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  1. #1

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    Can your meter do this? (LUX LUMENS)

    Normally, I use a Pentax Sotmeter for reflected metering or a Minolta (forgot exact name) for incident light readings...

    However, I currently find myself wanting to measure light in such a way as to indicate the approach of a constant given amount of light with a light source that is inconsistent... exposures are quite long so what this amounts to is a meter that will tell me the exposure deficiency remaning in sec/minutes... it needs to accommodate (calculate?) on the fly and adjust its indication according to the variable light that meets the sensor.

    Not exactly sure what I need.
    Not even sure what I need to measure... Lux, Lumens?
    Certainly not sure what device out there could do this sort of job...

    Can your meter do this?

  2. #2

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    Gossen Ultra Pro can, available used around the $100 mark.

  3. #3

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    Quote Originally Posted by epatsellis View Post
    Gossen Ultra Pro can, available used around the $100 mark.
    Thanks, I'll check to see if I can get the "op man" on line to make sure of the details!


  4. #4
    RalphLambrecht's Avatar
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    Quote Originally Posted by Ray Rogers View Post
    Normally, I use a Pentax Sotmeter for reflected metering or a Minolta (forgot exact name) for incident light readings...

    However, I currently find myself wanting to measure light in such a way as to indicate the approach of a constant given amount of light with a light source that is inconsistent... exposures are quite long so what this amounts to is a meter that will tell me the exposure deficiency remaning in sec/minutes... it needs to accommodate (calculate?) on the fly and adjust its indication according to the variable light that meets the sensor.

    Not exactly sure what I need.
    Not even sure what I need to measure... Lux, Lumens?
    Certainly not sure what device out there could do this sort of job...

    Can your meter do this?
    Lux and nits (candela/m^2) not lumen, but why don't you just record EVs? Most lightmeters measure in EVs.
    Attached Thumbnails Attached Thumbnails LuxNits.jpg  
    Regards

    Ralph W. Lambrecht
    www.darkroomagic.comrorrlambrec@ymail.com[/URL]
    www.waybeyondmonochrome.com

  5. #5
    nick mulder's Avatar
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    You describe an integrating (adding up over time) and comparator circuit (comparing the current value with a given final exposure value) which can be made with op-amps - the component utilised in most simple applications that require continuous/analog math um, 'doing'

    I've considered making one for a few reasons - alt process exposures under cloudy conditions, sunset/sunrise exposures, long exposures as you mention - but have always found another way around the problem...

    If it aint your thing I understand it may look like immediate gibberish, but electronics like this once you get over a little conceptual hump and have some vital tools can be very easy - having said that referencing such a circuit might be a chore :P
    Cleared the bowel problem, working on the consonants...

  6. #6

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    Quote Originally Posted by RalphLambrecht View Post
    Lux and nits (candela/m^2) not lumen, but why don't you just record EVs? Most lightmeters measure in EVs.
    Actually both of my meters do measure EV, but (and I think what Nick pointed out is related) they do not give the desired "T minus x" readings; on those meters set to EV, f stop control is anticipated not time; I wish to use a fixed aperture. Of course, I can use EV, I was just looking for an easier way.

  7. #7

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    Quote Originally Posted by nick mulder View Post
    You describe an integrating (adding up over time) and comparator circuit (comparing the current value with a given final exposure value) which can be made with op-amps - [cut] - having said that referencing such a circuit might be a chore :P
    Yes- I would like to build one if I can find a suitable circuit... I have a few for related projects, even one for a timer or something with an op-amp but nothing for this exact need... Any idea how I might I go about hunting for one?

    I guess those terms integrating and comparator circuits make a fair starting point?


  8. #8
    Lee L's Avatar
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    There is an electronic shutter controller cum integrating light meter design that was written about on the web a few years ago. The design also had programmable reciprocity failure compensation and was designed for use with pinhole cameras IIRC, and possibly with an interface to electronic cable release cameras.

    I don't have a URL or reference or product name, and not time to search, but a complete unit was designed and a prototype or two built, with a commercial design or kit in the works. A search for that might be fruitful. It might have been on, or mentioned in the f295 forums.

    Lee

  9. #9
    nick mulder's Avatar
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    yup,

    "integrator + op amp" and "comparator op amp" will get you places in google - I have had a look at some of the results and have realised they can be a bit sparse on specifics and deal with broader scale concepts, something I always had issues with when learning - but now I'm in a position to impart knowledge I can see how hard it is to be specific - as 'simple' as anything is, there is always fiddling - I dont think I ever got a circuit working first time... A lot of amateur electronics is learning how to strip away circuits into testable units as opposed to playing 3D chess with Spock - I digress...

    Reciprocity failure compensation huh ? One easy(ish) way to combat that is to use a PIC or similar with an LCD driver and what not - easiest implementation would be a look up table or two ... It could be done with op-amps also but the math would be undergraduate uni level (not too hard if you were that way inclined) and then getting the op-amps to behave, or at least figuring out a way to figure out if they were behaving would be well 'time consuming' (heh)

    Many ways to go about this but the most elegant and 'analog' would be via op-amps and a couple of indicator lights - if you're going all out you could even chuck in the photodiode/LDR into the camera itself and have the circuit reset when the shutter is tripped and have the shutter close again when the 'area under the graph' equated to your pre-determined exposure... The nice (or scary) part is that once you've tuned/referenced the circuit to your workflow, you don't have to think that much anymore
    Cleared the bowel problem, working on the consonants...

  10. #10
    nick mulder's Avatar
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    by the way...

    it rips my tits why the more computationally intensive light meters don't do this stuff already - at least put a damn stopwatch on them for flips sake !

    Hello Sekonic !!! ya listening !?
    Cleared the bowel problem, working on the consonants...

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