Enhanced focussing screens

Compiled by Q.-Tuan Luong for largeformatphotography.info

If you find it difficult to focus with your ground glass, you might want to consider a replacement. Two things can make a ground glass difficult to focus on:

In addition, the hot spot makes it difficult to assess the composition. A finer glass will tend to have a worse light fall-off. Two solutions are to add a Fresnel lens to even up the illumination, or to use a Boss screen. Although they do their job, the problem with Fresnel lenses is that they work optimally only for one focal length. On the other hand, ALL the users of the Boss screen seem to like it. The only drawback seem to be that this screen might be damaged by extreme temperatures (hot and cold). I was relatively satisfied with the screen on the 5x7 back of my tachi, which was a plastic fresnel/ground combination protected by a sheet of glass. I found the stock screen of my Canham difficult to focus on. I tried using a fresnel lens, but I got weird problems with it. Then I switched to a Toyo focussing screen, which has a considerably finer grain. This made focussing easier but the hot spot was terrible. Eventually I switched to a Boss screen, and I found it worked fine.

Fresnel lenses

Some general remarks about focusing screens. Most of these are "field lenses" usually of the Fresnel type, so they can be flat, which direct the light going through the ground glass toward the expected location of the viewer's eyes. For this scheme to work right the focal length of the field lens must be such as to focus the light from the lens at a convenient distance for viewing. This will be affected by the location of the lens so will vary with focal length of the taking lens and to a lesser extent with distance focused on. It is the angle of the cone of light leaving the lens which is important. It also depends on the whole optical path being centered. For this reason field lenses do not work well when the camera movements are used. The parts of the screen away from the optical center will be darker than with a conventional GG. The same for using WA lenses. The angle of the light striking the edges of GG are acute and a different FL of field lens is needed to make the image uniform. Richard Knoppow

I tried a fresnel lens made by Arca-Swiss. The illumination is a bit more even than before, but I don't find the image to be much brighter. The thing which bugs me is that when I use wide angles, there is a very weird effect, with concentric bright rings which look like double images. They are extremely disturbing with a 90 lens, and noticeable with a 120 lens, to the point of preventing me from assessing the composition of the image in the corners. Rod Klukas from Photomark says that with any Fresnel this is going to happen for some focal lenghts (he observes the same with this 45 lens on 4x5), and as a consequence there is a folk he knows who has different backs with different fresnels that he switches as he switches lenses. Tuan

The Beattie Intenscreen

The Beattie is, basically, a plastic "ground-glass" with a built-in fresnel lens on one side of the "ground-glass". get a glass cover plate to protect the plastic screen. I decided that I didn't like the Beattie and took it off and went back to using a plain ground glass and fresnel lens. Why? It really is brighter but: One person even said that the plastic screens aren't always perfectly flat so that prefect focus in the center of the screen may give out of focus negatives. The probably do make pretty good backup ground glass for carrying around. I would imagine they are much less fragle than real glass, and backups are rarely needed. Barry Sherman

The Linhof Super Screen

The Linhof Super Screen also incorporates a fresnel, but it didn't interfere with focusing in the same way as a Beattie Intenscreen. I think the Linhof was brighter than the Boss, but I did not care for the way it had bowed in the Technika it was installed in. To make matters worse, I looked at it one day, noted the bowing, then went back about a week later, and it was bowed differently. I didn't particularly care for the idea that the damn thing was not stable (it's a plastic screen). Paul Butzi

The Boss screen

The "Boss" screen, made in the Netherlands, is a thin layer of a light scattering wax/paraffin mixture between two glass layers. In contrast to a "ground" glass there is no visible grain, it is brighter and quite contrasty. In addition you dont need an extra fresnel lens for most focal length. I use one on my 4x5 with lenses from 75mm to 600mm and I am very pleased with it. With the 75mm there is a hot spot in the center, but the corners of the format are still clearly visible without fresnel. They have screens fitting most view cameras and you can also choose between a model with clear corners (similar to cut-away corners) and the standard rectangular shape. If I remember it right, the manufacturer advises that temperatures should not exceed 55 degrees C, but I never had any problems in summer. I noticed, however, that at temperatures below approximately -10 degrees C, some Newtons rings appeared after some hours in the cold at the edge of the ground glass, indicating a slight separation between the glass and the wax layer. This effect was reversible, though. I experienced a partial separation (1-2square cm) between the wax and (one of the) glass layers when the camera was subjected to temperatures below -15degrees C (5 deg. F) for several hours. It shows up as an area with Newton's rings, its not a crack pattern. You can easily test if its really separated, by applying a little bit of pressure with your fingers on the glass: when the Newton rings move, you have a separation ( and not some ice from breathing on your glass :-) ). Most of the time this was reversible and the rings disapperared when the camera was warmed up again, but one time (really cold) it was permanent. As you have mentioned, it is possible to "repair" this area by _careful_ heating with a hair dryer _just_ until the wax melts and becomes clear, then let it cool again. Dont forget to tape the edges of the inner glas, or else some wax will creep out (I forgot). The repaired area looks a little more translucent when the GG is held against the light, but in the camera it is only noticeable at certain angles. I assume this difference can be reduced by changing the cool-down process of the wax, but I did not want to make a test series with my Bosscreen. Be aware that according to the manufacturer separation can also happen if the screen is bent by tightening the mounting (screws or whatever device is used) of the ground glass too much. Despite the cold temperature problems I would still recommend the Bosscreen; its a real improvement over my former setup (Linhof ground glass and Fresnel). Arne Croell.

Bosscreen is made by a Dutch company called Stabitech (formerly "Stabilix", which went bankrupt towards the end of 2003). The company sells direct as well. The new website of the company is http://www.stabitech.nl You can place an order by email with them and wire your payment to their bank account. They can cut a screen at any size to fit your camera, but this took more than a month in my case. It's imported in the US and probably sold retail as well by Bromwell Marketing in Pittsburgh (412-321-4118). It was extremely difficult to get a screen through the specialty LF retailers.

I have heard that the temperature limit is around 140F, which is easily reached in summer in a car trunk. Chris Newman writes "I am on my third one, one damaged by extreme cold the other by moderate heat (90 degrees)". Myself, I didn't have any problems until a summer trip to the Rocky Mountains, (where it doesn't get that hot). Since then, I have the dreaded bubbles. They do not interfere so much that the screen would not be usable, however are enough of a nuisance that I will replace it. One frequent concern about the Boss screen is that the position of the plane of focus would be wrong, but this has been addressed properly:

Basically, the sheets of glass of the Bosscreen are two different sizes. The one which goes closest to the lens is small enough to fit INSIDE the area on which the ground glass usually rests. It is the inner surface of the piece of glass on the viewing side which actually seats on the routed out area that the ground glass normally sits. This then puts the inner surface of this outermost piece of glass in the correct focal plane, which means, of course, that the wax is actually too close to the lens at this point. To compensate for that, there is a piece of plastic (they call it "tape") along the edges on the inner side of the glass which sits in the rout. This tape is sufficient to correctly space the glass back far enough to put the wax in the correct focal plane. David Fokos.

The layer of glass between the lens and image forming plane probably affects the focus position. Probably why the real Boss screen comes with some shims. Otherwise the smaller front glass should put the wax layer in the same position as the ground side of the ground glass (assuming you are using a camera designed to have no fresnel between the ground glass and the lens, some cameras like most speed graphics were designed to always have a fresnel mounted in front of the GG). I've heard that the layer of glass moves the focus point back by about 1/3 the thickness of the glass if I'm remembering right. I'm sure it depends on the index of refraction of the glass, but this probably doesn't vary much unless you are using some exotic glass type. John Sparks

More information

Viewing Screens for Large Format Cameras by Ron Wisner. Explains how a ground glass work.

List compiled by Craig Blurton (originally posted in a LF Forum thread):


Beattie Intenscreen



Maxwell Precision Optics UNOFFICIAL website

Maxwell Precision Optics
Contact Bill Maxwell <maxwellprecisionoptics@yahoo.com>

Satin Snow

Velveteen View screen
Contact Greg Garret <garretart7@yahoo.com>


Ebony Fresnel Lenses

Canham Fresnel Lenses

Linhof Super Screen

Sinar Fresnel Lenses

Wisner Fresnel Lenses

Wista Fresnel Lenses



Edmund Optics

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