Ground Glass on Crown Graphicgreenspun.com : LUSENET : Large format photography : One Thread
I've recently bought an older Crown Graphic. The Camera seems to be in OK shape but the ground glass is really dark. Using a 90mm 6.8 Linholf Schneider lens wide open I just can't seem to get enough light to focus, even using a dark cloth. Can you get a "bright screen" for a Crown? I'm using this as a field camera so I'm shooing oftentimes in full sunlight. Thanks.
-- Anthony Williams (firstname.lastname@example.org), May 08, 2000
Anthony: try www.beattiesystems.com If you are unable to get one off the shelf from them I'm sure they will make one for you.Their UK devision made one for an odd 69 camera I was using a few years back.You should expect a gain in brightness from 2 to 4 stops from one of their screens. Hope this is of some help. Regards,Trevor.
-- Trevor Crone (email@example.com), May 08, 2000.
Anthony: Are you sure the lens is open all the way? I have an f8 90 mm that is bright enough for focusing even in early morning and evening with a dark cloth or the fold-out ground glass cover. My cameras have Fresnel lenses with the ground glass which helps brighten up the corners. Make sure your lens is opening all the way by looking at the diaphram. Also, the older ground glasses sometimes get pretty dirty. You might try removing it and washing it in detergent, rinsing good and reinstalling. Make sure the ground side of the glass faces forward. If that doesn't do it, you may have to go to a bright screen. Wide angle lenses tend to be darker at the corners if you don't have a Fresnel screen.
-- Doug Paramore (firstname.lastname@example.org), May 08, 2000.
Anthony: Again...are you sure you have the lens open all the way? I have an old Wollensak 90 f6.8 press lens that I use on a Speed Graflex and it's easy to focus in full sunlight (it's really sharp too). Also do you have a fresnel screen for your Crown? If so, is it installed corrctly? Hope this helps.
-- John Miller (email@example.com), May 08, 2000.
All I have is the ground glass - no fresnel. Any suggestions where I can get one to fit? As always - thanks.
-- Anthony (firstname.lastname@example.org), May 09, 2000.
-- Alec (email@example.com), May 10, 2000.
Some warnings on fresnel:
First, if your focus panel was not originally outfitted with a fresnel, installing one will mislocate the focus plane. On Graphics, the fresnel is correctly located between the ground glass and the lens. This will displace the groundglass away from the lens by the thickness of the fresnel lens.
A Beattie screen will keep the focal plane position undisturbed. You will pay dearly for one of these.
Second, fresnel lenses for Graphics are very hard to find, and brutally expensive. You are better off to buy an entire used back on eBay, but one that comes with a fresnel already installed. Many of those sellers strip the backs to sell the fresnel lenses separately, and that destroyes the focus plane alignment.
I have found the 90 Optar to be entirely satisfactory for viewing on my Crowns that do not have fresnel lenses installed. Focus cloth is required.
-- Bruce Gavin (firstname.lastname@example.org), May 17, 2000.
Bruce, I'm curious as to how the installation of the Beattie screen will not disturb the plane of focus? Is the brightscreen not a Fresnel?
-- Robert A. Zeichner (email@example.com), May 17, 2000.
The factory fresnel for the Graphics is a second physical piece of plastic. Eastman Kodak manufactured it as an Ektalite screen. It is placed between the ground glass and the lens, and has an effective focal length of approximately 135mm.
The factory focus panels were milled to keep the ground glass focus plane in the correct location, relative to the film plane in the holder, and account for the extra 0.060" of the fresnel.
If a user adds a fresnel to a non-fresnel back, he will displace the groundglass farther away from the film plane by the thickness of the fresnel lens.
It is my understanding the Beattie and other screens are a single piece, therefore the focus plane should remain undisturbed.
-- Bruce Gavin (firstname.lastname@example.org), May 19, 2000.