Printable View
Hi, All I've no more sharp eyes and my GG seems very dark, so I plan on to change it for a Bosscreen, or add a Fresnel. I'd like to have feedback from the community on the best choice. I use a Gandolfi 4X5. Does the Bosscreen exist with "cutcorners", so that I can keep on checking the v igneting? Thank's to all of you for your contribution to improve my knowledge! Best regards
Daniel,
depending on the focal length, applied tilt and/or shift, the light from the lens hits the ground glass at different angles. Apart from the refraction within the GG-Material and more or less scattering, the light is emitted by the GG in the same angle on the other side. This is why you see different bright areas on the GG depending on how and in which angle you look at it. A Fresnell Lens will diffract the light in a certain angle, trying to compensate this. Obviously, there cannot be a Fresnell Lens to correct all possible angles of incidence. The visual effect on a Fresnell Lens will vary with the focal length and the amount of tilt and/or shift you apply. However, the Fresnell Lens usually provides some enhancement.
The Bosscreen on the other hand works primarily by scattering the light in all directions. Although a Bosscreen still provides maximum brightness at the angle of incidence from the lens. But it scatters part of this light in all other directions. So you usually can see something on the GG, regardless of the the lens and its position. The Bosscreen further provides a structure less surface that can be magnified beyond 10x without disturbing the image and thus provides the most exact way to focus. A Fresnell Screen is built with concentric thin circles of plastic that diffract the light inbounds. Around 8x magnification this structure usually starts to disturb the image.
Summing it up, a Fresnell Screen will provide the brightest screen within certain limits of focal length and/or applied shift/tilt (there even do exist special Fresnell Screens for lenses with shorter focal length) and the Bosscreen will make sure, that you can see always something, although not very bright.
Regards,
Daniel,
I've seen posts talking about the high quality of screens/Fresnels made by Bill Maxwell, though I have no direct experience with the products. The archives list his contact info as: Bill Maxwell, phone:(404) 244-0095, address: Maxwell Precision Optics; P.O. Box 33146; Decatur, GA 30033-0146.
Good luck.
I use a Bosscreen with my Phillips 4x5 and have a fresnel on my Horseman FA. You have an answewr that gives you some of teh technical differences so I will stick to the emperical. Both seem equally bright with the same lens and movements. As noted, there is an appearance of more grainularity with the fresnel when viewing the image through a loupe.
On the Bosscreen specifically I do not know of any with cutcorners. Keep in mind:
The screen is a thin parafin layer in a glass sandwich and as such requires a teeeny bit of thought and care. In extreme heat (say extended use over 100 degrees F) it could melt. In extreme cold (extended use at below 0 degrees F) it could have some crystallization. I have uesd mine in some very cold conditions and had no problems.
After a year's use, I replaced my Bosscreen with a fresnel by Bill Maxwell. I don't remember ever subjecting the Bosscreen to excessive temperature, but bubbles appeared in the wax coating in annoying places. The Maxwell is the brightest fresnel I have ever seen. The view is excellent even with my G-Clarons. There is a degree of granularity but it is acceptable IMO.
I had Maxwell make me a special screen for my 8X10. Though this screen is VERY positional, it provides the brightest image I have ever seen on a GG, literally the image on the GG of a darkish corner of a room will be subjectively brighter than the eye registers it when looking at it directly. For 4X5, he has some "out of the box" screens which are excellent, but will make you a custom screen in any format. As is often the case in LF, his custom work is neither cheap nor fast, but the results are quite amazing. I have also had trouble with melting Boss screens, and not from leaving them in a car in the summer, but just from walking around with them in a pack. They are nice, but really too fragile for my taste under day to day use.
Good luck,
Nathan
I've had four different Bosscreens and currently use two, one on my 4x5 and the other on my 8x10. I use them regularly in Florida in the summer when 10 seconds under the dark cloth leaves sweat rolling down your face. I've never had any problems even in those kind of temperatures with bubbles or melting or anything else. If they melted or bubbled even in that heat I doubt that he's continue using them. I haven't used Maxwell's Fresnel screen but I had a Fresnel screen on my Tachihara. I liked it very much with lenses 150 mm and longer but it was terrible with a 90 mm lens. With that lens everything went so dark in the corners and for an inch or so all around the edges that it was impossible to compose. If Maxwell's Fresnel screen brightens the entire image equally regardless of the focal length of the lens then that would certainly be the way to go I would think. If not, then I'd go with the Bosscreen.
My Bosscreen has cut corners. I use it with a removable Horseman Fresnel on my T echnika. I think it's an excellent combo, main benefits are the possibility to make extremely precise focussing, es pecially beneficial with darker long lenses and the other point is that the screen remains bright and contrasty even if it is exposed to ambient light. In comparison, my Toyo VX-125 combo goes milky white in ambient light and I can't s ee much. I wish I could fit a Bosscreen on it, unfortunately it misses precise positioning by a few microns. S ome tiny bubbles have appeared after some years of use in the Bosscreen but it's not really a problem for me.
Bosscreen, actually Stabilix, the Dutch company which produces Bosscreen will provide any size required on demand, with or without cut corners (by the way, the corners are cut precisely to check if the lens produces any vignetting, if looking trough the cut you can see the lens opened you have no vignetting ). Answering another entry Bubbles can appear if the camera is exposed to extreme heat or if the GG is mounted very tightly and if you press too hard on it with your loupe (I can't imagine that I'd do that, but there is always someone who does strange things), the proble is a mechanical one the two glasses which make the Bossscreen will tend to separate if any warping is induced, like any glass GG or not tight fitting can give problems). Other than that, fresnel is very annoying if you are looking outside of the orthogonal axis. Good luck and be patient when phoning to Stabilix to order and specifying your product. Speak to mr. Schreuder personally and quote my name, they know me and it might just help to speed up the procedures. Stabilix is a somehow very traditional company and they do not react very promtly at times.
Thank's to all of you for your posts, they are very helpfull! It seems both increase the light for two stops. I think I'll purchase the fresnel since it is easier to fit on the camera. Good luck for your photos!