Re: TTL Flash Metering and Distance Info
You must then be talking in regard to autofocus cameras. My TTL flash experience is with an LX. Obviously, an LX doesn't take distance into account, nor would the TTL flash units that work with an LX. If I'm using TTL flash on a subject that doesn't fill frame and there is an obvious difference between it and the background, I don't get a perfect exposure without dialing in some compensation. Brendan wrote: Part of the debate is how does distance info play a part, or if it does. The reason for the whole question is lets say you have an off center subject that you focused on. Why is she ( the girl with the strapless dress ) correctly exposed when you have foreground and background ambient ETC ETC. --- Paul Stenquist [EMAIL PROTECTED] wrote: I've missed some of this, but I don't understand what the debate is about. All the TTL camera knows is how much light hits the senosr (or in the case of LX, the film plane). When there's enough for a proper exposure, the flash duration is terminated. The exposure will be correct as long as the flash's full output is sufficient for the stop and film speed you're using. Paul Bruce Dayton wrote: William, The biggest flaw I see to Tom's observations is when you bounce or diffuse the flash. How would the body go about knowing that is what you are doing? In those cases, you should see severe underexposure. My experience is that they work fine. Bruce Dayton Wednesday, March 13, 2002, 11:54:55 AM, you wrote: PWO Bruce Dayton wrote: I have often wondered what the metering pattern is for the TTL sensor - I'm guessing it is center-weighted. That could also account for some differences. PWO Hi Bruce, PWO I've wondered this same thing, and I'll bet you're right about the PWO center-weighted pattern. Somebody shot and posted links to a whole series PWO of TTL flash shots of some shiny metal object against a fairly neutral PWO background, a few months back. A bunch of different apertures, shutter PWO speeds, etc. Can't remember who it was -- I was thinking it was either you PWO or Doug Brewer, but I just can't remember. I remember the look of the PWO shots, though. As best as I can recall, those shots appeared as though the PWO TTL flash metering was center-weighted, or pretty darned close to PWO center-weighted. There were some overexposed shots at the fastest apertures PWO that were attributed to the flash not being able to quench in time. PWO I guess the way to test Tom V's idea (about the possibility that the flash PWO intensity is calculated from distance and guide number information, but not PWO controlled by an actual TTL sensor reading) is to fire a test shot with and PWO without the lens cap in place. If the TTL sensor doesn't matter, then the PWO flash intensities for both of these test shots should be about the same, and PWO the recycle times should be about the same. If the sensor really ~is~ PWO metering and controlling flash output, then the lens-cap-in-place test shot PWO should have a ~much~ longer recycle time. PWO Bill Peifer PWO Rochester, NY PWO - PWO This message is from the Pentax-Discuss Mail List. To unsubscribe, PWO go to http://www.pdml.net and follow the directions. Don't forget to PWO visit the Pentax Users' Gallery at http://pug.komkon.org . - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org . - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org . __ Find, Connect, Date! http://personals.yahoo.ca - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org . - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
Re: TTL Flash Metering and Distance Info
Actually I'd also like to know since when bounced or using the omni bounce cover it still exposes correctly even with 2 stops loss. It seems that it does it something more like this ( using your theory as a template ) - lens says it's focused at 10 feet - flash guide number is 40 - aperture is f/2 Fire the flash at 1/2 power but meter just in case. --- tom [EMAIL PROTECTED] wrote: I've noticed over the course of the last year that rolls of film that were shot with TTL flash metering (and flash) have much more consistent exposure across frames than rolls that used matrix metering and ambient light. I've come to this conclusion after proofing dozens of rolls of b+w. Seems to me the only way to explain the difference is that the flash output is determined by distance info transmitted by an FA lens. I'm not really sure what that implies...I was under the impression that TTL flash metering worked like so: - flash starts to discharge - ttl flash meter measures output - ttl flash meter determines that subject has received enough light - meter tells flash to stop However, if it's using distance info it's just using a calculation. - lens says it's focused at 10 feet - flash guide number is 40 - aperture is f/2 Fire the flash at 1/2 power and don't bother metering. Maybe it (I guess I'm talking pz-1p here) uses that calculation with FA lenses and uses quench metering with older lenses? I might have to test this Thinking out loud, tv - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org . __ Find, Connect, Date! http://personals.yahoo.ca - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
Re: TTL Flash Metering and Distance Info
tom, I was thinking that it had more to do with getting more even light do to flash fill moreso than TTL alone. On the older bodies, metering for TTL did not include ambient light at all, so most images ended up looking like dark backgrounds. With later bodies, ambient light is taken into account and shutter speeds are lowered to slowest handholding to allow as much ambient light as possible. Then the TTL is just going to fill in where necessary. That would produce more even results. Have you tried using slow films/fastest shutter speeds (1/250)? If you did I would think that you would get results that would show the inherent TTL metering problem of weddings - mostly white in frame - face gets underexposed - mostly black in the frame - face gets overexposed. I have often wondered what the metering pattern is for the TTL sensor - I'm guessing it is center-weighted. That could also account for some differences. Bruce Dayton Wednesday, March 13, 2002, 10:08:56 AM, you wrote: t I've noticed over the course of the last year that rolls of film that were shot with TTL flash metering (and flash) have much more consistent exposure across frames than rolls t that used matrix metering and ambient light. t I've come to this conclusion after proofing dozens of rolls of b+w. t Seems to me the only way to explain the difference is that the flash output is determined by distance info transmitted by an FA lens. t I'm not really sure what that implies...I was under the impression that TTL flash metering worked like so: t - flash starts to discharge t - ttl flash meter measures output t - ttl flash meter determines that subject has received enough light t - meter tells flash to stop t However, if it's using distance info it's just using a calculation. t - lens says it's focused at 10 feet t - flash guide number is 40 t - aperture is f/2 t Fire the flash at 1/2 power and don't bother metering. t Maybe it (I guess I'm talking pz-1p here) uses that calculation with FA lenses and uses quench metering with older lenses? t I might have to test this t Thinking out loud, t tv t - t This message is from the Pentax-Discuss Mail List. To unsubscribe, t go to http://www.pdml.net and follow the directions. Don't forget to t visit the Pentax Users' Gallery at http://pug.komkon.org . - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
Re: TTL Flash Metering and Distance Info
On 13 Mar 2002 at 11:03, Bruce Dayton wrote: tom, I was thinking that it had more to do with getting more even light do to flash fill moreso than TTL alone. On the older bodies, metering for TTL did not include ambient light at all, so most images ended up looking like dark backgrounds. With later bodies, ambient light is taken into account and shutter speeds are lowered to slowest handholding to allow as much ambient light as possible. Then the TTL is just going to fill in where necessary. That would produce more even results. I think I work a little differently...I always drag the shutter as much as I can get away with, so I'm in manual mode, with the shutter usually around 1/30 or 1/60 and the aperture at f/5.6 or f/8. So the ambient levels are fluctuating wildly, but the foregrounds are generally right on. The issue I'm referring to isn't about even lighting in one photo, it's consistent exposure across an entire roll. The thing that really made this click for me today was a shot I developed this a.mA girl with a strapless dress is down in the right lower corner, usually an area that doesn't get much meter weight. However, I'm focused on her, and she's perfectly exposed. Have you tried using slow films/fastest shutter speeds (1/250)? If you did I would think that you would get results that would show the inherent TTL metering problem of weddings - mostly white in frame - face gets underexposed - mostly black in the frame - face gets overexposed. What I'm saying is I don't get much of that with flash! I think it's got to be some sort of hybrid algorithm like Brendan says, because it's not *totally* predictable. I'm going to test it out, but I was just wondering if anyone had any info, since the FA lens distance info subject comes up now and again. tv - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
RE: TTL Flash Metering and Distance Info
On 13 Mar 2002 at 14:54, Peifer, William [OCDUS] wrote: I guess the way to test Tom V's idea (about the possibility that the flash intensity is calculated from distance and guide number information, but not controlled by an actual TTL sensor reading) I backed away from that...;) I'm wondering if distance info is used at all in TTL flash discharge, and if so, how. is to fire a test shot with and without the lens cap in place. If the TTL sensor doesn't matter, then the flash intensities for both of these test shots should be about the same, and the recycle times should be about the same. If the sensor really ~is~ metering and controlling flash output, then the lens-cap-in-place test shot should have a ~much~ longer recycle time. The test I have in mind involves testing A vs. FA lenses (I'm assuming A lenses have no distance info). tv - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
RE: TTL Flash Metering and Distance Info
I'm sure it uses distance info some how but at the same time it doesn't warn you when you choose certain apertures like F16 pointed at something 50 ft away. --- tom [EMAIL PROTECTED] wrote: On 13 Mar 2002 at 14:54, Peifer, William [OCDUS] wrote: I guess the way to test Tom V's idea (about the possibility that the flash intensity is calculated from distance and guide number information, but not controlled by an actual TTL sensor reading) I backed away from that...;) I'm wondering if distance info is used at all in TTL flash discharge, and if so, how. is to fire a test shot with and without the lens cap in place. If the TTL sensor doesn't matter, then the flash intensities for both of these test shots should be about the same, and the recycle times should be about the same. If the sensor really ~is~ metering and controlling flash output, then the lens-cap-in-place test shot should have a ~much~ longer recycle time. The test I have in mind involves testing A vs. FA lenses (I'm assuming A lenses have no distance info). tv - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org . __ Find, Connect, Date! http://personals.yahoo.ca - This message is from the Pentax-Discuss Mail List. To unsubscribe, go to http://www.pdml.net and follow the directions. Don't forget to visit the Pentax Users' Gallery at http://pug.komkon.org .
