Hi Kennedy,
Thank you very much for your time spend for the experiment, it is really
helpful. I think I have really got a bad 4Ti, I may try again with the OM
service center here to see if they can help. Even not, I think I can still
live with it and use spot mode at low light situation. And for OTF flash,
it is quite accurate.
Thanks again!
C.H.Ling
> Unfortunately, my Black OM-4Ti is in for service at the moment, but I
> have tried this on two other cameras - a Champagne OM-4Ti and a basic
> OM-4 (note the OM-4 appears to have a very low drain current, as posted
> on another thread, so this may have an updated circuit in it).
>
> On both cameras the results were exactly the same - indicated and
> memorised at 1/60 +/- 1/3 stop. In fact, I thought there was a problem
> since I expected the speed to be much slower without film. The meter of
> both cameras were out relative to each other by 2/3 stop, but the
> indicated and actual shutter speed stayed almost unchanged without film
> in either camera.
>
> I then extended your experiment and placed a sheet of white laser
> printer paper in the film plane and then a sheet of black paper (ie.
> fully black toner printed) and checked the indicated and actual
> exposures for a range of shutter speeds. The entire experiment took
> around half an hour with a couple of exposures at each speed to check
> for accuracy.
> _________________________________________________________________
> Champagne OM-4Ti Ser. No. 11559xx
> With BLACK paper in the focal plane :
>
> Indicated Speed Actual Memorised Speed Difference (in stops)
> 2000 2000 0
> |
> 250 250 0
> 125 125-1/3 +1/3
> 60 30 +1
> 30 15-1/3 +1 1/3
> 15 4+1/3 +1 2/3
> 8 2 +2
> 4 1 +2
> 2 ~3sec (by watch) +2 1/2
> _________________________________________________________________
> Black OM-4 Ser. No. 10398xx
> With BLACK paper in the focal plane :
>
> Indicated Speed Actual Memorised Speed Difference (in stops)
> 2000 2000 0
> |
> 125 125 0
> 60 30+1/3 +2/3
> 30 15 +1
> 15 4 +2
> 8 2 +2
> 4 1 +2
> 2 ~3sec (by watch) +2 1/2
> _________________________________________________________________
> Champagne OM-4Ti Ser. No. 11559xx
> With WHITE paper in the focal plane :
>
> Indicated Speed Actual Memorised Speed Difference (in stops)
> 2000 2000 0
> |
> 250 250 0
> 125 125+1/3 -1/3
> 60 125-1/3 -2/3
> 30 60 -1
> 15 30+1/3 -1 1/3
> 8 30-1/3 -1 2/3
> 4 15-1/3 -1 2/3
> 2 8-1/3 -1 2/3
> 1 4 -2
> _________________________________________________________________
> Black OM-4 Ser. No. 10398xx
> With WHITE paper in the focal plane :
>
> Indicated Speed Actual Memorised Speed Difference (in stops)
> 2000 2000 0
> |
> 250 250 0
> 125 250-1/3 -2/3
> 60 125 1
> 30 60+1/3 -1 1/3
> 15 60-1/3 -1 2/3
> 8 30 2
> 4 15 2
> 2 8+1/3 -2 1/3
> 1 4+1/3 -2 1/3
> _________________________________________________________________
>
> As you can see, neither of these cameras exhibited the sudden transition
> at 1/60 you are experiencing.
>
> Both of these cameras seem to follow the expected rule for exposure in
> auto mode by integrating the light reflected from a combination of the
> shutter blind and the film plane. I expect that the figures around 1/60
> with nothing in the film plane are the same because of the glossy
> reflection of the back plate - it changed by 2/3 to 1 stop when a matt
> black surface was put in the film plane.
>
> I tried the same experiment with a piece of Kodak Gold 100ASA film in
> the plane, but the differences were never greater than 1/3 of a stop -
> indicating that this film at least has a similar reflectivity to the
> shutter blind.
>
> I do no think that the Champagne OM-4Ti should exhibit any difference
> from the Black OM-4Ti since this model was only introduced for a short
> period due to fashion - what is inside is exactly the same. There
> should be far more difference between the 4 and the 4Ti than there is
> between Black and Champagne finishes of the Ti.
>
> Clearly the reflection of the film will cause a difference which is
> proportional to the shutter speed selected - as the results of the above
> experiments show. Others have posted large differences with Fuji Velvia
> and Sensia at slow speeds, which is a consequence of this mismatch
> between the shutter blind reflectivity and the film reflectivity. I
> have never used Velvia, but I would guess from the indicated exposures
> of around 1stop over the indicated exposure, that the film is darker
> than average and reflecting less light at long exposures. (This assumes
> that the quoted figures are the exposure difference, if they mean the
> shutter speed is about a stop faster then the film is lighter than
> average films).
>
> If you really are getting such a sudden transition at 1/60 (and if
> anyone else is experiencing the same) I would suggest returning your
> camera to the centre at which it was serviced and asking them to fix it
> properly - it neither behaves as theory nor practice indicates it
> should.
> --
> Kennedy
> Yes, Socrates himself is particularly missed;
> A lovely little thinker, but a bugger when he's pissed.
> Python Philosophers (replace 'nospam' with 'kennedym' when
replying)
>
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