Questions about fresnel lens/gg.greenspun.com : LUSENET : Large format photography : One Thread
I purchased my Horseman 450 used, Mint condition but used non the less, and I'm wondering, how do I know if I have a fresenl lens. Does it replace the gg, or is it on the rear standard in addition to the gg. I can focus fine with the gg now, as it is. But the visibility changes with the angle that I look at it with.
Any thoughts would be appreciated.
-- Clark King (email@example.com), September 17, 2001
it looks like a simple gg without fresnel, to improve your camera you should try different things : from fresnel to bosscreen and beattie intenscreen fresnel : you fix it on the back of your gg (not inside, it can affect focus!!!) or a new bright gg : bosscreen is suppose to be the sharpest, a lot of people use it on this forum(it can't handle extreme temperature, check previous thread...) http://hv.greenspun.com/bboard/q-and-a-one-category.tcl?topic=Large%20format%20photography&category=Focussing%20screens intenscreen is suppose to be the brighter and the more expensive, but not the sharpest! it's a question of taste, you should test it by yourself if you can !
-- dg (firstname.lastname@example.org), September 18, 2001.
You can tell if there is a Fresnel installed by looking for faint concentric circles that start in the center and grow in size as they approach the edges. This might be easier to see if you remove the bellows from the rear standard (if this is possible). this way you'll actually be looking at the Fresnel screen.
If you don't have one, you will want to make certain that your camera was designed to work without one. Ususally, with Horseman you have a choice. However, when you remove a Fresnel, you also need to remove some shims that are about .020" thick from beneath the ground glass. This, if the gound glass arrangement is similar to what Horseman does in their field camera, the 45FA. You have to keep in mind that a Fresnel screen is a lens. It actually moves rearward, the point at which things come into focus by a distance equal to 1/3 of it's thickness. If the Fresnel is behind (between the gg and your eyes) the ground glass, your eyes automatically compensate for this.
-- Robert A. Zeichner (email@example.com), September 18, 2001.
It sounds like you have a plain ground glass. This may not be so bad. I once used a camera with a fresnel and then switch to a camera with a plain ground glass. It took some time to get used to the ground glass, but now I like it better than a fresnel. The ground glass allows focusing in the corners, which is hard to do with a fresnel. A fresnel is better for bright viewing, but a plain ground glass is better for focusing. Also, fresnels are expensive and are easy to scratch, since they are made of plastic.
-- William Marderness (firstname.lastname@example.org), September 18, 2001.
Here's an unsolicited suggestion: Forget fresnel screens altogether. They're an expensive pain in the butt. -jeff buckels (albuquerque)
-- Jeff Buckels (email@example.com), September 18, 2001.
I grant you they have drawbacks, but there's no need for them to be expensive - certainly makes the shortcomings a bit more tolerable if you don't pay through the nose for 'em.
Mine was sold as a page magnifier for maps and so forth for the visually impaired. I think it cost $3.98 or something. I like Wisner's (et. al.) idea of a removable one, although then it's something else to loose, get dirty, break, etc. in the field....
-- Sean yates (firstname.lastname@example.org), September 18, 2001.
Well there is deffinently a fresnel lens on the camera. It is placed on the inside or bellows side of the gg. Does that mean that the focused image I see is not really in focus? I thought I read an answer to this question here that said the placement of the fl has an affect on focus. Would the camera specifications call for the Fresnel Lens to be in one position of the other? I can focus fine on the gg as it is now.
Thanks Clark King
-- Clark King (email@example.com), September 20, 2001.
If you can focus without difficulty, leave everything alone. Yes, as I mentioned earlier, the Fresnel shifts focus rearward. The placement of the gg in a well designed camera such as yours will compensate for this and your negatives should be perfectly sharp (assuming you did your job well). If the fall off you are experiencing annoys you, keep in mind that the price one pays for eliminating the Fresnel (and this should be done by a camera technician who knows what he's doing and can test the modified set up) is an overall darker image on the gg. A lot of us live with that and personally, it doesn't bother me since I always use a focusing cloth and spend a great deal of time checking my focus with a loupe. Good luck.
-- Robert A. Zeichner (firstname.lastname@example.org), September 20, 2001.