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  1. #11
    markbarendt's Avatar
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    Quote Originally Posted by Rudeofus View Post
    @PVia: The ultimate exposure guide just lists a number of light situations together with an exposure estimate for them. It does, unfortunately not tell me how long I can expose star trails before the back ground turns grey or how long to expose a very dark forrest or landscape (this is also where the in camera meter of my SLR falls short). For good negative film it's not a big deal if you are one or two stops off, for slide film being 2 stops off kills the image.
    Actually it does, it essentially provides you a zone 5 setting/reading, like all incident meters try to.

    It's up to you where to place the zones in your shot from there.

    Quote Originally Posted by Rudeofus View Post
    @wiltw: sure, reciprocity failure needs to be taken into account, but that's something you measure only once for every film (or look up numbers online). As long as I did night time exposures with negative film the results looked great, although I just guestimated the exposure time. Unfortunately slide film isn't that forgiving, so I started looking for a measurement device for extremely low light.
    Like reciprocity, the camera setting you might like for a given effect in a given lighting situation is only necessary once.
    Mark Barendt, Ignacio, CO

    "We do not see things the way they are. We see things the way we are." Ana´s Nin

  2. #12
    Rudeofus's Avatar
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    Quote Originally Posted by Lee L View Post
    Thanks. I believe you'll find that the EOS 3 has a 2.4% spot meter. The viewing angle of the metering area in degrees will change with the focal length with an in camera TTL spot meter. That's why I assumed from your description that you were using a handheld spot meter.
    Sorry for my confusion. You are correct, the spot meter of my EOS 3 covers 2.4% of the view finder screen, so it covers about 20mm^2 on the film. This corresponds to a circle with a diameter of 5mm. With my 70-210 F/4 I get angular coverage across the diameter of the spot metering circle of about 1.4░.

    So while I freely admit that I totally mixed up the spot meter properties, the result at the focal length I used closely resemble the coverage of a spot meter. So my exposure rule of thumb should work with these as well, provided they have lenses reasonably free of flare.
    Quote Originally Posted by markbarendt View Post
    Actually it does, it essentially provides you a zone 5 setting/reading, like all incident meters try to.
    It's up to you where to place the zones in your shot from there.
    The Ultimate Exposure Guide is a list of typical exposure situations, not a meter, and shouldn't be mistaken for one. IMHO it's exactly these kinds of guides and the need for bracketing which drove so many night shooters into the digital camp. My aim is to employ a device specifically made for measuring extremely low light szenarios for my photographic purposes. Bracketing is no fun if your exposures take hours.
    Quote Originally Posted by markbarendt View Post
    Like reciprocity, the camera setting you might like for a given effect in a given lighting situation is only necessary once.
    My aim is a device which tells me (directly or through conversion tables) what exposure an ideal film sans reciprocity failure would require for a zone 5 exposure. Adding or subtracting stops for specific purposes is trivial, and facturing in reciprocity failure should require much fewer failed shots than guestimating szene illumination with my bare eyes.

    I guess I'll just try it out and report ...

  3. #13
    Lee L's Avatar
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    Quote Originally Posted by Rudeofus View Post
    I guess I'll just try it out and report ...
    I'd definitely be interested in your results. Atmospheric conditions can be difficult to judge by eye, and can dramatically affect the outcome with astrophotography. BTW, the FAQ for the SQM indicates that it's sensitive to temperature, and has an internal temp sensor built into the circuit that compensates. But it needs some settling time, and greater lengths time when the meter is moved between environments of very different temperature.

    Lee

  4. #14
    markbarendt's Avatar
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    Quote Originally Posted by Rudeofus View Post
    The Ultimate Exposure Guide is a list of typical exposure situations, not a meter, and shouldn't be mistaken for one. IMHO it's exactly these kinds of guides and the need for bracketing which drove so many night shooters into the digital camp. My aim is to employ a device specifically made for measuring extremely low light szenarios for my photographic purposes. Bracketing is no fun if your exposures take hours.
    IMHO there are no magic bullet devices and the digi converts probably moved for other reasons because they face real limits for night use; their sensors and batteries tend to die or simply won't do what is asked when a truly long exposure, hours, is needed.

    All I'm suggesting here, and at least what I find in my shooting, is that the lighting in a given situation, at a given day and time, at a given location; rarely changes.

    Many wedding shooters set up at the equivalent of f4, ei400, at 1/400 for any backlit daylight shot; nail it every time. The reason this works is that the subject's surface that is facing the camera is simply in open shade when the sun is in position for this type of shot. The subject is just placed in the right zone for the shot. That's a subjective decision based on experience in getting what they want.

    The light quality outside my home on a moonless night is pretty well fixed, same thing in the forests 50 miles from home, or 500 miles out to sea. Each of these has it's own setting but once that value is known and you add a note the your EV chart on the ultimate exposure calculator, your going to be darn close every time.

    What messes me up most, on getting the effect I want in a given situation, is that I misjudge placement or I let a meter lead me astray. I don't think I'm abnormal here either.
    Last edited by markbarendt; 11-26-2009 at 12:24 PM. Click to view previous post history.
    Mark Barendt, Ignacio, CO

    "We do not see things the way they are. We see things the way we are." Ana´s Nin

  5. #15

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    Here's an 8 minute exposure using info from the Ultimate Exposure Guide. This was exactly the effect I was after. I took one shot, no bracketing...

    http://www.flickr.com/photos/viapiano/3346880205/

  6. #16
    AgX
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    Back to the original question: I can't find a sensitivity (stellar magnitude or whatever) given for that device.

  7. #17
    Rudeofus's Avatar
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    Quote Originally Posted by markbarendt View Post
    IMHO there are no magic bullet devices and the digi converts probably moved for other reasons because they face real limits for night use; their sensors and batteries tend to die or simply won't do what is asked when a truly long exposure, hours, is needed.
    Obviously some vocal converts may be driven more by ample supply of marketing dollars than by real photographic benefits. Some of the problems with quickly discharging batteries and excessive noise have been overcome years ago (battery grips, image stacking), while analog shooters still resort to bracketing once our light meters prove too insensitive for the task. I wasn't looking for a magic bullet which makes my shots better, just for a metering device for extremely low light situations. If I can see details in a scenery with my bare eyes, a sensitive light meter should be able to deliver accurate numbers.
    Quote Originally Posted by AgX View Post
    Back to the original question: I can't find a sensitivity (stellar magnitude or whatever) given for that device.
    It's reading corresponds do star magnitude per square arc second. Someone could calculate how this corresponds to exposure values, but I rather let the spot meter of my camera find this out for me (compare spot meter reading of a moderately dark spot to the reading of the SQM). One star magnitude is about a factor of 2.5 (it's a logarithmic measure), so I could put together a table very quickly.

    @PVia: I did plenty of night shots with negative film where I just random guessed the exposure time. These films have ridiculous latitude compared to slide film. It's my slide film night shots that look like crap so I started investigating devices for measuring very low light levels with some accuracy.

  8. #18
    markbarendt's Avatar
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    Quote Originally Posted by Rudeofus View Post
    Could this help me estimate accurate exposure times for night shots as well?
    Maybe this could give you some data, but EV may not be the whole, nor even the biggest issue with your slide film providing poor results.

    What is the difference between the real color of the scene and the way you want to render it?

    How are you going to judge your filtering to get all three color layers exposed properly for the result you want?

    Is your film sensitive to a broader or narrower set light wavelengths than the meter?
    Mark Barendt, Ignacio, CO

    "We do not see things the way they are. We see things the way we are." Ana´s Nin

  9. #19
    markbarendt's Avatar
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    One other question here is; how you plan to adjust the development to correct for the narrow scene contrast?
    Mark Barendt, Ignacio, CO

    "We do not see things the way they are. We see things the way we are." Ana´s Nin

  10. #20
    Rudeofus's Avatar
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    Quote Originally Posted by markbarendt View Post
    Maybe this could give you some data, but EV may not be the whole, nor even the biggest issue with your slide film providing poor results.
    What is the difference between the real color of the scene and the way you want to render it?
    How are you going to judge your filtering to get all three color layers exposed properly for the result you want?
    Once I got the exposure nailed I can deal with color casts (in the worst case in a hybrid work flow, my scanner does much much better with slides than negs). Right now I look at pics with bright white mountains in front of white sky and dim star trails on light grey sky. And very short star trails on black sky. I'd rather spend 10 minutes measuring light and thinking it through than spray&pray.
    Quote Originally Posted by markbarendt View Post
    Is your film sensitive to a broader or narrower set light wavelengths than the meter?
    Since it's used to estimate observability of stars with human eyes (bare or through a telescope) I assume it's mostly sensitive to the wave lengths we see. I don't have this thing yet but if I get it I can try shining some IR diodes at it and see whether it gets fooled by them. I asked my question not in an attempt to advertise some gadgetery but to find out whether other folks have already tried this.
    Quote Originally Posted by markbarendt View Post
    One other question here is; how you plan to adjust the development to correct for the narrow scene contrast?
    I was not aware that scene contrast would be narrow, in my experience I had to battle excessive contrast as soon as artificial lighting exists in small parts of the view. Moon light should yield similar contrast levels to sun light.

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