ISOs on M240 vs ISOs on external ambient meter

[Jon Warwick]

Advertisement (gone after registration)

Could be a daft question, we will see ....

 

I was pondering using my external ambient Sekonic meter to attempt to improve my exposure accuracy when using the M240.

 

Is the ISO (say 200) on such a digital ambient meter going to equate exactly to how the M240 is also programmed to think about ISO 200?

 

I assume 200 is 200, whether it’s on a digital meter, Leica, Canikon etc etc, and that no specific calibration needs to be done between camera and meter to ensure “ultimate accuracy”?

[a.noctilux]

Hello Jon,

 

ISO is only that ISO a Standization that changed over time:

Extract from here

https://en.wikipedia.org/wiki/Film_speed

 

 

Current system: ISO

The ASA and DIN film speed standards have been combined into the ISO standards since 1974.

The current International Standard for measuring the speed of color negative film is ISO 5800:2001^[17] (first published in 1979, revised in November 1987) from the International Organization for Standardization (ISO). Related standards ISO 6:1993^[15] (first published in 1974) and ISO 2240:2003^[16] (first published in July 1982, revised in September 1994, and corrected in October 2003) define scales for speeds of black-and-white negative film and color reversal film, respectively.

The determination of ISO speeds with digital still-cameras is described in ISO 12232:2006 (first published in August 1998, revised in April 2006, and corrected in October 2006).

The ISO system defines both an arithmetic and a logarithmic scale.^[36] The arithmetic ISO scale corresponds to the arithmetic ASA system, where a doubling of film sensitivity is represented by a doubling of the numerical film speed value. In the logarithmic ISO scale, which corresponds to the DIN scale, adding 3° to the numerical value constitutes a doubling of sensitivity. For example, a film rated ISO 200/24° is twice as sensitive as one rated ISO 100/21°.^[36]

Commonly, the logarithmic speed is omitted; for example, "ISO 100" denotes "ISO 100/21°",^[37] while logarithmic ISO speeds are written as "ISO 21°" as per the standard.

 

Compromise ...

 

There is nothing concerning "Ultimate Accuracy" as you stated.

And we can see that film and digital has each their own ISO Standard.

 

As practical note (in my actual use) in digital I'm happy to be able to change that ISO things as required by the subject.

Not so easy with film even less with positives, I used slides and learn to use lightmeter to obtain the best from those with sometimes bracketing if need be.

 

In each metering with hand held meters, even with same light, indications of each meter device can differ depending on their calbrations.

 

So comparing ISO is nothing to obtain "ultimate accuracy", but learn how to obtain accurately what "exposure you want" is more realistic.

 

IMHA, learn to use histograms in digital when it's possible (not really useful in back light or difficult contrast) is better than using external meter.

[Advertisement]

The Leica Q3 is available for pre-order at B&H Photo Video and Adorama

[ktmrider2]

My preferred metering method is incident.  I would suspect that it would work just as well on digital as film.  I always found it worked better for transparency film then a reflected reading.  Since digital (to my understanding) seems to respond similarly to slide film, I don't see why it would not work well to use a handheld meter.

 

Now, if you are asking if ISO 200 on digital gives the same sensitivity as ISO on a digital camera, well the good thing about digital is the result is available for immediate viewing.  My guess is yes it is but since all films respond just a bit differently why don't you test it out and let us know.

Edited March 25, 2018 by ktmrider2

[Jean-Michel]

Handheld meters do go off calibration. Do this test: use a Kodak 18% grey card, photograph it with you camera using manual setting, the histogram should be right smack down the middle. Now mesure the exposure with you handheld meter incident or reflected should not matter and expose the card Asmesured by the meter. Check that histogram, both should be the same, but may well not be. I have a Minolta meter that is almost exactly one stop off, a Lunasix that is almost correct in the lowere scale and off by various amounts on the upper scale and therefore useless.

[jmahto]

Not sure about exposure accuracy need for digital (if you post process DNG). All that matters is not to clip highlights and for that in-camera tool to show histogram and clipped highlight helps.

[ktmrider2]

Maybe I am just a primitive analogue user but it seems to me that there is usually an optimum exposure for each scene.  Now, each capture medium (b&w film, color negative film, color transparency film and digital capture) have some built in but different amounts of latitude to make a printable image.  But the bottom line is the optimum exposure will result in a better image.

 

And I don't care if the capture is RAW digital, TriX, or Ektar!  Is not capturing the correct composition at the correct instant at the correct exposure what photography is all about?

[Michael Geschlecht]

Advertisement (gone after registration)

Hello Jon,

 

What is it that you do NOT like about the way that your M240 is metering & what type of metering mode is set on the M240 & what do you do when you meter with the M240 now? A lot of questions.

 

Also, what does the histogram on the back look like when the exposure that you get is the exposure that you want?

 

How are the other histograms different when you get exposures that do not come out the way that you want them to be?

 

The answer to these questions might make answering your original question more do-able.

 

Best Regards,

 

Michael

Edited March 27, 2018 by Michael Geschlecht

[jmahto]

Maybe I am just a primitive analogue user but it seems to me that there is usually an optimum exposure for each scene. Now, each capture medium (b&w film, color negative film, color transparency film and digital capture) have some built in but different amounts of latitude to make a printable image. But the bottom line is the optimum exposure will result in a better image.

 

And I don't care if the capture is RAW digital, TriX, or Ektar! Is not capturing the correct composition at the correct instant at the correct exposure what photography is all about?

I see what you are saying about composition and exposure that you want, however on digital you can adjust the exposure later in post to what suits you. By exposing higher (just below clipping), you are maximizing information capture (since more electrons in the sensor get excited) resulting into image with less noise. This is simply one extra tool (optional) you have in digital capture.

[ECohen]

Maybe I am just a primitive analogue user but it seems to me that there is usually an optimum exposure for each scene.  Now, each capture medium (b&w film, color negative film, color transparency film and digital capture) have some built in but different amounts of latitude to make a printable image.  But the bottom line is the optimum exposure will result in a better image.

 

And I don't care if the capture is RAW digital, TriX, or Ektar!  Is not capturing the correct composition at the correct instant at the correct exposure what photography is all about?

 

To a certain extent I agree with this post. But like with film, expose for the highlight's and develop for the shadows Unless its transparency film then you best be dead on.

 

With digital shoot RAW and expose for the highlights.

 

Edited March 27, 2018 by ECohen

[Jon Warwick]

Hello Jon,

 

What is it that you do NOT like about the way that your M240 is metering & what type of metering mode is set on the M240 & what do you do when you meter with the M240 now? A lot of questions.

 

Also, what does the histogram on the back look like when the exposure that you get is the exposure that you want?

 

How are the other histograms different when you get exposures that do not come out the way that you want them to be?

 

The answer to these questions might make answering your original question more do-able.

 

Best Regards,

 

Michael

Thanks to all for your answers.

I’m using classic - centre weighted.

In the past, I’ve probably been guilty of swinging too far towards underexposure ..... thinking this was key to control highlights in digital....but causing me to then constantly need to lighten most of the image in post and not helping mid-tones or colour accuracy in the process.

I have now started to better expose for the key mid-tone range of the image, and it’s often the case that the highlights are STILL ok, even in that instance. No need for such underexposure in the past, after all.

I’ve also watched some good videos on YouTube on histograms, and have learnt a lot more about analysing the histogram across the tonal range of the image. It was revealing how much info can be gleaned by scrolling into the image and re-reviewing the histogram for enlarged sections of the image.

I won’t know for sure how this will look until I get back from hols and look at the files on the iMac, but so far it all looks better on the camera back and histogram.

Thanks again!

Edited March 27, 2018 by Jon Warwick

[Jon Warwick]

Not sure about exposure accuracy need for digital (if you post process DNG). All that matters is not to clip highlights and for that in-camera tool to show histogram and clipped highlight helps.

This was certainly the approach I’ve been taking ..... until very recently. In hindsight, pending a more detailed look into it, I think it’s more important to get exposure really correct in camera than I’d given it justice. Given my (too great an) emphasis on purely the highlights, I’d inadvertently often underexposed in situations that might not have needed quite so much underexposure ..... to the detriment of colour tonality that was potentially thrown away, and “muddying” the image in general. Edited March 27, 2018 by Jon Warwick

[Jon Warwick]

Handheld meters do go off calibration. Do this test: use a Kodak 18% grey card, photograph it with you camera using manual setting, the histogram should be right smack down the middle. Now mesure the exposure with you handheld meter incident or reflected should not matter and expose the card Asmesured by the meter. Check that histogram, both should be the same, but may well not be. I have a Minolta meter that is almost exactly one stop off, a Lunasix that is almost correct in the lowere scale and off by various amounts on the upper scale and therefore useless.

I’ll be doing just this in the next week or so! Thanks for the suggestion.

[pico]

Digital ISO is not at all like film. Digital sensors have no native ISO above 100 or so.

Higher sensitivity is entirely digitally modified.

 

Film shooters have to adapt to the concept of digital gain. Digital shooters have

already adapted to "what works, who cares?"

[jmahto]

When I shot slide film, I expected that some part of the picture may have blown highlights (depending on the DR of the scene). Even with limited DR, properly exposed slides looked good. Ironically, with digital, I worry about blowing highlights too much.

[Exodies]

Isn’t digital iso done by analogue amplification and then the push range by digital multiplication?

[RMF]

You most likely will always see a slight difference between an incident ambient reading (handheld) vs an incamera reflected metering; the incident reads light that is “falling” on the subject vs incamera metering which measure light directly reflecting back into the camera. You have to take into account the both base their metering on neutral grey card as well, so that also needs to be taken into account.

[Jean-Michel]

Setting the exposure with the built-in meter is easy enough, as long as you remember that, in Classic mode, it is a strongly centre-weighed measurement. I don't carry a light-meter anymore, the camera meter is all I need for most uses. I do use a flash meter to set studio lighting,and also use a meter (incident) to check lighting in gallery settings where there are large expanses of either white or painted walls, and therefore the exposure as read by the camera could easily be off.

 

Optimum exposure for digital files is similar, but not identical to that of film. The "expose to the right, ETTR" method works well as long as you do not overexpose (clip) the highlights. Unfortunately the highlight clipping warning on the camera screen is not accurate, as it is based on the jpg file; what may be clipped in the jpg may not be in the dng. 

 

Some years ago, Michael Reichmann at Luminous Landscape wrote a article on this, and later demonstrated this in a tutorial video. Worth reading and viewing.

[jmahto]

Setting the exposure with the built-in meter is easy enough, as long as you remember that, in Classic mode, it is a strongly centre-weighed measurement. I don't carry a light-meter anymore, the camera meter is all I need for most uses. I do use a flash meter to set studio lighting,and also use a meter (incident) to check lighting in gallery settings where there are large expanses of either white or painted walls, and therefore the exposure as read by the camera could easily be off.

 

Optimum exposure for digital files is similar, but not identical to that of film. The "expose to the right, ETTR" method works well as long as you do not overexpose (clip) the highlights. Unfortunately the highlight clipping warning on the camera screen is not accurate, as it is based on the jpg file; what may be clipped in the jpg may not be in the dng. 

 

Some years ago, Michael Reichmann at Luminous Landscape wrote a article on this, and later demonstrated this in a tutorial video. Worth reading and viewing.

Highlight mine...

 

True, there is also a complication due to scene luminance difference between different color channels. It is possible that a particular color is "blown/clipped" while rest is ok (ex: yellow flowers in green foliage). The combined color histogram (and clipping) is only a simplification.

 

Bottom line is that exposing digital is different than film, in the same way regular film was different than reversal film.

Edited March 28, 2018 by jmahto

[adan]

Could be a daft question, we will see ....

 

I was pondering using my external ambient Sekonic meter to attempt to improve my exposure accuracy when using the M240.

 

Is the ISO (say 200) on such a digital ambient meter going to equate exactly to how the M240 is also programmed to think about ISO 200?

 

I assume 200 is 200, whether it’s on a digital meter, Leica, Canikon etc etc, and that no specific calibration needs to be done between camera and meter to ensure “ultimate accuracy”?

 

To get back to the original question:

 

ISO speeds for film and for digital imaging are supposed to be approximately equivalent.

 

However, the means of measuring the ISO for sensors vs. film is different. With film, ISO is based on measuring the density of the silver created by a given amount of light, using a densitometer (X amount of light produces X amount of silver). Usually working off the shadow detail (what ISO setting produces "just enough" silver in an area 3-4 stops darker than a medium gray (18% reflectance gray card gray).

 

...whereas with digital, the ISO is determined by measuring the signal output (X amount of light produces X amount of signal, i.e. electrons flowing off the sensor).

 

It is rather like trying to measure the "horsepower" of a piston engine, a jet engine, and an electric motor - one can eventually get a measure of final output power for each, but the internal workings are such that how the measurement is made is different, and the "equivalence" may be skewed by the different measuring techniques.

 

On top of that, manufacturers of both digital cameras and film are given some leeway in how they themselves "spec" the ISO sensitivity - Kodak uses shadow density, Ilford uses middle gray density, and Leica and Nikon and Canon (to the extent that they are now "film manufacturers" in producing the light-sensitive surface themselves) may each produce different results with their cameras set to "ISO 200" (see DxOMark tests of how (in)accurate camera ISO labelling can be).

 

Practically speaking, you would need to do some testing yourself with your external meter to find out which meter ISO setting gives you the results you prefer with a given camera ISO setting. You might find that your hand-held meter gives the best exposures - with the M240 set to ISO 200 - by being set to 160, or 200, or 250, or even other ISOs. This is not that big a deal, since many photographers, even with film, may test and then decide that they prefer Tri-X exposed (according to their meter) at 200 or 500 or 800 instead of the "box" ISO of 400.

 

Then, of course, there are the differences between ttl metering in the M240 (a very narrow, almost "spot" part of the picture center in "classic" mode) compared to normal hand-held reflected-light metering (usually an area about equal to the total subject coverage of a 50mm lens) compared to incident metering (which ignores the subject and its brightness completely and simply measures the light falling on the subject - same reading whether the subject is black, white or gray).

Edited April 12, 2018 by adan

[Advertisement]

Hallo,

Look here: Leica M

[sblutter]

I 1st choose the f: stop for the image I want.  Then ISO so the shutter speed will be above 30 or 60 on auto.  Then using center metering, I grab a "just less than white" part of the frame to lock the speed - not wanting blown out brights and knowing I can easily bring up the lows in PS.  The process is now ingrained & is very quick

 

If I'm doing night shots, a monopod really helps

 

Am very happy with my results - which are always intended for print, these days all B&W with piezography inks

 

Have a look:  https://www.flickr.com/photos/sblutter/26496201989/in/album-72157687139294452/