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Posted 19/04/2005 - 23:17
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Hi Andy,
According to the specifications in the manual, the meter range is EV1 to EV21.5 Outside of this the meter will not work. Even in the dark, the camera assumes EV1 which would equate to the lens wide open and 2 secs at 200ASA. As you stop the lens down you need to increase the exposure time to keep the same EV or exposure value. Very few cameras can deal with light levels below EV1 or sometimes 0. One of the few exceptions to this was the LX which meters accurately to EV-6.5 which equates to 125 secs at F1.4 with 100ASA.
Kim
According to the specifications in the manual, the meter range is EV1 to EV21.5 Outside of this the meter will not work. Even in the dark, the camera assumes EV1 which would equate to the lens wide open and 2 secs at 200ASA. As you stop the lens down you need to increase the exposure time to keep the same EV or exposure value. Very few cameras can deal with light levels below EV1 or sometimes 0. One of the few exceptions to this was the LX which meters accurately to EV-6.5 which equates to 125 secs at F1.4 with 100ASA.
Kim
Posted 20/04/2005 - 09:22
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Thanks for your reply, Kim. I guessed it was probably to do with that, and the camera assuming open aperture in the absence of lens communication! A shame it does that and doesn't work quite like my Z1-P that will take on the fact that 'its dark out there'!
Andy
Andy
Posted 20/04/2005 - 11:31
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Hi again,
The Z1P meter is quoted as being accurate in the range EV0 to EV20. EV0 if my memory serves me correctly (which isn't always that good these days) equates to 1sec at F1.4 ASA100. At lower light levels than this, the camera may appear to give the correct slow exposure but I wouldn't rely on it and would bracket. This is especially true as you are getting into the realms of reciprocity failure. As I said before, the only "normal" camera that is accurate at very low light levels is the LX and even seems to cope with reciprocity. I suspect the reason is that it integrates to light reflected from the film plane and can even adjust the exposure time during the exposure. This integration would appear to also be affected by reciprocity and therefore it cancels itself out.
Regards
Kim
The Z1P meter is quoted as being accurate in the range EV0 to EV20. EV0 if my memory serves me correctly (which isn't always that good these days) equates to 1sec at F1.4 ASA100. At lower light levels than this, the camera may appear to give the correct slow exposure but I wouldn't rely on it and would bracket. This is especially true as you are getting into the realms of reciprocity failure. As I said before, the only "normal" camera that is accurate at very low light levels is the LX and even seems to cope with reciprocity. I suspect the reason is that it integrates to light reflected from the film plane and can even adjust the exposure time during the exposure. This integration would appear to also be affected by reciprocity and therefore it cancels itself out.
Regards
Kim
Posted 20/04/2005 - 12:11
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Kim,
Nothing can cope with reciprocity failure, which is all to do with the chemicals making up the film.
The LX is a great camera, with the best meter of any camera ever made, but even it can't change the film chemistry.
G
Nothing can cope with reciprocity failure, which is all to do with the chemicals making up the film.
The LX is a great camera, with the best meter of any camera ever made, but even it can't change the film chemistry.
G
Posted 20/04/2005 - 17:47
Link
Hi George,
I understand the problems of reciprocity and why it is caused. Indeed it can also be a problem with very short exposures. The early Pentax flashguns such as the Superlite quoted different guide numbers for colour and b/w film because the early colour emulsions had problems with the duration of electronic flashes. All I can tell you is that in my experience the LX seems to be able to cope with it and in some way compensate automatically.
When I bought my first LX, it was just before a trip to NZ where I was born. On the way out we stopped among other places in Oman and Singapore. I took various night shots and bracketed all of them but the best results were all with the settings decided by the camera. I have also used the LX to take photos of the Northern Lights in Norway and Iceland. Many of these were well in the area where I would expect to have to increase the exposure and bracketed. Again, the camera seemed to cope.
Despite trying, I have been unable to find an official explanation. However, my best guess is that it is due to the way the OTF metering works in auto mode. With most SLRs, the meter is in the head so the camera will compute the exposure and then send this to the shutter as it becomes ineffective once the mirror up. With the LX, particularlyat low speeds, it meters during the exposure. So the shutter opens, the meter kicks in and once sufficient light is reflected off the film plane, the meter closes the shutter. In this way it can also cope with changing light levels during the exposure. Now I come to the supposition bit - whether, the meter cell reacts more slowly to very low light levels or whether the electronics recognises a long exposure and increases the time I don't know, (I rather suspect it is the former) but however it does it, the effect does seem to compensate for the problem. According to the specs of the film at the time, I should have had to increase the exposure time, but the best results were always with any exposure compensation off.
As I said in my post, all my experience with the LX would suggest that it copes with very low light levels (Indeed well below the capabilities of my Gossen meter) and so I always use it in these cases. If I were using any other camera, I would be using tables and guessing.
Regards
Kim
I understand the problems of reciprocity and why it is caused. Indeed it can also be a problem with very short exposures. The early Pentax flashguns such as the Superlite quoted different guide numbers for colour and b/w film because the early colour emulsions had problems with the duration of electronic flashes. All I can tell you is that in my experience the LX seems to be able to cope with it and in some way compensate automatically.
When I bought my first LX, it was just before a trip to NZ where I was born. On the way out we stopped among other places in Oman and Singapore. I took various night shots and bracketed all of them but the best results were all with the settings decided by the camera. I have also used the LX to take photos of the Northern Lights in Norway and Iceland. Many of these were well in the area where I would expect to have to increase the exposure and bracketed. Again, the camera seemed to cope.
Despite trying, I have been unable to find an official explanation. However, my best guess is that it is due to the way the OTF metering works in auto mode. With most SLRs, the meter is in the head so the camera will compute the exposure and then send this to the shutter as it becomes ineffective once the mirror up. With the LX, particularlyat low speeds, it meters during the exposure. So the shutter opens, the meter kicks in and once sufficient light is reflected off the film plane, the meter closes the shutter. In this way it can also cope with changing light levels during the exposure. Now I come to the supposition bit - whether, the meter cell reacts more slowly to very low light levels or whether the electronics recognises a long exposure and increases the time I don't know, (I rather suspect it is the former) but however it does it, the effect does seem to compensate for the problem. According to the specs of the film at the time, I should have had to increase the exposure time, but the best results were always with any exposure compensation off.
As I said in my post, all my experience with the LX would suggest that it copes with very low light levels (Indeed well below the capabilities of my Gossen meter) and so I always use it in these cases. If I were using any other camera, I would be using tables and guessing.
Regards
Kim
Posted 20/04/2005 - 21:11
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Kim,
You don't know what reciprocity failure is. It's not wrong exposure, it's a failure of the film to respond in a predictable manner when very long or very short exposures are made.
Different films will fail to work properly at different time settings, and as the camera has no idea of the characteristics of a particular film (all it knows is the ISO rating of the film) there is no way at all in which it can cope with, or compensate for, reciprocity failure.
George
You don't know what reciprocity failure is. It's not wrong exposure, it's a failure of the film to respond in a predictable manner when very long or very short exposures are made.
Different films will fail to work properly at different time settings, and as the camera has no idea of the characteristics of a particular film (all it knows is the ISO rating of the film) there is no way at all in which it can cope with, or compensate for, reciprocity failure.
George
Posted 20/04/2005 - 22:27
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George, at the risk of putting a spanner in the works, I think Kim is saying that with the older films, whose reciprocity failure was worse than the newer ones, that the characteristics of the metering of his LX somehow compensated for the film reciprocity. With newer films (espec Fuji slide films) I haven't been too aware of recip failure anyway (ie I have been happy with the picture produced with long exposures!)
Andy
Andy
Posted 20/04/2005 - 22:29
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Hi George,
I do know what the law states as enunciated by Bunsen and Roscoe in 1862. The point I was making is that the LX doesn't just double the exposure time if you decrease the aperture by 1 stop at low levels. I first noticed it when taking photos of the Northern Lights and I did some tests on it. If it gives say 30 secs at f4 then if you select F5.6 you would expect an exposure time of 60 secs to be in accordance with the law of reciprocity. However, it gives a longer exposure than 60 secs ie allowing more light particles in. Furthermore, at F8 it gave well over 3 minutes rather than 2 minutes as you would expect. This is not in accordance with the reciprocity law and is what you would normally have to compute manually in accordance with the film specs to overcome the problem. I can't tell you which one should be "correct" in terms of EV value because I don't have another light meter that works at such low levels. Prior to using the LX, I used the KX and had to compute the values required. I agree that different film stocks will need slightly different compensation values, however in practice, I found that the differences were not that great certainly between Fuji and Kodak slide films. What I did find is that the results with the exposure compensation turned off were better than when I tried to give it slightly more as I expected to have to do with exposures up to 4 minutes.
Now how the IDM system in the LX does this, I don't know. Very few manufacturers use silicon cells at such low levels. As I said earlier I can only suppose that the cells react less strongly than they should if they followed the reciprocity rule thus cancelling the effect. What it definately won't cope with is the colour shift caused by the same problem.
BTW Films do not behave unpredictably at low light levels. They behave in a very controlled way but just need longer exposures and these are published by the film makers. Pro films are worse. Velvia needa up to an extra stop over 30 secs but the more amatuer films need less. The Sensia emulsions from Fuji don't need compensation until you reach 2 mins where a 1/3 stop is enough and 2/3 at over 8 minutes.
Regards
Kim
I do know what the law states as enunciated by Bunsen and Roscoe in 1862. The point I was making is that the LX doesn't just double the exposure time if you decrease the aperture by 1 stop at low levels. I first noticed it when taking photos of the Northern Lights and I did some tests on it. If it gives say 30 secs at f4 then if you select F5.6 you would expect an exposure time of 60 secs to be in accordance with the law of reciprocity. However, it gives a longer exposure than 60 secs ie allowing more light particles in. Furthermore, at F8 it gave well over 3 minutes rather than 2 minutes as you would expect. This is not in accordance with the reciprocity law and is what you would normally have to compute manually in accordance with the film specs to overcome the problem. I can't tell you which one should be "correct" in terms of EV value because I don't have another light meter that works at such low levels. Prior to using the LX, I used the KX and had to compute the values required. I agree that different film stocks will need slightly different compensation values, however in practice, I found that the differences were not that great certainly between Fuji and Kodak slide films. What I did find is that the results with the exposure compensation turned off were better than when I tried to give it slightly more as I expected to have to do with exposures up to 4 minutes.
Now how the IDM system in the LX does this, I don't know. Very few manufacturers use silicon cells at such low levels. As I said earlier I can only suppose that the cells react less strongly than they should if they followed the reciprocity rule thus cancelling the effect. What it definately won't cope with is the colour shift caused by the same problem.
BTW Films do not behave unpredictably at low light levels. They behave in a very controlled way but just need longer exposures and these are published by the film makers. Pro films are worse. Velvia needa up to an extra stop over 30 secs but the more amatuer films need less. The Sensia emulsions from Fuji don't need compensation until you reach 2 mins where a 1/3 stop is enough and 2/3 at over 8 minutes.
Regards
Kim
Posted 21/04/2005 - 00:38
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Kim,
Exactly.
Different films behave differently. The best the LX can do is to progressively increase exposure times in low light conditions, but whilst the degree to which it does this (if it does) might work for some films, it won't for others.
I think you have been lucky with the emulsions you have used.
G
Exactly.
Different films behave differently. The best the LX can do is to progressively increase exposure times in low light conditions, but whilst the degree to which it does this (if it does) might work for some films, it won't for others.
I think you have been lucky with the emulsions you have used.
G
Posted 21/04/2005 - 09:25
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Hi George,
It's not luck but more research, experimentation and experience.
Research. The figures I quoted for Sensia are within 10% of most medium speed emulsions. They cover all the Sensia ones and are very close to the medium speed Kodaks such as Ektachrome. These haven't changed much over the years and probably account for the vast bulk of reversal sales. Print films are slightly different but the greater exposure latitude allows the LX to cover them. As one would expect the very slow emulsions suffer more from recip but the figures for 50ASA velvia are also good for such things as Kodachrome 25 and 64. I don't have the figures for the very high speed emulsions as I see no point in using these unless I have to handheld when the problem doesn't arrive. In the past I would have to get the spec sheets from the film distributers but it is much easier now with the net.
Experimentation. As I said I bracketed to start with at low light levels until I was happy with the resuts and knew how the LX would cope. If a new emulsion comes out, I will get a couple of rolls and try it out before I would consider using it in earnest. With this I make a careful record of each exposure and vary as many of the conditions as possible and then analyse the results. Only when I am happy that I know the characteristics of the film will I use it on something important. If I get a new lens or body, I will do something similiar before I will rely on them. By doing this, I can choose the right camera/lens/film combination to get the effect that I want.
Experience. I have been using at least one LX for 23 years and have put over 2500 films through them. I "know" the LX and I am comfortable using it. I "know" the film I use and can vary the stock I use to get the photo I want. The meter system has a fantastic range but is relatively simple and can be fooled. That is why I carry a Gossen meter. We had a discussion some time ago about the relative merits of the Z1P and the MZ-S. The Z1P is probably the most highly specified camera that Pentax have produced and has a narrower but more flexible meter system. However, I could never get comfortable using it and couldn't get to understand it. The MZ-S is different. It is more intuative and I find I am coming to understand it and it may take over from the LX in time. It will be somewhat longer before I rely on the D, it is great for snapshots and webwork but it will be a while before I can get the best out of it. Not only do I have to undersatnd the vagaries of the camera but also the post image manipulation required on the PC and this is a vast field. Whether I will fully achieve this remains to be seen. To be honest, I would rather be out and about taking photos with the LX rather than stuck indoors learning how to manipulate images in front of a computer screen.
Regards
Kim
It's not luck but more research, experimentation and experience.
Research. The figures I quoted for Sensia are within 10% of most medium speed emulsions. They cover all the Sensia ones and are very close to the medium speed Kodaks such as Ektachrome. These haven't changed much over the years and probably account for the vast bulk of reversal sales. Print films are slightly different but the greater exposure latitude allows the LX to cover them. As one would expect the very slow emulsions suffer more from recip but the figures for 50ASA velvia are also good for such things as Kodachrome 25 and 64. I don't have the figures for the very high speed emulsions as I see no point in using these unless I have to handheld when the problem doesn't arrive. In the past I would have to get the spec sheets from the film distributers but it is much easier now with the net.
Experimentation. As I said I bracketed to start with at low light levels until I was happy with the resuts and knew how the LX would cope. If a new emulsion comes out, I will get a couple of rolls and try it out before I would consider using it in earnest. With this I make a careful record of each exposure and vary as many of the conditions as possible and then analyse the results. Only when I am happy that I know the characteristics of the film will I use it on something important. If I get a new lens or body, I will do something similiar before I will rely on them. By doing this, I can choose the right camera/lens/film combination to get the effect that I want.
Experience. I have been using at least one LX for 23 years and have put over 2500 films through them. I "know" the LX and I am comfortable using it. I "know" the film I use and can vary the stock I use to get the photo I want. The meter system has a fantastic range but is relatively simple and can be fooled. That is why I carry a Gossen meter. We had a discussion some time ago about the relative merits of the Z1P and the MZ-S. The Z1P is probably the most highly specified camera that Pentax have produced and has a narrower but more flexible meter system. However, I could never get comfortable using it and couldn't get to understand it. The MZ-S is different. It is more intuative and I find I am coming to understand it and it may take over from the LX in time. It will be somewhat longer before I rely on the D, it is great for snapshots and webwork but it will be a while before I can get the best out of it. Not only do I have to undersatnd the vagaries of the camera but also the post image manipulation required on the PC and this is a vast field. Whether I will fully achieve this remains to be seen. To be honest, I would rather be out and about taking photos with the LX rather than stuck indoors learning how to manipulate images in front of a computer screen.
Regards
Kim
Posted 22/04/2005 - 10:54
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Kim,
In all the stuff I have read on the LX, I have never heard that the meter attempts to compensate for reciprocity failure. I should be most interested to see if you can point me to some corroboration of this theory.
I've been trawling astrophotography sites, but turned up nothing. I'm sorry, but I believe that this is a figment of your imagination. If I'm wrong, I shall eat humle pie and apologise profusely.
George
In all the stuff I have read on the LX, I have never heard that the meter attempts to compensate for reciprocity failure. I should be most interested to see if you can point me to some corroboration of this theory.
I've been trawling astrophotography sites, but turned up nothing. I'm sorry, but I believe that this is a figment of your imagination. If I'm wrong, I shall eat humle pie and apologise profusely.
George
Posted 22/04/2005 - 14:45
Link
Hi George,
As I said in an earlier post, "Despite trying, I have been unable to find an official explanation." I went on to say "Now I come to the supposition bit - whether, the meter cell reacts more slowly to very low light levels or whether the electronics recognises a long exposure and increases the time I don't know, (I rather suspect it is the former) "
I can't quote you which SPD cell the LX uses but most LDRs do not have a linear response near the extremes. I don't think it is designed to do this but rather it is a rather useful quirk or fault.
What you wish to believe is your perogative. If you wish to believe that I have made it all up, that I know nothing about recip and that any good photos I take (including the ones on my website) are the result purely of good luck, that is up to you.
Regards
Kim
As I said in an earlier post, "Despite trying, I have been unable to find an official explanation." I went on to say "Now I come to the supposition bit - whether, the meter cell reacts more slowly to very low light levels or whether the electronics recognises a long exposure and increases the time I don't know, (I rather suspect it is the former) "
I can't quote you which SPD cell the LX uses but most LDRs do not have a linear response near the extremes. I don't think it is designed to do this but rather it is a rather useful quirk or fault.
What you wish to believe is your perogative. If you wish to believe that I have made it all up, that I know nothing about recip and that any good photos I take (including the ones on my website) are the result purely of good luck, that is up to you.
Regards
Kim
Posted 22/04/2005 - 23:43
Link
Kim,
You said: "......... the only "normal" camera that is accurate at very low light levels is the LX and even seems to cope with reciprocity."
My point is simply that I don't believe the meter of the LX is designed to make allowance for reciprocity failure. That's all I am saying.
I certainly wouldn't wish to disparage your skills as a photographer.
Regards
George
You said: "......... the only "normal" camera that is accurate at very low light levels is the LX and even seems to cope with reciprocity."
My point is simply that I don't believe the meter of the LX is designed to make allowance for reciprocity failure. That's all I am saying.
I certainly wouldn't wish to disparage your skills as a photographer.
Regards
George
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1949 posts
21 years
North Devon
Can anyone explain this?
Thanks
Andy