 L and the EOS
5
>>set an exposure compensation of -1 on the camera"
>>The manual only mentiones the EOS 5 here, and only in combination with a
2x
>>teleconverter. Does anybody know why I should have to dial in this amount
>>of exposure compensation with my EOS 5??? Until now I was under the
>>impression that the camera's meter doesn't care if there is a
teleconverter
>>attached or not...
Hubert Wachter wrote (he replied directly to me, but I think this may be
interesting for others, too):
> All EOS bodies have exposure-compensation tables built in to correct
> certain 'anomalies' that occur whe combining some equipment. In the case
of
> the EOS 5 these tables only go up to an aperture of f5.6. The combination
> that you are using results in an aperture of f8 which isn't covered in
the
> build in table anymore. Thus you have to set a manual correction. Note
that
> a manual correction may not always be necessary.
> I'm including an explanation from Canon USA as attachment.
The attachment contained the following text:
---------------------------------------------------------------------------------------
�RECOMMENDED EXPOSURE COMPENSATION FOR EOS 5/A2E/A2 WHEN USING
������������ SUPER-TELEPHOTO LENSES COMBINED WITH EXTENDERS
������������Metering Pattern����� EF300/4L��� EF400/5.6L��� EF 500/4.5L��� EF600/4L
----------------------------------------------------------------------------------------
Extender��� Evaluative, CWA������� None�������-0.5����������-0.5���������� -0.5
EF 1.4x���� Spot�������������������__���������-0.5����������None������������None
Extender��� Evaluative, CWA��������-0.5�������-1.0����������-1.0����������� -1.0
EF 2x������ Spot�������������������-0.5�������-1.0����������-0.5������������-0.5
The reasons why compensation is only necessary for the EOS 5/A2E/A2 are fairly
complicated. It boils down to the following:
1. The EOS 5/A2/A2E focusing screens are optimized for brightness. As a result,
they pass disproportionately more light to the metering system at moderate
apertures than other screens that are not optimized for brightness.
2. All EOS cameras with bright screens incorporate a program that automatically
compensates for these anomalous light transmission characteristics. This
program was originally designed to work properly at all apertures up to f/5.6.
(EOS cameras introduced after the 5/A2E/A2 contain additional programming that
negates the need for user-set exposure compensation when EF Extenders are used
with any compatible EF lens.)
3. All EOS cameras with multi-point AF systems must incorporate an additional
exposure compensation program that accounts for variations in the amount of
illumination received by off-center metering segments compared to central
metering segments; in older models such as the EOS 5/A2E/A2, this compensation
program is also tied in to maximum apertures of f/5.6 or greater.
4. The use of extenders with lenses having nominal maximum apertures of f/4 or
smaller results in effective maximum apertures smaller than f/5.6, which exceed
the parameters of the 5/A2E/A2's built-in compensation programs, thus requiring
user-set exposure compensation.
---------------------------------------------------------------------------------------
End of attachment.
End of Huberts e-mail
Thanks you Hubert for this information!
But now I'm wondering.... Apparently exposure compensation is necessary if
I use a teleconverter/extender. Normaly, the compensation is done
automatically by the camera, using its built-in exposure compensation
table. But this would only work with teleconverters, like the original
Canon extender, that have this special electronic circuit installed that
will report the true maximum aperture to the camera. So if I use my cheapo
Tamron teleconverter, the camera does not know about the smaller maximum
aperture, ergo it will not use it's compensation table, regardless if I use
the EOS 5 or an EOS 3 for example. So, does this mean that with a
third-party teleconverter I ALWAYS have to apply the correct amount of
exposure compensation manually???
Kind regards,
Bart
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