What happened to OTF in E-500?

[OlyFlyer]

Hi,

My previous camera was the good old OM2n. That camera has something called TTL Direct "Off-the-Film" Light Measuring - NOT just TTL flash that is so commonly found in every modern electronic SLR and P&S today, BUT the proprietary TTL OTF metering is also apply to ambient light. That is, with the shutter operated in total darkness you'd get very long exposure time. But the shutter speed is changed as ambient light changed during the exposure. If for example a flash (any flash) is fired manually by pushing the manual fire button the shutter would close, resulting in an over exposed or correct exposed image depending on the light intensity. No chance of underexposure since the metering could take care of that.

The use of this is in photographing for example fast moving objects, like a gun bullet flying through the air. It seems to be very difficult to do that without special high-speed camera if that feature is not implemented. I have an E-500 now, and to me it seems that there has been a technology degradation since that camera has only TTL flash and it seems that even that is a bad one since it is based on measurements that are done before the shutter opens, never corrected during the actual exposure.

The super FP flash mode is of no help here since that is limited to the 1/4000 second speed of the shutter, while a flash fires at about three to ten times slower that speed normally. The Super FP mode is actually just a fake, not a real FP. In FP the flash is burning for a long time allowing short shutter speed. In Super FP mode the flash is giving bursts of flashes creating a strobe effect, which is preventing the photographing of fast moving objects.

Did I misunderstand something? Is there a mode where TTL is a real TTL OTF (or maybe it should be called OTS as in "Off The Sensor") and not just a flash TTL? Is there any Oly camera where this actually works?

Please help! It is really important to me.

[tomcat]

Off-The-Film (OTF) is not possible in digital cameras because no film is used. That may sound mocking but it is the truth... it is difficult to get a good exposure reading off the surface of a CCD/CMOS sensor because it has a shiny surface and not matt like film. And this is also the reason why TTL flash system for digital cameras are based on the 'pre-flash' method.

I didn't make it all up. Got them from this site:
http://www.camerasunderwater.info/ar...y/index.html#t


TTL flash: 'Through The Lens' flash metering. Another term, which never caught on, is 'Off The Film' (OTF) flash metering. It is basically an improved form of automatic flash control which takes account of the film speed, lens aperture setting, and any filters which might have been fitted to the camera.

Although the full burst of energy from a flash unit may seem instantaneous, it usually last for about 1.5 thousandths of a second (~1.5ms). The light output can therefore be controlled by reducing the time duration of the flash, ie., by switching off the current in the tube before the storage capacitor is fully discharged. A TTL flash unit is one which can accept a signal from the camera telling it to 'switch off now'. The important thing to understand about this system is that the flash unit plays no part in calculating the exposure; it simply accepts the instruction to switch off at a point determined by the electronics in the camera, and will usually issue some kind of error signal if no such instruction is received. In 'OTF' metering, the camera determines the exposure by measuring light reflected from the film and summing (integrating) it over time. It compares the amount of light received against a level determined by the ISO (ASA) setting, and issues a stop (quench) signal at the appropriate point. If you reduce the amount of light falling on the film by stopping the lens down or fitting a filter, the camera will take longer to issue the stop signal. The camera can therefore compensate for all relevant variables until a point is reached when there is insufficient light to complete the exposure; in which case no stop signal is sent, and the flash unit issues a warning (Sea & sea strobes have a green 'TTL OK' light which comes on if a quench signal is received. Nikon and Ikelite strobes flash the red 'ready' light if no quench signal is received.). It follows, that a TTL flash system requires a TTL capable flash unit and a TTL capable camera; and less obviously, that the two units must be compatible (ie, they must conform to the same electronic interface standard).

With the advent of digital photography, the definition of 'TTL flash' has expanded to include the 'pre-flash' method of exposure evaluation. It is difficult to devise a good 'off the film' metering system when using a digital sensor, because the sensor has a shiny rather than a matte surface. The solution is to issue a pre-flash, determine the exposure level obtained by averaging information read from the CCD, and use this to calculate the required duration for the main flash. The same system of start and stop (trigger and quench) signals can be used to control the flash unit, provided that the flash unit can recover and be ready to fire again in the short (less than 100ms) interval between the pre-flash and the main flash. A disadvantage of the pre-flash system is that it increases shutter lag (i.e., the time between pressing the button and taking the photograph), and it may cause portrait subjects to blink. Improvements in flash technology (the use of an IGBT as the switch-off device), can reduce the pre-flash - main flash interval to about 30ms.

[OlyFlyer]

Originally Posted by tomcat Off-The-Film (OTF) is not possible in digital cameras because no film is used. That may sound mocking but it is the truth... it is difficult to get a good exposure reading off the surface of a CCD/CMOS sensor because it has a shiny surface and not matt like film. And this is also the reason why TTL flash system for digital cameras are based on the 'pre-flash' method.

Yes, thanks I know there is no film, but unlike the OM2 which had two sensors in the camera the E-500 has 8 million. Each could be used to measure the light during exposure. I think the digital technology is not "there" yet, meaning it has still some catching up to do compared to analog film cameras. I understand the reflected light can not be measured like from film but I see the pre-flash type of TTL as a kind of fake measurement. I don't really know what this guy is talking about. My flash fires at 1/40000 second which is 25 microsecond, not millisecond. I think he is just misinformed about a few things. I would not use him as a reference, at least not in this subject.

Sorry tomcat but thanks anyway. I just hope some manufacturer will catch up soon.

[tomcat]

If things are as simple as you think they are, given the competitive nature of the industry, don't you think one of the big companies would have 'reinvented' OTF for digital photography the way you wanted it to be?
You seem like quite a hands-on guy. So maybe you might like to give it a try and become filthy rich in the process if you are successful, seliing the technology to the big boys.

[OlyFlyer]

Yes, some things are technically simple. Unfortunately big companies are often driven by gready people who just want to maximize profit so they chicken out because it costs a few cents or dollars more per camera. Companies are no longer driven by engineers who are proud about an invention but by economists who are proud about saving one cent on a product costing several hundred dollars. Argument is that in mass production you save a lot more, which is true if saving and increasing profit is the goal not a product to be proud of.

Oly invented OTF and the others followed back at the end of 1970s. But they did not follow immediately, they kept on saying that this OTF thing is not necessary, never will be used, too complicated to implement, not needed by a pro and so on, just like today. Then when Oly gained market from the big ones because of technology advance they followed one by one. Just like today with the SSWF which is an Oly invention and just like with the OTF, a lot of ppl are arguing against, like: "I don't have dust in my XXXYYY camera" and are laughing. Not anymore, now people start to admit and more and more companies include some sort of cleaner.

I really hope Oly will re-invent things and not just adopt the "it is good as it is" way of living and mentality. And as of becoming filthy rich, yes, why not. I will do the design develop the hardware and the software I amy even be able to produce some sort of prototype. Would you be the one who finace and market the thing? I am more than willing to share my filthy richness, 50% for you 50% for me.

Will have to wait a few more days for Photokina to see what that gives. I hope there will be something under the Christmas tree even for me.

[Mikefellh]

Originally Posted by OlyFlyer Hi, My previous camera was the good old OM2n. That camera has something called TTL Direct "Off-the-Film" Light Measuring - NOT just TTL flash that is so commonly found in every modern electronic SLR and P&S today, BUT the proprietary TTL OTF metering is also apply to ambient light. That is, with the shutter operated in total darkness you'd get very long exposure time. But the shutter speed is changed as ambient light changed during the exposure. If for example a flash (any flash) is fired manually by pushing the manual fire button the shutter would close, resulting in an over exposed or correct exposed image depending on the light intensity. No chance of underexposure since the metering could take care of that.

It's weird, because the C-700 used to do something similar to that. I used a slave flash with my C-700, and while the camera (in Program mode) initially chooses settings based on current light level and the power level of the internal flash, the camera will adjust exposure when it sees the slave flash firing and realizes there's suddenly more light than what was initially measured and what the internal flash is putting out.

People never believed me, but I would tell them what the Program mode initally measured with the internal flash up by half-pressing, and then told them the info that was recorded in the Exif in the photo.

It's a shame that a higher-end camera would not have that feature.

[Blu-By-U]

How do we test that?? Lets say, Blu puts his E-330 into P then enables the internal flash and adds the FL-50...shoot then check the exif for details...too bad the FL-40 no longer with blu else can fire that in manual. Tell blu what to do. maybe can conduct a test.

[OlyFlyer]

Originally Posted by Blu-By-U How do we test that?? Lets say, Blu puts his E-330 into P then enables the internal flash and adds the FL-50...shoot then check the exif for details...too bad the FL-40 no longer with blu else can fire that in manual. Tell blu what to do. maybe can conduct a test.

Easy. Just go into a very dark room, place your camera on a tripod, switch the internal flash off, trigger the camera shutter. Then fire an external flash manually or turn on some strong light. If the camera shutter closes automatically and immediately then you have a true TTL OTF, or actually OTS, as in Off The Sensor since there is no film in digital cameras. That is how it should work. To save you some time, do not do the test because you will fail. The shutter will not close because it bases it's measurements on values before the opening, and in that case the darkness, not changing the values when ambient light changes during exposure. I found out elsewhere that it is not implemented for some reason. I found that to be a very good and useful function in my old OM2n. Unfortunately technology in DSLR has not reached the technology of end of 1970s film cameras yet in this respect.