Bosscreen with 90mm lens on 4x5" ?greenspun.com : LUSENET : Large format photography : One Thread
I have red thru the information about the Bosscreen in the LF homepage. I realize the screen is superior to the normal ground glasses and "improved" ones like beattie and brightscreen in terms of grain and contrast.
Could anyone enlighten me on the following points on using the Bosscreen on a 4x5" camera:
1) Should I use an additional fresnel with the Bosscreen with a 90mm lens ? How much does the view vignette without a fresnel ?
2) How much brighter it is actually, for example compared to a basic ground glass and/or a fresnel ? (I am having problems with heavy vignetting with the 90mm on the standard "fresnel ground glass" of my Wista DX)
3) What about compared to a Beattie ? Does anyone actually use a beattie or brightscreen screen on a 4x5" with wide angle lenses ?
Any info and/or thoughts would be extremely welcome!
-- Antti-Pekka Virtanen (Antti-Pekka.Virtanen@aumec.com), April 14, 1998
1. No, you wouldn't want to add a Fresnel screen to the Bosscreen. Not sure what you mean about the view "vignetting without the screen." If you mean how much does the image darken towards the edges as you get away from the center of the screen, without a fresnel lens or a Bosscreen and with a 90mm lens, the answer is it darkens a whole lot. I personally couldn't use a 90mm lens on a plain ground glass screen.
2. Strictly speaking, the Bosscreen isn't a brightener. What it does is spread the bright area evenly around the ground glass so that it isn't concentrated in the center of the screen as it is with a standard ground glass. It is easier to focus with the Bosscreen than with a Fresnel screen because you don't have the "grain" that you see when you use a loupe with a Fresnel screen.
I assume that by "standard Fresnel ground glass" you mean that your standard ground glass has a Fresnel screen attached to it. I used the Bosscreen when I owned a Technikardan camera but I sold that camera and now have a Tachihara which includes a Fresnel screen. I also have some difficulty with a 90mm lens. Unfortunately, I don't remember whether the Bosscreen improved the situation on the Technikardan or not. It's been about three years since I sold the camera and I rarely use my 90mm lens.
3. I don't know the answer to this. My only experience with a Beattie screen was on my Pentax 67 camera. I got severe vignetting with it and had to have it removed and the standard Pentax screen put back on. The whole experience wasn't very pleasant.
-- Brian Ellis (email@example.com), July 10, 1998.