[adwb]

Can some one please explain why the following happens and is there a way round this effect?
Any Pentax body with Pttl. [not ttl] fitted with a 28-200 zoom.used inside or in any very low light situation the flash exposes perfectly at any zoom. even if there is a window in the metered area.
However when used as a fill flash outside all is well till the you zoom to 100mm or more. at these higher zooms the subject is very under exposed and the background blacked out. I have found that if auto exposure is used on these images in adobe raw the image is corrected by about 2 stops and looks fine, so if at any zoom in excess of 100mm I expose 2 stops over ,the image is pretty close to being correctly exposed.
So not a disaster as long as remember to alter the exposure.
However I thought the whole idea of PTTL was that as fill flash it works based on increasing a the darker area to balance with the surrounding ambiant light so why does it not fill at greater zoom levels?
Pentax k5 and metz 48 or k10d and metz 48 or K-r and metz 48 with tamron 8-200 lens at f8 at all zoom settings . iso fixed at 200 - shutter at 160 fixed
same result each time. subject 6 meter away from lens

[RioRico]

Bump.

Hey people, this one was asked nearly a month ago. Doesn't anyone have an idea? C'mon now!

[philbaum]

Can some one please explain why the following happens and is there a way round this effect?
Any Pentax body with Pttl. [not ttl] fitted with a 28-200 zoom.used inside or in any very low light situation the flash exposes perfectly at any zoom. even if there is a window in the metered area.
However when used as a fill flash outside all is well till the you zoom to 100mm or more. at these higher zooms the subject is very under exposed and the background blacked out. I have found that if auto exposure is used on these images in adobe raw the image is corrected by about 2 stops and looks fine, so if at any zoom in excess of 100mm I expose 2 stops over ,the image is pretty close to being correctly exposed.
So not a disaster as long as remember to alter the exposure.
However I thought the whole idea of PTTL was that as fill flash it works based on increasing a the darker area to balance with the surrounding ambiant light so why does it not fill at greater zoom levels?
Pentax k5 and metz 48 or k10d and metz 48 or K-r and metz 48 with tamron 8-200 lens at f8 at all zoom settings . iso fixed at 200 - shutter at 160 fixed
same result each time. subject 6 meter away from lens

PTTL tries to keep up but when one establishes conditions that exceeds the flash's power capabilities, it underexposes.

In this case, I think those flashes don't zoom more than 105mm about. Which means that when you zoom your optical lens more than that, you are sampling only a portion of the light that is spread out over the scene. Also, the GN is about 34/f8=Distance in meters =4 meters about. You are overtaxing the flashes power. Your 200 iso helped, but i don't think it was enough.

You need to enlarge the aperture and/or select a higher ISO and/or reduce the amount of optical zoom.

So RioRico, how did i do