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Old 21-02-2011, 16:54   #1 (permalink)
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Measuring light with a handheld meter

...I must be getting on but am confused about light measuring .
With any camera's own in built lightmeter - it will measure the light coming through the lens [reflected ] , whether good or badly depending on meter .
This measuring includes any particularites of the lens /any extension from film plane when lens is focussed at infinity or up close [ barrel extened ] or if macro , and any filters if absorbing .
As I have been slow to get into digital and still use slide/chrome film where proper exposure is still ,after [how many years ? ? ] a bit hit and miss , I am looking for a good ambient/reflected light meter .

If you use a seperate lightmeter to measure reflected or as I was taught, better ambient , then readings given are accurate , but no account taken for vagaries as above . Yes filters have exp factors which you need to take account off , but beyond that there is lens focussing factors / different manufacturers glass absorbtion .....

If a lens is set at a particular point of focus -say 20 feet away , the absortion of light will be different if switched to its macro close up setting at 25inches . So the exp will be affected , even though the ambient handheld meter reading may be f8 at 250sec etc . Likewise , if I switch from a tel zoom to a fixed prime mid shooting , surely this will have an affect on exposure on film .

Am I missing something ? Should I stop thinking too much ? Instead of ambient light measuremnt should I opt for a decent Spot meter ?
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Old 21-02-2011, 19:16   #2 (permalink)
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re: Measuring light with a handheld meter

Despite decades in photography I had not heard the term ambient light meter but understand it to be the same as Incident light meter. This does indeed have a number of advantages over reflective metering but is an average measurement so still does not tell you vital information such as the dynamic range.

The key is to understand your camera and its dynamic range and what you are trying to measure in any particualr circumstances. Modern SLR cameras (including film cameras) normally offer a range of reflective metering options which may include:

Evaluative
Average
Partial Spot
Spot

Evaluative metering measures 35 (in my camera) areas of the scene and compares the pattern with stored patterns to select the nearest and use the stored exposure setting. This works well in many cases but not all. At the other extreme, you can use spot metering to measure the brightest and darkest parts of the scene and determine manually the exposure and whether multiple exposures are needed. There are many other variations of using these metering modes and in some cases combining with a compensation setting. There is little substitute for experience.

If you are considering using a spot meter, I cannot see any particular advantage in using a separate meter if your camera offers spot metering.
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Old 21-02-2011, 20:01   #3 (permalink)
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re: Measuring light with a handheld meter

Exposure is almost always a compromise unless you are taking a shot of something or a section of something with even lighting.

You could measure the darkest and lightest parts of the frame and either take an average, or bias the exposure to toward one end of the range. Modern meters are much better than older ones and also have better control systems to add or remove from the exposure by way of the compensation controls.

If you control the bright end of the spectrum you can usually recover detail from the under exposed areas in the picture. There are several post processing techniques that will enable you to even out the exposure too.
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Old 22-02-2011, 14:27   #4 (permalink)
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Re: Measuring light with a handheld meter

Thanks for the input . I am looking at a seperate lightemeter as I run 3 cameras with basic metering.
With a handheld meter measuring ambient incident light the query is - as compared to in camera reflected metering [ using matrix spot average or ... ] that takes its measurement form the light hitting thru glass, added filters , filters , extension of lens , added macro rings decreasing light even further etc etc , how can a seperate ambient reflected lightmeter manage to give anything like a decent exposure , when apart from say a filter 'factor' that can be dialed in , this sort of metering does not take into account other differences .
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Old 22-02-2011, 14:59   #5 (permalink)
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Re: Measuring light with a handheld meter

Quote:
Originally Posted by fujijon View Post
...that takes its measurement form the light hitting thru glass filters extension of lens etc etc
If you are using filters that have an impact on the amount of light going through them, you should not be metering in camera with the filters in position, otherwise the meter will over-ride the effect of the filter.

If you want to standardise your light measurement, I think you will have to use a meter with incident light reading facility as this will be the only constant. Measuring reflected light with a hand held meter can give variable results if the meter is not held in exactly the same alignment, and arguably, the best way is to spot meter the darkest and lightest areas, then average the result to obtain the median. You will then have to make a judgment if this reading will have to be modified to suit the subject, or the camera. Just as different film used to have different characteristics, different cameras will similarly be different in the way that they process the image. What this boils down to is a bespoke measurement to suit every shot, which is where the built-in camera meters have the advantage.

Quote:
added macro rings decreasing light even further etc
I'm no macro expert, but I suspect that macro needs either TTL metering or manual.

I think that rather than trying to standardise your metering you need to know what kind of result each of your cameras will produce and work around that.
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Old 22-02-2011, 21:22   #6 (permalink)
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re: Measuring light with a handheld meter

Quote:
If you are using filters that have an impact on the amount of light going through them, you should not be metering in camera with the filters in position, otherwise the meter will over-ride the effect of the filter.
Are you sure you mean that the way it sounds, Dabs?

The whole point of Through The Lens metering is that it takes account of filtration, extension and all those other good things you can put between your subject and the recording medium.

Incident metering, on the other hand, is good because it totally standardises the exposure process. The system tells you how much light is falling on the subject and you then decide how close to that hoary old 18% grey card your image falls. For dark and moody, decrease the exposure. For bright and bubbly, increase it. BUT if your camera isn't totally standard, so that, for example, setting f8 on the aperture lets in the same amount of light as any other lens set to f8, you'll have to apply some sort of correction to the exposure, to get the image you're after.

One thing to remember - there's no such thing as "correct" exposure. If you're serious about your image making, you can do nothing better than to get a copy of Roger Hicks's and Frances Schultz's book "Perfect Exposure", which will explain that last assertion in great and entertaining detail.
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Old 22-02-2011, 22:19   #7 (permalink)
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re: Measuring light with a handheld meter

Quote:
Originally Posted by sejanus View Post
Are you sure you mean that the way it sounds, Dabs?
Yes - absolutely. If you use, say, a two stop ND filter and put it on the camera before you meter, the meter will calculate the exposure on the light reaching the sensor and the result will be a picture that will (or should) look the same as one with no filter. The camera does not know that you are using a filter and want a two stop under exposure, it just reads lower light and will increase the exposure to compensate.

Metering the scene first and using these settings manually and then placing the ND over the lens will result in a two stop under exposure.
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Old 23-02-2011, 13:46   #8 (permalink)
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re: Measuring light with a handheld meter

I see where you're coming from, now. Of course, you're right. In that scenario, you're using the camera as if it were a meter, then making any changes according to what filters, extension or so on that you add.

It's actually quite a good way to teach the principles of exposure.
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Old 23-02-2011, 15:18   #9 (permalink)
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re: Measuring light with a handheld meter

Using the camera to meter the exact shot rather than using a hand held meter to take an average reading.

Conversely - just to be, well, converse, if you wanted to use a wide aperture to reduce the depth of field, but it was way too bright or if you needed a slower shutter speed, then metering through an ND filter would allow these options as the camera would read the scene as having less light than there actually was.
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Old 28-02-2011, 11:52   #10 (permalink)
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Re: Measuring light with a handheld meter

Quote:
Originally Posted by fujijon View Post
...I must be getting on but am confused about light measuring .
With any camera's own in built lightmeter - it will measure the light coming through the lens [reflected ] , whether good or badly depending on meter .
This measuring includes any particularites of the lens /any extension from film plane when lens is focussed at infinity or up close [ barrel extened ] or if macro , and any filters if absorbing .
As I have been slow to get into digital and still use slide/chrome film where proper exposure is still ,after [how many years ? ? ] a bit hit and miss , I am looking for a good ambient/reflected light meter .

If you use a seperate lightmeter to measure reflected or as I was taught, better ambient , then readings given are accurate , but no account taken for vagaries as above . Yes filters have exp factors which you need to take account off , but beyond that there is lens focussing factors / different manufacturers glass absorbtion .....

If a lens is set at a particular point of focus -say 20 feet away , the absortion of light will be different if switched to its macro close up setting at 25inches . So the exp will be affected , even though the ambient handheld meter reading may be f8 at 250sec etc . Likewise , if I switch from a tel zoom to a fixed prime mid shooting , surely this will have an affect on exposure on film .

Am I missing something ? Should I stop thinking too much ? Instead of ambient light measuremnt should I opt for a decent Spot meter ?
Save your money and download a copy of "The Ultimate Exposure Meter",its based on ambient light and works just fine.I use it all the time and its surprising how quickly it becomes 2nd nature!
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