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+--- Thread: Using a light meter - what am I doing wrong (/showthread.php?tid=3839)
Using a light meter - what am I doing wrong - obsoquasi - 06-19-2010
Dear zoners,
I am turning to you again in utter despair <img src='http://forum.photozone.de/public/style_emoticons/<#EMO_DIR#>/smile.gif' class='bbc_emoticon' alt='
' />. I just got a light meter today, a Kenko KFM-1100 (a rebranded version of the Minolta Auto Meter V). Now I know that using a light meter is not that easy, but the basics seem straight-forward. For (flash) portraits: set camera and meter to the same ISO and exposure, set the meter to cordless flash, place it on subjects cheek (facing the camera) and take a reading (triggering the flash) and use the aperture value on the camera. The weird thing is, that I get totally overexposed shots this way - and I mean like 8 stops overexposed, not just slightly off. And I just don't see what went wrong in the process: Flash meter dome is on, the flash itself fires through a white umbrella at 1/4 power (a 580 EX II speedlite) my ISO is at 200, exposure at 1/160 s. But my meter suggests 1.4 for this setting. This can't be right! Now, the background as well as the subject's shirt are white - but since I am taking an incidend reading, the meter doesn't take that into account and assumes there's a neat wall of medium gray behind it, right? So in theory, while the white cloth will be blown out, the skin tones will be perfectly exposed. But far from it, almost all of the skin is blown out as well. I have no clue what it is I am doing wrong and so you guys are my last resort.
Using a light meter - what am I doing wrong - Rainer - 06-19-2010
From your description, there are only few reasons left ...
- you''ve set camera and meter to the same iso-setting.
- you're at 1/160sec ... well within X-sync-time
- The camera is in M mode, ynd you set the aperture from
the meter reading.
so either
- the meter does not see the flash ... and therefore gives you a
reading for the ambient light
or
- the meter is not set for flashmetering and averages the light
over longer times ... and again gives you a reading for the ambient light
In both cases, since ambient light is magnitudes darker than the flash, the
resulting picture will be overexposed. ... by 8 stops ... well that is much, but
since it depends on the level of ambient light you have, it is possible.
But lets do the reverse calculation ... the 580ex has a GN of 58 (max) at 100iso.
This is approx. 80 at 200iso. Using a distance flash to subject of say 3 meters
you would have to use f/27 ... the flash was set to 1/4 and it goes through
the umbrella ... this costs about 3 stops ... this would bring you down to f/8
So ... around f/8 should give you a well exposed image ... using f/1.4 is
5 stops overexposed ... the 8 stops you mention are at least possible
(different distance ... umbrealla that doesn't eat up one stop).
Using a light meter - what am I doing wrong - wim - 06-19-2010
As Rainer says, the only thing I can come up with is that the meter reads ambient rather than flash light, so do check the settings on the meter. That would certainly explain the difference.
I would also suggest trying to do a reading from the camera side of things, without dome, to see if the meter gets it right in that case. There could also be a problem with the meter itself, of course.
HTH, kind regards, Wim
Using a light meter - what am I doing wrong - obsoquasi - 06-21-2010
Hi you two and thanks a lot for your suggestions as to what might cause the problem. I seriously suspect that there is a problem with the meter. I did some further tests comparing the results of an ambient reading and a mixed reading. The result: ambient reading are fine, mixed will often overexpose, especially if the ratio flash:ambient is to 100%. I'd love to see what the results would be if a sync cord is attached, but my 580 EX II's aren't sync-cord-compatible without some serious tinkering. In any case, thanks again for your thoughts, it was reassuring to hear I was basically on the right track.
Using a light meter - what am I doing wrong - wim - 06-21-2010
I don't really know how good the Kenkos are of course, but I am a little weary about their pricing, considering the (extremely good) alternatives. I would honestly suggest to maybe return it and exchange it for either a Gossen or Sekonic.
If you only want a flashmeter, it would be Sekonic L-308S Flashmate or Gossen Digiflash if you only want a flashmeter and nothing else, a Sekonic L-358 if you want to control your flashes too, a Sekonic L-758D or DR, or Gossen Starlite (1 or 2) if you want an allround meter, and the Sekonic again if you also want to control your flash with it. The transmitter for the flash with Sekonic may be extra, certainly for the L-308S.
Sekonic: [url="http://www.sekonic.com/main/"]http://www.sekonic.com/main/[/url]
Gossen: [url="http://www.gossen-photo.de/english/"]http://www.gossen-photo.de/english/[/url]
Kind regards, Wim
Using a light meter - what am I doing wrong - DonAndre - 06-21-2010
Exposure time in studio setups with flash light do not really influence the result (I assume you're not doing some high-speed stunning freeze-action shots). The flash is just a tiny fraction of the exposure time, but is responsible for the whole exposure. So increasing or decreasing your exposure time does not really change anything. ISO is better be left at the base value. You should always have enough light to get a proper exposure even at base ISO.
The only thing that changes is aperture. You take some readings here and there with the light meter to see how much light will be received. Take a look at this video: http://layersmagazine.com/studio-photography-with-a-light-meter.html