How do I calibrate Minolta Booster II on ground glass?greenspun.com : LUSENET : Large format photography : One Thread
Does anyone know a good procedure to calibrate a Minolta Booster II (accessory for a Minolta III flashmeter) to meter exposure on the ground glass? I purchased it used without a manual. It looks like a great way to spot meter through the lens and allow for bellows extension, lenses etc. A friend suggested I shoot a grey card and measure film with my densitometer...which would work but I have several lenses and it seems like there must be a better, easier way without burning up a bunch of film, trial and error.... Thanks!
-- Ron Luce (email@example.com), April 03, 2002
I've placed a set of lo-res scans of the pages of the manual pertinent to the view camera usage of the Booster II on a web page for download. I will leave these up for a few days. I don't have the time right now, but someone might want to paraphrase these for the archive. I believe the manual is still available from Minolta, so I'm a bit sensitive about copyright issues with excerpting excessively. The URL is
This site is not a photography oriented site (nor professional, sorely needing an upgrade), but I have some space there for the scans.
-- Paul Coppin (firstname.lastname@example.org), April 03, 2002.
Minolta maintains PDF versions of manuals on their website. I know they have the Autometer IIIf, and believe the Booster II is also available so you can simply download the appropriate complete manual.
-- Ed Haertel (email@example.com), May 04, 2002.
If it's not on Minolta's manual page, they'll send you a photocopy for $5.
The procedure is this:
1. Aim the camera with the lens focused at infinity at an evenly illuminated surface. The surface need not (and ideally should not) be in focus.
2. Take a direct reflected reading of the surface (not through the camera) by removing the groundglass attachment from the booster, extending the shield at the end of the probe, and reading with the booster set at its minimum setting. Note the reading. You can take reflective readings in general in this way.
3. Now replace the groundglass attachment and take a reading in the center of the glass with the lens wide open and the glass well shielded from stray light with a darkcloth. Adjust the dial on the booster and recheck until you get the same reading as the direct reflective reading. If you cannot equalize the readings (usually because the lens does not have a sufficiently large maximum aperture), then set the booster to the maximum and note the difference from the reflective reading, and just add the difference as a correction factor to your exposures.
You should do this for each lens, and you need to do it again if you change groundglass or add or remove a fresnel, etc. The same basic procedure works with any of the attachments.
-- David A. Goldfarb (firstname.lastname@example.org), May 04, 2002.