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Flash & Flash Metering By Proxy, Using 35mm Hardware
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Harold Gough



Joined: 09 Mar 2008
Posts: 5787
Location: Reading, Berkshire, England

PostPosted: Mon Apr 09, 2012 7:28 am    Post subject: Flash & Flash Metering By Proxy, Using 35mm Hardware Reply with quote

I don't think I have had cause to start a topic in this forum before, not having anything much to contribute.

This has been a project at the back of my mind almost since I got my digital camera a year ago.

The situation is that I have just about every T series flashgun to go with my legacy Olympus OM 35mm film cameras. I invested in the OM system because it was then (mid 1980s) the only one with through the lens (TTL) off the film (OTF) metering, including for flash.

I seemed to me that an open flash technique (open diaphragm, fire flash, close diaphragm) with the E-P2, firing and metering the flash via the OM body, should be a means of gaining correctly-metered flash exposure with no additional expense. I was concerned that life always throws a spanner in the work and than there would be an insurmountable technical barrier to such a simple idea being a practical success.

Today I decided to stop putting off my testing of this idea because I thought I would need a darkened room and the days are getting rapidly longer. So I was getting my gear ready for a late evening session. The OM4 was empty of film (the film flattening plate gives an approximation to film reflectance.

Anyway I got the subject and the E-P2 on a tripod in the room I planned to use. I got the OM4 together with a battery-filled T32 flashgun (GN32m) and Tamron SP 90mm macro. Then I though "What the hell". I would see what would happen if at all, in terms of capturing an image on the sensor.

I had considered that I would need a similar lens on each camera, set at the same aperture, and cameras at the same distance for the subject, to make the exposure viable.*

Here are some images, uncropped:

A bowl of scented pot pourri about 120mm across. (In a polished glass dish, which which does have that pattern of swirls):

With Elmarit 90mm lens at f11



With Elmarit 60mm macro lens at f11

A small cactus, about as thick as my thumb. (The white spot is a firmly attached remnant of a mealy bug infestation). The background was dark wood, chosen deliberately:



Both cameras were set to ISO 100. I set the E-P2 on manual (I have never used manual before) and selected 2.5 seconds. When I heard the shutter open I pointed and fired the OM4/T32 combination.

*That all seems to support my simplistic theory. However, I had to set the Tamron at its maximum aperture (f2.5) and hold it something like twice as far from the subject as was the E-P2, otherwise I got severe overexposure.

Processing in PS comprised Auto Contrast, two passes of Unsharp Mask and one of Noise Ninja.

This was desperately rough and ready and the system needs calibration but I am very pleased with the results from this first attempt. Watch this space!

This might be only of use in a 'studio' situation. One limitation, according to the known facts, is that I had to use f2.5 on the film lens alongside f11 on the digital camera and, had the room been slightly brighter (it is a dull day) this would probably allow a daylight exposure at 1/60 on the OM4, preventing the flash from firing (no fill flash is possible with the OM series). I need to investigate the full ISO range on the OM4, which goes down to 12, opening up some hope of daylight flash by this technique. Early days!

Harold
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Last edited by Harold Gough on Wed Apr 18, 2012 11:35 pm; edited 2 times in total
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soldevilla



Joined: 16 Dec 2010
Posts: 552
Location: Barcelona, more or less

PostPosted: Mon Apr 09, 2012 8:32 am    Post subject: Reply with quote

I want to apologize first because maybe I did not fully understand your text, my English is not very good.

When we use flash as the only source of light, the only important parameters are the diaphragm and the distance from the object to be photographed until the light source. The distance from the model until the camera has no importance. And the lens focal length does not matter either.

Knowing that the amount of light received by the model varies with the square of the distance flash - model, it is easy to get good pictures of interiors of caves leaving the camera with the shutter open and walk through the cave while the flash fires repeatedly pointing different zones.

And in our small set we can do the same, we put the camera on tripod, went down to a minimum ambient light, shoot the camera in B mode and flash in hand, fired the flash repeatedly from different places and distances for a complex lighting.
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Harold Gough



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Location: Reading, Berkshire, England

PostPosted: Mon Apr 09, 2012 9:11 am    Post subject: Reply with quote

soldevilla wrote:
When we use flash as the only source of light, the only important parameters are the diaphragm and the distance from the object to be photographed until the light source. The distance from the model until the camera has no importance. And the lens focal length does not matter either.

Thanks for your input.

Perhaps I did not make it quite clear that the flashgun was on the hotshoe of the OM4, such that its distance from the subject governed the maximum light intensity. In theory, the camera would have given much the same exposure at any distance within the limits of the small room, provided the aperture was not small enough, or the ISO low enough, to require full output. However, once we get involved with magnification factors, we have to allow for changes in exposure with close distances. The fact is that moving the flash further back stopped the overexposure.

What is important is the light intensity on the subject. The main point is that the cameras side by side with the same ISO and aperture set did not give a workable setup in that there was overexposure. One thing I know is that if the subject was framed in the OM4 the flash was pointed in the right direction and was being metered. It is possible, l as it was hand-held that my concentration on getting the flash fired at the right time may have let the lens point a little away from the subject. Both cameras need to be on a tripod to eliminate this. However, the need for the cameras to be at a (consistently) different distance seems significant. Perhaps I made a consistent error?

Essentially, I wanted to minimise the number of variables. That said, the x2 cropping factor remains present. (I don't have a 45mm lens or a 30mm lens to use alongside the 90mm and 60mm lenses, respectively).

This needs further thought and experiment and I hope it is more simple than it appears. For the moment I am pleased that I got the results I did, irrespective of the theoretical considerations.

I will now start again, knowing that good results are possible and making careful measurements notes, as appropriate. Only then will I know the way it will work consistently.

Harold
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soldevilla



Joined: 16 Dec 2010
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Location: Barcelona, more or less

PostPosted: Mon Apr 09, 2012 3:02 pm    Post subject: Reply with quote

I think I understand now: The flash is mounted atop the old Oly, and electronics of this camera controls that the flash duration is enough to produce a proper lighting of a particular model.
If so, the theory says if you use this flash shot to take a correctly exposed picture with another camera of this model, simply respects the same ISO and same aperture, regardless of where you situes the second camera. If this is not complies strictly is because minor mechanical differences between the mechanical apertures of the diaphragms of the both objectives.


Since the cameras have a screen that shows the histogram, I almost do not remember this ... Very Happy
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Harold Gough



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Location: Reading, Berkshire, England

PostPosted: Mon Apr 09, 2012 10:15 pm    Post subject: Reply with quote

soldevilla wrote:
I think I understand now: The flash is mounted atop the old Oly, and electronics of this camera controls that the flash duration is enough to produce a proper lighting of a particular model.
If so, the theory says if you use this flash shot to take a correctly exposed picture with another camera of this model, simply respects the same ISO and same aperture, regardless of where you situes the second camera. If this is not complies strictly is because minor mechanical differences between the mechanical apertures of the diaphragms of the both objectives.

Correct, but we have to remember to allow for how the magnification factor requires more light. I would rather do that with a macro lens than by calculation. As for which lens needs to be used on the camera doing the metering, it needs the same angle of view for macro, to ensure that it is not metering the background rather than the subject. If I were to use, say, bounced flash from the ceiling, the intensity on the subject and on the wall would be the same and the target for metering less critical, provided the reflectance of the wall is appropriate or can be allowed for by a standard exposure compensation setting. However, in such a bounced flash setup, I can see that metering could be off a 'grey card' somewhere not too far from the subject. Again, the magnification factor needs to be included.

Harold
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Harold Gough



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PostPosted: Mon Apr 09, 2012 10:43 pm    Post subject: Reply with quote

Having 'slept on' this, where am I with it?

Essentially, yesterday afternoon should not have happened. I had been peering into our attic and into an outdoor cupboard with no window, expecting to have to make the exposures in darkness to avoid ambient light interfering.

Having considered the cramped and uncomfortable prospect of such arrangements, I decided I liked my comfort and was preparing to operate in the hours of darkness in a room not used much during daily living but with central heating. Exposure would be after turning the room lights, turning them on again to set up shots.

Having got the gear together, I wanted to check the flash function and, out of curiosity, and a touch of impatience, I thought I might as well make it realistic, in terms of the type of shot I wanted to try that evening.

Apart from the aperture and distance anomalies I encountered, I was astounded to get an excellent result on about the third or fourth shot. I was probably a bit 'light-headed' after that! I hadn't prepared pen and paper our a tape measure so my observations were a bit empirical. The point is that what i was unsure could be done had been done form some almost casual experimentation. Yes, I would have to do it properly but some input from those who understand digital better than I do might be stimulating.*

* For example, what is the noise situation with a digital camera in manual mode, opening the shutter for, say, a second, in the dark with a brief flash exposure?

Someone is bound to ask the question "why bother?". I have from ring flash to massive hammerhead flash, will all sorts in between, some with dedicated diffusers and including twin macro units, all at no additional cost. All those units are completely controlled by the film camera and can be used in any combination, up to nine units at a time (I don't have quite enough connections for this maximum number but don't see the need).

Tbe easier option may be to operate after the hours of darkness (or with balckout over the window) as I think I would have problems with ambient light on bright days. However, using neutral density(ND) filters on both lenses in the setup might offer posibilities in bright light.

Harold
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Chris S.
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PostPosted: Mon Apr 09, 2012 11:15 pm    Post subject: Reply with quote

Harold, the approach you're experimenting with is clever. But might it be more difficult than it needs to be? TTL isn't as useful for macro as it once was, and most old flashes will still work fine with digital cameras if you set them on manual.

When TTL flash metering first came along, back in the film days, it was a godsend for macro. Since we didn't have immediate feedback to tell us if we'd exposed properly, and because bellows factors and other things made macro flash difficult, we'd typically use TTL, bracket a bit, and one of the shots would likely be pretty decent shot. Right? Today, it's so much easier--just shoot macro with manual flash, look at the histogram, and adjust the flash accordingly. If you're not yet a fan of the histogram, you might want to give it a chance. There are some excellent tutorials for it on the Web, and I for one would never have gotten the hang of the histogram without them.

You'll recall that the old TTL systems were actually fairly simple--they assumed that average objects in the the world reflected 18 of the light that hit them, and cut the flash when enough light had reflected off the film to give an 18 percent gray average exposure. Your histogram--in combination with your judgement--is much more powerful. Shooting a white water lily floating in black, tannic water? Remember how the old TTL would give you gray water with a blown-out lily? Today, your histogram will give you a pair of spikes--one near the left for the dark water, another near the right for your white lily. Just expose so that the lily is pretty far to the right, but not off the chart, and you have your shot. Brilliant!

Not that modern flashes with digital-friendly TTL are not useful. I recently shot an event with constantly-changing people pictures under fluorescent light. I wanted a bit of fill, but not the dreaded flash look. So I gelled my flash to match the fluorescent color temperature, set it on TTL, and shot it at -1.3 stops (mostly), usually bounced off of whatever wall or ceiling was handly. I could change my f/stop to adjust depth-of field to keep the faces in focus and the background as much out of focus as possible, without having to constantly do guide-number math. Heavenly, compared with the pre-TTL days. But much macro doesn't require--or even benefit from--this. Especially if you have some older flash units that don't play TTL with digital sensors.

For freedom of light placement, and to avoid any problems with potentially high trigger voltages associated with some old flash units, you might want to look at wireless radio flash triggers such as the Yongnuo rf-602 units that I use. (They are very inexpensive.) Then set your flashes on manual, place them wherever you like, and shoot away, adjusting the flashes as per the histogram.

Cheers,

--Chris
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Harold Gough



Joined: 09 Mar 2008
Posts: 5787
Location: Reading, Berkshire, England

PostPosted: Mon Apr 09, 2012 11:57 pm    Post subject: Reply with quote

Chris,

Thanks.

Don't fall off your chair but I am about to agree with you, partly. Very Happy

Before my OM days I had a Canon A1. This coincided with my introduction to macro. With no TTL to tempt me, I used a pair of flashguns, a Vivitar 283 and a Sunpak (can't remember the model offhand but it had about half the power of the Vivitar) on a Kennett Macro Flash ring.

I had calibrated that for all magnifications/distances out from 1:1 to 1:10 for my Tamron 90mm plus x2 TC with Kodachrome 25. That gave the equivalent of incident light i.e it gave correct exposure irrespective of the subject being dark, light or mid-tone. I once impressed a moss expert, during a foray, by holding identified samples of moss on my left palm and holding the camera/flash in my right hand to shoot at 1:1, successful every time.

I still have the ring and the guns. It is on my to do list to recalibrate that for at least film use. (Just to turn what I am now doing on its head, I could use the E-P2 to do that, rather than all those calculations I had to do last time).

The problem with that was loosening the arm joints and repositioning them to aim the flash guns for every change in magnification, distance. It was almost infallible for exposure but could be slow to use. I think there is a place for a metered flash system, not least if changing subject sizes, even in studio conditions. Also, bounced and diffuse light has its place, as does, occasionally, ring flash.

As I have found few situations in outdoor macro/close-ups (mushrooms may be an exception*) where flash would be really useful in recent years, I am not too bothered. Also, I am getting stiffness in my forearm muscles from long periods of use of the E-P2, which is lighter that my OM kit, and flashguns would add an unwelcome additional weight. So, if I do get the Kennett ring back into use, it will be selectively.

My position re flash is somewhat fluid but I am more likely to use the guns I have than to invest in more hardware. Also, there is one problem with the E-P2: The V-F2 covers the hot-shoe. So if I wanted to use a suitable flash on the E-P2 I would be relying on the low-resolution screen possibly resulting in well-exposed but OOF images.

* For mushrooms the system I am working on now would be fine.

Harold
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Last edited by Harold Gough on Wed Apr 18, 2012 11:42 pm; edited 1 time in total
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Harold Gough



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PostPosted: Tue Apr 10, 2012 2:47 pm    Post subject: Reply with quote

Second session, this evening, the room darkened except when adjusting/aiming the camera:

E-P2, shutter priority, 1 second or 2 seconds, ISO 100, Elmarit 60mm macro, f11.

The OM4, aperture priority, auto flash speed of 1/60, ISO 400, Tamron SP 90mm Macro, f2.5.

Both cameras (focal planes) were about equidistant from the subject during each exposure.

This gave consistent results, whether the flash was pointed straight at the subject or bounced off the ceiling, like this. In PhotoShop: Auto Contrast, 2 passes of Unsharp Mask, no noise reduction:



Crop:



That this comes from a huge difference in the aperture and ISO settings on the two cameras suggests that the sensor behaves in a much diffferent way from film to the flash illumination. Is this the experience when legacy film flashguns are used with digital cameras?

Harold
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rjlittlefield
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PostPosted: Tue Apr 10, 2012 5:30 pm    Post subject: Reply with quote

Quote:
That this comes from a huge difference in the aperture and ISO settings on the two cameras suggests that the sensor behaves in a much diffferent way from film to the flash illumination. Is this the experience when legacy film flashguns are used with digital cameras?

I agree with your expectation that film and digital cameras should give similar images when exposed at same ISO and f-stop.

I have no explanation for your results, except that I'm a bit concerned about the following combination:
Harold Gough wrote:
E-P2, shutter priority, 1 second or 2 seconds, ISO 100, Elmarit 60mm macro, f11.

Given that magic word "priority" and the fact that the E-P2 would have been metering a dark room, are you sure that the E-P2 actually did expose at f/11 and ISO 100?

--Rik
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ChrisR
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PostPosted: Tue Apr 10, 2012 6:26 pm    Post subject: Reply with quote

You do know that with the 283 you can use the light reflected back off the subject and the sensor on the front of the unit? There are still remote leads on ebay, to put it nearer the subject.
Also with a some soldering of resistors you can make up a box to give you lower power in steps, over something like an 8 stop range.
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Harold Gough



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PostPosted: Tue Apr 10, 2012 10:21 pm    Post subject: Reply with quote

rjlittlefield wrote:
I agree with your expectation that film and digital cameras should give similar images when exposed at same ISO and f-stop.

I have no explanation for your results, except that I'm a bit concerned about the following combination:
Harold Gough wrote:
E-P2, shutter priority, 1 second or 2 seconds, ISO 100, Elmarit 60mm macro, f11.

Given that magic word "priority" and the fact that the E-P2 would have been metering a dark room, are you sure that the E-P2 actually did expose at f/11 and ISO 100?


Thanks, Rik,

There is no linkage to the diaphragm of the lens so it has no choice, the lens works totally manually. The ISO is set manually, and changing it causes overexposure. The E-P2 was on totally manual or shutter priority in the two sessions, If the flash failed (i.e. I fogot to 'advance the film' to cock the shutter) the images were black. Results were identical for different shutter settings on the E-P2: 1, 2 or 3.5 seconds.

I have just run an elimination check. I actually put some film in, in case my recall of the reflectivity of the film plate was incorrect. I did not set the ISO to match the film speed the film, leaving it as previously. The results were identical. The film was superfluous and will not be used in further experimentation.

To freeze movement requires the shortest duration of the flash and this should happen at wider aperture and/or higher ISO. The lens on the metering OM4 camera was already wide open so I increased the ISO on each camera to 200 and 800, respectively and then to 400 and 1600. Results were identical. Of course, increasing ISO makes exposure from ambient light increasingly likely, such that this is not the way to go for working outside of a darkened room.

In a final check on a possible cause of the huge difference in film and sensor sensitivity I changed cameras. I put another OM4 in the system and got identical results, including at the various ISOs. I did this because the one problem I have had with the OM4s in recent years is with the shutter magnets, causing up to a couple of stops over (I think) exposure. This was serviced in one of the bodies in the past 6 months and the other exposes accurately.

So, I have a working system, even if we don't yet understand why.

Harold
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Last edited by Harold Gough on Tue Apr 10, 2012 11:50 pm; edited 1 time in total
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Harold Gough



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Location: Reading, Berkshire, England

PostPosted: Tue Apr 10, 2012 10:40 pm    Post subject: Reply with quote

Chris S. wrote:
Shooting a white water lily floating in black, tannic water? Remember how the old TTL would give you gray water with a blown-out lily?

I may have just the solution.

Assuming the ambient illumination be low enough to allow my OM4 to fire its flash:

The metering camera in my system need not 'see' the framed subject. Thus, anything under flash illumination, say a mid-green lily leaf, or a green frog, or a red brick wall or grey rocks, could be used for a metering target. You could even place a 'grey card' outside the frame. The metering camera does not even have to point in the same direction as the digital one. This could offer spot metering for flash, not something I have found to be generally available (last time I looked).

I predict that I will be able to illuminate a tiny subject and photograph it at high magnification, with a macro lens on a long extension. I may not be able to see the subject, other than through the E-P2 viewfinder, because my view is blocked by a huge lighting unit, and I will meter off a grey card, or equivalent which is visible within the area covered by the flash, possibly from somewhat to one side.

Harold
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Last edited by Harold Gough on Wed Apr 18, 2012 11:45 pm; edited 1 time in total
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Harold Gough



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PostPosted: Tue Apr 10, 2012 11:57 pm    Post subject: Reply with quote

rjlittlefield wrote:
I agree with your expectation that film and digital cameras should give similar images when exposed at same ISO and f-stop.

I have no explanation for your results, except that I'm a bit concerned about the following combination:
Harold Gough wrote:
E-P2, shutter priority, 1 second or 2 seconds, ISO 100, Elmarit 60mm macro, f11.

Given that magic word "priority" and the fact that the E-P2 would have been metering a dark room, are you sure that the E-P2 actually did expose at f/11 and ISO 100?


Thanks, Rik,

Of course, the term "shutter priority" looks weaker than it is. It means that the camera determines the aperture to be used during exposure, where it has a linkage. There is no linkage to the diaphragm of the lens used here so the camera has no choice, the lens works totally manually. Thus, correct exposure is a matter of correct manual metering or, in this case, correct intensity/duration of the flash.

The ISO is set manually, and changing it causes overexposure or underexposure*. The E-P2 was on totally manual or shutter priority in the two sessions, If the flash failed (i.e. I forgot to 'advance the film' to cock the shutter) the images were black. Results were identical for different shutter settings on the E-P2: 1, 2 or 3.5 seconds.

* I have not yet done much investigation in the direction of underexposure and have no data recorded so far.

I have just run an elimination check. I actually put some film in, in case my recall of the reflectivity of the film plate was incorrect. I did not set the ISO to match the film speed the film, leaving it as previously. The results were identical. The film was superfluous and will not be used in further experimentation.

To freeze movement requires the shortest duration of the flash and this should happen at wider aperture and/or higher ISO. The lens on the metering OM4 camera was already wide open so I increased the ISO on each camera to 200 and 800, respectively and then to 400 and 1600. Results were identical. Of course, increasing ISO makes exposure from ambient light increasingly likely, such that this is not the way to go for working outside of a darkened room.

In a final check on a possible cause of the huge difference in film and sensor sensitivity I changed cameras. I put another OM4 in the system and got identical results, including at the various ISOs. I did this because the one problem I have had with the OM4s in recent years is with the shutter magnets, causing up to a couple of stops over (I think) exposure. This was serviced in one of the bodies in the past 6 months and the other exposes accurately.

[Edit] I also tried Manual mode with the shutter on "Bulb" option. My reason was that, if anywhere in its options, this was likely to be where open flash might be allowed for. The results were the same, except that there was an extra fumble factor while I held down the E-P2 release button while I fired the flash via the OM4. [Edit ends]

So, I have a working system, even if we don't yet understand why. [Edit] I have refered this to a specialist Olympus forum.[Edit ends]

Harold
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DQE



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PostPosted: Wed Apr 11, 2012 11:14 am    Post subject: Reply with quote

In spite of considerable risk of inadequately understanding all aspects of this thread, I would like to offer the following caveat:

ISO speed for digital cameras is not defined so as to be comparable or to have the same meaning as ISO speed for a film or a film+camera system.

As best I can recall, digital camera ISO speed is essentially based on setting the camera, with many escape paths for the manufacturer, at a certain fraction of its digital saturation level. Plenty of details are here:

https://en.wikipedia.org/wiki/Film_speed#The_ISO_12232:2006_standard

An excerpt:

"The ISO standard ISO 12232:2006[54] gives digital still camera manufacturers a choice of five different techniques for determining the exposure index rating at each sensitivity setting provided by a particular camera model. Three of the techniques in ISO 12232:2006 are carried over from the 1998 version of the standard, while two new techniques allowing for measurement of JPEG output files are introduced from CIPA DC-004.[55] Depending on the technique selected, the exposure index rating can depend on the sensor sensitivity, the sensor noise, and the appearance of the resulting image."

another excerpt:

"The Recommended Exposure Index (REI) technique, new in the 2006 version of the standard, allows the manufacturer to specify a camera model’s EI choices arbitrarily. The choices are based solely on the manufacturer’s opinion of what EI values produce well-exposed sRGB images at the various sensor sensitivity settings. This is the only technique available under the standard for output formats that are not in the sRGB color space. This is also the only technique available under the standard when multi-zone metering (also called pattern metering) is used."

The de facto standard reference for digital camera ISO speed can be obtained online:

http://www.cipa.jp/english/hyoujunka/kikaku/pdf/DC-004_EN.pdf

I wish the digital standard for camera system speed were clearly and usefully defined. Perhaps this would be in terms of some sort of spectrally weighted absolute light required to achieve a certain signal-to-noise ratio. If that is too complex, defining it in absolute light energy terms, with suitable spectral weighting, would at least allow one to perform well-defined comparisons of different cameras and camera models.

As it is, the manufacturer is surprisingly free to do whatever suits their sales and business needs and still quote ISO speed numbers. Most people assume that one can easily and accurately compare photos made at the same ISO speed with different cameras and have one's efforts be accurate, repeatable, and easily and directly interpretable.

I couldn't find many good online tutorials or technical discussions of these fundamental issues, which seems odd.

As always, if I've misunderstood the issues at hand, I look forward to learning from others' better information and experience.
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