Can your meter do this? (LUX LUMENS)

[Ray Rogers]

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?

 

[epatsellis]

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

 

[Ray Rogers]

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!

 

[RalphLambrecht]

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.

 

[nick mulder]

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

 

[Ray Rogers]

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.

 

[Ray Rogers]

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

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?

:confused:

 

[Lee L]

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

 

[nick mulder]

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

 

[nick mulder]

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 !?

 

[BetterSense]

I made a rudimentary meter like this for my pinhole cameras, because I was tired of the sun going behind clouds and messing up my exposures. I describe it on my (very embryonic) website


http://chazmiller.com/projects/pinmeter.html

 

[RalphLambrecht]

I made a rudimentary meter like this for my pinhole cameras, because I was tired of the sun going behind clouds and messing up my exposures. I describe it on my (very embryonic) website


http://chazmiller.com/projects/pinmeter.html

Cool!

 

[Steve Smith]

Lux and nits (candela/m^2) not lumen, but why don't you just record EVs? Most lightmeters measure in EVs.

Shouldn't that be LV for light value? My understanding is that EV is exposure value and is a combination of shutter speed and aperture Whereas LV is an actual light value.

EV only being equal to LV at EI 100.



Steve.

 

[Kirk Keyes]

Ray - your Minolta incident meter when equipped with a flat diffuser disk will make Lux readings. It reads in EV and then your meter manual should have a conversion table and the formula. My Flashmeter IV does this.

 

[Q.G.]

I'm not sure this is what you are after, but i have used Gossen Profisix and Lunasix F meters to do something similar on days when clouds raced across the sky.
Measured, zeroed the needle, locked the meter's on button, and watched the needle move to see when light levels were up to the measured value again and/or how much under or over the light at any moment was.
Worked fine, though not very battery friendly.

Should work fine with any meter that has a "constant metering" mode.

 

[Lee L]

Love google, it came up with the one I recalled as the first result, searching on: pinhole integrating light meter

http://www.ringsurf.com/tv/905252-integrating_pinhole_light_meter_shutter_driver.html

Lee

 

[RalphLambrecht]

Shouldn't that be LV for light value? My understanding is that EV is exposure value and is a combination of shutter speed and aperture Whereas LV is an actual light value.

EV only being equal to LV at EI 100.



Steve.

Steve

Yes, EV for a given film speed is the better idea.

 

[Ray Rogers]

Love google, it came up with the one I recalled as the first result, searching on: pinhole integrating light meter

http://www.ringsurf.com/tv/905252-integrating_pinhole_light_meter_shutter_driver.html

Lee

Lee;

Yes. Thanks. Actually I found the long discussion made during it's development and was reading through the years... unfortunately things seemed to die down around 2007, I am waiting on a response at the moment.

Kirk, Q.G.;

Yes, but as you may have guessed, that only tells me what the Light intensity WAS for an instant in the past. During the exposure we usually just cross our fingers (or, if we're printing and lucky, perhaps we have a voltage stablizer)

Kirk;
Thanks for reminding me! I did find a conversion chart on the internet and that will help me if I find I can't find the manual any more.

Ray

 

[nick mulder]

I'm not sure this is what you are after, but i have used Gossen Profisix and Lunasix F meters to do something similar on days when clouds raced across the sky.
Measured, zeroed the needle, locked the meter's on button, and watched the needle move to see when light levels were up to the measured value again and/or how much under or over the light at any moment was.
Worked fine, though not very battery friendly.

Should work fine with any meter that has a "constant metering" mode.

Yup, but you need a system that will tell you the area under the graph that this output is plotting over time ...

An 'integrator'

Should note that as long as you use the same scheme to collect the light 'intensity' (or whatever) units are a bit redundant with an integrator once its set up.

 

[nick mulder]

Bettersense has linked his project above - pretty much exactly what I described earlier. Heaps of work done for you right there !

 

[Chan Tran]

what kind of camera do you use and what is your typical exposure time? I understand that you want to build an integrating lightmeter that display remaining time. But since it's integating and the light is changing shouldn't it display percentage of exposure with 100% is complete

 

[Ray Rogers]

Bettersense has linked his project above - pretty much exactly what I described earlier. Heaps of work done for you right there !

Yes and pretested too!
I will try it and see how it works out.

 

[Graham06]

I watched a Charles & Ray Eames short recently on how Polaroid cameras worked, and it described how a light sensor would trigger the end of exposure when the right amount of light had been let in.

It seems therefore that it would be possible to modify one to provide the timing information you require.

 

[Ray Rogers]

what kind of camera do you use and what is your typical exposure time? I understand that you want to build an integrating lightmeter that display remaining time. But since it's integating and the light is changing shouldn't it display percentage of exposure with 100% is complete

MF Mamiya with exposures expected to range from 1 sec. to perhaps an hour... A % display w/o time indication would not be ideal... as I hope the lighting exhibits no actual variation and therefore exposure duration may actually be predictable... and I have a better sense of how long x minutes or seconds are than how long 3 or 7% takes to complete. But, yes either could be used.

 

[nick mulder]

I would have made one by now but had the issue of wanting into integrate UV light intensity over time only - I needed a UV band pass filter... There were lots of ideas around it but they all equated to equal or more work than building an indoor UV bank anyway - so I built one of those and haven't looked back since