Can someone answer this question about ETTL vs iTTL/CLS vs PTTL?

Started Oct 25, 2011 | Discussions
Matthew Miller
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Can someone answer this question about ETTL vs iTTL/CLS vs PTTL?
Oct 25, 2011

Someone on Stack Exchange asked this excellent question http://photo.stackexchange.com/q/16643/1943 , and no one really familiar with all three systems has stepped up to provide an answer. In short, the question is: Canon, Nikon and Pentax each have their own preflash-based TTL flash metering systems. How do they differ, and what are the strengths and weaknesses of each?

It'd be awesome it get a good answer on Stack Exchange, but I'd also be very interested in discussion here. Not looking for brand-wars, though: I'd like to see a levelheaded and fair comparison of each. Are you familiar with each of these systems, or at least any two of them for direct comparison?

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John Deerfield
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Re: Can someone answer this question about ETTL vs iTTL/CLS vs PTTL?
In reply to Matthew Miller, Oct 26, 2011

I don't see any value in trying to compare the systems so much as understanding how your system and methodology works. At a fundamental level, each does the same thing: the flash fires a pre-flash for the camera's metering system to determine how much flash is needed and then the "real" flash fires. Everything else is in how to work your system. As example, Nikon's system is holistic: if you dial in negative compensation on your camera, this translates to negative flash compensation as well. Whereas with Canon systems, the flash is separate from the camera which is to say that if you dial in negative compensation on the camera, that does NOT carry over to the flash. Now this doesn't make one better than the other, just different. Now, in my experience, iTTL flash photography is more consistent with Nikon (having shot with Canon for close to 6-years and Nikon for 4). Which means that in my experience, Nikon's flash system seems to meter better or more consistently. And for me, I understand Nikon's system better: BL = balanced light. Where the flash is balancing foreground (flash) and background (ambient). Or, I can use iTTL (non-BL) where the flash assumes more of a key light assumption rather than a fill light. With Canon, this fill vs key determination is, at least in part, determined by the mode you are shooting in. Of course this could also be why my flash exposures where more inconsistent with Canon: it wasn't intuitive for me . I have no experience with Pentax or any other TTL system.

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Matthew Miller
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Re: Can someone answer this question about ETTL vs iTTL/CLS vs PTTL?
In reply to John Deerfield, Oct 26, 2011

John Deerfield wrote:

I don't see any value in trying to compare the systems so much as understanding how your system and methodology works.

That's a good point. I think, though, that understanding systems in comparison to others can help one understand the potential and limitations of their own system — it's a possible learning/teaching tool. And, the question is useful for someone who isn't really committed to a particular system yet.

Thanks for your answers — that's definitely a good start.

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BAK
BAK
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Why would anyone care?
In reply to Matthew Miller, Oct 26, 2011

Sure would be a lot of work to answer this question.

Nikon and Canon treat flash exposure comp differently.

BAK

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Matthew Miller
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Well, you've given one reason someone would care already.
In reply to BAK, Oct 31, 2011

Sure would be a lot of work to answer this question.

I guess. I'm surprised that they're so different — that's worth explaining in itself, isn't it?

Nikon and Canon treat flash exposure comp differently.

How so? Plus or minus one EV is still one EV, isn't it?

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Hugowolf
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Re: Can someone answer this question about ETTL vs iTTL/CLS vs PTTL?
In reply to Matthew Miller, Oct 31, 2011

Matthew Miller wrote:

Someone on Stack Exchange asked this excellent question http://photo.stackexchange.com/q/16643/1943 , and no one really familiar with all three systems has stepped up to provide an answer. In short, the question is: Canon, Nikon and Pentax each have their own preflash-based TTL flash metering systems. How do they differ, and what are the strengths and weaknesses of each?

I don’t think you realize just how ridiculously complex covering the differences between two of these systems would be. I have no idea about Pentax, except that its flash system is tiny compared to Canon and Nikon.

Try reading this brief, 64,000 word, introduction to the Canon flash system, just so you have some idea of what you are broaching. A comparison between the two would necessarily be longer. You are getting pretty close to 42, the meaning of life, the universe, and everything.
http://photonotes.org/articles/eos-flash/

Brian A

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Graystar
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Re: Well, you've given one reason someone would care already.
In reply to Matthew Miller, Oct 31, 2011

Matthew Miller wrote:

Nikon and Canon treat flash exposure comp differently.

How so? Plus or minus one EV is still one EV, isn't it?

It’s not flash exposure compensation that’s treated differently. It’s exposure compensation as applied to the camera that gets treated differently.

When you apply EC to a Nikon, that EC is also applied to the flash. This works well indoors because you can adjust your flash exposure the same way you control your ambient exposure. Outdoors, it’s less successful because you are unable to use EC to control ambient exposure. If you want to control your background exposure separately from your foreground exposure, then you must switch the camera to manual mode. But manual mode is difficult in changing light. If you’re in light that’s constantly changing, then you want to use an auto mode for ambient exposure. This results in having to apply a “correction” to the flash exposure compensation. So let’s say you’re in A mode and you want the ambient light underexposed by two stops. You have to set your EC to -2. But now your flash is underexposing by two stops as well. So you have to “correct” the flash by applying +2 of FEC.

With Canon, EC that’s applied at the camera doesn’t affect the flash. So the situation above is handled easily. If you want your ambient exposure underexposed, then you simply apply -2 EC. The flash will continue to provide the same illumination. Of course, indoors, if you want to control your flash exposure then you must always do it through the FEC controls, which usually means either messing with the flash unit or working with the LCD on the camera. Either way, it’s not as effortless as with Nikon, which can be adjusted without taking your eye from the viewfinder.

.

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BAK
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Re: Well, you've given one reason someone would care already.
In reply to Matthew Miller, Oct 31, 2011

Once yu read Greystar's response, you know the fdifference, and it does not matter as far as getting good pictures goes.

Just different.

BAK

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Matthew Miller
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Re: Can someone answer this question about ETTL vs iTTL/CLS vs PTTL?
In reply to Hugowolf, Oct 31, 2011

Hugowolf wrote:

Try reading this brief, 64,000 word, introduction to the Canon flash system, just so you have some idea of what you are broaching. A comparison between the two would necessarily be longer. You are getting pretty close to 42, the meaning of life, the universe, and everything.
http://photonotes.org/articles/eos-flash/

I've looked at that link, and the fact is that a huge portion (80%? 90%?) of it would appy to any modern flash system. This question is about the differences, which are mostly in the details. I don't think it logically follows that a comparison would have to be longer, unless the systems were much more different than similar, which I don't think is the case.

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Matthew Miller
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Re: Well, you've given one reason someone would care already.
In reply to Graystar, Oct 31, 2011

Thanks! That's the concrete and useful sort of thing I was looking for.

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ScratchDisk
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Re: Can someone answer this question about ETTL vs iTTL/CLS vs PTTL?
In reply to Matthew Miller, Oct 31, 2011

Hi,
For Canon, there's quite good info here;
http://cpn.canon-europe.com/content/education/masterclass/canon_flash.do
It certainly lists the differences between ETTL and ETTL(II) which is helpful.

ETTL(II) was introduced with the EOS-ID Mark II and 20D. The 20D had 35 metering zones (for flash the 1DII used 17 of its 21 zones), whereas recent bodies typically have 63 metering zones.

As a result ETTL(II) itself has morphed since its introduction. The 20D for instance protected highlights very assiduously leading to complaints of under exposure - whereas - the 7D, for instance, more readily 'discerns' a really bright highlight as 'spectral' & allows it to blow, especially if what it 'thinks' might be the main subject is well exposed by flash. The 5DII falls into the former camp allegedly - I have not used a 5DII. Canon has never fully spelled out how their Evaluative algorythms work - but they have dropped crumbs (usually in their White Papers).

Switching to 'Average' for flash (not CW Average) is done through the cam's flash menu (not from the cam's top-plate) - & does simply what it says.

FEL over-rules either setting & imposes a central (only) c3% 'pre-flash' spot meter & lock.

The EC & FEC issue detailed above, is a critical difference from Nikon - swings & roundabouts there, I think.
Cheers, Donald

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