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wstotler

To EV or not to EV?

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Sorry, having trouble with the quote function but this is from a post above.....

You should note that although your camera indicated 320ISO, it may be 400ISO. So you have to find out the true ISO of your camera (just like we did with 100 feet of film) to have the correct incident reading.

 

My question

So, I've never gone through the process of understanding the true ISO with 100 feet of film. The DPReview review said that the M8 is a bit more sensitive than the listed ISO. So, how does one do this test in digital.

 

I have followed this thread and will be making one of my too frequent B&H visits to get a meter today to also work on exposure!

 

This post got a little lost. I would love to know how to do this ISO test...

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This post got a little lost. I would love to know how to do this ISO test...

 

A very simple way is to shoot a gray card. It should look like a single "spike" dead center of your LCD. Too left or too right means under or over exposure. Alternatively, you could shoot a MacBeth chart and use the same logic.

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Hey JR--great to see you back here! I hope you're having a great year!

 

Of course I wholeheartedly agree that the RGB histogram on the back of the camera is a great device, and I have no doubt you can place exposure without using your 358 anymore

 

For the most part, I can too, but I like having it along eve these days (it's most important with the M3, I admit, which has no meter at all).

 

But the point of getting the meter to me, even with digital, so that you build up your internal repertoire of exposure situations till you know when the reflective meter inside the camera is likely to fool you. IOW, if all goes well, you will need the meter less and less.

 

For me, the histogram is of most use when you already understand exposure, though., and exposure on digital is still pretty unforgiving. So yes, you can learn exposure through the histogram, but I think a meter makes the relationships between ISO / aperture and shutter, and light most explicit.

 

There was a time (a different lifetime ago) that I wouldn't have been without a good external meter and yes--that was on film. But I still think it helps for people to understand about the light falling on a scene vs the light reflected from objects.

 

The point made about getting the incident meter in the light you're shooting is a good one; I thought I made it in my early post... Sometimes you have no choice but to meter reflectively (for far-away subjects).

 

Jamie,

 

Great year indeed.

I never left -- I was reading but not posting.

 

One "tip" I forgot to mention. I use two bodies all the time. A wide and a tele. I use the "tele" body to measure my lighting. I use the longer lens to isolate a specific area of the image -- a little like I would with a spot meter. I'll "measure" different areas via the LCD and determine the final exposure from that. The advantage is that, in many instances, a "broad" scene will provide a much to "flat" histogram. By isolating areas with a tele, it purks up the histogram and makes it easier to see exactly where the highlights are shadows precisely lie -- without having to walk over to the scene. This is very useful in high contrast situation.

 

Hope this helps.

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I've been off-net for a few days—thus the lateness of my response. But I think some technical elucidation is in order.

 

First, the Zone System has nothing to do with the EV count. Ansel & Edward (Adams & Weston) invented the Zone System in the late 1920's in order to make it possible to print various negs on the same grade of paper – reasonable in those days, when many papers didn't come in different contrast grades – and with the same print exposure, which was just a gratuitous curlicue (look Mom, no hands!). There were quite a few scientific mistakes in the system, and later it was transmogrified into a substitute religion. — EV started in the 1950's when manufacturers started to build selenium meters into hobbyist cameras. These were not coupled, so how transfer the values to the camera? The manufacturers of the Compur shutters got the idea of a) creating a shutter speed sequence which worked in even steps of doublings and halveings, and this is the sequence we have today, and

having the meter readout in similar even logarithmic steps, called Exposure Values, EVs. Those early EV leaf shutters made it possible to lock speeds to apertures, so that if, e.g., you had set 1/125th and 5.6 and changed to 1/250th, the aperture changed automatically to 4. This particular feature went out with the development of cross-coupled built-in meters.

 

Second, what the incident meter does is to create a diffuse c. 90% highlight – that little white dome – and meter this. By nailing the diffuse highlight the meter nails all other reflectances in the subject. No exposure error is possible, which is why so many pros who make their living off correct exposures like incident meters.

 

Third, 'overexposure' does properly mean that important highlight detail is lost by being burnt out. Similarly, 'underexposure' means that important shadow detail is lost by being dropped down the black hole. Biasing exposure off the value indicated by a built-in or handheld meter is just biasing, not over- or underexposure proper. It is in fact usually done in order to *prevent* over-or underexposure!

 

Fourth, in the days of slide film we often found that slavishly following the recommended film speed, we consistently got too light or too dark slides. So we bracketed our exposures (still a good idea – the subject may have run away when you are done chimping) and we did often set our meters to, say 80 when we used Kodachrome 64. In that case, '80' was not an ISO speed (or ASA or DIN as we reckoned then) because determining film speed is a strictly delimited procedure, but we called it an Exposure Index or EI in order to avoid confusion.

 

The pedantic old man from the Age of Kodachrome

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Those early EV leaf shutters made it possible to lock speeds to apertures, so that if, e.g., you had set 1/125th and 5.6 and changed to 1/250th, the aperture changed automatically to 4. This particular feature went out with the development of cross-coupled built-in meters.

 

 

"went out" is a bit OTT current H'blad V system Zeiss lenses still have this feature of locking the two rings and very handy it is.

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Yes, and what a delightful relic of the 1950's the film 'Blad is! But in this case of course meters internally cross-coupled to bot shutter and aperture never came in ... and my folding Retinas have the system too of course.

 

The old man from th Age of Selenium Meters

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I've been off-net for a few days—thus the lateness of my response. But I think some technical elucidation is in order.

 

First, the Zone System has nothing to do with the EV count. Ansel & Edward (Adams & Weston) invented the Zone System in the late 1920's in order to make it possible to print various negs on the same grade of paper – reasonable in those days, when many papers didn't come in different contrast grades – and with the same print exposure, which was just a gratuitous curlicue (look Mom, no hands!). {snipped}

 

I'm not sure your "elucidation" will be clearing things up for a lot of people here, as historically accurate as it is

 

The Zone System as written by Adams in his classic works The Negative and The Print has nothing particularly to do with compensating for the lack of contrast grades (filters or paper--take your pick), though I understand that's how it started out.

 

And while it has nothing to do with "Exposure Values" per se, it has everything to do with exposure and (then) development of the negative to place certain gray values in certain places in the print (so with respect to paper white and paper black). That those may change, as well as the contrast, doesn't invalidate the approach or the thought process--for those interested in developing and printing their own images, that is.

 

Anyway, I do agree it's become a bit of a religion, and doesn't translate 1:1 to a digital workflow.

 

It's still very useful analytic exercise to understand how to place areas of interest, however, and RAW converters actually let you do this (with a number of different techniques) far more easily than rolls of 35mm film ever did!

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Yes, and what a delightful relic of the 1950's the film 'Blad is!

 

yes a relic you simply remove the film back from and slap on a 38MP state of the art digital back

(if you can afford one).

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Jamie,

 

Great year indeed.

I never left -- I was reading but not posting.

 

One "tip" I forgot to mention. I use two bodies all the time. A wide and a tele. I use the "tele" body to measure my lighting. I use the longer lens to isolate a specific area of the image -- a little like I would with a spot meter. I'll "measure" different areas via the LCD and determine the final exposure from that. The advantage is that, in many instances, a "broad" scene will provide a much to "flat" histogram. By isolating areas with a tele, it purks up the histogram and makes it easier to see exactly where the highlights are shadows precisely lie -- without having to walk over to the scene. This is very useful in high contrast situation.

 

Hope this helps.

 

That's a great tip JR! Thanks. This is even more useful in combination with your histogram changing when you zoom in, no?

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I'm surprised that nobody has mentioned the ultimate handheld incident meter that you never leave in the car, is aways available and has lots of other useful capabilities: Your own hand!

 

I still follow the old expose against the palm of your hand for an EV +1 (calibrate as necessary for your own brand!) reading.

 

A basic understanding of Sunny-16 / Overcast-8/11 rules will always be useful to provide you with a base exposure for sanity checking.

 

Ultimately getting experience with the histogram and calibrating that with the final exposed images so you know what really does clip or block up will make setting exposure a simple task. I am very impressed overall with the accuracy of the M8's metering in the vast majority of situations I encounter.

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That's a great tip JR! Thanks. This is even more useful in combination with your histogram changing when you zoom in, no?

 

 

Absolutely! The longer lens plus the zoom histogram allows the evaluation of very specific areas of the scene to see whether or not they "fit" without your capture boundaries.

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I'm surprised that nobody has mentioned the ultimate handheld incident meter that you never leave in the car, is aways available and has lots of other useful capabilities: Your own hand!

 

I still follow the old expose against the palm of your hand for an EV +1 (calibrate as necessary for your own brand!) reading.

 

- - - - - -

 

If you want to follow that procedure, then I do strongly recommend that you calibrate your own palm against either a Kodak Gray Card or a reliable incident meter. You may well be surprised.

 

Also, the sunny 16 rule may well hold in California, where it seems to have arisen, but in most of Sweden during most of the year, 'sunny 11' is not too pessimistic. The 'solar constant' nothwithstanding, actual insolation varies drastically with latitude and time of the year, even if the sky is crystal clear. And up north in midwinter, it is 'use flash at noon because the sun won't be up for two months'.

 

But yes, the histogram is a great aid, especially if you have to do bounce flash with a non-TTL unit without a tilting reflector ...

 

The old man from the Age of Selenium Meters

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A very simple way is to shoot a gray card. It should look like a single "spike" dead center of your LCD. Too left or too right means under or over exposure. Alternatively, you could shoot a MacBeth chart and use the same logic.

 

JR--I'm missing something here.

 

Pardon my density: I don't understand how that would help check the accuracy of my ISO setting.

 

Seems to me just shooting a gray card would show that the camera's meter is tuned to accuracy with a gray card. But If I shot a camera at indicated ISO 160, assuming the meter, shutter and aperture are calibrated to each other, mightn't it give me the same exposure as another camera shooting the same at indicated ISO 320?

 

I know one has to know one's accurate ISO, particularly when using flash and flash meters, or when using using an external meter instead of the camera's meter--but I've never understood how to check that.

 

Thanks!

 

--HC

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JR--I'm missing something here.

 

Pardon my density: I don't understand how that would help check the accuracy of my ISO setting.

 

Seems to me just shooting a gray card would show that the camera's meter is tuned to accuracy with a gray card. But If I shot a camera at indicated ISO 160, assuming the meter, shutter and aperture are calibrated to each other, mightn't it give me the same exposure as another camera shooting the same at indicated ISO 320?

 

I know one has to know one's accurate ISO, particularly when using flash and flash meters, or when using using an external meter instead of the camera's meter--but I've never understood how to check that.

 

Thanks!

 

--HC

 

Oups! I left out the important part! This is the one time the incident meter comes it. Measure the falling on the gray card (use the flat diffuser, not the dome) and expose for it with the camera... This will tell you if the camera exposes what the meter sees.

 

Let me know if I now told "the whole story".

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These most recent posts(of JR, Lars, ho_co, &c.) plus the added "ISO accuracy" have me missing the dreary "limitations" of film stock and the one or three incident readings made with the handheld... well, no, not really. I've not had the opportunity to require a change of the EV setting using an M8 because the histogram usually provides enough information for adjustments of shutter and f-stop.

 

That said, I'm not sync'ing my kit with flash, nor expecting the bride's gown and surrounding flora to have consistent values... I'm not shooting products.

 

From what I gather, the EV setting is not a "push/pull" of DR, but that of gain on the sensor, or "noise". Perhaps this is why Jaime tried and left it? Jaime? Or have I completely missed it, and EV +/- is merely effecting the light meter display? Somehow, given EXIF data written, EV adjustments are applied, not enforced in data capture... and this sides with Lars' recent post on /processing/ the data, data captured at a fixed ISO. So "where's the 'noise'?" In post-processing, whilst altering the data.

 

Back to ho_co: an ISO of 160 with an M8 should--yet may not--equal the same ISO of another camera because each treats the data slightly differently(eg the M8 "8bit" DNG). With digital, the data capture via "film photogrphic norm" is camera-specific. Similar, yes, but not reasonably the same, exactly. Please recall posts about "profiles" and this becomes clearer. Yes, JR's camera+handheld incident can get you close to "normal"... but then what handheld are you using?

 

In sum: lowkey, or highkey, wide or tele lens, still or moving subject... if your processing software uses the EXIF EV value, then you might employ it in-camera. From my brief experiments, it alters the light meter display and EXIF data only... the in-camera histogram is not too easily verified in this testing... ISO 160 is ISO 160, and pixel value 137, is 137 as recorded to file.

 

Others have found otherwise?

 

rgds,

Dave

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Dave--

 

You're overthinking this, I think.

 

A minus EV setting only affects the meter in manual exposure; obviously it effects the exposure in Av automatic

 

In other words, when you dial in a negative EV compensation in Av the shutter is faster than it would be normally, and you let in less light. The end.

 

That some ISO settings on digital cameras tend to be high or low depending on the manufacturer's amplification tweaks doesn't really matter, as long as your metering technique takes it into account.

 

So for example, my M8's ISO readings are completely in synch with my incident meter's (and the spot meters, but you need to test these separately).

 

IOW, once I test, I don't worry about it anymore, but when you're working with multiple cameras, it's good to know how different they are when it comes to performance and ISO.

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The M8 has an unusual 8-bit encoding, as some threads have covered. It is not linear. In other words, the brightest stop of data is not stored in the values 128-156. Instead, the square root of the value is taken, and that is then stored instead. This moves some of the bits from the highlights to the shadows, but unfortunately, even with the shadows improved in this manner, 8 bits is really very tight for storing images, and the result is inferior to full 16-bit storage, at least in theory.

 

Given this bit shuffling, is exposing to the right with the M8 still beneficial?

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Less so than normal, but there are still more bits in the highlights than in the shadows. The ratio is just less severe than usual. I don't bother with it any more, personally.

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Dave--

 

You're overthinking this, I think.

I think so too

 

A minus EV setting only affects the meter in manual exposure; obviously it effects the exposure in Av automatic

 

In other words, when you dial in a negative EV compensation in Av the shutter is faster than it would be normally, and you let in less light. The end.

Ah, yes... I don't use A mode usually. Will give this a try and see what the EXIF contains... and having just now tried it:

 

In "A" mode, the shutter speed(exposure time, and shutter speed value) EXIF data reflects the in-camera speed adjustment made when "dialing in" a non-zero EV value, plus records that EV comp value.

 

In manual mode(!), if the shutter speed is kept fixed, only the EV comp value differs... which is handy because the aperture is not recorded and this might remind whether between two shots one has opened or stopped down.

 

That some ISO settings on digital cameras tend to be high or low depending on the manufacturer's amplification tweaks doesn't really matter, as long as your metering technique takes it into account.

[snipped]

IOW, once I test, I don't worry about it anymore, but when you're working with multiple cameras, it's good to know how different they are when it comes to performance and ISO.

So true. And after the data is written, the EXIF EV value refers to what adjustment may have been made...

 

...and this is why, if shooting "manually" as I do mostly, it puzzles me that folks want another button/dial to adjust EV on the fly... the ISO, I get that.

 

Thanks for removing some of my thinking, and replacing it with new!

 

So, if one uses "A" mode , then EV comp permits a helpful push or pull. In that other mode, it adjusts the display if you've grown tired of " > o ", or " o < " meter LEDs, and more importantly, you want an EXIF record that you pushed or pulled.

 

rgds,

Dave

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