Checking Light meter accuracy- Did I do something wrong?

Discussion in 'Beginner Questions' started by johnmikka, Sep 7, 2020.

  1. William Michael

    William Michael Moderator Staff Member

    You are confusing "correct exposure" thinking that it relies on colour of the Subject - it doesn't

    Re read what AJG wrote.


    Look at it this way: you have a black cat and a white cat sitting on a fence, it's a bright sunny day, the cats are facing the sun (i.e. "Front Lit")

    The light illuminating each cat is exactly the same.

    To make a "correct exposure" of each cat you'll need to use the exactly the SAME exposure setting for the camera, and those exposure settings will very close to: 1/100s @ F/16 @ ISO100.

    It doesn't matter one iota what colour the cats are: throw a ginger cat onto the fence and the exposure settings for the picture will still be the same.

  2. An incident meter is meant to be used (dome up) at the subject position and pointed back towards the camera.

    I'm pretty sure that's clearly stated in the Sekonic instruction manual, but that's not what you're doing is it?

    Additionally, backlit, trans-illuminated and self-luminous subjects need to be close metered or spot metered using the reflective method.

    As well as reading the manual, Sekonic have some good instructional articles on their website.
    Last edited: Sep 8, 2020
  3. Yes, I agree with AjG, I guess I worded it wrong. But that I meant, if a person is wearing a white shirt and a black shirt, it will be impossible to use a spot meter and get the "correct" exposure since it will average the two colors to compensate for a neutral grey, which translate to white is kind of grey
    and black is kind of grey.... am I correct this time?
  4. Yes, they are meant to work that way, but I'm making up a hypothetical scenario where my camera has no meter, and I'm shooting to expose the curtain correctly. I'm putting the dome closely against the curtain, is it not "close metered" as you mentioned?
  5. If I'm not mistaken, were you to bring your camera close enough to the subject and focus only on an 18% grey card and then compare that to the incident reading (and the meters were both calibrated) I think you'd get close to the same reading. One thing you could do is to take a picture with both readings. Looking at the pictures (keep careful notes) you will see what is correctly exposed in the pictures and what each one misses.

    An incident meter isn't "fooled" into giving you a bad reading on a bright white subject or a dark subject, but it assumes you want to expose as if the subject is 18% grey. So if the subject IS white, it will be white in the picture (ditto black) BUT that doesn't mean that the white won't be blown out or the black blocked up. It depends on the dynamic range of the scene. So using a reflective meter you can spot meter the shadows/blacks and the highlights/whites and determine if your film (or sensor) can handle it. If not, YOU can choose whether to preserve the highlights or preserve detail in the shadows.

    Neither of them guarantee a good picture. Camera makers have been working on "matrix metering" and its descendants to analyze the scene (highlights and shadows) and "guess" what the best meter reading should be (rather than you doing it). Some of them are quite good, but actually using a normal meter (reflective, spot, or incident) requires you know what they measure and learn how to use them correctly.
    movingfinger and johnmikka like this.
  6. William Michael

    William Michael Moderator Staff Member

    I think that you might be trying to express a method to get the correct exposure, if you only had a Spot Meter: you could Spot Meter either the black shirt OR the white shirt and compensate those readings to arrive at the correct exposure.

    If you are using a Spot Meter the area being measured is very small, so the Spot Meter does not do any "averaging" - you would have to do the compensation.

    If I only had Spot Meter, and I had a person in black trousers and white shirt, then I would probably Spot Meter and area on the person's face and compensate that exposure reading based on the type of the Subject's skin.

    I think that Spot Metering is not often used, nowadays.

    johnmikka likes this.
  7. William Michael

    William Michael Moderator Staff Member

    As an observation, I think that you should consider that these hypothetical scenarios may be adding to confusion, rather than moving you forward in learning Real World Photography.

    AJG likes this.
  8. I'm beginning to wonder ...
    William Michael likes this.
  9. AJG


    I think the OP needs to take more photographs and do a little less theorizing about how things work. The best advice I ever got from someone when I was young and asking these kinds of questions was "Try it and see what you get..."
    movingfinger and William Michael like this.
  10. If you want to check the Nikon FM meter against the Sekonic L358 in incident mode you need to do the following.
    1. Use the Sekonic with the lumisphere down.
    2. Put an 18% gray card where the subject is.
    3. Measure the light with the Sekonic meter at the gray card but facing the camera.
    4. Measure the light with the Nikon FM that is close enough to the gray card so the gray card fill the viewfinder. It doesn't matter if the graycard is out of focus. Make sure you or the camera doesn't cast shadlow on the gray card.
    5. Compare the reading and the Sekonic should read the same as the Nikon FM.

    The Nikon FM doesn't have a built in spot meter. It has a reflective center weighted at 60/40. To eliminate the weighting make sure the fill the frame with a subject with even brightness. Your reading of 3 stops off is about correct.
    William Michael and johnmikka like this.
  11. I don't understand why I got so many criticism over a scenario that I'm observing in my bedroom: There is a white/ beige silk curtain backlit by the window, I have camera (pretending with no meter), I have an incidence meter --> how would I meter this curtain to get the right exposure.... is this so remote and "theoretical"???

    Anyways, I just measured it, the Sekonic incidence gives consistently 2-2.5 stops under than the spot meter in my camera. And I attribute it to the reflective element of the curtain.
  12. You can't measure a backlit curtain with an incident meter. Not criticizing you but that is one of the situation when the incident meter doesn't work.
    glen_h, William Michael and AJG like this.
  13. James G. Dainis

    James G. Dainis Moderator

    With an incident meter you use it by aiming it back at the camera not at the subject. That measures the light falling on the subject not the light reflecting off of the subject.

    Ergo, if you have the incident meter facing the curtain, you are not using it correctly, are you?
    William Michael likes this.
  14. AJG


    All three Sekonic incident meters that I have owned came with a reflected light adapter that can be put in place of the incident dome. I don't know about your specific model, but it is possible that if you bought a used meter that the reflected light adapter is missing. On mine these are small parts and easily lost, so I am careful to keep them in the compartment in the case that came with the meter. If you have the adapter and meter carefully with it you should get a very similar if not identical reading to what you're getting with your Nikon FM.
    William Michael likes this.
  15. William Michael

    William Michael Moderator Staff Member


    This scenario this is both 'remote' and also, it is well beyond 'theoretical'.

    As has been mentioned many times using an Incident Meter to meter a backlit curtain is using the wrong tool. We might as well be discussing how to drive a nail into hardwood with a screwdriver.
    Secondly, as has been also mentioned, your camera has no spot meter.

    Thirdly, also as has been previously explained, your conclusion that the curtain's reflective element causes the metering difference between the camera's meter and the Sekonic meter, is simply wrong.


    I have re-read every response: I read no criticism of you whatsoever.

    I do read many responses which provide accurate technical information; advice based on experience and knowledge to see you progress in your knowledge; or both.

    Moreover, this conversation has bounced around, for whatever reason, across a few different topics and the responses have attempted to correct your inaccurate assumptions and steer you to better understanding at each new bounce.

    Also, in is well worth noting, contrary to your opinion "valuable lesson learnt, again for free through the internet" - the lessons you are being provided in this conversation are not free, they come at the cost of the generosity of the time, given by many very experienced folk, who have contributed to this conversation, simply, in attempt to assist you.

    Here is a LINK where you can find the User Manual for the Sekonic 358 and in that manual I am reasonably confident that you will find how that light meter can be used to make reflected light meter readings: and a lot more information, also.

    M. Butkus
    provides many of these manuals for out of production photographic gear and asks for a small donation (I think it is US$3.00) for those who use his service.

    SCL and John Seaman like this.

  16. 1) Your previous post as quoted before said the reflective meter is affected by color, so I'm reasoning the meter in the camera is affected by the curtain being white, therefore F stops lower by 2/3 stops. why is this wrong?
    2)Could you explain why my scenario is remote and well beyond 'theoretical'? Why is a backlit curtain is remote but a stained glass window is "close example"
    3) When people tell me something is wrong or not supposed to used for that, I just couldn't take that as an answer. I have re-read every single post people has take the time to write, but here is my follow up questions still. They are basically asking the same thing.

    a)Why can't I used an incidence meter for backlit subject?
    b) What dictates a spot meter only measures reflected light, and an incidence measures lighting falling on the subject?
    c) They are both essentially a calculator with a light sensor, one is with a 1% 3% lens, one with a dome/ sphere But both are measuring light falling on the sensor... so how come when I point a spot meter at the backlit curtain it is ok, and when I point the incidence it is not?
    As a matter of fact, as mentioned Sekonic meters have accesories/adpaters to turn incidence meter into a spot. So could someone explain to me in fundamental terms, instead of the conclusive:

    What I'm after is why are you not supposed to "drive a nail into hardwood with a screwdriver.", because it will strip the wood, because the nail has no notches for the screwdriver?

    I'm here to learn, and that's all
  17. William Michael

    William Michael Moderator Staff Member

    Because it is the screwdriver is the incorrect tool to use for that job: as is an incident light meter the incorrect tool to use to meter a backlit curtain

    Why you ask? Because an Incident Light meter is designed to do a different job and that job and how to use an Incident Light Meter (and also how to use a Reflected Light Meter) has been outlined several times, by several respondents.

  18. Sometimes it's easier to just admit that you don't know...
    you are turning this whole thing into a gospel truth from the church... "You are not supposed to have sex untill you get married" Why? you are just not supposed to because that's what this manual said called holy bible!
  19. William Michael

    William Michael Moderator Staff Member

    You are quoting out of context to advance an argument by either mistakenly combining two vastly different points, or worse, using this form of questioning as a baiting technique.

    In either case: please don't do that.

    The former is irritating, please note that the latter is against forum rules.


    That stated, the following two points addresses the question at hand:

    1. Your scenario is remote and well beyond theoretical because you insist that it be done by using the incorrect tools for the job.

    2. The task of measuring the exposure of a Back Lit Curtain is a close example to the task of measuring the exposure for a stained glass window and (importantly) when that similarity was made in Post #10, a method of how to achieve that task was clearly outlined and noted that method did NOT include using an Incident Meter.

  20. William Michael

    William Michael Moderator Staff Member


    Please step very carefully and think hard before you publish your commentary here.

    On the face of this commentary, it could easily be interpreted as a personal attack and/or purposefully directing the thread off track: both actions are also against forum rules.

    Please also note: it is against forum rules to comment on Moderation within the forums.

    If a member has issue with Moderation they may contact the Moderator concerned or any other Moderator by PM.


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