Spotmeter the ground glass?
I've been interested in focal-plane metering with LF. Has anyone had any success simply using a spot meter, from the back of the ground glass? It seems to me that if it were to work at all, it would require a very good dark cloth for consistency.
Haven't done it myself, but I remember some other active APUG member writing about it, maybe Jason (JBrunner), or Ian Grant?
Do an APUG Google search with spotmeter and ground glass as keywords, you may be able to find the thread...
Last edited by Marco B; 08-20-2010 at 10:02 AM. Click to view previous post history.
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Haven't tried it, but I'm pretty sure flare will be a huge issue.
I am just guessing, but it seems to me that you would not get accurate readings since the amount (intensity) of light has been altered by passing through both the fstop of the lens and the ground glass.
But, beyond that, my question would be "why?" If you are standing there with a spot meter, why not just meter the scene directly?
I've written about it but only in the context of comparing focus screens. You need the proper probe attachment that fits certain meters and slips under the screen for accurate spot readings from an LF camera itself..
It's reflections rather than flare that are the main issue, but I guess using a spot meter might be possible, however I'd say why when used direct is so much more accurate, as long as you take the extension factor into account.
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You can meter on (as opposed to under) the GG too.
I have used the Gossen fiberoptic probe for that without problems.
I believe a spotmeter will work too, but, as mentioned, reflections will be something to avoid.
Minolta made an accessory for that, called the Booster II. It plugged into a jack on the side of the Flash Meter II, III, IV, and V and Autometer III and IIIf (and maybe the newer meters, I am not sure). Sekonic sells a device that looks identical in every way and is probably made by the same subcontractor for some of their meters (I've tried the minolta one on a Sekonic meter and it works!)
There is a spot meter made for LF cameras. It is made by Gossen, and comes in 3 parts.
1. A special back for the camera with a slit and mounting stage for the probe.
2. A movable probe that moves anywhere on the GG and can measure light.
3. A Gossen meter that attaches to the probe and gives the reading for exposure.
These are excellent units, but IDK if they are still available.
That's the thing Ian mentioned.
It was indeed also available to fit Minolta meters.
The problem with metering from the glass side (rear) is calibration as screens can vary in brightness by at least 3 stops, and the coarseness/fineness of the ground side will also play a big part. This is why they are best internal.
Some people make their own meters, and it would be very easy to make an internal spot version if you were prepared to adapt or make a new LF back. It needs a good light seal around where the probe fits and moves.