Hi all,
Excuse me if I repeat what others have said, I have been away and may
have missed some of this thread.
Hans writes:
<< The manuals of the OM-2S and OM-40 say regarding program mode under 'other
cautions':
"When the OM-2S [OM-40] Program is used with other brand lenses, Olympus can
not
assume any responsibility for poor image quality or other problems. This is
particularly true when other brand lenses are used in PROGRAM mode."
I'm not sure how serious one must take this warning. I think it only applies
if
the aperture mechanism including the levers of the lens does not operate as
smoothly as Zuiko's.
Wether Cosina zooms are included in this warning is unsure ;)
>>
Actually, even some of Olympus's own lenses don't all work as advertised in
Program mode due to differences in diaphragm construction. The exposure time
is meant to be fine adjusted (regular OTF method) after stop down to make up
for diaphragm stop down setting errors but, probably due to long bounce times
for some lenses, this is less than perfect affecting overall accuracy.
Olympus specifically mentions the following aspects (my abreviated version)
of their bad actors using Olympus house codes (my translations are guesses
marked ?) :
MZ3510K : aperture mechanism different so program setting not as described
but overall exposure still ok.
MT1820 (180mm F2.0?).MT2520 (250mm F2.0?), MT3528 (350mm F2.8?), MT6065
(600mm F6.5?), MT1011 ( 1000mm F11?): Large apertures cause problems in
stabilizing aperture blades in a short enough time. This causes inaccurate
high speed exposures.
MZ3570AF (35-70mm Auto focus zoom?) Use only in SINGLE AF mode when in low
light 9because of the focusing delaying stop down?).
"Certain lenses" with "early operation-start timing" are slightly stopped
down at low luminance so they are not fully open used in PGM mode. Overall
exposures are still correct. Third party lenses with different timing might
be a problem here as well?
M8FE (8mm Fisheye) can be used if the aperture is set to F22. The description
is a bit unclear.
Even with a standard lens Aperture accuracy is specified loosely:
Olympus specifies an **overall** exposure accuracy of +/-0.4EV in PGM mode
(specified test conditions,50/1.8/ASA 100,BV6-15)
but an accuracy of **aperture** setting (with a 50mm F1.8 lens) of:
F8: +0.7 to -1.2 EV
F3.7 +0.8 to -1.0 EV
F1.8 +0.8 to -1.0 EV
The last value makes no sense but maybe it is an "early operation start" type
see above.....
Of course the program mode does not know the lens maximum aperture so the
program setting depends on the lens maximum aperture. So in a sense there is
no fixed program for a fixed light value since it depends on the particular
lens's max aperture. With slower lenses of F3.5 F4 etc there are fewer
program steps available too.
Warren wrote:
>> I suppose the design specs for Zuiko lens set forth that xx mm. of
lever movement corresponded with yy aperture stop down.
<<
The stop down mechanism does not rely on the position of the aperrture stop
lever because the camera actually measures the light during stoping down and
halts the lever movement at the predetermined light value for the
predetermined program setting. ( that it decided on just prior to performing
stop down. )
Regards,
Tim Hughes
>>Hi100@xxxxxxx<<
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