[Eruditass]

I tried taking some wireless P-TTL macro shots today with the Metz-48 and it was blowing tons of highlights. In-camera flash EV compensation was at -2 EV, Metz-48 was at -3 EV.

This was outdoors with plants, flowers, and bugs. I've found that the over/under exposure depends on the subject. I went and shot some notebooks that are probably less reflective and the same settings were underexposed.

The flash was the main lighting source. Same camera settings without the flash produces a nearly black output. Adding a diffuser, bringing the flash closer or further did not alleviate the problem.

I got here, did a test outside just now and repeated it. I updated the flash to the newest firmware (couldn't tell if it already had it), same thing.

When you can't dial in any negative flash EV, what do you do? Of course I don't want to have to set the exposure settings so the flash bottoms out. Are the Pentax brand flashes better?

edit: so my split-image may be causing this, even though the focus screen should only affect spot metering (does P-TTL meter using what the camera is set to or something completely different?). Anyways, looking for alternatives other than taking out the split-image...

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Last edited by Eruditass; 10-08-2010 at 03:33 PM.

[Rupert]

I tried taking some wireless P-TTL macro shots today with the Metz-48 and it was blowing tons of highlights. In-camera flash EV compensation was at -2 EV, Metz-48 was at -3 EV.

This was outdoors with plants, flowers, and bugs. I've found that the over/under exposure depends on the subject. I went and shot some notebooks that are probably less reflective and the same settings were underexposed.

The flash was the main lighting source. Same camera settings without the flash produces a nearly black output. Adding a diffuser, bringing the flash closer or further did not alleviate the problem.

I got here, did a test outside just now and repeated it. I updated the flash to the newest firmware (couldn't tell if it already had it), same thing.

When you can't dial in any negative flash EV, what do you do? Of course I don't want to have to set the exposure settings so the flash bottoms out. Are the Pentax brand flashes better?

edit: so my split-image may be causing this, even though the focus screen should only affect spot metering (does P-TTL meter using what the camera is set to or something completely different?). Anyways, looking for alternatives other than taking out the split-image...

I can only answer part of your question, and then only my personal experience. I have the 540 and 360, and despite the occasional glitch, they seem to get the exposure very accurate in most circumstances, inside or out.

Someone else can answer the focus screen question, but I would suspect it is playing a role in your problem.
I do often shoot with the 105 Kiron Macro, manual lens, and when I do the best settings on the 540 Flash are Manual and then vary the power until I get the desired result. Slower, but very effective!
Best Regards!

[Eruditass]

I suppose I could shoot manual wireless flash (though I'd need to switch flashes), but I hold it with my hand at variable lengths.

[sveinmb]

Seriously, if you have to use -5 ev there is something wrong either with your camera, your flash or your settings. Are you sure it is even using P-TTL and not just full power?

[Eruditass]

Seriously, if you have to use -5 ev there is something wrong either with your camera, your flash or your settings. Are you sure it is even using P-TTL and not just full power?

Yes, the Metz 48 doesn't even allow manual built-in optical trigger wireless.

As I said, with different subjects and the same settings, it doesn't overexpose.

Others have reported split-image focus-screen as the cause. I am also using center weighted as it is a A-series lens, but I can try the foil trick to get matrix metering.

[Digitalis]

matrix metering won't solve your problem, use a smaller aperture f/8 to f/16 in conjunction with a low ISO that should help, and using the flash in manual mode is always a good place to start because you are controlling the flash not the camera.

[sveinmb]

I am also using center weighted as it is a M-series lens, but I can try the foil trick to get matrix metering.

There you have it then! You will not get P-TTL with a K, M or screwmount series lens. You need one from the A-series or newer.

It does not help to fool the camera to say that it is an A-lens when it isn't. The camera will not be able to meter and stop down to the correct aperture. A K/M-series lens is wide open until the camera pulls the aperture lever all the way down (green button/shutter). If you tell your camera it's an A-lens it will just pull the aperture lever down a slight amount to where the corresponding linear position of the right F-stop is.

The only way to get automatic flash with a K/M/Screwmount lens on Pentax is to either have a flash with built in auto sensor and use the correct manual settings according to it's table or use an ist D, DS or DS2 body with a TTL flash.

It *might* be possible to use a stopped down screwmount lens and let the camera meter it stopped down tricked to think it's an A-lens used wide open, but it will probably not be consistent and is not supported according to the manual.

[Eruditass]

matrix metering won't solve your problem, use a smaller aperture f/8 to f/16 in conjunction with a low ISO that should help, and using the flash in manual mode is always a good place to start because you are controlling the flash not the camera.

The problem is the metering. Apertures used were from f4 to f22 at ISO 100 to 800. All produced similar results. That shows again that the problem is the P-TTL metering (if that is affected by the metering mode).

[Eruditass]

There you have it then! You will not get P-TTL with a K, M or screwmount series lens. You need one from the A-series or newer.

It does not help to fool the camera to say that it is an A-lens when it isn't. The camera will not be able to meter and stop down to the correct aperture. A K/M-series lens is wide open until the camera pulls the aperture lever all the way down (green button/shutter). If you tell your camera it's an A-lens it will just pull the aperture lever down a slight amount to where the corresponding linear position of the right F-stop is.

The only way to get automatic flash with a K/M/Screwmount lens on Pentax is to either have a flash with built in auto sensor and use the correct manual settings according to it's table or use an ist D, DS or DS2 body with a TTL flash.

It *might* be possible to use a stopped down screwmount lens and let the camera meter it stopped down tricked to think it's an A-lens used wide open, but it will probably not be consistent and is not supported according to the manual.

Sorry, I misspoke, it's a Phoenix 100mm Macro and I get Av mode (that works other than wide-open), Tv mode and such, so I misclassified it as a M-series, when it should be A-series. If it was M-series, it'd shoot full power every time, and overexpose every time, independent of subject, but it doesn't. I'll have to double check to see if I get matrix with this lens, as I don't remember if A-series are supposed to or not. If I remember, P-TTL wireless doesn't even fire with M-series lenses.

But yeah, fooling the camera does work on lenses that stop down with the ring on the body in the limited situations I have tried. I also forgot M-series don't stop down on the body (been using too many screwmounts) and I can't remember if I found an easy way to get K/M series to stop down with the ring.

[sveinmb]

I've never noticed any major metering problems with A-series lens and the 540fgz. I have however noticed that it can, in certain situations, be difficult to get correct exposure with P-TTL flashgun at macro distances. In fact I've had better luck with TTL on my DS for macro.

The exposure has never been anywhere near 5 ev off though. Maybe 1 to 1.5 ev off, but not more than that.

Do you have any examples of subjects that get that amount of overexposure? A small white dot against a large black background?

[Eruditass]

Same settings:




So the second one really is somewhere around -5 EV underexposed.

[Digitalis]

he problem is the metering. Apertures used were from f4 to f22 at ISO 100 to 800. All produced similar results. That shows again that the problem is the P-TTL metering (if that is affected by the metering mode).

it is affected by the metering pattern you are using, and as I said before matrix metering won't help you with your problems with flash exposure in any case, matrix metering isn't any more accurate than CWA. I never rely on automatic P-Ttl for my macro work in any case and I certainly don't rely on AF either.

even though I work manually I have no problem getting high quality results.