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01-15-2007, 07:33 PM   #1
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P-TTL VS TTL.... what is the difference to the average user?

I was looking at the wish list for pentax k10 and some people were saying they wish it had TTL,
What are the differences between P-TTL and TTL as far as the "end results" are concerned?

any input appreciated

randy


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01-15-2007, 07:43 PM   #2
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I sold my ring flash as the k100d/k10d didn't support TTL.. I think that is why people want it. We have older flashes that no longer work. For ring flash it is worse as I don't think there is a P-TTL ring flash available.. The Sigma 140 with Pentax support seems MIA, and is very expensive anyway compared to the older TTL ones (like the vivitar I had)...

End results: P-TTL should be more accurate, though the preflash for some people results in blinks (closed eyes) I haven't had that problem with mine though.
01-15-2007, 08:26 PM   #3
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You shouldn't be concerned about TTL if you're a typical user with automatic lenses.

However, if you have M, K, or M42 lenses, or if you're using extension tubes or non-automatic teleconverters, you'll need TTL support to get images correctly lit.

P-TTL calculates lighting before exposure using a preflash shot, while TTL uses a real-time sensor to control lighting during exposure. This sensor is only avaiable in the *ist D, DS, and DS2.

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01-15-2007, 08:50 PM   #4
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So from what I have been reading in reguards to flash in K100 or the K10D is that I am better off planning on purchasing a Pentax Flash and more than likely the AF540FGZ to even get good results?

This P-TTL system still confuses me even after reading three or four explanations.. LOL

01-15-2007, 10:33 PM   #5
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QuoteOriginally posted by Mo Quote
You shouldn't be concerned about TTL if you're a typical user with automatic lenses.

However, if you have M, K, or M42 lenses, or if you're using extension tubes or non-automatic teleconverters, you'll need TTL support to get images correctly lit.

P-TTL calculates lighting before exposure using a preflash shot, while TTL uses a real-time sensor to control lighting during exposure. This sensor is only avaiable in the *ist D, DS, and DS2.

You can get properly lit images with M, K, etc using the Pentax 540 flash - you just have to switch it to manual and control the output yourself - there isn't much automatic about it any more.

I've taken quite a few macros with my M50/1.7 on the end of extension tubes and my 540 flash - works great - Usually have to take a few test shots to figure out how much power to set it for.
01-15-2007, 10:42 PM   #6
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beats the heck outa me on a versus point of view, even though I have read it and used both (there is a degree of exageration in this statement). From an average point of view for simple shots I have had about as much luck or lack of with one or the other. I do know that with My 10D I am limited to just my 540, in any of the lens metered modes. If the 10D had a TTL meter/sensor I could throw on 4 other flashes that could be metered with my camera. I hope that Pentax has enough steam left in the tank after retooling for cameras and lenses to get a new ring light. For now I will be using my DS when I want to do macro work with my ring light.
01-16-2007, 07:41 AM   #7
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P-TTL Vs TTL

QuoteOriginally posted by slipchuck Quote
I was looking at the wish list for pentax k10 and some people were saying they wish it had TTL,
What are the differences between P-TTL and TTL as far as the "end results" are concerned?

any input appreciated

randy


K10
Sigma 17-70 2.8-4.5
Sigma 500 super flash
01-16-2007, 08:30 AM   #8
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QuoteOriginally posted by Mo Quote
You shouldn't be concerned about TTL if you're a typical user with automatic lenses.

However, if you have M, K, or M42 lenses, or if you're using extension tubes or non-automatic teleconverters, you'll need TTL support to get images correctly lit.
On the other hand, I've used extreme extensions with my 4x5 camera and calculated the light properly. There's a formula that you can use if you don't have TTL, and it was around long before there was such a thing as TTL flash.

I've never used TTL flash, so I don't know much about it, but it's not necessary for correct exposure.

01-16-2007, 08:53 AM   #9
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QuoteOriginally posted by Dana G Quote
I've never used TTL flash, so I don't know much about it, but it's not necessary for correct exposure.
Same here - I've had a DL (now a K100D) and a bunch of old M lenses, and without actually knowing enough about flash photography I manage to get acceptable results with a minimum of messing around. If I would just write down the relevant guide numbers and formulae I'd probably do fewer test shots, although I'm surprised how well I can do just guessing!

TTL and P-TTL are a convenience. If I'm feeling lazy, I'll stick on the kit lens and P-TTL flash. It would be nice to have the same degree of automation with my old lenses, but I don't, so I'm learning guide numbers (sort of).

Julie
01-16-2007, 09:54 AM   #10
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As to the original question.... Both systems measure the light bouncing off your subject from the flash and determines when to shut the flash off to get accurate exposure. TTL does this during the actuall exposure. P-TTL does this during the split second before the actuall exposure using a pre-flash.

There is one possible phyisical explaination for the omittion of TTL in many DSLRs today. When DSLRs first came out and used the same flash systems as their film cousins there were a LOT of complaints that the exposures were far less consistent than with film. A common consensus was that the CCD/CMOS/AA filter was shinier than film and was confusing the TTL sensors. Afterall, TTL works by reading the light on the film plane. Inconsistent reflections would result in inconsistent exposures. The answer would be to get the flash duration info before the exposure.

I don't know if this is the definitive answer, but I do know that my flash exposures on my *istD were very inconsistent so I ended up using manual all the time.

Another note is that most TTL flashes do have an "A" position which turns the unit into an auto thyristor.
01-16-2007, 11:28 AM - 1 Like   #11
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P-TTL vs. TTL primer . . .

In response to the OP,
Here is (I hope) an explanation of the differences between P-TTL and TTL as I have observed/learned:

The regular camera meter exists up in the viewfinder box. This allows you to meter things before you click the shutter button.

To meter and control the amount of flash WHILE the shutter is open (and the mirror is up) requires a different sensor in front (or off to the side obviously) of the film sensor itself. It was very popular with film, but most manufacturers have discovered that the reflection of light off a digital sensor is not as reliable as that off a film plane.

So, a new solution was invented. That of the preflash. Pentax calls it P-TTL. It is still through the lens, but it uses the regular meter in the viewfinder box and fires the flash just prior to raising the mirror. Based on this "PreFlash", the camera has a good idea of how much flash to deliver for the actual flash/shot.

If you look through the viewfinder during a P-TTL shot, you can actually see the 1st preflash through the viewfinder/lens when you take the shot.

If you look through the viewfinder during a TTL shot, the mirror is up and the viewfinder is black during the actual flash.

P-TTL yields very reliable exposure.

The downside of P-TTL is that there is a small (but real) minority of people who have such a fast blink reflex that the preflash causes them to blink and the actual exposure catches them with "lazy eye" My two sons are "normal" i.e. the time between preflash and actual shot is less than the time taken to blink, but my daughter is a blinker.

Does that help?
01-16-2007, 11:35 AM   #12
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QuoteOriginally posted by GregNS Quote
In response to the OP,
Here is (I hope) an explanation of the differences between P-TTL and TTL as I have observed/learned:

The regular camera meter exists up in the viewfinder box. This allows you to meter things before you click the shutter button.

To meter and control the amount of flash WHILE the shutter is open (and the mirror is up) requires a different sensor in front (or off to the side obviously) of the film sensor itself. It was very popular with film, but most manufacturers have discovered that the reflection of light off a digital sensor is not as reliable as that off a film plane.

So, a new solution was invented. That of the preflash. Pentax calls it P-TTL. It is still through the lens, but it uses the regular meter in the viewfinder box and fires the flash just prior to raising the mirror. Based on this "PreFlash", the camera has a good idea of how much flash to deliver for the actual flash/shot.

If you look through the viewfinder during a P-TTL shot, you can actually see the 1st preflash through the viewfinder/lens when you take the shot.

If you look through the viewfinder during a TTL shot, the mirror is up and the viewfinder is black during the actual flash.

P-TTL yields very reliable exposure.

The downside of P-TTL is that there is a small (but real) minority of people who have such a fast blink reflex that the preflash causes them to blink and the actual exposure catches them with "lazy eye" My two sons are "normal" i.e. the time between preflash and actual shot is less than the time taken to blink, but my daughter is a blinker.

Does that help?
did you just cut & paste a bunch of this from a previous post of yours?
01-16-2007, 04:13 PM   #13
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Yes.
Different forum. Different (somewhat) audience.

Just trying to be helpful.
If you genuinely find this offensive, I will remove it.
01-16-2007, 06:24 PM   #14
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Offensive?
No not at all. I guess I shoulda thrown a smiley in there too, so there was no implied offense taken.
Just maken sure I wasn't sufferin from days eh view.

take care,
John
01-16-2007, 07:06 PM   #15
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QuoteOriginally posted by jnorth Quote
Just maken sure I wasn't sufferin from days eh view.
Ain't that daisy view??
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