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Thread: What is EI?

  1. #11

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    Quote Originally Posted by roteague
    I agree with David. I've always thought of EI as a personal index of what to rate film speed. I know a lot of people w ho use Velvia 50 rate it at 40, so that would be ISO 50 but EI 40.

    BTW, this is not a strickly B&W rating, although I imagine that is where you will see it mostly used; you can also use it for color.
    This is an interesting point. As a colour neg user and home processor, I don't think I have ever seen it mentioned in any colour photography book I have read. Mind you colour workers( transparency and neg) seem to be the poor relations in terms of good books. There's no equivalent of Les McLean's " Creative B&W Photography" or "Way Beyond Monochrome" etc. All colour books are about taking photos with little about processing other than to say follow manufacturer's instruction to the letter.

    Given that there's no leeway with the developing times, how would it work? Presumably overexposing a little affects colour saturation but what other less desirable effects does it have? I have never seen any film testing routine to establish EI. If I can increase saturation and improve shadows by a lower ISO than the stated by the manufacturer, what are the downsides?

    I would appreciate information on this and which books cover it?

    Thanks

    Pentaxuser

  2. #12
    Lee L's Avatar
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    Quote Originally Posted by Woolliscroft
    Are you sure it was the EI of the camera, rather than film? If so, it might be the lowest light level the meter can record accurately.

    David.
    If it is the lowest light level the meter can read, it would be referred to as EV (exposure value), and not EI (exposure index).

    Lee

  3. #13

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    You will also see the term EFS, Effective Film Speed.

  4. #14

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    Quote Originally Posted by pentaxuser
    This is an interesting point. As a colour neg user and home processor, I don't think I have ever seen it mentioned in any colour photography book I have read. Mind you colour workers( transparency and neg) seem to be the poor relations in terms of good books. There's no equivalent of Les McLean's " Creative B&W Photography" or "Way Beyond Monochrome" etc. All colour books are about taking photos with little about processing other than to say follow manufacturer's instruction to the letter.

    Given that there's no leeway with the developing times, how would it work? Presumably overexposing a little affects colour saturation but what other less desirable effects does it have? I have never seen any film testing routine to establish EI. If I can increase saturation and improve shadows by a lower ISO than the stated by the manufacturer, what are the downsides?

    I would appreciate information on this and which books cover it?

    Thanks

    Pentaxuser
    Since this was brought up by another poster earlier, I will weigh in and say that yes color materials are routinely rated differently then the ISO rating.

    I can't direct you to specific places where this has been published but suffice it to say it has been published many, many times over the past twenty five years.

    The norm is to under expose color transparencey materials to achieve better color saturation and to over expose color negative materials.

    Color transparency materials have a much narrower latitude...thus it is fairly common to depart from the ISO by 1/3 stop...example of ISO 64 Kodachrome rated at EI 80.

    Color negative materials are commonly wider latitude and departures can approach one stop, much the same as black and white film. Example ISO 200 rated at EI 100.

  5. #15

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    Quote Originally Posted by Donald Miller
    Since this was brought up by another poster earlier, I will weigh in and say that yes color materials are routinely rated differently then the ISO rating.

    I can't direct you to specific places where this has been published but suffice it to say it has been published many, many times over the past twenty five years.

    The norm is to under expose color transparencey materials to achieve better color saturation and to over expose color negative materials.

    Color transparency materials have a much narrower latitude...thus it is fairly common to depart from the ISO by 1/3 stop...example of ISO 64 Kodachrome rated at EI 80.

    Color negative materials are commonly wider latitude and departures can approach one stop, much the same as black and white film. Example ISO 200 rated at EI 100.
    Thanks Donald. I have settled on Fuji Superia 100 as my standard colour neg film in reasonably bright conditions. This film has particularly good saturation in normal light so pretty happy with its performance but I have noticed that my negs are thinner and colours paler in poor light conditions such as the inside of buildings.

    As processing time is standard, I presume that I could treat the film similarly to Ilford XP2 and rate it at 50 in poor light, reverting to 100 again in brighter conditions.

    Second question:Rating 100 at 50 can give problems with exposures handheld. What are the losses of using Superia 200 and rating at 100 in poor light compared to using 100 and keeping it at 100. Do I get the best of both worlds of extra saturation in low light with easier handholding exposures and negligible quality loss compared to using 100 at 100?

    Anyone out there with experience of rating Fuji Superia 100 at other than 100 or indeed using Superia 200 at 100? If so I would appreciate your opinions on the effect.

    Unless the quality of neg begins to suffer appreciably at 200 then it may pay me to switch to 200 and rate at 100 where extra saturation and avoidance of thinness in the neg is desired. I am unlikely to want to enlarge greater than 8 x 10.
    Thanks

    Pentaxuser

  6. #16
    Helen B's Avatar
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    In general colour neg film responds very well to 'overexposure'. I'm not sure about Superia, but Kodak Ultra 100 (a misnomer - it isn't ultra-saturated) has about 13 stops of useful range and the new Fuji Pro 160S seems to be very similar in many respects. Setting your meter to half or even a quarter of the box speed tends to place your exposure closer to the middle of the film's response curve, improving shadow detail, lowering the graininess and helping with light temperature mis-match. The more exposure you give dye-image negative film, the lower the graininess. In mis-matched lighting (eg shooting daylight film in tungsten light) 'overexposing' allows all the layers to have full exposure. In the 'daylight film in tungsten light' example, the blue-sensitive layer keeps from being a horrible grainy mess while the film's overexpose latitude keeps the red-sensitive layer from being blown out in the highlights. This could be one reason for the quality difference you see between outdoor and indoor photos, and why you should set a lower EI indoors than out.

    As an aside Pro 160S is available in 220 and 4x5, which Ultra 100 isn't, as far as I know. They are both superb films.

    Best,
    Helen

  7. #17

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    One more thing. EI tends to be a function of your equipment. Maybe your shutter is off 10%. Or your meter reads high. Using an EI instead of the box speed will give you better results. The downside is you have to put the effort into finding your EI.

  8. #18

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    Quote Originally Posted by Helen B
    In general colour neg film responds very well to 'overexposure'. I'm not sure about Superia, but Kodak Ultra 100 (a misnomer - it isn't ultra-saturated) has about 13 stops of useful range and the new Fuji Pro 160S seems to be very similar in many respects. Setting your meter to half or even a quarter of the box speed tends to place your exposure closer to the middle of the film's response curve, improving shadow detail, lowering the graininess and helping with light temperature mis-match. The more exposure you give dye-image negative film, the lower the graininess. In mis-matched lighting (eg shooting daylight film in tungsten light) 'overexposing' allows all the layers to have full exposure. In the 'daylight film in tungsten light' example, the blue-sensitive layer keeps from being a horrible grainy mess while the film's overexpose latitude keeps the red-sensitive layer from being blown out in the highlights. This could be one reason for the quality difference you see between outdoor and indoor photos, and why you should set a lower EI indoors than out.

    As an aside Pro 160S is available in 220 and 4x5, which Ultra 100 isn't, as far as I know. They are both superb films.

    Best,
    Helen
    Helen. Thanks for taking the trouble to do a detailed reply. Can you indulge me a little more. Looking at those of your photos which included sky has reminded me of another problem I have on some prints but not all. I am sure that on some, the sky was blue at the time of taking but has shown up as a disappointing grey/white on the print rather like that of a B&W print with no filter and clear sky.

    I had assumed that this was due to the in-camera meter metering for the foreground which was the bulk of the picture and the exposure effectively burning out the sky. I don't recall this happening ever with a polariser. This should tell me something, I feel but not sure what except that the blue sky is darkened to an extent that prevents burn out even where the sky is over exposed. If I am right about sky over exposure(no polariser) then am I also right that those negs which were OK for foreground before reducing box speed will now have an even more burned out sky in return for better saturation in foreground colours and I can expect even less blue skies by reducing film speed.

    I had assumed that the cure for grey skies when there should be at least a hint of blue is either a ND grad at the taking stage or dodging the sky at the printing stage. I have seen examples of increasing sky exposure at the print stage by 50% and printing through extra yellow while dodging the rest.

    Dodging and burning in colour has been more miss than hit to date and I'd rather avoid it.

    The strange thing is that sometimes in negs which exposurewise seem to have been taken in almost identical circumstances, the sky has turned out OK.

    So to summarise, what effect can I expect on skies if I lower box speed?

    Nick. Thanks. Yes I must try and set my own EI some day for both colour and B&W as you may very well be right about a meter problem. I have a Pentax MZ7. No separate meter and I don't know how good the in-camera meter is.

    Pentaxuser

  9. #19
    Mick Fagan's Avatar
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    Firstly, Helen I think your replys to technical questions are brilliant, this current reply is no different.

    Pentaxuser, I use Fuji Reala, now called Superior Reala or something like that. I've found it's most useful true speed to be 80 ASA externally and 64ASA internally.

    If you wish to push process C41 you can, it's not the greatest but it can be done, I have done it and it gets you an image. If you wish for the best possible colour reproduction then push processing isn't the go.

    To push C41 1 stop, add 15 seconds. To push it 2 stops add 30 seconds and hold your breath for the results.

    I have used this procedure quite a few times over the years, it's reasonably successful. In mixed lighting the colour accuracy isn't going to be brilliant so the push processing isn't noticed.

    For Erin, this has been knocked off of Wikpedia and possibly is the real answer to EI (Exposure Index)

    Film speed is found by referencing the Hurter & Driffield curve for the film. This is a plot of density vs. exposure (lux-s). There are typically five regions in the curve: the base + fog, the toe, the linear region, the shoulder, and the overexposed region. Following the curve to the point where it exceeds the base + fog by 10%, find the corresponding exposure. Dividing 0.1 into that yields the speed.

    The speed is used in the Exposure Index equation to find the appropriate exposure. Four variables are available to the photographer to obtain the desired effect: light, film speed, f/#, and exposure time (shutter speed). The equation may be expressed as ratios, or, by taking the logarithm (base 2) of both sides, by addition. In this form, it was easier at the time it was proposed to put into a nomograph (slide rule) so non-scientists could obtain good results. As a result, every increment of 1 is a doubling of light intensity, known as a "stop". The f/# is the ratio between the lens focal length and aperture, which in turn is proportional to the lens area by the square root. Thus, a lens set to f/2 allows twice as much light to strike the focal plane as a lens set to f/1.4. Therefore, each increment of the square root of two (approximately 1.4) is also a stop, so lenses are typically marked in that progression: 1.4, 2, 2.8, 4, 5.6, 8, 11, 16, 22, 32, etc.

    Or you can go here to see the whole article, it's short but interesting, and, presumably, reasonably accurate!

    http://en.wikipedia.org/wiki/Film_speed


    Mick.
    Last edited by Mick Fagan; 12-06-2005 at 05:27 AM. Click to view previous post history. Reason: Spelling

  10. #20
    Mick Fagan's Avatar
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    I've just read the above thread in which I inserted some Wikpedia information.

    "Thus, a lens set to f/2 allows twice as much light to strike the focal plane as a lens set to f/1.4".

    The above sentence is to my understanding completely wrong.

    It should read:-

    Thus, a lens set to f/1.4 allows twice as much light to strike the focal plane as a lens set to f/2.

    Somehow the figures were put in back to front, unless I'm very much mistaken.

    Anyone else care to comment?

    Mick.

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