Dynamic real-time OTF-style metering for digital?

[mars486]

Some 35mm cameras, like my old Olympus OM-PC, on their automatic exposure mode, do OTF (off the film) metering by sensing the average light bouncing off the film with a photodiode and integrating over time. This has an interesting effect: The camera dynamically adjusts to a changing scene when the shutter is open.

If on automatic, and the display on the viewfinder says '10 seconds', that is actually just an estimation based on the current instanteneous conditions. If you take a shot, and the scene changes in brightness while the shutter is open, it will cut the exposure short or extend the exposure.

Do any digital cameras behave like this? If I have a modern mirrorless camera set to auto, and it says it wants a 10 second exposure when I click the button, will it always shoot the 10 full seconds? Say I start a shot, and someone zooms by with their headlights on... my old film camera will cut the shot short. Will any digital camera know to do this?

I know image sensors can't really read out until the exposure is complete. And most cameras probably just meter by noticing the preview shot it over/under exposed and then adjusting. But has any manufacturer went and put in a photodiode to measure the light of the sensor, or maybe integrated a "real" light meter on the sensor itself?

 

[Ysarex]

Some 35mm cameras, like my old Olympus OM-PC, on their automatic exposure mode, do OTF (off the film) metering by sensing the average light bouncing off the film with a photodiode and integrating over time. This has an interesting effect: The camera dynamically adjusts to a changing scene when the shutter is open.

If on automatic, and the display on the viewfinder says '10 seconds', that is actually just an estimation based on the current instanteneous conditions. If you take a shot, and the scene changes in brightness while the shutter is open, it will cut the exposure short or extend the exposure.

Do any digital cameras behave like this? If I have a modern mirrorless camera set to auto, and it says it wants a 10 second exposure when I click the button, will it always shoot the 10 full seconds? Say I start a shot, and someone zooms by with their headlights on... my old film camera will cut the shot short. Will any digital camera know to do this?

None that I'm aware of. But if it were a feature in one of my mirrorless cameras I'd disable it. I don't want my exposure based on a meter reading that's an average or weighted average or even algorithmically weighted average of the sensor area.

I base my exposures on my camera's highlight alert function. It always immediately finds the brightest highlight in the scene and that's the info I want to set an exposure.

I know image sensors can't really read out until the exposure is complete. And most cameras probably just meter by noticing the preview shot it over/under exposed and then adjusting. But has any manufacturer went and put in a photodiode to measure the light of the sensor, or maybe integrated a "real" light meter on the sensor itself?

 

[ahaslett]

Depending on what you are trying to do, Olympus Live Bulb, Time & Composite might be relevant. People use Live Composite to photograph lightning for example.

A

 

[mars486]

When I'm shooting a stably lit scene, highlight alert and then adjusting the exposure is fine. When shooting long exposures with wildly varying lighting conditions... Not sure how to deal with it. I suppose live composite modes and such have made some of these ideas obsolete. I haven't bought a interchangeable lens camera since the E-PL1 in 2010, so I have no idea what is really out there in terms of new features... I just learned of live composite and think its pretty cool.

 

[Ysarex]

When I'm shooting a stably lit scene, highlight alert and then adjusting the exposure is fine. When shooting long exposures with wildly varying lighting conditions... Not sure how to deal with it. I suppose live composite modes and such have made some of these ideas obsolete. I haven't bought a interchangeable lens camera since the E-PL1 in 2010, so I have no idea what is really out there in terms of new features... I just learned of live composite and think its pretty cool.

Live composite is news to me too. Long exposures with wildly changing light -- not something I can imagine encountering.

 

[Mike B USA]

Some 35mm cameras, like my old Olympus OM-PC, on their automatic exposure mode, do OTF (off the film) metering by sensing the average light bouncing off the film with a photodiode and integrating over time. This has an interesting effect: The camera dynamically adjusts to a changing scene when the shutter is open.

If on automatic, and the display on the viewfinder says '10 seconds', that is actually just an estimation based on the current instanteneous conditions. If you take a shot, and the scene changes in brightness while the shutter is open, it will cut the exposure short or extend the exposure.

Do any digital cameras behave like this? If I have a modern mirrorless camera set to auto, and it says it wants a 10 second exposure when I click the button, will it always shoot the 10 full seconds? Say I start a shot, and someone zooms by with their headlights on... my old film camera will cut the shot short. Will any digital camera know to do this?

None that I'm aware of. But if it were a feature in one of my mirrorless cameras I'd disable it. I don't want my exposure based on a meter reading that's an average or weighted average or even algorithmically weighted average of the sensor area.

I base my exposures on my camera's highlight alert function. It always immediately finds the brightest highlight in the scene and that's the info I want to set an exposure.

It's really handy for automatic exposure of second curtain flash (sometimes called slow sync flash) where the flash pops just before the shutter closes to freeze the moment but leaving motion trails leading up to it.

 

[alcelc]

Yes this is a very interesting and useful tool on those situation: we can stop the exposure in real time when the simulated image would look good enough.

This permit us to produce output more closer to what we are looking at with less experience and a lot less guessing work in advance. Good to me who without those knowledge on the genrecof shooting.

 

[alcelc]

I doubted this as per my experience, since Nikon EM (a 60s era entry class model), which was my first auto (semi auto only instead) exposure mode,l camera, then the later (film slrs or compacts), later the the early digital compacts, superzoom bridges to the MILCs nowadays...

Because before a full clicking on shutter button, generally most cameras would support half shutter button pressing. It is not only to lock focus (AF), it will also take metering for the AE system to work. If we keep the shutter button half pressed, the focusing and exposure value would be locked. So, even if the lighting condition at the last moment of shooting might change, the exposure value would not change in responding to the latest changing.

This is the foundamental logic of operation for the focus - recompose style of shooting which I am still using today.

The AE Lock or AF Lock works in similar manner as keep shutter button half pressed.

If I am not wrong your described operation could be happened to p&s only, i.e. put up the camera and full shutter release to capture the image without pre-locking of exposure nor AF. Doing this will cancel any pre locked exposure value even if you might have set it up before firing :-( .

 

[Overrank]

I think that’s a feature of some of the Olympus OM’s, but I’m not sure how widespread it is for normal exposure. Some of the OMs have two meters and you can have the situation (I’ve had both) where the display meter doesn’t work but the camera exposes perfectly, and the opposite, where the camera doesn’t expose at all, but the meter in the viewfinder is correct.

The later film Nikons have off the film exposure for flash, but with the introduction of digital the sensor was too shiny and so Nikon had to introduce a new range of flashes that do a pre-flash and calculate exposure from that. I’m guessing that any “OTF “ like system would suffer the same problems as for flash - that the sensor is too shiny compared to film emulsion.

(btw some films were too shiny and broke OTF exposure for flash, PolaChrome instant 35mm being one)

 

[Overrank]

When I'm shooting a stably lit scene, highlight alert and then adjusting the exposure is fine. When shooting long exposures with wildly varying lighting conditions... Not sure how to deal with it. I suppose live composite modes and such have made some of these ideas obsolete. I haven't bought a interchangeable lens camera since the E-PL1 in 2010, so I have no idea what is really out there in terms of new features... I just learned of live composite and think its pretty cool.

Live composite is news to me too. Long exposures with wildly changing light -- not something I can imagine encountering.

Fireworks

 

[mars486]

Fireworks... exactly. And lightning. When I was a kid my Dad and I would go out, and he's set up the camera on a tripod, stop it down, and put it on automatic, and click the shutter. The camera would wait for a lightning strike, sometimes 2 or 3. As a kid, I thought it was pretty cool, but as an adult thinking back, that was such an impressive feature. I suppose with film it makes senses for the camera to have an option to try to 'save' as many shots as possible by adjusting the exposure... otherwise you're just wasting film. With digital, I guess just take a bunch of shots and stack them, which I guess live composite and such are actually doing.

 

[GeoffRG]

Olympus' OTF exposure metering worked by reading the light reflected off the shutter curtain or the film, unexposed, undeveloped film being near enough mid grey. The shutter curtain had a pattern of squares to equate to mid grey. It only worked in aperture priority or flash modes and it actually worked rather well. As has been said Nikon used OTF metering for TTL flash.

Nikon's 3D colour matrix metering uses a similar arrangement with the sensor in the bottom of the mirror box, exposed by a part silvered section on the mirror and a sub mirror, AF uses the same location. Whether Nikon metering is active during exposure I couldn't say, probably not.

If you can find an OM2 brochure it was explained quite well, not sure if I still have mine.

You can find the brochure here.

 

[saltydogstudios]

I think that’s a feature of some of the Olympus OM’s, but I’m not sure how widespread it is for normal exposure. Some of the OMs have two meters and you can have the situation (I’ve had both) where the display meter doesn’t work but the camera exposes perfectly, and the opposite, where the camera doesn’t expose at all, but the meter in the viewfinder is correct.

The later film Nikons have off the film exposure for flash, but with the introduction of digital the sensor was too shiny and so Nikon had to introduce a new range of flashes that do a pre-flash and calculate exposure from that. I’m guessing that any “OTF “ like system would suffer the same problems as for flash - that the sensor is too shiny compared to film emulsion.

(btw some films were too shiny and broke OTF exposure for flash, PolaChrome instant 35mm being one)

This reminds me of the thryristor system where the flash would have a light meter that would turn the flash off once enough light had bounced back from the scene into the flash.

OTF is new to me.

Olympus has a couple of interesting photo composite modes. One acts as a pseudo long exposure where it would keep reading the scene but only add new information. So the exposure wouldn’t change from your settings but any new [edit: different from before] light reaching the sensor would add to it.

Sort of like a “lighten only” layer in photoshop. Useful for capturing fireworks and lightning.

it might be done with consecutive exposures that are added together in camera, I’m not sure.

--
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[D Cox]

When I'm shooting a stably lit scene, highlight alert and then adjusting the exposure is fine. When shooting long exposures with wildly varying lighting conditions... Not sure how to deal with it. I suppose live composite modes and such have made some of these ideas obsolete. I haven't bought a interchangeable lens camera since the E-PL1 in 2010, so I have no idea what is really out there in terms of new features... I just learned of live composite and think its pretty cool.

Live composite is news to me too. Long exposures with wildly changing light -- not something I can imagine encountering.

Maybe a stage play or a rock concert ?