Newbie question: metering the GG

Dumb newbie again. I'm still waiting for the camera to get here, so I poked
a hole in the bottom of a cardboard crate, and made a viewing screen from
sheet mylar and the negative carrier. The 90 f/6.8 seems to cover
pretty well even wide open, but I can't tell much about light drop off.
While pondering how I would measure this...

I can't think of any reason why I can't meter off the groundglass with a
spot meter. I understand that a fresnel evens out the GG
brightness, so I ordered a fresnel. (eBay, of course.) Would it be
reasonable then to meter the GG with the spotmeter? Certainly some
adjustment will need to be applied, but it seems this would be a consistent
factor. Wouldn't this be useful for figuring enlargement and filter pack
losses? It's odd that I haven't come across this in writing, not that my
search was very broad or deep. Is it just too obvious to mention? or is
there something fundamentally wrong with the idea?

Mike.

Would it be reasonable then to meter the GG with the spotmeter? Certainly
some adjustment will need to be applied, but it seems this would be a
consistent
factor. Wouldn't this be useful for figuring enlargement and filter pack
losses?

Most SLR's with TTL metering that is not done via photosensors behind the
mirror via half-silvered mirror, measure the ground glass. And some hand-held
meter manufacturers (like Minolta) offer such an attachment for use with their
meters. You simply need to calibrate your reading so that you know accurately
the correspondence of transmitted light thru the GG to the sensor which is
reading the GG, since the GG transmission varies by the design of the GG
surface.

--Wilt

In article ,
"MikeWhy" wrote:

Dumb newbie again. I'm still waiting for the camera to get here, so I poked
a hole in the bottom of a cardboard crate, and made a viewing screen from
sheet mylar and the negative carrier. The 90 f/6.8 seems to cover
pretty well even wide open, but I can't tell much about light drop off.
While pondering how I would measure this...

I can't think of any reason why I can't meter off the groundglass with a
spot meter. I understand that a fresnel evens out the GG
brightness, so I ordered a fresnel. (eBay, of course.) Would it be
reasonable then to meter the GG with the spotmeter? Certainly some
adjustment will need to be applied, but it seems this would be a consistent
factor. Wouldn't this be useful for figuring enlargement and filter pack
losses? It's odd that I haven't come across this in writing, not that my
search was very broad or deep. Is it just too obvious to mention? or is
there something fundamentally wrong with the idea?

Mike.


You can meter off the GG with a spot meter, however their will be light lost
as a result of the transmitance of the glass, how much is something you"ll have
to determine.
--
LF website http://members.bellatlantic.net/~gblank

Why would you want to meter from the GG? If the bellows factor is
confusing, then there are some very simple remedies, 'the stick', mark
your rail(s), carry a small tape measure. Then you can use the highly
selective, undiminished handheld or spot meter to make better readings.

Subject: Newbie question: metering the GG
From: "MikeWhy"
Date: 2/1/2004 12:28 PM Mountain Standard Time
Message-id:

Dumb newbie again. I'm still waiting for the camera to get here, so I poked
a hole in the bottom of a cardboard crate, and made a viewing screen from
sheet mylar and the negative carrier. The 90 f/6.8 seems to cover
pretty well even wide open, but I can't tell much about light drop off.
While pondering how I would measure this...

I can't think of any reason why I can't meter off the groundglass with a
spot meter. I understand that a fresnel evens out the GG
brightness, so I ordered a fresnel. (eBay, of course.) Would it be
reasonable then to meter the GG with the spotmeter? Certainly some
adjustment will need to be applied, but it seems this would be a consistent
factor. Wouldn't this be useful for figuring enlargement and filter pack
losses? It's odd that I haven't come across this in writing, not that my
search was very broad or deep. Is it just too obvious to mention? or is
there something fundamentally wrong with the idea?

Mike.


You are being way too anxious. Just be patient and wait for your camera. If you
want to meter off the gg you will have to calibrate how much light it eats.
There are devices that measure the light hitting the gg/film plane from inside
the camera but you do not need to go there.

Since you've bought the lens shoot some photos and see if the falloff is a
problem.

Just get a spot meter and leanr to use it by metering light reflected from
different parts of the scene. We will do some articles about this in upcoming
issues of View Camera.

steve simmons