Digital Equivalent of OTF Metering

[Graham_of_Rainham]

Are any manufacturers implimenting metering using the sensor that provides for changes in light levels during exposures, to give a similar functional capability as OTF Metering did ???

My particular interest is for a project that involves painting with coloured lights. I'll end up doing it all manually by trial and error, but it got me thinking about the old film days when you just snapped the shutter open and the camera shut it once it had seen enough light.

Thanks

[Ian]

Are any manufacturers implimenting metering using the sensor that provides for changes in light levels during exposures, to give a similar functional capability as OTF Metering did ???

My particular interest is for a project that involves painting with coloured lights. I'll end up doing it all manually by trial and error, but it got me thinking about the old film days when you just snapped the shutter open and the camera shut it once it had seen enough light.

Thanks

I wonder if the problem for DSLRs is that there are so many layers of glass in front of the sensor (anti-aliasing filter, low pass filter, dust filter, etc.) that it's too difficult to measure light reflected back off the sensor plane.

Ian

[Graham_of_Rainham]

I wonder if the problem for DSLRs is that there are so many layers of glass in front of the sensor (anti-aliasing filter, low pass filter, dust filter, etc.) that it's too difficult to measure light reflected back off the sensor plane.

Ian

Indeed, rather than metering off the sensor, I was thinking of metering by the sensor, using subsets of sensor pixels that match the areas that the camera meters from. I can't believe it hasn't already been thought of (If not I lay claim to the idea :D ) With the speed of the latest processors, I can't see why this can't be implimented.

Previously even flash was linked into it and flash duration adjusted by the OTF system. I'd really like to know why this is no longer a capability ???

*chr

[Ian]

Indeed, rather than metering off the sensor, I was thinking of metering by the sensor, using subsets of sensor pixels that match the areas that the camera meters from. I can't believe it hasn't already been thought of (If not I lay claim to the idea :D ) With the speed of the latest processors, I can't see why this can't be implimented.

Previously even flash was linked into it and flash duration adjusted by the OTF system. I'd really like to know why this is no longer a capability ???

*chr

Mmmmm... to read the sensor you need to dump its contents to the A/D converter do you not? So to make a reading you have to interrupt the exposure?

Ian

[Graham_of_Rainham]

Mmmmm... to read the sensor you need to dump its contents to the A/D converter do you not? So to make a reading you have to interrupt the exposure?

Ian

In my imagination... the Analog signals from various sites on the sensor,(equivalent to, and selectable, in the same way as the metering areas) are fed into the exposure system. Once preset levels are reached the shutter is closed. The preset exposure levels could be based on all manner of things that would produce different effects.

Ok so we do all this manually and it's great fun doing it and learning as we do so. But so were all the other effects and features that camera manufactures have added into their latest offerings. A digital equivalent of OTF functionality for me would be a lot more useful than all the "Scene Modes".

I do appreciate these "techy" threads. Since I retired I miss all the "What if" discussions. :cool:

[Ian]

In my imagination... the Analog signals from various sites on the sensor,(equivalent to, and selectable, in the same way as the metering areas) are fed into the exposure system. Once preset levels are reached the shutter is closed. The preset exposure levels could be based on all manner of things that would produce different effects.

Ok so we do all this manually and it's great fun doing it and learning as we do so. But so were all the other effects and features that camera manufactures have added into their latest offerings. A digital equivalent of OTF functionality for me would be a lot more useful than all the "Scene Modes".

I do appreciate these "techy" threads. Since I retired I miss all the "What if" discussions. :cool:

Yes, I understand what you would like :) ..but if my knowledge of imaging sensors is correct, you can use the sensor as a light meter or an image capture device, but not at the same time. So for a single shot exposure, the metering can be established by the sensor prior to the exposure, but you can't use the sensor to meter during the exposure.

Ian

[devilgas]

now, if there were 2 AD convertors, the 2nd dedicated to metering, using only a fraction of the photosites, then there's no reason why this wouldn't be feasible.
also, what happens during 'live view'? iirc, metering goes on there as well as the camera processing the signal to display on the monitor. from what i remember with the 40d (i rarely use live view), there is processing lag. the lag far outweighs the shutter speed. so.....back to my dual A/D convertors then.....

[Ian]

now, if there were 2 AD convertors, the 2nd dedicated to metering, using only a fraction of the photosites, then there's no reason why this wouldn't be feasible.
also, what happens during 'live view'? iirc, metering goes on there as well as the camera processing the signal to display on the monitor. from what i remember with the 40d (i rarely use live view), there is processing lag. the lag far outweighs the shutter speed. so.....back to my dual A/D convertors then.....


In live view there are several dozen frames produced per second. Each one is effectively a separate 'exposure'. You can evaluate the frames as they stream off for expsoure, but evaluating exposure during the creation of one frame is very different.

Ian

[devilgas]

which is where my 2nd ADC comes in ;)
as the 2nd ADC is only measuring 20 or so photosites compared to the 12million odd that the primary ADC would serve, then the processing required for the 2nd ADC is minimal and could easily be done in real time, even with shutter speeds in excess of 1/4000s. if i were tasked to solve OTF metering, then this would be where i'd start.

[Graham_of_Rainham]

which is where my 2nd ADC comes in ;)
as the 2nd ADC is only measuring 20 or so photosites compared to the 12million odd that the primary ADC would serve, then the processing required for the 2nd ADC is minimal and could easily be done in real time, even with shutter speeds in excess of 1/4000s. if i were tasked to solve OTF metering, then this would be where i'd start.


I'm wondering if there even needs to be a 2nd ADC... If the Analogue levels from the areas of the sensor selected for determining exposure are fed to a comparitor that has the exposure levels preset then as soon as the accumulative level of signal from the sensor sites is the same the exposure is complete. I'd imagin that this could all be done on a chip the size of a pin head and would have the capacity for 100s of other functions as well.

Oh! things are so simple in "What-if-World"... All we need now is a camera circuit designer to tell us why it can't be done, or better still that it's the next "big" thing that is going to be available.

Are there any circuit diagrams floating about for DSLRs that could give any hints as to the viability of thes thoughts ???

[Ian]

I'm wondering if there even needs to be a 2nd ADC... If the Analogue levels from the areas of the sensor selected for determining exposure are fed to a comparitor that has the exposure levels preset then as soon as the accumulative level of signal from the sensor sites is the same the exposure is complete. I'd imagin that this could all be done on a chip the size of a pin head and would have the capacity for 100s of other functions as well.

Oh! things are so simple in "What-if-World"... All we need now is a camera circuit designer to tell us why it can't be done, or better still that it's the next "big" thing that is going to be available.

Are there any circuit diagrams floating about for DSLRs that could give any hints as to the viability of thes thoughts ???

Guys! I don't think my message is getting across :eek:

You can't measure the charge accumulating in a sensor photosite well during the exposure process. The charging process has to stop, and then the charge is shifted to an amplifier (next to the photosite on MOS-type sensors, or off the sensor array in CCD sensors), then digitised. To do this, the photosite has to be reset.

I cannot see any way you can do a meter reading off the sensor in the middle of an exposure.

Ian

[Graham_of_Rainham]

Guys! I don't think my message is getting across :eek:

You can't measure the charge accumulating in a sensor photosite well during the exposure process. The charging process has to stop, and then the charge is shifted to an amplifier (next to the photosite on MOS-type sensors, or off the sensor array in CCD sensors), then digitised. To do this, the photosite has to be reset.

I cannot see any way you can do a meter reading off the sensor in the middle of an exposure.

Ian

In that case another approach could be to use a multiple exposure technique that builds up the image in the buffer with successive short exposures until the preset exposure values are reached.

There are cameras that can do upto 60fps, if the data from a number of those frames could be added the result would be the same. It would be a similar but reverse processing of noise reduction where long exposures are followerd by another exposure with the shutter closed and the closed exposure subtracted from the open one.

Would that, or something similar work ???

[devilgas]

In that case another approach could be to use a multiple exposure technique that builds up the image in the buffer with successive short exposures until the preset exposure values are reached.

There are cameras that can do upto 60fps, if the data from a number of those frames could be added the result would be the same. It would be a similar but reverse processing of noise reduction where long exposures are followerd by another exposure with the shutter closed and the closed exposure subtracted from the open one.

Would that, or something similar work ???
i guess it would be ok for longer exposures (t< 1/60s), however the processing involved is significant so isn't that practical. i tend to look at things from the shooting i do (action mainly) and feel that the above would not be suited to how i use the camera.

thinking about it further, is there really a need for OTFM? the camera will give a good metering indication, depending on the metering region chosen, before the shot is taken so shouldn't blow the highlights anyway.

[Graham_of_Rainham]

i guess it would be ok for longer exposures (t< 1/60s), however the processing involved is significant so isn't that practical. i tend to look at things from the shooting i do (action mainly) and feel that the above would not be suited to how i use the camera.

thinking about it further, is there really a need for OTFM? the camera will give a good metering indication, depending on the metering region chosen, before the shot is taken so shouldn't blow the highlights anyway.


If you don't take the type of images that OTF was designed for then it's of as much use as many of the other features that you never use...;)

OTF metering was all about mixed light, changing light, painting with light and with the film version flash duration control.

It was something I used more than perhaps most would but that the type of photography I like doing.

*chr

[devilgas]

If you don't take the type of images that OTF was designed for then it's of as much use as many of the other features that you never use...;)

OTF metering was all about mixed light, changing light, painting with light and with the film version flash duration control.

It was something I used more than perhaps most would but that the type of photography I like doing.

*chr

fair comment. hadn't appreciated where it's use lay, despite your examples, and had assumed a general mode rather than the more specialised circumstances where it would be used.

i dabble with light painting etc every now and again, and due to lack of OTFM have to use trial and error....your original point :rolleyes:

had noticed there were some pictures and other junk on the dial, but mine only ever hits M, S & A :)

i don't think internal stacking of images would be the solution as the sensitivity / resolution of the photosite on the ACD would get compromised due to it being allowed to collect significantly less light than for a single exposure, which when 'totalled' would give a less accurate value than for a single exposure.

[Graham_of_Rainham]

...
had noticed there were some pictures and other junk on the dial, but mine only ever hits M, S & A :)

I actually bought one specifically that only has BPASM and 90% of the time it's in either A or M

...
i don't think internal stacking of images would be the solution as the sensitivity / resolution of the photosite on the ACD would get compromised due to it being allowed to collect significantly less light than for a single exposure, which when 'totalled' would give a less accurate value than for a single exposure.

That's what they pay these really clever circuit designers and programmers, oodles of cash for. I'm going to try a 5sec burst and see if I can get the effect with layers. The cumulative data approach is what I believe they use on the Hubble telescope where one of the "cameras" collects single photons (or there abouts) and the image is built up from many samples.

My other approach will be to use my OM4Ti and scan the slides :D

[devilgas]

shows my brain wasn't in gear when i wrote that cr*p! had totally forgotten about astro stacking, although how practical it would be (real time processing) in this situation, i don't know.

[jojo]

*ipop Wow, reading this thread has seriously damaged my neurons *crazy. I don't even know what OTF metering is, let alone being able to comprehend the debate!

[Stephen]

*ipop Wow, reading this thread has seriously damaged my neurons *crazy. I don't even know what OTF metering is, let alone being able to comprehend the debate!

Thats because its techy bloke stuff jojo. If I'm honest it leaves me cold too *LOL

[Graham_of_Rainham]

*ipop Wow, reading this thread has seriously damaged my neurons *crazy. I don't even know what OTF metering is, let alone being able to comprehend the debate!

Without trying to describe how it works, try this little test.

Set up the camera in a fairly dark room on Aperture Priority and adjust it so that the exposure is for about 10 seconds

Press the shutter, and take an image. Now do another but this time once you have pressed the shutter, switch on a main light. The second image will be over exposed.

With OTF metering the camera will detect the additional light and close the shutter to prevent over exposure.

The rest of the thread is "Tech Talk" but more wishfull thinking than reality ;)

[devilgas]

*ipop Wow, reading this thread has seriously damaged my neurons *crazy. I don't even know what OTF metering is, let alone being able to comprehend the debate!

OTF = off the film. basically the camera does realtime metering, cutting the exposure short when it's detected that enough light has hit the film / sensor.

so, in theory, you could set your exposure for 10s, but the camera could stop the exposure after only a second or two, 'preventing' overexposure.

hth.

[Graham_of_Rainham]

When OTF metering was first introduced on film cameras it was seen as a very big step in technology and quickly adopted by many manufacturers.

If it was such a good thing back then, why is it no longer functionally available.

My other wish is for the return of Multi-Spot metering, I've got it on my Olympus C8080WZ and still use it (sometimes :o)

Maybe the manufactures are holding on to these functions for when all cameras are so similar that they need something different. The "Drip Feed" of technology to maintain the market interest, or am I being too synical ???

*chr

[jojo]

Well why didn't you say so in the first place *whack !

Thank you for taking the time to translate Graham*inlove

jo

[jojo]

OTF = off the film. basically the camera does realtime metering, cutting the exposure short when it's detected that enough light has hit the film / sensor.hth.


... and there was me thinking OTF stood for "on the fly" :rolleyes:

Thank you once again Devilgas.

jo

[devilgas]

... and there was me thinking OTF stood for "on the fly" :rolleyes:
jo
pretty much the same thing really as that's exactly what it's doing. :)