Fresnel Lens placement?greenspun.com : LUSENET : Large format photography : One Thread
I have a Crown Graphic and I read on Graflex.org that someone did a test and determined that his Speed Graphic was designed to have the Fresnel lens between the lens and the groundglass for proper registration. Then, in the archives here I found a thread linking to Ron Wisner talking about Fresnel lenses saying they should be used on the outside of the camera, between the viewer and the groundglass. Which is correct here?
My Crown Graphic has the fresnel between the groundglass and the lens, and just from eyeballing it, it looks like it has to be this way to put the groundglass at the proper position to match the film plane. Will this cause be great troubles? For those of you with Graphics, how is yours set up.
As soon as I get my lens back from SK Grimes I'm going do a test to see if the film and groundglass are in the same spot. My first set of negs from this camera are a little soft, but they wern't exposed under ideal conditions either.
-- Chris Long (email@example.com), May 15, 2002
Chris: Assuming you have the original set up (Kodak Ektalite fresnel lens) leave it alone, you're fine. It is supposed to go on the inside, ribs facing the lens. There is no one rule about placement which will always apply, it depends how the camera was designed. Shooting down a fence rail with small objects on it at wide aperture will help you discover register errors pretty quickly. Polaroid makes this quick and easy. Make sure you focus off the ground glass with a loupe, not the rangefinder, since that may be off too, compounding (or masking) an error in the ground glass.
-- Kevin Crisp (KRCrisp@aol.com), May 15, 2002.
The correct placement for fresnel lenses is the garbage can. They are very little real help (assuming you have a good darkcloth), they are expensive, and they are a hassle. -jeff buckels
-- jeff buckels (firstname.lastname@example.org), May 15, 2002.
Cameras can be designed so that the position of a fresnel lens is either in front of or behind the groundglass. Cameras have been designed both ways. The design decision to locate the fresnel lens behind the ground glass (on the side away from the lens) makes the most sense because it allows the user to either use a fresnel or, without effecting focus, to remove the fresnel lens. If the fresnel lens is designed to be in front the ground glass, the user no longer has a choice because focus accuracy will suffer if the fresnel lens is removed.
-- Michael Briggs (MichaelBriggs@EarthLink.net), May 15, 2002.
There are, in fact, cameras that will allow removal of the Fresnel from between the lens and gg, for those who prefer just a straight gg for focusing. You'll notice that on such models, the Fresnel is suspended in front of the gg instead of sandwiched between the gg and the mounting pads. You'll also notice some shims between the gg and the pads that roughly equal one third of the thickness of the Fresnel. Remove the Fresnel and those shims and you're in business.
-- Robert A. Zeichner (email@example.com), May 16, 2002.
I have a Speed Graphic, and it didn't come with the fresnel. Note: it didn't come from the factory that way, the previous owner had lost it. Yours is "soft" because the ground glass and the film plane are in different positions.
A fresnel lens or shims are absolutely necessary for proper registration. Mine is out of focus without something there. If I flip the glass around then I am closer to being in focus, but it is *not* on the same plane as the film. I bought a fresnel lens from a bookstore, and while it improves the focus, it's on the thin side. I need to add some shims to it.
The fresnel lens for the Graphlex Speed Graphic should be on the inside.
I have ordered a replacement ground glass from Brightscreen, and hopefully that should correct everything.
-- Brian C. Miller (firstname.lastname@example.org), May 16, 2002.