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04-08-2010, 11:54 AM   #16
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That makes sense, I guess I'm making it more difficult than it needs to be.

If shooting at f2, iso 100 and 180 is overexposed, than I don't use flash. That's pretty clear, and if I really want to shoot at f2 with a flash I need to shoot in the shade or a darker area with less ambient light.

Now I just need to actually take some photo's and see what gets me the best result.

Thanks to all who responded

04-08-2010, 12:09 PM   #17
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QuoteOriginally posted by Blue Quote
I'm not going to argue with you guys about it. However, the system uses a pre-flash to determine ttl, that what is is meant by p-ttl. Some people are sensitive to it. A blink of an eye is p.d.q.
I'm not going to argue with you either

TTL, p-TTL, or whatever, are just names probably picked by the marketing department. I'm interested in what they actually do, not in the meanings of the terms.

Pentax uses p-TTL to distinguish with TTL. For most SLRs or DSLRs, the light sensors are in the prism. They measure the light through the lens and reflected by the mirror. In TTL metering (Olympus used a better term: OTF for Off-The-Film), there are additional light sensors in the mirror box to measure the light during exposure when the mirror is in the up position. When the sensors determine enough light, it shuts down the flash.

TTL flash metering does not need a pre-flash strobe, and it doesn't care what is attached to the camera; even a pin-hole lens will yield correct exposure.

p-TTL flash metering, on the other hand, uses the same sensors in the prism to determine exposure. The metering has to be done before the mirror going up and at full aperture. This necessitates the pre-flash strobe and the communication between the camera body and the lens.

Why doesn't Pentax (or any other camera makers) keep TTL? I think they just try to save a few bucks. TTL requires additional light sensors in the mirror box and the additional electronics. I've heard many people saying that because the light reflected from the digital sensor is more difficult to predict than that reflected from the film. But I don't believe it. Pentax used to have TTL flash metering in the *ist series.

I myself don't like p-TTL. I use it only when I absolutely have to.

Last edited by SOldBear; 04-08-2010 at 05:30 PM.
04-08-2010, 01:14 PM   #18
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QuoteOriginally posted by pbo Quote
'

Hm... How much lag is there between the preflash and actual flash? I use P-TTL almost all the time - and never noticed the preflash, even if I take the eye off the viewfinder. Does it have anything to do with me bouncing the flash?
QuoteOriginally posted by EsBee Quote
Ditto here. When I use either 360 or 540 mounted to my K20D and shoot in P-TTL mode, and I don't notice any pre-flash and usually the exposure is spot-on, although I have the flash compensated at +0.7.

I know the technical description of how P-TTL works does say there is a pre-flash followed almost instantaneously, by the secondary camera-directed flash, yet I have not seen any unusual amount of closed-eyes on my subjects so far.
If you watch for it, it's pretty easy to see the preflash through the viewfinder an instant before the VF blacks out. If you just fire the shutter and look for the flash, it's so quickly followed by the main flash that you probably won't be able to distinguish the two.

In my experience, only a relatively small percentage of people (less than 10%) are fast enough in their reaction time to matter in P-TTL. At my 40th High School Reunion, 1 of 170 people blinked with P-TTL, and I have only one relative that consistently is a blinker, so I've been able to note the "blinkers" and whenever I have one in a shot, I change to Auto mode on the 540 or 360 and shoot that way. This has not been much of an issue to me.

Scott
04-08-2010, 05:25 PM   #19
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QuoteOriginally posted by SOldBear Quote
Because the pre-flash strobe is used for metering, the mirror has to be down during the pre-flash strobe (to reflect light to the light sensors). In practice, the pre-flash strobe happens just before the mirror going up. IIRC, the time lag between the pre-flash and the main strobe is around 1/50 sec.

To see the pre-flash, take a photo in p-TTL mode and the camera in 2 sec delay mode.

My son recently develops sensitivity to the pre-flash. His eyes are closed in all photos taken in p-TTL mode. I've never used p-TTL when photographing a group of people.
I was taking images of an event at work to day and tried to get a shot of the group different ways, with p-ttl, there was always someone with their eyes closed. There were 2 people that were particularly effected by it. I did a little messing around with the flash because of this thread. I also wish Pentax had kept ttl as an option.

04-08-2010, 07:24 PM   #20
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QuoteOriginally posted by dmoon911 Quote
That makes sense, I guess I'm making it more difficult than it needs to be.

If shooting at f2, iso 100 and 180 is overexposed, than I don't use flash.
Of course, there *are* situations where you might still want flash, or at least some form of additional lighting: not because there isn't *enough* light, but because you would like to control the direction and type of light. But still, you wouldn't be using the built-in flash for this - you'd be using an external flash. And hopefully, one that lets you control the output. Although it might not be able to dial down far enough.

Really, the bottom line is that if you plan to be using flash - especially if you are using it for creative effect, like in situations where you actually have enough light already without it - you don't shoot with manual lenses. It's the fact that an f/2 lens means you don't necessarily *need* flash just to get enough light that makes lenses like this useful.
04-09-2010, 10:28 AM   #21
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QuoteOriginally posted by Blue Quote
I also wish Pentax had kept ttl as an option.
Even tho I keep my DS for its TTL support and have 3 TTL guns, I really appreciate the added versatility of P-TTL. I found the TTL supported settings (ISO 200-400, and good exposure metering only towards the mid range apertures) a bit limiting for my use. Trying to look at this objectively, considering that I've become pretty comfortable with P-TTL for my uses, and the fact that I have 3 P-TTL flashes, I can see the case for not including the TTL sensor in most new models. I do think this might be a good feature to include in Pentax's flagship bodies where they could also "uncripple" the mount by including the old stop down lever to give it the greatest possible backward compatibility -- fitting for the top-of-the-line model. I would not include these features in entry or mid level bodies tho. . . this would push new adopters to the system towards purchasing new flash units, but allow the dedicated Pentax system users a model that allows full use of older technology (Pentax has bills to pay too. . .and they only benefit directly from new sales)

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04-09-2010, 12:53 PM   #22
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I just thought of something else that might help... What about a Neutral Density Filter? Instead of making the room darker, can I restrict the light coming into the camera with a filter? How well do those filters work with flash? Will I lose image quality?
04-09-2010, 06:08 PM   #23
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QuoteOriginally posted by pbo Quote
'

Hm... How much lag is there between the preflash and actual flash? I use P-TTL almost all the time - and never noticed the preflash, even if I take the eye off the viewfinder. Does it have anything to do with me bouncing the flash?
It's just long enough for sensitive people to blink. I blink every time pre-flashes fire, no matter what the brand. My friend shoots Nikon and I always look like I'm stoned when she takes my picture with iTTL

04-09-2010, 06:14 PM   #24
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QuoteOriginally posted by dmoon911 Quote
I just thought of something else that might help... What about a Neutral Density Filter? Instead of making the room darker, can I restrict the light coming into the camera with a filter? How well do those filters work with flash? Will I lose image quality?
An ND filter will affect ambient and flash, darkening both.
09-14-2010, 05:52 AM   #25
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QuoteOriginally posted by alohadave Quote
An ND filter will affect ambient and flash, darkening both.
Yeah, which can be OK to enable open aperture exposure in other wise over exposed compositions (a lot of light and/or very long exposure to capture dynamics).

I understand de camera rat-race in direction of high ISO performance, but won't be nice for artistic reasons to also have good low ISO performance?
- And / or focus more on effective dynamic range?
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