TTL vs iTTL, ETTL, pTTL etc.

[hjoseph7]

I know this topic has been beat down for quite a while now, but why didn't camera manufacturers give photographers the option to use both TTL and  iTTL, ETTl, PTTL, etc ?

To keep it simple,  iTTL, ETTL, PTTL, etc.  all use a pre-flash to help determine flash exposure. This pre-flash combines with the cameras ambient metering system to determine flash exposure. The problem with this pre-flash is that it can make people blink,  or it can trigger off-camera flash. So if that's the case, why not just use ordinary TTL that does not fire a pre-flash, but still determines the amount of light  coming through the lens. TTL although not perfect, had a very short life, however, it was still better than using guide numbers and flash to subject distance on the fly, or using  inconvenient light meters. It also was very convenient with Close-up and Macro photography.

Edited April 11 by hjoseph7

[Ken Katz]

TTL used flash meter sensors that measured light reflecting off of the film during exposure to determine when to shut down the flash output.  I don't think that works well if there is a sensor instead of a piece of film.  Of course Canon introduced ETTL when the Elan II was introduced, so they had other reasons for introducing the pre flash system during the film era.

[John Seaman]

7 hours ago, hjoseph7 said:

TTL although not perfect, had a very short life, however, it was still better than using guide numbers and flash to subject distance

Between guide numbers and TTL there was the non-TTL auto system in which the flashgun controlled the exposure via a light sensor on the front. it's still very usable as I suggested in an earlier post:

But yes, TTL was found to be unreliable on digital SLR's because of the shiny nature of the sensor.

[ilkka_nissila]

8 hours ago, hjoseph7 said:

I know this topic has been beat down for quite a while now, but why didn't camera manufacturers give photographers the option to use both TTL and  iTTL, ETTl, PTTL, etc ?

To keep it simple,  iTTL, ETTL, PTTL, etc.  all use a pre-flash to help determine flash exposure. This pre-flash combines with the cameras ambient metering system to determine flash exposure. The problem with this pre-flash is that it can make people blink,  or it can trigger off-camera flash. So if that's the case, why not just use ordinary TTL that does not fire a pre-flash, but still determines the amount of light  coming through the lens. TTL although not perfect, had a very short life, however, it was still better than using guide numbers and flash to subject distance on the fly, or using  inconvenient light meters. It also was very convenient with Close-up and Macro photography.

While it's true that pre-flashes can cause eye blinks, I've found this to be mainly the case with the cheapest cameras (i.e. Nikon D3x00 series etc.) and more advanced models time the preflashes so that the eye blink is not likely to happen during the actual taking of the picture. However, there are some people who are particularly sensitive to the flash and may still blink, in which case the use of manual flash could work. Radio triggering of remotes instead of using optical triggering can also help minimize or avoid the issue. Profoto has a nice system where you can take a test shot on TTL and once the settings (flash exposure compensation and main exposure) are correct, then you can switch the flash(es) to manual and then the starting flash energy in manual mode picks up the last settings that were determined using TTL, and so further shots will have the same exposure and flash energy and no preflashes are needed. Of course, if the subject moves or the situation otherwise changes dramatically manual mode doesn't exactly help, but it's often workable. And you do get higher confidence of eyes open using it.

[Nick D.]

I have found non of those mods really reliable, I mostly use manual mode with few test shots.

[AJG]

I have always gotten more reliable exposures with my Vivitar 285 on auto than with my much more expensive Pentax 540 Z flashes with TTL auto.  The Pentax flashes frequently over or under expose on TTL where the Vivitar 285's almost never do.  The Pentax flashes are superior in many ways--they recycle faster on the same batteries, their manual output is far more adjustable and they are much more sturdily built but their exposure automation with every Pentax DSLR that I have used is hit or miss.

[BeBu Lamar]

First I must agree with AJG that some how the non TTL auto is more reliable than TTL. I don't know how. 

But back to TTL. In the beginning the TTL needs a light sensor sitting at the bottom of the mirror box reading light reflected of the film and when digital came around they found that the reflection from the imaging sensor doesn't work well. So they had to do preflash. Now that all mirrorless camera use the imaging sensor for AF, ambient light exposure measurement can they use the imaging sensor to measure flash as well? 

I guess not.

[rodeo_joe1]

On 4/13/2024 at 12:44 PM, BeBu Lamar said:

Now that all mirrorless camera use the imaging sensor for AF, ambient light exposure measurement can they use the imaging sensor to measure flash as well? 

I guess not.

Getting a fast enough readout from the sensor in real-time to control the flash exposure, which might need be only tens of microseconds in duration, is definitely problematic. 

So a pre-flash is the easy and pragmatic solution. 

However, the pre-flash has to have a very low energy (and consequent short duration), otherwise the flash would need a recycling delay between pre-flash and main flash. This very brief burst of 'test' flash needs to (ideally) be of fixed intensity and duration, and then needs multiplying by some factor depending on the lens aperture and ISO speed to set the main flash duration.

Setting such a short duration test flash accurately isn't easy, due to temperature variations, electrical component tolerances, age of the flash-tube, etc. Then rapidly calculating the needed actual flash duration from the returned test-flash reflection also adds room for more error. Small wonder then that iTTL/ETTL/whatever is pretty erratic in the exposure it delivers. 

Whereas a simple servo system, that has a sensor looking directly at the subject and then cutting off the flash at a pre-determined level during the actual exposure, is far more robust and reliable.

Give me a flash with Auto-Aperture mode every time over xTTL! But of course that decades old technology doesn't sell expensive new whizz-bang speedlights, or trigger systems with incomprehensible setup menus.