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04-08-2010, 11:19 AM   #46
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The LX does not meter off the film surface for fast expsoure times down to 1/75s (the sync speed). Only longer times will be metered off the film surface. For the shorter exposure times there is a reflective print on the first shutter curtain, off which the metering is taken. Quite similar to the Olympus OM method, though the Pentax metering pattern looks nicer…

--

Good point.

04-08-2010, 11:50 AM   #47
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QuoteOriginally posted by kunaalbhasin Quote
With exposures of this length reciprocity failure becomes a real issue. I'm not certain how one copes.
I would imagine you cope as with any means of shooting a long exposure. You either use the camera's calculated exposure or an external light meter, attach a cable release, put the camera on bulb, find new exposure on reciprocity chart and time the shutter yourself.
04-08-2010, 01:05 PM   #48
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QuoteOriginally posted by tuco Quote
So what is the relationship between a film's surface and its reciprocity characteristics that the camera can measure and adjust its time, I wonder.

Would it know, for instance, that this surface is 400TX and a calculated exposure of 100 seconds needs an actual 20 minute exposure?
The LX don't know anything about the Shwarzschild effect of the film you put in the box...
I think reciprocity depends on the light sensitivity of the emulsion, the interaction from the light with crystals (crystals shape?).

But the reflectivity is more a question of rugosity, the kind of top layer/protection layer you find on different films (Tmax when you prewash your film before development put purple color in the water...). For color films if you inspect the emulsion layer they have different colors. The sensor will observe what's reflected by this layer. If the color is different, you absorbed some and rejected the other part of the spectrum. And finally the sensor/meter will find + or - light even if the lightflow coming from the lens is the same.

I think It's not an obvious question. I'll think about it.

Nicolas.
04-08-2010, 01:39 PM   #49
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QuoteOriginally posted by mine.cola Quote
The LX don't know anything about the Shwarzschild effect of the film you put in the box...
I think reciprocity depends on the light sensitivity of the emulsion, the interaction from the light with crystals (crystals shape?).
So I would suspect that if a camera could determine a film's reciprocity characteristics without reading a 135 film canister's bar code and using a look up table of film brands stored in the camera, it would be such a huge marketing feature that we wouldn't even be talking about it right now.

I looked up the LX manual and there is no mention of that capability of its IDM metering system. For such an advance feature, how could it not be advertised or noted in the manual.

04-08-2010, 02:49 PM   #50
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QuoteOriginally posted by tuco Quote
So I would suspect that if a camera could determine a film's reciprocity characteristics without reading a 135 film canister's bar code and using a look up table of film brands stored in the camera, it would be such a huge marketing feature that we wouldn't even be talking about it right now.

I looked up the LX manual and there is no mention of that capability of its IDM metering system. For such an advance feature, how could it not be advertised or noted in the manual.
I think Ben's simple explanation was better--that the reciprocity effect just ends up preserving the night time mood. If you tried to expose a subject that you wanted to averag out to 18% reflectance, as metered, you would need to do some calculations that the LX is definitely not set up to do. Whatever the juxtaposition of circumstances, Pål gets some marvelous images.
04-09-2010, 05:59 AM   #51
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QuoteOriginally posted by tuco Quote
So what is the relationship between a film's surface and its reciprocity characteristics that the camera can measure and adjust its time, I wonder.

Would it know, for instance, that this surface is 400TX and a calculated exposure of 100 seconds needs an actual 20 minute exposure?
No - such intelligent features are beyond analogue cameras. They would have needed a reflectity database of sorts etc. No, the exposure system is set to a "medium" or "average" film reflectivity, which is good in most cases. There are some films, where the LX needed correction, though, like the original Velvia, which had a different reflectivity than the average film - but then, Velvia was anything but average.

Ben
04-09-2010, 06:03 AM   #52
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QuoteOriginally posted by tuco Quote
So I would suspect that if a camera could determine a film's reciprocity characteristics without reading a 135 film canister's bar code and using a look up table of film brands stored in the camera, it would be such a huge marketing feature that we wouldn't even be talking about it right now.

I looked up the LX manual and there is no mention of that capability of its IDM metering system. For such an advance feature, how could it not be advertised or noted in the manual.
No film camera could do that and certainly not the LX, which, despite being a great camera, did not sport the most sophisticated electronics. The later coming F5/F6 modells, were much more advanced electronics-wise - but even they could not recognize film types and their properties (apart from ISO and film length, the basic info stored in the bar code).

Ben
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